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Genetic mechanisms of secondary pore development zones of Es 4 x in the north zone of the Minfeng Sag in the Dongying Depression, East China

Genetic mechanisms of secondary pore development zones of Es 4 x in the north zone of the Minfeng... Pet. Sci. (2016) 13:1–17 DOI 10.1007/s12182-016-0076-7 ORIGINAL PAPER Genetic mechanisms of secondary pore development zones of Es in the north zone of the Minfeng Sag in the Dongying Depression, East China 1 1 1 1 • • • • Yan-Zhong Wang Ying-Chang Cao Shao-Min Zhang Fu-Lai Li Fan-Chao Meng Received: 27 October 2014 / Published online: 22 January 2016 The Author(s) 2016. This article is published with open access at Springerlink.com Abstract The genetic mechanisms of the secondary pore slightly changed because of protection from early hydro- development zones in the lower part of the fourth member carbon charging and fluid overpressure during deep burial. of the Shahejie Formation (Es ) were studied based on core Finally, the present secondary pore development zones observations, petrographic analysis, fluid inclusion analy- were formed when many primary pores were filled by sis, and petrophysical measurements along with knowledge asphalt and pyrite from oil cracking in deeply buried paleo- of the tectonic evolution history, organic matter thermal reservoirs. evolution, and hydrocarbon accumulation history. Two secondary pore development zones exist in Es , the depths Keywords Secondary pore development zone  Genetic of which range from 4200 to 4500 m and from 4700 to mechanism  Diagenetic evolution sequences  Secondary 4900 m, respectively. The reservoirs in these zones mainly pores  Dongying depression consist of conglomerate in the middle fan braided channels of nearshore subaqueous fans, and the secondary pores in these reservoirs primarily originated from the dissolution 1 Introduction of feldspars and carbonate cements. The reservoirs expe- rienced ‘‘alkaline–acidic–alkaline–acidic–weak acidic’’, As the degree of hydrocarbon exploration in middle-shal- ‘‘normal pressure–overpressure–normal pressure’’, and ‘‘formation temperature increasing–decreasing–increas- low formations continues to improve, deeply buried for- mations are gradually becoming important targets for ing’’ diagenetic environments. The diagenetic evolution sequences were ‘‘compaction/gypsum cementation/halite hydrocarbon exploration (Hu et al., 2013; Sun et al. 2013, 2015). Studies of anomalously high porosity and perme- cementation/pyrite cementation/siderite cementation–feld- spar dissolution/quartz overgrowth–carbonate cementation/ ability in deeply buried sandstone reservoirs by Bloch et al. quartz dissolution/feldspar overgrowth–carbonate dissolu- (2002) showed that deep formations can still develop abnormally high porosity zones that can form oil and gas tion/feldspar dissolution/quartz overgrowth–pyrite cemen- tation and asphalt filling’’. Many secondary pores (fewer fields with commercial value (Bloch et al. 2002). Under- standing the genesis of deep, abnormally high porosity than the number of primary pores) were formed by feldspar dissolution during early acidic geochemical systems with zones (AHPZs) is important for precisely predicting deeply buried high-quality reservoirs. This issue has been studied organic acid when the burial depth of the reservoirs was relatively shallow. Subsequently, the pore spaces were many times. Although the controlling factors of the for- mation of deep, abnormally high porosity zones vary in different regions, most geologists generally believe that & Yan-Zhong Wang mineral dissolution, shallow fluid overpressure, early wangyanzhong1980@163.com hydrocarbon charging, and grain rims are the main factors School of Geosciences, China University of Petroleum, that control the development of deep AHPZs (Bloch et al. Qingdao 266580, Shandong, China 2002; Ehrenberg 1993; Warren and Pulham 2001; Meng et al. 2011, 2010; Taylor et al. 2010; Wilkinson and Edited by Jie Hao 123 2 Pet. Sci. (2016) 13:1–17 Haszeldine 2011; Cao et al. 2014; Yuan et al. 2015; Dongying Depression are simply interpreted as having Ajdukiewicz and Larese 2012; Wang et al. 2014; Jiang formed from deep burial mineral dissolution (Yuan and et al. 2009). Wang 2001; Zhu et al. 2007). Some questions require Secondary pore development zones (SPDZ) are a typical further studies, such as whether these deep secondary pore type of abnormally high porosity zone. Since Schmidt and development zones were originally shallow secondary pore McDonald (1977) proposed the theory that secondary pores development zones that were preserved effectively during in clastic reservoirs can form during diagenetic processes deep burial and how these shallow secondary pore devel- (Schmidt and McDonald 1977), scientists worldwide have opment zones were preserved during deep burial. These made significant progress in identifying the distinguishing unresolved problems produce great difficulties and risks for features, genetic mechanisms, distribution, and geological the exploration and development of hydrocarbons in these significance of secondary pores (Schmidt and McDonald reservoirs. For instance, the drilling of the Fengshen2 and 1979; Giles and De Boer 1990; Osborne and Swarbrick Fengshen3 wells close to the Fengshen1 well was not 1999; Higgs 2007; Zhu et al. 2006; Zhang 2007; Zeng successful (the former were dry wells and the latter only 4 3 2001; Yuan and Wang 2001; Liu and Zhu 2006; Wang produced 2.64 9 10 m of gas daily) (Zhong et al. 2004). et al. 1995; Wang and Zhao 2001; Ma et al. 2005; Zhang The characteristics and genetic mechanisms of the et al. 2008; Dutton and Loucks 2010; Taylor et al. 2015). SPDZs in Es in the Minfeng Sag were systematically Currently, SPDZs in shallow layers, which correspond to studied based on a combination of core observations, thin the mature stage of organic matter evolution, are consid- section identification, SEM observations, fluid inclusion ered to be generated from the dissolution of aluminum analysis, core X-ray analysis, vitrinite reflectance tests, and silicates and carbonate minerals by organic acids and CO core properties analysis, along with additional knowledge from organic matter evolution (Zeng 2001; Yuan and regarding the tectonic evolution history, thermal evolution Wang 2001; Liu and Zhu 2006; Wang et al. 1995; Zhang of organic matter, and history of hydrocarbon accumulation et al. 2014). However, different viewpoints exist regarding in the study area. The results of this study show that the the generation of deep SPDZs. Some authors believe that deep SPDZs in the study area experienced the formation of these features form by mineral dissolution in low porosity significant secondary pores at shallow depth and the reservoirs at deep burial depths (Yuan and Wang 2001). occupation of many primary pores by massive asphalt and Other authors, however, believe that the large amounts of pyrite from oil cracking in deeply buried paleo-reservoirs secondary pores that form in these shallow formations are under high temperature. This achievement is significant for effectively preserved during deep burial, while primary re-evaluating the genetic mechanisms and distribution of pores are destroyed, which results in the formation of deep deep high-quality reservoirs and the deployment of SPDZs (Wang et al., 2001; Ma et al. 2005; Zhang et al. hydrocarbon exploration in deep formations. 2008; Bjørlykke and Jahren 2012; Bjørlykke 2014). Petroleum exploration in the deeply buried nearshore subaqueous fans in the Es sub-member in the Minfeng 2 Geological background Sag, Dongying Depression, has greatly improved in recent years. For example, the daily oil production from depths of The Dongying Depression is a sub-tectonic unit that lies in 4316.6–4343 m in the Fengshen1 well in Es is 81.7 t, and the southeastern part of the Jiyang sub-basin of the Bohai the daily gas production is 118,336 m . The reservoirs in Bay Basin in East China. This unit is a Meso-Cenozoic half the nearshore subaqueous fans, which are closely related to graben rift-downwarped lacustrine basin, which developed gypsum layers and the source rocks, experienced a com- on Paleozoic bedrock paleotopography (Yuan and Wang plex burial evolution, including tectonic subsidence— 2001). The Dongying Depression, which lies east of the uplift—subsidence and an alternating acidic-alkaline dia- Qingtuozi Salient, south of the Luxi Uplift and Guangrao genetic environment. The current reservoir space mainly Salient, west of the Linfanjia and Gaoqing Salients, and consists of secondary pores, and primary pores have been north of the Chenjiazhuang-Binxian Salient, covers an area mostly destroyed. Exploration of the Dongying Depression of 5850 km with an east–west axis of 90 km and a north– x s shows that four sets of source rocks exist in the Es ,Es , south axis of 65 km. Additionally, the depression is gen- 4 4 x z Es , and Es sub-members and that the total thickness of erally NE-trending. In profile view, the Dongying 3 3 these source rocks exceeds 2000 m. Depression is a half graben with a faulted northern margin The reservoirs in the Es sub-member could potentially and a gentle southern margin. In plan view, this depression form abundant secondary pores during shallow burial is further subdivided into secondary structural units, such because the organic matter in Es ’s source rocks could as a northern steep slope zone, a middle uplift, the Lijin, supply organic acids in a shallow open system. However, Minfeng, Niuzhuang, and Boxing sags, and a southern all the deep SPDZs in the Paleogene sandstones in the gentle slope zone (Zhang et al. 2006) (Fig. 1). 123 Qingtuozi Salient Shicun fault zone Pet. Sci. (2016) 13:1–17 3 42° (a) (b) Sag 0 100km N 0 20 km Uplift 40° Beijing Yanshan Č Dalian Ċ Chenjiazhuang Salient A’ Bohai Bay 38° ċ Coastline China Jinan 36° Fsh1 Beijing Fsh3 Tanlu Strike-slip Minfeng Fsh2 Fault Zone Binxian subsag 114° 116° 118° 120° 122° 124° Salient Lizezheng subsag Qingcheng Boxing subsag Salient Paleogene Paleogene system system area overlap zone Uplift Luxi Major Paleogene system fault denuded zone Nm-Q (c) S0 Ng Ng 1.0 1 S Es -Ed 1 S 1 S z 4 2 s S Es Es -Es 3 2 3 S z 2.0 4 Es 4 x S 3 6 Es S 6 S 6’ 6’ Es 3.0 Up S :Nm-Q S -S :Ng 0 0 1 7 Es Ek S -S :Es -Ed S -S :Es -Es SR 4.0 1 2 1 2 4 3 2 S -S :Es 4 6 3 S -S :Es 6 6’ 3 S -S :Es S -S :Ek 6’ 7 4 7 R Fig. 1 a Tectonic setting of the Dongying Depression in the Jiyang Sub-basin (III) of the Bohai Bay Basin. Other sub-basins in the Bohai Bay Basin in East China include the Jizhong Sub-basin (I), Huanghua Sub-basin (II), Bozhong Sub-basin (IV), Liaohe Sub-basin (V), and Dongpu Sub-basin (VI) (according to Liu et al. 2012). b Structural map of the Dongying Depression with well locations. The area in the green line is the study area, which is located in the northern zone of the Minfeng Sag of the Dongying Depression. c Section of A–A in map (b). S ,S ,S ,S ,S , 0 1 2 4 6 S 0,S , and S are major seismic reflection boundaries. Nm Neocene Minghuazhen Formation; Q Quaternary Period; Ng Neocene Guantao 6 7 R Formation; Ed Paleogene Dongying Formation; Es The first member of the Paleogene Shahejie Formation (Es); Es The second member of Es; 1 2 s z x Es The upper part of the third member of Es; Es The middle part of the third member of Es; Es The lower part of the third member of Es; Es 3 3 3 4 The fourth member of Es; Ek Paleogene Kongdian Formation (Liu et al. 2012) The Minfeng Sag lies in the northeastern area of the small lake-water area, and high salinity. The northern steep Dongying Depression, north of the Chenjiazhuang Salient, slope zone of the Minfeng Sag is a structural belt in the south of the middle uplift, east of the Qingtuozi Salient, steep slope zone that is controlled by the Chennan and west of the Lijin Sag (Fig. 1). During the depositional boundary fault, which is located near the subsidence center period of the Es sub-member, the Dongying Depression in with deeper water. Terrigenous clastic sediments were this early rift stage was characterized by an arid climate, a transported by seasonal floods to the deep lake, leading to Northern steep slope Binnan-lijin fault zone Tuo-Sheng-Yong fault zone Boxing fault zone Middle area Uplift Guangrao Salient Chennan Southern Slope Niuzhuang subsag fault Chenguanzhuang-wangjiagang fault zone Lijin subsag Linfanjia Salient Bamianhe fault zone Xinbei fault Fold Belt Uplift Gaoqing fault zone Liaodong Uplift Cangxian Uplift Luxi Uplift Jiaodong Uplift Taihangshan Round trip time, s 4 Pet. Sci. (2016) 13:1–17 the deposition of the nearshore subaqueous fans in the suggest that an SPDZ is the depth interval for which the downthrown side of the Chennan fault. These fans were real porosity evolution curve is higher than the normal distributed close to lacustrine source rocks (Sui et al. porosity evolution curve and the percent of secondary 2010). During flood stagnation, the water evaporated pores is over 50 % (Liu and Zhu 2006; Zhu et al. 2007;Shi rapidly, and thick gypsum and halite were deposited. In et al. 2005; Zhong et al. 2003; Zhang et al. 2003; Zheng vertical profile view, the strata show a sedimentary and Wu 1996). However, the porosity values of reservoirs assemblage of interbedded gypsum and clastic rocks. in secondary pore development zones and the methods that are used to determine the normal porosity evolution curve have not been clearly explained. Additionally, the methods 3 Methodology and database that are used to determine the real porosity evolution curve have not yet been unified. For example, one method that is This study used cast thin sections and SEM observations to used to determine this curve is to fit the functional rela- analyze the characteristics of the reservoir spaces based on tionship between the porosity and depth (Liu and Zhu effective reservoir porosity cutoffs. Porosity data were 2006; Zhu et al. 2007; Zhong et al. 2003; Zhang et al. combined with porosity cutoffs to determine the distribu- 2003). Another method uses the porosity envelope curve of tion of SPDZs. The sedimentary characteristics, secondary the porosity-depth profile as the real porosity evolution pore features, and diagenetic evolution sequences of the curve (Yuan and Wang 2001; Zhu et al. 2010; Liu et al. reservoirs in these SPDZs were studied based on the 2010). In this paper, an SPDZ is first defined as a zone identification of these zones. The genetic mechanism and where high porosity reservoirs with more than 50 % sec- evolutionary model of the secondary pore development ondary pores develop. This definition includes three zones, the evolution of the diagenetic environment, and the meanings: (1) the percent of secondary pores is greater than reservoir reconstruction process were discussed. 50 %; (2) the porosity of the reservoirs is higher than the The database that was used in the study includes effective reservoir porosity cutoff because the absolute approximately 250-m cores from eight wells, porosity data content of secondary pores is high; (3) high porosity from 172 samples, 70 thin sections, 30 cast thin sections, reservoirs concentrate to form belts at a particular depth six SEM samples, and 80 fluid inclusion samples. The core interval in the porosity-depth profile, with the porosity samples were provided by the Geological Scientific envelope curve bulging towards higher porosities. Research Institute of the Sinopec Shengli Oilfield Com- The effective reservoir porosity cutoff is the basis for pany. The porosity was tested by a 3020-62 helium determining SPDZs. Only when the effective porosity porosity analyzer at the Exploration and Development cutoff is known, can the development of high porosity Research Institute of the Sinopec Zhongyuan Oilfield reservoirs be confirmed and the distribution of secondary Company. The SEM samples were examined with a pore development zones determined. Based on collections Quanta200 SEM with an EDAX energy dispersive X-ray and arrangements of a large number of porosity and per- spectrometer at the Geological Scientific Research Institute meability data and the interpretation of oil, gas, water of the Sinopec Shengli Oilfield Company. The thin sections layers, and dry layers, the quantitative functional rela- were made by the CNPC Key Laboratory of Oil and Gas tionship between the effective porosity cutoff and burial z x Reservoirs at the China University of Petroleum and were depth from the Es to Es sub-members in the northern 3 4 examined by the authors with an Axio Scope A1 APOL zone of the Minfeng Sag was obtained using the oil test digital polarizing microscope, which was produced by the method, which was developed by Wang (2010): German company Zeiss. The fluid inclusions were ana- u ¼8:1623 lnðÞ H þ 73:765 R ¼ 0:8833 cutoff lyzed using a THMSG600 conventional inclusion temper- ature measurement system, which was produced by the u : porosity cutoff, %; H: burial depth, m. cutoff Using point-counting methods, a quantitative analysis of British Company Linkam. various pores in cast thin sections shows that the percent- age of secondary pores in the reservoirs in the nearshore subaqueous fans in the Es sub-member is greater than 4 Results 50 % (Fig. 2). Overlapping the u curve and the cutoff porosity envelope curve in the porosity-depth profile shows 4.1 Distribution of SPDZs that two secondary pore development zones, whose depths range from 4200 to 4500 m and from 4700 to 4900 m, The term ‘‘secondary pore development zone’’ has been developed in the Es sub-member in the northern zone of generally applied by scientists around the world but has not 4 the Minfeng Sag. been defined precisely and scientifically. Most geologists 123 Porosity envelope curve Porosity lower limit Pet. Sci. (2016) 13:1–17 5 Percentage of secondary pores, % Porosity, % 50 75 100 0 5 10 15 4.0 4.0 4.5 4.5 Measured data 5.0 5.0 Interpreted data Fig. 2 By overlapping the effective reservoir porosity cutoff in the porosity-depth profile, the relationship between the porosity envelope curve and the porosity lower limit shows two secondary pore development zones, which range from 4200 to 4500 m and from 4700 to 4900 m, in Es in the northern zone of the Minfeng Sag 4.2 Reservoir characteristics in secondary pore typical turbidites, which mainly consist of dark-gray development zones mudstones with thin interbedded sandstones and pebbly sandstones (Fig. 3). 4.2.1 Sedimentary characteristics The relationship between different micro-facies in the nearshore subaqueous fans and their physical properties Multi-phase nearshore subaqueous fans developed in the were identified based on sedimentary analyses of individual Es sub-member in the northern zone of the Minfeng Sag. wells. This relationship shows that the high porosity reser- The nearshore subaqueous fans can be subdivided into voirs in the SPDZs are located in the center of thick sand beds inner fan, middle fan, and outer fan sub-facies according to that were deposited in braided channels in the middle fan, in the sedimentary features and hydrodynamic conditions. contrast to the reservoirs in the inner and outer fans or the The inner fan sub-facies are dominated by major channels inter-distributaries in the middle fan. The low porosity that are mainly filled with thick matrix-supported con- reservoirs that correspond to the SPDZs include thin sand glomerates and lack normal lacustrine mudstones between bodies in the outer fan, inter-distributaries in the middle fan, multi-phase fans. The poorly sorted conglomerates have a marginal reservoirs in thick sand beds in the middle fan, and high proportion of matrix, with sub-angular grains floating thick conglomerates in the inner fan (Fig. 3). among them, and scoured bases can be identified, which indicates proximal and rapid accumulation. The middle 4.2.2 Secondary pores fans are dominated by braided channels and inter-dis- tributaries. The lithology of the braided channels mainly The secondary pores in the SPDZ reservoirs in the Es sub- consists of massive gravel sandstones and superimposed member include pores that formed from the dissolution of coarse sandstones with scoured bases, which have grain- feldspars and acid extrusive rock debris, detrital quartz supporting characteristics, medium-poor sorting, moderate grains and quartz overgrowths, carbonate and pyrite thickness, and low matrix content. Normally graded bed- cements and compacted cracks in feldspars and other brittle ding, scouring structure, and intensely contemporaneous grains. These secondary pores originated from the disso- deformation structures are present. The inter-distributaries lution of feldspars and rock debris. They mainly occur as are typical turbidites, which contain thin and fine-grained intra-granular pores and grain boundary pores (Appendix sediments with high matrix content. Lacustrine mudstones Fig. 7A, B, C). The quartz grains and quartz overgrowths are generally deposited among multi-stage middle fans usually dissolved along the boundaries, which formed (Fig. 3). The lithology of the outer fan sub-facies includes irregular pores (Appendix Fig. 7D). Euhedral ankerite Depth, km Depth, km 6 Pet. Sci. (2016) 13:1–17 x0 Table 1 Types and percentages of secondary pores in Es s sec- Sedimentary 4 Porosity, % facies ondary pore development zones in the northern zone of the Minfeng Depth Core section Sag Facies 0 5 10 15 Secondary pore development zone 4200–4500 m 4700–4900 m Types of secondary pores Feldspar-dissolved pores, % 25–70/48.6 62.5–72.9/ 67.7 Carbonate-dissolved pores, % 12.7–69.0/ 10.4–15.6/ 40.4 13.0 Rock debris-dissolved pores, % 0–6.33/1.58 0–6.25/3.13 Quartz-dissolved pores, % 0–12.5/4.7 6.25–15.6/ 10.9 Pyrite-dissolved pores, % 0–12.5/3.13 0–6.25/3.13 Cracks, % 0–6.33/1.58 0–4.17/2.08 Note: ‘‘25-70/48.6’’ means ‘‘Minimum–Maximum/Average’’ The diagenetic evolution sequences of the reservoirs in the SPDZs were established based on an analysis of the types and features of the diagenesis, including the texture of authigenic minerals, the metasomatism-crosscutting rela- tionship, the dissolution-filling relationship, and the homogenization temperatures of fluid inclusions. The siderite cements are mainly granular and lumpy and are products of early diagenesis (Appendix Fig. 8A). The Fig. 3 Sedimentary characteristics and physical properties of the reservoirs in the Es sub-member in the northern zone of the Minfeng 4 halite is completely crystalline (Appendix Fig. 8B), and the Sag. The effective reservoirs are the conglomerate in the central part anhydrite was replaced by dolomite or ankerite, which of the positive sedimentary cycle of braided channels in the middle suggests that the halite and gypsum were early cements, fan of the nearshore subaqueous fans with gypsum turning into anhydrite after dehydration at cement dissolved along its boundaries, while dolomite high temperatures. Quartz overgrowths were replaced by cement dissolved to form secondary pores in cements ankerite and pyrite, which demonstrates that the quartz (Appendix Fig. 7E, F). Pyrite-dissolved pores are mostly overgrowths formed earlier than the ankerite and pyrite found within cements (Appendix Fig. 7G). Compacted (Appendix Fig. 8D, E). Multi-stage quartz overgrowths can cracks in feldspars, which generally cut through the grains, be identified in thin sections. The homogenization tem- are wide at one end and narrow at the other side of the perature (Th) of the aqueous inclusions in the early stage of grains (or are irregular) (Appendix Fig. 7H). Quantitative quartz overgrowths in Es is only 115 C (Table 2). The data regarding the amounts of different types of secondary combination of Th with burial and thermal history of the pores in cast thin sections show that feldspar-dissolved Fengshen8 well suggests the precipitation of the quartz pores and carbonate-dissolved pores dominate in the cements at 42 Ma. The homogenization temperature of the reservoirs in the SPDZs in the Es sub-member at depths late stage quartz overgrowths reached 155–160 C from 4200 to 4500 m and from 4700 to 4900 m, followed (Table 2), which suggests that the quartz overgrowths by quartz-dissolved pores, a few acid extrusive rock debris- occurred later. Ankerite was identified in the secondary dissolved pores, pyrite-dissolved pores, and compacted pores in the feldspar grains (Appendix Fig. 8F) and car- cracks (Table 1). bonate cements (Appendix Fig. 7E, F), which indicates that the reservoir experienced two stages of acidic dissolution: 4.2.3 Diagenetic evolution sequence an early stage of feldspar dissolution and a late stage of carbonate cement dissolution. The diagenesis processes that occurred in the Es reservoirs In an acidic geochemical environment, SiO (aq) that is 4 2 in the SPDZs include the multi-stage dissolution of min- released from feldspar dissolution can precipitate in the erals (e.g., feldspar, carbonate, and quartz), multi-stage form of quartz overgrowths. In this study, the homoge- cementation (e.g., carbonate, silica, anhydrite, pyrite, and nization temperatures of the oil inclusions in the quartz asphalt), and complex replacement (Appendices 1, 2, 3). overgrowths and the fillings of the feldspar-dissolved pores Porosity lower Porosity lower limit Porosity lower limit limit Nearshore Nearshore subaqueous fan Nearshore subaqueous fan subaqueous fan Middle fan Middle fan Outer fan Subfacies Micro- Interdistributary Braided channels facies Fengshen1 Fengshen1 Fengshen1 Typical well Pet. Sci. (2016) 13:1–17 7 Table 2 Homogenization temperatures of fluid inclusions from reservoirs in Es in the northern zone of the Minfeng Sag Well number Depth, m Horizon Host minerals Types Inclusion Average number homogenization temperature, C Feng8 4397.5 Es Quartz overgrowth Brine 6 115 Feng8 4200.7 Es Quartz cement Brine 5 124.1 Fengshen3 3785.6 Es Quartz cement Brine 8 133.9 Feng8* 4055.35 Es Quartz overgrowth Brine 3 143.3 Fengshen3 4867 Es Quartz overgrowth Brine 1 155 Fengshen3 4785.7 Es Quartz overgrowth Brine 1 155 Fengshen10 4260.6 Es Quartz overgrowth Brine 1 155.5 Fengshen3 4785.7 Es Quartz overgrowth Brine 1 160 Feng8* 4055.35 Es Quartz overgrowth Oil 3 99.1 Feng8* 4055.35 Es Quartz overgrowth Oil 5 112.6 Feng8* 4201.1 Es Fillings of feldspar-dissolved pores Oil 5 88.7 Feng8* 4055.35 Es Fillings of feldspar-dissolved pores Oil 9 91.9 Fengshen1* 4321.6 Es Fillings of feldspar-dissolved pores Oil 4 98.8 Feng8* 4201.1 Es Fillings of feldspar-dissolved pores Oil 4 108.1 Fengshen1* 4348.8 Es Fillings of feldspar-dissolved pores Oil 2 108.7 Feng8* 4055.35 Es Fillings of feldspar-dissolved pores Oil 4 109.6 * Means data from the Geological Scientific Research Institute of the Sinopec Shengli Oilfield Company (such as SiO ) mainly range from 88 C to 110 C, and the et al. (2010a, b) proposed that the asphalt in the Fengshen1 homogenization temperatures of paragenetic aqueous well was a product of oil pyrolysis when temperatures inclusions are about 115 C, which suggest that the oil and exceeded 160 C. Additionally, Li et al. (2010a, b) found aqueous inclusions formed simultaneously. This observa- that secondary pores in the feldspar grains were filled with tion means that feldspar dissolution and early quartz asphalt, and tension fractures that are associated with the overgrowth cementation occurred roughly during the same secondary pores were produced by overpressure from oil early period. Both carbonate cementation and quartz dis- cracking (Appendix Fig. 8H). The above analysis shows solution occur in an alkaline environment, so they may that the asphalt formed relatively late. Before being filled have formed during the same period. The replacement of with asphalt, the reservoirs should have had high porosity, feldspar overgrowths by ankerite (Appendix Fig. 8G) which indicates that the porosities were well preserved suggests that the ankerite formed later than the feldspar during deep burial. Pyrite cements developed extensively overgrowths, whereas the ankerite and feldspar over- in the northern zone of the Minfeng Sag. Partial cloddy growths both formed in an alkaline environment, which pyrites are products of early cementation (Appendix indicates that they are probably products from the same Fig. 9G). Because mostly pyrite cements replaced quartz period. Strong asphalt cementation is typical in the reser- overgrowths (Appendix Fig. 8E), feldspar overgrowths, voirs in the SPDZs of Es . Many primary pores and various and ankerite (Appendix Fig. 9H), they should have formed secondary pores (from the dissolution of feldspars, anker- during a late diagenetic stage. The textures of both the ite, quartz grains, and quartz overgrowths) are largely filled pyrite cements and asphalt suggest that they formed during by asphalt (Appendix Fig. 8H, 3A, B, C, D, E, F). These the same period. During paragenesis with asphalt, pyrite is textures suggest that asphalt formed very late, and many considered to be a reaction product of hydrogen sulfide primary and secondary pores existed in the reservoirs (H S) from crude oil cracking under high temperatures and 2? before being filled with asphalt. For example, the thin Fe in reservoir fluids. section porosity of the asphalt in the reservoir at a depth of According to these comprehensive analyses, the diage- 4323.3 m in the Fengshen1 well is approximately 10 %, netic evolution sequence of the reservoirs in the SPDZs of and the porosity that was filled by asphalt may be 22 % Es is as follows: compaction/gypsum cementation/halite according to the relationship between the thin section cementation/pyrite cementation/siderite cementation ? porosity and core porosity. Song et al. (2009a) suggested feldspar dissolution/quartz overgrowth ? carbonate that crude oil in the deep buried reservoirs in the Feng- cementation/quartz dissolution/feldspar overgrowth ? shen1 well started to crack into gas and asphalt during the carbonate dissolution/feldspar dissolution/quartz over- late depositional period of the Minghuazhen Formation. Li growth ? pyrite cementation and asphalt filling. 123 8 Pet. Sci. (2016) 13:1–17 Es Es Es Es x 4 3 2 1 Ng Q Es Ed Nm 60 °C 80 °C 100 °C R =0.5% 120 °C R =0.7% 140 °C R =1.0% Zone of maximum concentration of organic acid 4 160 °C Zone of favorable preservation R =1.3% of organic acid Zone of decarboxylation of organic acid 50 40 30 20 10 0 Time before present, Ma Fig. 4 The burial history and evolutionary history of organic matter from the Fengshen1 well (modified from Song et al. 2009a) From the deposition of the Es sub-member to 44 Ma 5 Discussion before the present (the end of the deposition of Es ), the top Models of the diagenetic environment evolution and boundary of the Es was buried to a depth shallower than 750 m at formation temperatures below 50 C, and the reservoir reconstruction were established using the burial evolution history of the Fengshen1 well based on research bottom boundary was buried less than 1400 m at temper- atures below 75 C. The main diagenesis during this period of the sedimentary characteristics, secondary pore features, and diagenetic evolution of the reservoirs in Es ’s SPDZs was compaction, which led to the drainage of formation water. At this time, the salinity of the water in the pore in the northern zone of the Minfeng Sag (Fig. 4). The genetic mechanism and evolutionary model of the SPDZs spaces increased, which resulted in the early precipitation of gypsum and halite. Anaerobic bacteria broke down in Es are discussed from the perspective of the SPDZ at 2- organic matter and SO in the pore water, releasing depths from 4200 m to 4500 m (Fig. 5, Fig. 6). organic acids, H S, CO , and other gases. Under these Gypsum-halite layers were deposited in the Es sub- 4 2 2 3? 2? conditions, the Fe in the sediments was reduced to Fe member, and the thickness of the gypsum-halite layers in Es is 1287.5 m in the Fengshen2 well and 267.7 m in the and formed spherulitic pyrite and agglomerate siderite cement (Curtis 1978). Because the organic acids that Fengshen1 well. Three sets of high-quality source rocks developed in Es (Song et al. 2009a), and studies suggest formed during this period were mostly destroyed by bac- teria, the formation water remained alkaline, and the for- that the gypsum-halite layer is contemporaneous with deep water source rocks. Gypsum precipitates under physico- mation exhibited normal fluid pressure. The conglomerate bodies of the nearshore subaqueous fans were similar to chemical conditions with pH higher than 7.8 (Qiu and Jiang dome-shaped anticlines, with a flat bottom and convex top 2006), which suggests the development of an alkaline-re- in a cross-section and was defined by Zhong et al. (2004)as ducing environment in the salt lake during the depositional ‘‘fan-anticlines’’ that formed by sedimentation. The inner period of the Es sub-member. Depth, km Weak acid Acid Alkaline Acid Alkaline Meteoric fresh water Clay minerals transformation Gypsum dehydration Organic acids evolution Accumulation period Strata Normal pressure Middle-over pressure Normal pressure pressure Pet. Sci. (2016) 13:1–17 9 Temperature Depth, m °C Age pH Reservoir reconstruction section Ma Top Bottom Top Bottom boundary boundary boundary boundary 0 3890 4490 150 170 ¥¥ ¥ ¥ Condensate gas charged, crude oil in paleo-reservoir cracked, TSR reaction, pyrite cemented, third phase quartz overgrowth 2 3600 4200 140 165 Normal pressure charging of hydrocarbon, TSR reaction, third phase quartz overgrowth 7 2990 3590 120 140 Organic acids form again, strata uplifted, hydrocarbon partly lost, overpressure released, fresh water infiltrated 14 2680 3280 110 135 Mainly carbonate dissolved, a few feldspar dissolved; second phase quartz overgrowth 24.6 3090 3690 130 150 Organic acids decomposed, gypsum dehydrated, clay minerals transformed, hydrocarbon charged under overpressure 32 2640 3250 120 145 - 2+ 2+ 2+ + 4+ OH , Ca , Fe , Mg , Na , Si CO flowed into reservoirs, 2 2 quartz and its overgrowth dissolved, carbonate cemented 41 1700 2380 90 120 42.5 1400 2100 75 110 Organic acids generated, feldspar dissolved, kaolinite filled pores, first phase quartz overgrowth developed 750 1480 50 75 Compaction dominated, pyrite, siderite, gypsum and halite cemented 1 Kaolinite converts to illite and chlorite 2 Smectite converts to illite ¥¥ Hydrocarbon Gas reservoir Gypsum-halite Source Carbonate Second Migration direction Migration Inner fan Middle fan Outer fan Mudstone Fault reservoirs filled by asphalt layer rocks cementation dissolution of hydrocarbon direction of fault Fig. 5 Diagenetic environment evolution and reservoir reconstruction model of Es in the northern zone of the Minfeng Sag Legend 10 Pet. Sci. (2016) 13:1–17 Porosity, % 010 20 30 40 1.0 (1) 44 Ma before present, reservoir space was primary pores (1) (2) 41 Ma before present, dissolution generated 1.5 secondary pores, and reservoir space was mainly primary pores (3) 24.6 Ma before present, carbonate cementation 2.0 decreased porosity, quartz dissolution increased porosity. Hydrocarbon charging and overpressure (2) protected pores, reservoir space was mainly primary pores (4) 14 Ma before present, the strata uplifted, hydrocarbon 2.5 reservoirs were destroyed, overpressure released, a few secondary pores were formed in organic acidic environment, reservoir space was mainly primary pores 3.0 (5) 7 Ma before present, the basin subsided, organic acids (4) decomposed, a few secondary pores formed, reservoir space was mainly primary pores (5) 3.5 (6) 2 Ma before present, hydrocarbon charged, compaction decreased the porosity, reservoir space (3) was mainly primary pores Now, crude oil cracked, a large amount 4.0 (7) (6) of primary pores were destroyed, reservoir space was mainly secondary pores, (7) secondary pore development zones formed 4.5 Reservoir space is mainly primary pores Tested porosity Log interpreted porosity Reservoir space is mainly secondary pores Fig. 6 Genetic mechanism and evolutionary model of Es s secondary pore development zones in the northern zone of the Minfeng Sag fans of the nearshore subaqueous fans are mainly com- this time. When the temperature was higher than 160 C, the posed of matrix-supported conglomerates, whose resistance organic acids were completely converted to CO , and the pH to compaction is weak. The middle fans mainly consist of of the solution during this time was mainly controlled by the pebbly sandstones and sandstones in braided channels, concentration of CO . During this stage, the organic matter in whose resistance to compaction is relatively strong. The Es had begun to mature and released a large quantity of high part of the conglomerate fans had an anticlinal attitude organic acids. The temperature range during this stage was and formed dome traps as a result of differential com- favorable for the preservation of organic acids, which caused paction (Wang 2003). During this period, the reservoir the pH of the formation water to become acidic. Because of spaces were dominated by primary pores after compaction the shallow burial, the development of primary porosity, and and early cementation (Fig. 6). good pore connectivity, the strata also exhibited the prop- From 44 to 41 Ma before the present (the early period of erties of an open hydrologic system with normal fluid pres- the deposition of Es ), the top boundary of the strata was sure. In this environment, feldspar dissolved to form buried at 1700 m at temperatures of 90 C, and the bottom secondary pores. This resulted in the precipitation under boundary was buried at 2380 m at temperatures of 120 C. appropriate conditions of authigenic kaolinite and first phase According to Surdam’s studies (Surdam et al. 1984, 1989), quartz overgrowths. As stated above, the time of the early significant organic acid generation occurs during burial feldspar dissolution as determined by the homogenization evolution. The temperature range of the maximum concen- temperatures of aqueous inclusions in the quartz over- tration of short-chain carboxylic acids is 75–90 C (a peak of growths was approximately dated to 42 Ma before the pre- kerogen releasing oxygen-containing groups), and the opti- sent, which is the same as the feldspar dissolution under an mum temperature for organic acid preservation is organic acid environment. A study by Wang (2010) sug- 80–120 C. At lower temperatures, organic acids may be gested that gypsum began to convert to anhydrite through decomposed by bacteria. When the temperature rose to dehydration as the formation temperature exceeded 90 C, 120–160 C, carboxylate anions were converted into and large-scale dehydration can be expected during hydrocarbons and CO by thermal decarboxylation, raising 100–150 C. Thus, at approximately 42 Ma, significant the concentration of CO in solution and reducing the con- amounts of gypsum started to dehydrate as the bottom tem- - 2? centration of organic acids. However, the presence of perature reached 100 C, with a portion of OH and Ca organic acids maintained the pH of the fluids at 5–6 during dissolving in the water from dehydration of gypsum. Depth, km Porosity lower limit Pet. Sci. (2016) 13:1–17 11 However, the concentration of organic acids in the strata evolution of formation pressure showed that this hydrocar- during this period reached a maximum, which caused the bon charging period was accompanied by fluid overpressure, formation water to remain acidic. Under conditions of acidic which protected the reservoir pores. The point contacts of 2? formation water, Ca does not precipitate as carbonate. As grains and abundant primary pores can still be identified in the temperature reached 100 C, smectite gradually trans- the Fengshen1 well (Wang 2007) (Appendix Fig. 10A). formed into illite through the middle state of the mixed-layer Carbonate cementation was significantly inhibited in reser- of illite/smectite (I/S) in alkaline potassium-rich solutions voirs with hydrocarbon charging, and the present reservoirs (Wang 2010). Although the temperature reached the con- are characterized by a lower amount of euhedral carbonate version temperature of smectite to I/S, and although the cements (Appendix Fig. 10B). However, reservoirs without ? 3? formation water was rich in K and Al because of feldspar hydrocarbon charging were intensely filled by carbonate dissolution, smectite was not converted to I/S because of the cements because of the long duration of the alkaline envi- presence of the acidic formation water. Although secondary ronment. A statistical analysis of the percentage of secondary pores were abundant during this stage, primary pores still pores after carbonate cementation showed that the reservoir dominated the reservoir spaces in the SPDZs in Es because spaces in the SPDZs were mainly primary pores, and the of the short dissolution time (only 3 Ma) and the develop- percentage of secondary pores was less than 15 % (Wang ment of primary pores (Fig. 6). From 41 to 24.6 Ma before 2010) (Fig. 6). the present (late depositional period of the Dongying For- The strata experienced uplift and then subsidence from mation), the top boundary of the strata was buried at 3090 m 24.6 to 7 Ma before the present (the end of the depositional at temperatures of 130 C, and the bottom boundary was period of the Guantao Formation). During this period, the buried at 3690 m at temperatures of 150 C. The decar- top boundary was uplifted to 2680 m and then subsided to boxylation of organic acids began during this period, which 2990 m, while the bottom was uplifted to 3280 m and then formed CO and hydrocarbons and significantly reduced the subsided to 3590 m. The temperature of the top boundary concentration of organic acids. Gypsum entered the large- fell to 110 C and then increased to 120 C, while the scale dehydration stage, during which the presence of alka- temperature of the bottom boundary fell to 135 C and then line water controlled the pH of the formation water. In this increased to 140 C. During this period, the organic matter alkaline environment, smectite quickly transformed into I/S, stopped producing hydrocarbons, but the evolution of the 2? ? 2? 2? which released metal ions such as Ca ,Na ,Fe ,Mg , organic matter still generated large amounts of organic 4? ? and Si . In this alkaline environment, which was rich in K , acids, which were preserved at a favorable temperature and 2? 2? Fe , and Mg , the early kaolinite was rapidly converted to caused the formation water to be acidic. The tectonic 2? illite and chlorite. Under alkaline conditions with Ca , movements of the Chennan Fault destroyed the initial 2? 2? Fe , and Mg , detrital quartz and the early stage over- hydrocarbon reservoirs and caused the loss of hydrocarbons growths dissolved to form secondary pores, and significant and release of fluid overpressure. Meanwhile, meteoric amounts of carbonate cements precipitated to fill primary freshwater penetrated deep formations using faults as con- x x pores and early feldspar pores. The reservoirs in Es exhibit duits. The strata in Es were thought to have been buried 4 4 three stages of hydrocarbon accumulation. The first stage relatively deeply during the uplift stage; thus, meteoric fresh occurred from the end of the depositional period of Es (or water had a weak effect on reservoir reconstruction. the early depositional period of Es ) to the late depositional During this stage, the organic acids primarily recon- period of the Dongying Formation, from approximately structed the reservoirs at the bottom of ‘‘paleo-reservoirs’’, 38 Ma (or 41 Ma) to 24.6 Ma before the present. The second which had been charged with fewer hydrocarbons, or in and third stages experienced continuous charging of hydro- reservoirs where hydrocarbons had leaked. The organic carbons, which occurred from the mid-late depositional acids dissolved carbonate cements and small amounts of period of the Guantao Formation to the present (Song et al. feldspars, which caused second phase quartz overgrowths to 2009a, b). A study by Sui et al. (2010) showed that when the develop in the reservoirs. This process occurred because nearshore subaqueous fans in the northern zone of the Min- these reservoirs were protected by overpressure and feng Sag were buried deeper than 3200 m, the inner fan sub- hydrocarbons, which made the early cementation relatively facies acted as lateral seals for the hydrocarbon reservoirs. weak and led to higher porosity and good fluidity in these Therefore, the middle fan could have formed lithologic traps reservoirs. However, acidic fluids had difficulty in flowing because of the lateral plugging of the inner fan and the nor- into reservoirs with strong carbonate cementation, which mal lacustrine mudstone seal. Thus, when the organic matter acted as an obstacle for reservoir reconstruction and effec- became highly mature, massive amounts of oil and gas tive reservoir formation. The degree of reservoir recon- migrated into the top part of the ‘‘fan-anticlines’’ and middle struction was limited during this stage; thus, the reservoir fan lithologic traps at depths greater than 3200 m, which spaces in the secondary pore development zones were formed early hydrocarbon reservoirs. A study on the mainly primary pores (Fig. 6). 123 12 Pet. Sci. (2016) 13:1–17 The strata subsided quickly from 7 to 2 Ma before the secondary pores to exceed that of primary pores (Fig. 2, present (the end of the depositional period of the Minghuazhen Fig. 6). According to the definition of the SPDZ, the Formation). The top boundary was buried at 3600 m, and the SPDZs in Es in the northern zone of the Minfeng Sag bottom was buried at 4200 m. The temperatures of the top and formed when many primary pores were filled with asphalt bottom boundaries were 140 and 165 C, respectively. and pyrite from oil cracking since 2 Ma. Organic matter reached the second hydrocarbon generation peak and produced large amounts of crude oil and associated gas. The center of the Minfeng Sag had already entered the 6 Conclusions condensate gas stage. Many organic acids began to decompose by thermal decarboxylation, which decreased the acidity of the (1) Secondary pore development zones can be defined in formation water. Later, the reservoirs were mainly charged three ways: (1) the percent of secondary pores is with oil and gas, which were further supplements to the ‘‘paleo- greater than 50 %; (2) the porosity of the reservoirs is reservoirs’’. Li et al. (2010a, b) showed that normal pressure higher than the effective reservoir porosity cutoff charging occurred during this period. When little formation because the absolute content of secondary pores is water was flowing, the degree of hydrocarbon charging was high; and (3) high porosity reservoirs concentrate to limited. Thus, the oil charging during this period was only a form belts at particular depth intervals in the porosity- supplement to early stage hydrocarbon reservoirs. According depth profile, with the porosity envelope curve bul- to Li et al. (2010a, b), the gas reservoirs in Es in the Fengshen1 ging toward higher porosities. Accordingly, two well were mainly gas from oil cracking, which demonstrated secondary pore development zones exist in Es in the that the contribution of later-stage charging to the present northern zone of the Minfeng Sag, which range from reservoirs was subordinate. During this period, the rocks had 4200 to 4500 m and from 4700 to 4900 m. basically consolidated and the emplacement of hydrocarbons (2) The secondary pore development zones in Es in the inhibited diagenesis, so compaction and cementation had little northern zone of the Minfeng Sag experienced the effect on reservoir reconstruction. At the same time, the for- following processes. Significant numbers of secondary mation temperature reached the threshold for the thermo- pores (although fewer than primary pores) formed from chemical sulfate reduction (TSR) reaction, and organic acids the dissolution of feldspar in an early organic acid and H S were formed from hydrocarbon and anhydrite reac- environment. During this stage, the burial depth of the tions. These acidic fluids could dissolve feldspars and car- reservoirs was shallow. The pore spaces were slightly bonates, forming third phase quartz overgrowths with fluid changed during strata subsidence—uplift—subsidence inclusions with homogenization temperatures from 140 to because of early hydrocarbon charging and overpres- 160 C (Table 2). However, the formation was a relatively sure protection. Finally, the present secondary pore closed geochemical system during this period, and large development zones formed when many primary pores amounts of water flow and material transport were impossible, were filled by massive asphalt and pyrite from oil so the amount of acidic fluids from the TSR reaction and the cracking in deeply buried paleo-reservoirs. amount of secondary pores from the dissolution of feldspar and carbonate were small. Therefore, primary pores still dominated in the reservoirs in the SPDZs (Fig. 6). Acknowledgments The research is co-funded by National Natural Science Foundation of China (Grant No. 41102058, Grant No. From 2 Ma to the present, the top boundary of the strata U1262203, and Grant No. 41202075), the National Science and was buried at 3890 m at temperatures of 150 C, and the Technology Special Grant (Grant No. 2011ZX05006-003), the Fun- bottom boundary was buried at 4490 m at temperatures of damental Research Funds for the Central Universities (Grant No. 170 C. During this stage, the organic acids had almost 14CX02181A, Grant No. 15CX08001A, and Grant No. 15CX0 5007A), and Shandong Natural Science Foundation (Grant No. been completely decomposed, which caused the formation ZR2011DQ017). The authors thank the Geological Scientific water to be weakly acidic with a pH of 6–7. Organic matter Research Institute of Sinopec Shengli Oilfield Company, the Explo- began generating condensate gas, and crude oil in the ration and Development Research Institute of Sinopec Zhongyuan ‘‘paleo-reservoirs’’ started to crack and form large amounts Oilfield Company, and the CNPC key laboratory of oil and gas reservoirs in China University of Petroleum for providing database of asphalt and H S. The TSR reactions also produced some 2? and technological assistance. H S. Later pyrite from the reaction between H S and Fe 2 2 in the reservoirs replaced the initial cements and filled the Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://crea pores. Evidence of petroleum cracking in the ‘‘paleo- tivecommons.org/licenses/by/4.0/), which permits unrestricted use, reservoirs’’ was discussed in detail as part of the diagenetic distribution, and reproduction in any medium, provided you give evolution sequence. The later cementation of asphalt and appropriate credit to the original author(s) and the source, provide a pyrite destroyed a large amount of primary porosity in the link to the Creative Commons license, and indicate if changes were ‘‘paleo-reservoirs’’, which caused the proportion of made. 123 Pet. Sci. (2016) 13:1–17 13 Appendix 1 See Appendix Fig. 7. Feldspar-boundary dissolved pores Feldspar intra-granular dissolved pores Quartz-boundary dissolved pores Dissolved pores of acid-extrusive rock debris C D Dissolved pores of ankerite cements Dissolved pores of dolomite cements Compacted crack in feldspar grains Dissolved pores of pyrite cements G H Fig. 7 A Fengshen1 well, 4321.9 m, intra-granular-dissolved pores in feldspar grains. B Fengshen1 well, 4321.9 m, dissolved pores along feldspar grain boundaries. C Fengshen1 well, 4321.9 m, dissolved pores in acid extrusive rock debris. D Fengshen1 well, 4321.9 m, dissolved pores along quartz grain boundaries. E Fengshen1 well, 4323.3 m, dissolved pores in ankerite cement. F Fengshen4 well, 4476.15 m, dissolved pores in dolomite cement. G Fengshen1 well, 4348.25 m, dissolved pores in pyrite cement. H Fengshen3 well, 4867 m, compacted cracks in feldspar grains 123 14 Pet. Sci. (2016) 13:1–17 Appendix 2 See Appendix Fig. 8. Halite Lumpy siderite cement Ankerite Quartz overgrowth Anhydrite C D Pyrite Quartz overgrowth Ankerite Feldspar dissolved pores Dolomite Feldspar overgrowth Asphalt G H Fig. 8 A Fengshen1 well, 4323.3 m, lumpy siderite cement. B Feng8 well, 4397.15 m, halite-filled pores (SEM). C Feng8 well, 4397.15 m, anhydrite that replaced ankerite. D Fengshen3 well, 4867 m, ankerite that replaced quartz overgrowths. E Fengshen3 well, 4867 m, pyrite that replaced quartz overgrowths. F Fengshen3 well, 4867 m, ankerite filling parts of the feldspar-dissolved pores. G Fengshen1 well, 4350 m, dolomite that replaced feldspar overgrowths. H Fengshen1 well, 4321.9 m, asphalt filling intra-granular-dissolved pores in feldspar grains (Li et al. 2010a, b) 123 Pet. Sci. (2016) 13:1–17 15 Appendix 3 See Appendix Fig. 9. Fig. 9 A Fengshen1 well, 4323.3 m, asphalt and star-like pyrite filling intergranular pores. B Fengshen1 well, 4323.3 m, reflected light, the same visual area as A. C Fengshen1 well, 4321.9 m, asphalt and pyrite filling quartz-dissolved pores. D Fengshen1 well, 4321.9 m, reflected light, the same visual area as C. E Fengshen1 well, 4321.9 m, asphalt filling dissolved pores in ankerite cement. F Fengshen1 well, 4321.9 m, reflected light, the same visual area as E. G Fengshen1 well, 4323.3 m, reflected light, pyrite cement. H Fengshen3 well, 4867 m, pyrite that replaced ankerite 123 16 Pet. Sci. (2016) 13:1–17 Appendix 4 See Appendix Fig. 10. Fig. 10 A Fengshen1 well, 4322.5 m, primary pores (Wang 2010). B Fengshen1 well, 4321.9 m, complete crystal ankerite filling intergranular pores Jiang ZX, Qiu LW, Chen GJ. 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Genetic mechanisms of secondary pore development zones of Es 4 x in the north zone of the Minfeng Sag in the Dongying Depression, East China

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Springer Journals
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Copyright © 2016 by The Author(s)
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Earth Sciences; Mineral Resources; Industrial Chemistry/Chemical Engineering; Industrial and Production Engineering; Energy Economics
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1672-5107
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1995-8226
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10.1007/s12182-016-0076-7
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Pet. Sci. (2016) 13:1–17 DOI 10.1007/s12182-016-0076-7 ORIGINAL PAPER Genetic mechanisms of secondary pore development zones of Es in the north zone of the Minfeng Sag in the Dongying Depression, East China 1 1 1 1 • • • • Yan-Zhong Wang Ying-Chang Cao Shao-Min Zhang Fu-Lai Li Fan-Chao Meng Received: 27 October 2014 / Published online: 22 January 2016 The Author(s) 2016. This article is published with open access at Springerlink.com Abstract The genetic mechanisms of the secondary pore slightly changed because of protection from early hydro- development zones in the lower part of the fourth member carbon charging and fluid overpressure during deep burial. of the Shahejie Formation (Es ) were studied based on core Finally, the present secondary pore development zones observations, petrographic analysis, fluid inclusion analy- were formed when many primary pores were filled by sis, and petrophysical measurements along with knowledge asphalt and pyrite from oil cracking in deeply buried paleo- of the tectonic evolution history, organic matter thermal reservoirs. evolution, and hydrocarbon accumulation history. Two secondary pore development zones exist in Es , the depths Keywords Secondary pore development zone  Genetic of which range from 4200 to 4500 m and from 4700 to mechanism  Diagenetic evolution sequences  Secondary 4900 m, respectively. The reservoirs in these zones mainly pores  Dongying depression consist of conglomerate in the middle fan braided channels of nearshore subaqueous fans, and the secondary pores in these reservoirs primarily originated from the dissolution 1 Introduction of feldspars and carbonate cements. The reservoirs expe- rienced ‘‘alkaline–acidic–alkaline–acidic–weak acidic’’, As the degree of hydrocarbon exploration in middle-shal- ‘‘normal pressure–overpressure–normal pressure’’, and ‘‘formation temperature increasing–decreasing–increas- low formations continues to improve, deeply buried for- mations are gradually becoming important targets for ing’’ diagenetic environments. The diagenetic evolution sequences were ‘‘compaction/gypsum cementation/halite hydrocarbon exploration (Hu et al., 2013; Sun et al. 2013, 2015). Studies of anomalously high porosity and perme- cementation/pyrite cementation/siderite cementation–feld- spar dissolution/quartz overgrowth–carbonate cementation/ ability in deeply buried sandstone reservoirs by Bloch et al. quartz dissolution/feldspar overgrowth–carbonate dissolu- (2002) showed that deep formations can still develop abnormally high porosity zones that can form oil and gas tion/feldspar dissolution/quartz overgrowth–pyrite cemen- tation and asphalt filling’’. Many secondary pores (fewer fields with commercial value (Bloch et al. 2002). Under- standing the genesis of deep, abnormally high porosity than the number of primary pores) were formed by feldspar dissolution during early acidic geochemical systems with zones (AHPZs) is important for precisely predicting deeply buried high-quality reservoirs. This issue has been studied organic acid when the burial depth of the reservoirs was relatively shallow. Subsequently, the pore spaces were many times. Although the controlling factors of the for- mation of deep, abnormally high porosity zones vary in different regions, most geologists generally believe that & Yan-Zhong Wang mineral dissolution, shallow fluid overpressure, early wangyanzhong1980@163.com hydrocarbon charging, and grain rims are the main factors School of Geosciences, China University of Petroleum, that control the development of deep AHPZs (Bloch et al. Qingdao 266580, Shandong, China 2002; Ehrenberg 1993; Warren and Pulham 2001; Meng et al. 2011, 2010; Taylor et al. 2010; Wilkinson and Edited by Jie Hao 123 2 Pet. Sci. (2016) 13:1–17 Haszeldine 2011; Cao et al. 2014; Yuan et al. 2015; Dongying Depression are simply interpreted as having Ajdukiewicz and Larese 2012; Wang et al. 2014; Jiang formed from deep burial mineral dissolution (Yuan and et al. 2009). Wang 2001; Zhu et al. 2007). Some questions require Secondary pore development zones (SPDZ) are a typical further studies, such as whether these deep secondary pore type of abnormally high porosity zone. Since Schmidt and development zones were originally shallow secondary pore McDonald (1977) proposed the theory that secondary pores development zones that were preserved effectively during in clastic reservoirs can form during diagenetic processes deep burial and how these shallow secondary pore devel- (Schmidt and McDonald 1977), scientists worldwide have opment zones were preserved during deep burial. These made significant progress in identifying the distinguishing unresolved problems produce great difficulties and risks for features, genetic mechanisms, distribution, and geological the exploration and development of hydrocarbons in these significance of secondary pores (Schmidt and McDonald reservoirs. For instance, the drilling of the Fengshen2 and 1979; Giles and De Boer 1990; Osborne and Swarbrick Fengshen3 wells close to the Fengshen1 well was not 1999; Higgs 2007; Zhu et al. 2006; Zhang 2007; Zeng successful (the former were dry wells and the latter only 4 3 2001; Yuan and Wang 2001; Liu and Zhu 2006; Wang produced 2.64 9 10 m of gas daily) (Zhong et al. 2004). et al. 1995; Wang and Zhao 2001; Ma et al. 2005; Zhang The characteristics and genetic mechanisms of the et al. 2008; Dutton and Loucks 2010; Taylor et al. 2015). SPDZs in Es in the Minfeng Sag were systematically Currently, SPDZs in shallow layers, which correspond to studied based on a combination of core observations, thin the mature stage of organic matter evolution, are consid- section identification, SEM observations, fluid inclusion ered to be generated from the dissolution of aluminum analysis, core X-ray analysis, vitrinite reflectance tests, and silicates and carbonate minerals by organic acids and CO core properties analysis, along with additional knowledge from organic matter evolution (Zeng 2001; Yuan and regarding the tectonic evolution history, thermal evolution Wang 2001; Liu and Zhu 2006; Wang et al. 1995; Zhang of organic matter, and history of hydrocarbon accumulation et al. 2014). However, different viewpoints exist regarding in the study area. The results of this study show that the the generation of deep SPDZs. Some authors believe that deep SPDZs in the study area experienced the formation of these features form by mineral dissolution in low porosity significant secondary pores at shallow depth and the reservoirs at deep burial depths (Yuan and Wang 2001). occupation of many primary pores by massive asphalt and Other authors, however, believe that the large amounts of pyrite from oil cracking in deeply buried paleo-reservoirs secondary pores that form in these shallow formations are under high temperature. This achievement is significant for effectively preserved during deep burial, while primary re-evaluating the genetic mechanisms and distribution of pores are destroyed, which results in the formation of deep deep high-quality reservoirs and the deployment of SPDZs (Wang et al., 2001; Ma et al. 2005; Zhang et al. hydrocarbon exploration in deep formations. 2008; Bjørlykke and Jahren 2012; Bjørlykke 2014). Petroleum exploration in the deeply buried nearshore subaqueous fans in the Es sub-member in the Minfeng 2 Geological background Sag, Dongying Depression, has greatly improved in recent years. For example, the daily oil production from depths of The Dongying Depression is a sub-tectonic unit that lies in 4316.6–4343 m in the Fengshen1 well in Es is 81.7 t, and the southeastern part of the Jiyang sub-basin of the Bohai the daily gas production is 118,336 m . The reservoirs in Bay Basin in East China. This unit is a Meso-Cenozoic half the nearshore subaqueous fans, which are closely related to graben rift-downwarped lacustrine basin, which developed gypsum layers and the source rocks, experienced a com- on Paleozoic bedrock paleotopography (Yuan and Wang plex burial evolution, including tectonic subsidence— 2001). The Dongying Depression, which lies east of the uplift—subsidence and an alternating acidic-alkaline dia- Qingtuozi Salient, south of the Luxi Uplift and Guangrao genetic environment. The current reservoir space mainly Salient, west of the Linfanjia and Gaoqing Salients, and consists of secondary pores, and primary pores have been north of the Chenjiazhuang-Binxian Salient, covers an area mostly destroyed. Exploration of the Dongying Depression of 5850 km with an east–west axis of 90 km and a north– x s shows that four sets of source rocks exist in the Es ,Es , south axis of 65 km. Additionally, the depression is gen- 4 4 x z Es , and Es sub-members and that the total thickness of erally NE-trending. In profile view, the Dongying 3 3 these source rocks exceeds 2000 m. Depression is a half graben with a faulted northern margin The reservoirs in the Es sub-member could potentially and a gentle southern margin. In plan view, this depression form abundant secondary pores during shallow burial is further subdivided into secondary structural units, such because the organic matter in Es ’s source rocks could as a northern steep slope zone, a middle uplift, the Lijin, supply organic acids in a shallow open system. However, Minfeng, Niuzhuang, and Boxing sags, and a southern all the deep SPDZs in the Paleogene sandstones in the gentle slope zone (Zhang et al. 2006) (Fig. 1). 123 Qingtuozi Salient Shicun fault zone Pet. Sci. (2016) 13:1–17 3 42° (a) (b) Sag 0 100km N 0 20 km Uplift 40° Beijing Yanshan Č Dalian Ċ Chenjiazhuang Salient A’ Bohai Bay 38° ċ Coastline China Jinan 36° Fsh1 Beijing Fsh3 Tanlu Strike-slip Minfeng Fsh2 Fault Zone Binxian subsag 114° 116° 118° 120° 122° 124° Salient Lizezheng subsag Qingcheng Boxing subsag Salient Paleogene Paleogene system system area overlap zone Uplift Luxi Major Paleogene system fault denuded zone Nm-Q (c) S0 Ng Ng 1.0 1 S Es -Ed 1 S 1 S z 4 2 s S Es Es -Es 3 2 3 S z 2.0 4 Es 4 x S 3 6 Es S 6 S 6’ 6’ Es 3.0 Up S :Nm-Q S -S :Ng 0 0 1 7 Es Ek S -S :Es -Ed S -S :Es -Es SR 4.0 1 2 1 2 4 3 2 S -S :Es 4 6 3 S -S :Es 6 6’ 3 S -S :Es S -S :Ek 6’ 7 4 7 R Fig. 1 a Tectonic setting of the Dongying Depression in the Jiyang Sub-basin (III) of the Bohai Bay Basin. Other sub-basins in the Bohai Bay Basin in East China include the Jizhong Sub-basin (I), Huanghua Sub-basin (II), Bozhong Sub-basin (IV), Liaohe Sub-basin (V), and Dongpu Sub-basin (VI) (according to Liu et al. 2012). b Structural map of the Dongying Depression with well locations. The area in the green line is the study area, which is located in the northern zone of the Minfeng Sag of the Dongying Depression. c Section of A–A in map (b). S ,S ,S ,S ,S , 0 1 2 4 6 S 0,S , and S are major seismic reflection boundaries. Nm Neocene Minghuazhen Formation; Q Quaternary Period; Ng Neocene Guantao 6 7 R Formation; Ed Paleogene Dongying Formation; Es The first member of the Paleogene Shahejie Formation (Es); Es The second member of Es; 1 2 s z x Es The upper part of the third member of Es; Es The middle part of the third member of Es; Es The lower part of the third member of Es; Es 3 3 3 4 The fourth member of Es; Ek Paleogene Kongdian Formation (Liu et al. 2012) The Minfeng Sag lies in the northeastern area of the small lake-water area, and high salinity. The northern steep Dongying Depression, north of the Chenjiazhuang Salient, slope zone of the Minfeng Sag is a structural belt in the south of the middle uplift, east of the Qingtuozi Salient, steep slope zone that is controlled by the Chennan and west of the Lijin Sag (Fig. 1). During the depositional boundary fault, which is located near the subsidence center period of the Es sub-member, the Dongying Depression in with deeper water. Terrigenous clastic sediments were this early rift stage was characterized by an arid climate, a transported by seasonal floods to the deep lake, leading to Northern steep slope Binnan-lijin fault zone Tuo-Sheng-Yong fault zone Boxing fault zone Middle area Uplift Guangrao Salient Chennan Southern Slope Niuzhuang subsag fault Chenguanzhuang-wangjiagang fault zone Lijin subsag Linfanjia Salient Bamianhe fault zone Xinbei fault Fold Belt Uplift Gaoqing fault zone Liaodong Uplift Cangxian Uplift Luxi Uplift Jiaodong Uplift Taihangshan Round trip time, s 4 Pet. Sci. (2016) 13:1–17 the deposition of the nearshore subaqueous fans in the suggest that an SPDZ is the depth interval for which the downthrown side of the Chennan fault. These fans were real porosity evolution curve is higher than the normal distributed close to lacustrine source rocks (Sui et al. porosity evolution curve and the percent of secondary 2010). During flood stagnation, the water evaporated pores is over 50 % (Liu and Zhu 2006; Zhu et al. 2007;Shi rapidly, and thick gypsum and halite were deposited. In et al. 2005; Zhong et al. 2003; Zhang et al. 2003; Zheng vertical profile view, the strata show a sedimentary and Wu 1996). However, the porosity values of reservoirs assemblage of interbedded gypsum and clastic rocks. in secondary pore development zones and the methods that are used to determine the normal porosity evolution curve have not been clearly explained. Additionally, the methods 3 Methodology and database that are used to determine the real porosity evolution curve have not yet been unified. For example, one method that is This study used cast thin sections and SEM observations to used to determine this curve is to fit the functional rela- analyze the characteristics of the reservoir spaces based on tionship between the porosity and depth (Liu and Zhu effective reservoir porosity cutoffs. Porosity data were 2006; Zhu et al. 2007; Zhong et al. 2003; Zhang et al. combined with porosity cutoffs to determine the distribu- 2003). Another method uses the porosity envelope curve of tion of SPDZs. The sedimentary characteristics, secondary the porosity-depth profile as the real porosity evolution pore features, and diagenetic evolution sequences of the curve (Yuan and Wang 2001; Zhu et al. 2010; Liu et al. reservoirs in these SPDZs were studied based on the 2010). In this paper, an SPDZ is first defined as a zone identification of these zones. The genetic mechanism and where high porosity reservoirs with more than 50 % sec- evolutionary model of the secondary pore development ondary pores develop. This definition includes three zones, the evolution of the diagenetic environment, and the meanings: (1) the percent of secondary pores is greater than reservoir reconstruction process were discussed. 50 %; (2) the porosity of the reservoirs is higher than the The database that was used in the study includes effective reservoir porosity cutoff because the absolute approximately 250-m cores from eight wells, porosity data content of secondary pores is high; (3) high porosity from 172 samples, 70 thin sections, 30 cast thin sections, reservoirs concentrate to form belts at a particular depth six SEM samples, and 80 fluid inclusion samples. The core interval in the porosity-depth profile, with the porosity samples were provided by the Geological Scientific envelope curve bulging towards higher porosities. Research Institute of the Sinopec Shengli Oilfield Com- The effective reservoir porosity cutoff is the basis for pany. The porosity was tested by a 3020-62 helium determining SPDZs. Only when the effective porosity porosity analyzer at the Exploration and Development cutoff is known, can the development of high porosity Research Institute of the Sinopec Zhongyuan Oilfield reservoirs be confirmed and the distribution of secondary Company. The SEM samples were examined with a pore development zones determined. Based on collections Quanta200 SEM with an EDAX energy dispersive X-ray and arrangements of a large number of porosity and per- spectrometer at the Geological Scientific Research Institute meability data and the interpretation of oil, gas, water of the Sinopec Shengli Oilfield Company. The thin sections layers, and dry layers, the quantitative functional rela- were made by the CNPC Key Laboratory of Oil and Gas tionship between the effective porosity cutoff and burial z x Reservoirs at the China University of Petroleum and were depth from the Es to Es sub-members in the northern 3 4 examined by the authors with an Axio Scope A1 APOL zone of the Minfeng Sag was obtained using the oil test digital polarizing microscope, which was produced by the method, which was developed by Wang (2010): German company Zeiss. The fluid inclusions were ana- u ¼8:1623 lnðÞ H þ 73:765 R ¼ 0:8833 cutoff lyzed using a THMSG600 conventional inclusion temper- ature measurement system, which was produced by the u : porosity cutoff, %; H: burial depth, m. cutoff Using point-counting methods, a quantitative analysis of British Company Linkam. various pores in cast thin sections shows that the percent- age of secondary pores in the reservoirs in the nearshore subaqueous fans in the Es sub-member is greater than 4 Results 50 % (Fig. 2). Overlapping the u curve and the cutoff porosity envelope curve in the porosity-depth profile shows 4.1 Distribution of SPDZs that two secondary pore development zones, whose depths range from 4200 to 4500 m and from 4700 to 4900 m, The term ‘‘secondary pore development zone’’ has been developed in the Es sub-member in the northern zone of generally applied by scientists around the world but has not 4 the Minfeng Sag. been defined precisely and scientifically. Most geologists 123 Porosity envelope curve Porosity lower limit Pet. Sci. (2016) 13:1–17 5 Percentage of secondary pores, % Porosity, % 50 75 100 0 5 10 15 4.0 4.0 4.5 4.5 Measured data 5.0 5.0 Interpreted data Fig. 2 By overlapping the effective reservoir porosity cutoff in the porosity-depth profile, the relationship between the porosity envelope curve and the porosity lower limit shows two secondary pore development zones, which range from 4200 to 4500 m and from 4700 to 4900 m, in Es in the northern zone of the Minfeng Sag 4.2 Reservoir characteristics in secondary pore typical turbidites, which mainly consist of dark-gray development zones mudstones with thin interbedded sandstones and pebbly sandstones (Fig. 3). 4.2.1 Sedimentary characteristics The relationship between different micro-facies in the nearshore subaqueous fans and their physical properties Multi-phase nearshore subaqueous fans developed in the were identified based on sedimentary analyses of individual Es sub-member in the northern zone of the Minfeng Sag. wells. This relationship shows that the high porosity reser- The nearshore subaqueous fans can be subdivided into voirs in the SPDZs are located in the center of thick sand beds inner fan, middle fan, and outer fan sub-facies according to that were deposited in braided channels in the middle fan, in the sedimentary features and hydrodynamic conditions. contrast to the reservoirs in the inner and outer fans or the The inner fan sub-facies are dominated by major channels inter-distributaries in the middle fan. The low porosity that are mainly filled with thick matrix-supported con- reservoirs that correspond to the SPDZs include thin sand glomerates and lack normal lacustrine mudstones between bodies in the outer fan, inter-distributaries in the middle fan, multi-phase fans. The poorly sorted conglomerates have a marginal reservoirs in thick sand beds in the middle fan, and high proportion of matrix, with sub-angular grains floating thick conglomerates in the inner fan (Fig. 3). among them, and scoured bases can be identified, which indicates proximal and rapid accumulation. The middle 4.2.2 Secondary pores fans are dominated by braided channels and inter-dis- tributaries. The lithology of the braided channels mainly The secondary pores in the SPDZ reservoirs in the Es sub- consists of massive gravel sandstones and superimposed member include pores that formed from the dissolution of coarse sandstones with scoured bases, which have grain- feldspars and acid extrusive rock debris, detrital quartz supporting characteristics, medium-poor sorting, moderate grains and quartz overgrowths, carbonate and pyrite thickness, and low matrix content. Normally graded bed- cements and compacted cracks in feldspars and other brittle ding, scouring structure, and intensely contemporaneous grains. These secondary pores originated from the disso- deformation structures are present. The inter-distributaries lution of feldspars and rock debris. They mainly occur as are typical turbidites, which contain thin and fine-grained intra-granular pores and grain boundary pores (Appendix sediments with high matrix content. Lacustrine mudstones Fig. 7A, B, C). The quartz grains and quartz overgrowths are generally deposited among multi-stage middle fans usually dissolved along the boundaries, which formed (Fig. 3). The lithology of the outer fan sub-facies includes irregular pores (Appendix Fig. 7D). Euhedral ankerite Depth, km Depth, km 6 Pet. Sci. (2016) 13:1–17 x0 Table 1 Types and percentages of secondary pores in Es s sec- Sedimentary 4 Porosity, % facies ondary pore development zones in the northern zone of the Minfeng Depth Core section Sag Facies 0 5 10 15 Secondary pore development zone 4200–4500 m 4700–4900 m Types of secondary pores Feldspar-dissolved pores, % 25–70/48.6 62.5–72.9/ 67.7 Carbonate-dissolved pores, % 12.7–69.0/ 10.4–15.6/ 40.4 13.0 Rock debris-dissolved pores, % 0–6.33/1.58 0–6.25/3.13 Quartz-dissolved pores, % 0–12.5/4.7 6.25–15.6/ 10.9 Pyrite-dissolved pores, % 0–12.5/3.13 0–6.25/3.13 Cracks, % 0–6.33/1.58 0–4.17/2.08 Note: ‘‘25-70/48.6’’ means ‘‘Minimum–Maximum/Average’’ The diagenetic evolution sequences of the reservoirs in the SPDZs were established based on an analysis of the types and features of the diagenesis, including the texture of authigenic minerals, the metasomatism-crosscutting rela- tionship, the dissolution-filling relationship, and the homogenization temperatures of fluid inclusions. The siderite cements are mainly granular and lumpy and are products of early diagenesis (Appendix Fig. 8A). The Fig. 3 Sedimentary characteristics and physical properties of the reservoirs in the Es sub-member in the northern zone of the Minfeng 4 halite is completely crystalline (Appendix Fig. 8B), and the Sag. The effective reservoirs are the conglomerate in the central part anhydrite was replaced by dolomite or ankerite, which of the positive sedimentary cycle of braided channels in the middle suggests that the halite and gypsum were early cements, fan of the nearshore subaqueous fans with gypsum turning into anhydrite after dehydration at cement dissolved along its boundaries, while dolomite high temperatures. Quartz overgrowths were replaced by cement dissolved to form secondary pores in cements ankerite and pyrite, which demonstrates that the quartz (Appendix Fig. 7E, F). Pyrite-dissolved pores are mostly overgrowths formed earlier than the ankerite and pyrite found within cements (Appendix Fig. 7G). Compacted (Appendix Fig. 8D, E). Multi-stage quartz overgrowths can cracks in feldspars, which generally cut through the grains, be identified in thin sections. The homogenization tem- are wide at one end and narrow at the other side of the perature (Th) of the aqueous inclusions in the early stage of grains (or are irregular) (Appendix Fig. 7H). Quantitative quartz overgrowths in Es is only 115 C (Table 2). The data regarding the amounts of different types of secondary combination of Th with burial and thermal history of the pores in cast thin sections show that feldspar-dissolved Fengshen8 well suggests the precipitation of the quartz pores and carbonate-dissolved pores dominate in the cements at 42 Ma. The homogenization temperature of the reservoirs in the SPDZs in the Es sub-member at depths late stage quartz overgrowths reached 155–160 C from 4200 to 4500 m and from 4700 to 4900 m, followed (Table 2), which suggests that the quartz overgrowths by quartz-dissolved pores, a few acid extrusive rock debris- occurred later. Ankerite was identified in the secondary dissolved pores, pyrite-dissolved pores, and compacted pores in the feldspar grains (Appendix Fig. 8F) and car- cracks (Table 1). bonate cements (Appendix Fig. 7E, F), which indicates that the reservoir experienced two stages of acidic dissolution: 4.2.3 Diagenetic evolution sequence an early stage of feldspar dissolution and a late stage of carbonate cement dissolution. The diagenesis processes that occurred in the Es reservoirs In an acidic geochemical environment, SiO (aq) that is 4 2 in the SPDZs include the multi-stage dissolution of min- released from feldspar dissolution can precipitate in the erals (e.g., feldspar, carbonate, and quartz), multi-stage form of quartz overgrowths. In this study, the homoge- cementation (e.g., carbonate, silica, anhydrite, pyrite, and nization temperatures of the oil inclusions in the quartz asphalt), and complex replacement (Appendices 1, 2, 3). overgrowths and the fillings of the feldspar-dissolved pores Porosity lower Porosity lower limit Porosity lower limit limit Nearshore Nearshore subaqueous fan Nearshore subaqueous fan subaqueous fan Middle fan Middle fan Outer fan Subfacies Micro- Interdistributary Braided channels facies Fengshen1 Fengshen1 Fengshen1 Typical well Pet. Sci. (2016) 13:1–17 7 Table 2 Homogenization temperatures of fluid inclusions from reservoirs in Es in the northern zone of the Minfeng Sag Well number Depth, m Horizon Host minerals Types Inclusion Average number homogenization temperature, C Feng8 4397.5 Es Quartz overgrowth Brine 6 115 Feng8 4200.7 Es Quartz cement Brine 5 124.1 Fengshen3 3785.6 Es Quartz cement Brine 8 133.9 Feng8* 4055.35 Es Quartz overgrowth Brine 3 143.3 Fengshen3 4867 Es Quartz overgrowth Brine 1 155 Fengshen3 4785.7 Es Quartz overgrowth Brine 1 155 Fengshen10 4260.6 Es Quartz overgrowth Brine 1 155.5 Fengshen3 4785.7 Es Quartz overgrowth Brine 1 160 Feng8* 4055.35 Es Quartz overgrowth Oil 3 99.1 Feng8* 4055.35 Es Quartz overgrowth Oil 5 112.6 Feng8* 4201.1 Es Fillings of feldspar-dissolved pores Oil 5 88.7 Feng8* 4055.35 Es Fillings of feldspar-dissolved pores Oil 9 91.9 Fengshen1* 4321.6 Es Fillings of feldspar-dissolved pores Oil 4 98.8 Feng8* 4201.1 Es Fillings of feldspar-dissolved pores Oil 4 108.1 Fengshen1* 4348.8 Es Fillings of feldspar-dissolved pores Oil 2 108.7 Feng8* 4055.35 Es Fillings of feldspar-dissolved pores Oil 4 109.6 * Means data from the Geological Scientific Research Institute of the Sinopec Shengli Oilfield Company (such as SiO ) mainly range from 88 C to 110 C, and the et al. (2010a, b) proposed that the asphalt in the Fengshen1 homogenization temperatures of paragenetic aqueous well was a product of oil pyrolysis when temperatures inclusions are about 115 C, which suggest that the oil and exceeded 160 C. Additionally, Li et al. (2010a, b) found aqueous inclusions formed simultaneously. This observa- that secondary pores in the feldspar grains were filled with tion means that feldspar dissolution and early quartz asphalt, and tension fractures that are associated with the overgrowth cementation occurred roughly during the same secondary pores were produced by overpressure from oil early period. Both carbonate cementation and quartz dis- cracking (Appendix Fig. 8H). The above analysis shows solution occur in an alkaline environment, so they may that the asphalt formed relatively late. Before being filled have formed during the same period. The replacement of with asphalt, the reservoirs should have had high porosity, feldspar overgrowths by ankerite (Appendix Fig. 8G) which indicates that the porosities were well preserved suggests that the ankerite formed later than the feldspar during deep burial. Pyrite cements developed extensively overgrowths, whereas the ankerite and feldspar over- in the northern zone of the Minfeng Sag. Partial cloddy growths both formed in an alkaline environment, which pyrites are products of early cementation (Appendix indicates that they are probably products from the same Fig. 9G). Because mostly pyrite cements replaced quartz period. Strong asphalt cementation is typical in the reser- overgrowths (Appendix Fig. 8E), feldspar overgrowths, voirs in the SPDZs of Es . Many primary pores and various and ankerite (Appendix Fig. 9H), they should have formed secondary pores (from the dissolution of feldspars, anker- during a late diagenetic stage. The textures of both the ite, quartz grains, and quartz overgrowths) are largely filled pyrite cements and asphalt suggest that they formed during by asphalt (Appendix Fig. 8H, 3A, B, C, D, E, F). These the same period. During paragenesis with asphalt, pyrite is textures suggest that asphalt formed very late, and many considered to be a reaction product of hydrogen sulfide primary and secondary pores existed in the reservoirs (H S) from crude oil cracking under high temperatures and 2? before being filled with asphalt. For example, the thin Fe in reservoir fluids. section porosity of the asphalt in the reservoir at a depth of According to these comprehensive analyses, the diage- 4323.3 m in the Fengshen1 well is approximately 10 %, netic evolution sequence of the reservoirs in the SPDZs of and the porosity that was filled by asphalt may be 22 % Es is as follows: compaction/gypsum cementation/halite according to the relationship between the thin section cementation/pyrite cementation/siderite cementation ? porosity and core porosity. Song et al. (2009a) suggested feldspar dissolution/quartz overgrowth ? carbonate that crude oil in the deep buried reservoirs in the Feng- cementation/quartz dissolution/feldspar overgrowth ? shen1 well started to crack into gas and asphalt during the carbonate dissolution/feldspar dissolution/quartz over- late depositional period of the Minghuazhen Formation. Li growth ? pyrite cementation and asphalt filling. 123 8 Pet. Sci. (2016) 13:1–17 Es Es Es Es x 4 3 2 1 Ng Q Es Ed Nm 60 °C 80 °C 100 °C R =0.5% 120 °C R =0.7% 140 °C R =1.0% Zone of maximum concentration of organic acid 4 160 °C Zone of favorable preservation R =1.3% of organic acid Zone of decarboxylation of organic acid 50 40 30 20 10 0 Time before present, Ma Fig. 4 The burial history and evolutionary history of organic matter from the Fengshen1 well (modified from Song et al. 2009a) From the deposition of the Es sub-member to 44 Ma 5 Discussion before the present (the end of the deposition of Es ), the top Models of the diagenetic environment evolution and boundary of the Es was buried to a depth shallower than 750 m at formation temperatures below 50 C, and the reservoir reconstruction were established using the burial evolution history of the Fengshen1 well based on research bottom boundary was buried less than 1400 m at temper- atures below 75 C. The main diagenesis during this period of the sedimentary characteristics, secondary pore features, and diagenetic evolution of the reservoirs in Es ’s SPDZs was compaction, which led to the drainage of formation water. At this time, the salinity of the water in the pore in the northern zone of the Minfeng Sag (Fig. 4). The genetic mechanism and evolutionary model of the SPDZs spaces increased, which resulted in the early precipitation of gypsum and halite. Anaerobic bacteria broke down in Es are discussed from the perspective of the SPDZ at 2- organic matter and SO in the pore water, releasing depths from 4200 m to 4500 m (Fig. 5, Fig. 6). organic acids, H S, CO , and other gases. Under these Gypsum-halite layers were deposited in the Es sub- 4 2 2 3? 2? conditions, the Fe in the sediments was reduced to Fe member, and the thickness of the gypsum-halite layers in Es is 1287.5 m in the Fengshen2 well and 267.7 m in the and formed spherulitic pyrite and agglomerate siderite cement (Curtis 1978). Because the organic acids that Fengshen1 well. Three sets of high-quality source rocks developed in Es (Song et al. 2009a), and studies suggest formed during this period were mostly destroyed by bac- teria, the formation water remained alkaline, and the for- that the gypsum-halite layer is contemporaneous with deep water source rocks. Gypsum precipitates under physico- mation exhibited normal fluid pressure. The conglomerate bodies of the nearshore subaqueous fans were similar to chemical conditions with pH higher than 7.8 (Qiu and Jiang dome-shaped anticlines, with a flat bottom and convex top 2006), which suggests the development of an alkaline-re- in a cross-section and was defined by Zhong et al. (2004)as ducing environment in the salt lake during the depositional ‘‘fan-anticlines’’ that formed by sedimentation. The inner period of the Es sub-member. Depth, km Weak acid Acid Alkaline Acid Alkaline Meteoric fresh water Clay minerals transformation Gypsum dehydration Organic acids evolution Accumulation period Strata Normal pressure Middle-over pressure Normal pressure pressure Pet. Sci. (2016) 13:1–17 9 Temperature Depth, m °C Age pH Reservoir reconstruction section Ma Top Bottom Top Bottom boundary boundary boundary boundary 0 3890 4490 150 170 ¥¥ ¥ ¥ Condensate gas charged, crude oil in paleo-reservoir cracked, TSR reaction, pyrite cemented, third phase quartz overgrowth 2 3600 4200 140 165 Normal pressure charging of hydrocarbon, TSR reaction, third phase quartz overgrowth 7 2990 3590 120 140 Organic acids form again, strata uplifted, hydrocarbon partly lost, overpressure released, fresh water infiltrated 14 2680 3280 110 135 Mainly carbonate dissolved, a few feldspar dissolved; second phase quartz overgrowth 24.6 3090 3690 130 150 Organic acids decomposed, gypsum dehydrated, clay minerals transformed, hydrocarbon charged under overpressure 32 2640 3250 120 145 - 2+ 2+ 2+ + 4+ OH , Ca , Fe , Mg , Na , Si CO flowed into reservoirs, 2 2 quartz and its overgrowth dissolved, carbonate cemented 41 1700 2380 90 120 42.5 1400 2100 75 110 Organic acids generated, feldspar dissolved, kaolinite filled pores, first phase quartz overgrowth developed 750 1480 50 75 Compaction dominated, pyrite, siderite, gypsum and halite cemented 1 Kaolinite converts to illite and chlorite 2 Smectite converts to illite ¥¥ Hydrocarbon Gas reservoir Gypsum-halite Source Carbonate Second Migration direction Migration Inner fan Middle fan Outer fan Mudstone Fault reservoirs filled by asphalt layer rocks cementation dissolution of hydrocarbon direction of fault Fig. 5 Diagenetic environment evolution and reservoir reconstruction model of Es in the northern zone of the Minfeng Sag Legend 10 Pet. Sci. (2016) 13:1–17 Porosity, % 010 20 30 40 1.0 (1) 44 Ma before present, reservoir space was primary pores (1) (2) 41 Ma before present, dissolution generated 1.5 secondary pores, and reservoir space was mainly primary pores (3) 24.6 Ma before present, carbonate cementation 2.0 decreased porosity, quartz dissolution increased porosity. Hydrocarbon charging and overpressure (2) protected pores, reservoir space was mainly primary pores (4) 14 Ma before present, the strata uplifted, hydrocarbon 2.5 reservoirs were destroyed, overpressure released, a few secondary pores were formed in organic acidic environment, reservoir space was mainly primary pores 3.0 (5) 7 Ma before present, the basin subsided, organic acids (4) decomposed, a few secondary pores formed, reservoir space was mainly primary pores (5) 3.5 (6) 2 Ma before present, hydrocarbon charged, compaction decreased the porosity, reservoir space (3) was mainly primary pores Now, crude oil cracked, a large amount 4.0 (7) (6) of primary pores were destroyed, reservoir space was mainly secondary pores, (7) secondary pore development zones formed 4.5 Reservoir space is mainly primary pores Tested porosity Log interpreted porosity Reservoir space is mainly secondary pores Fig. 6 Genetic mechanism and evolutionary model of Es s secondary pore development zones in the northern zone of the Minfeng Sag fans of the nearshore subaqueous fans are mainly com- this time. When the temperature was higher than 160 C, the posed of matrix-supported conglomerates, whose resistance organic acids were completely converted to CO , and the pH to compaction is weak. The middle fans mainly consist of of the solution during this time was mainly controlled by the pebbly sandstones and sandstones in braided channels, concentration of CO . During this stage, the organic matter in whose resistance to compaction is relatively strong. The Es had begun to mature and released a large quantity of high part of the conglomerate fans had an anticlinal attitude organic acids. The temperature range during this stage was and formed dome traps as a result of differential com- favorable for the preservation of organic acids, which caused paction (Wang 2003). During this period, the reservoir the pH of the formation water to become acidic. Because of spaces were dominated by primary pores after compaction the shallow burial, the development of primary porosity, and and early cementation (Fig. 6). good pore connectivity, the strata also exhibited the prop- From 44 to 41 Ma before the present (the early period of erties of an open hydrologic system with normal fluid pres- the deposition of Es ), the top boundary of the strata was sure. In this environment, feldspar dissolved to form buried at 1700 m at temperatures of 90 C, and the bottom secondary pores. This resulted in the precipitation under boundary was buried at 2380 m at temperatures of 120 C. appropriate conditions of authigenic kaolinite and first phase According to Surdam’s studies (Surdam et al. 1984, 1989), quartz overgrowths. As stated above, the time of the early significant organic acid generation occurs during burial feldspar dissolution as determined by the homogenization evolution. The temperature range of the maximum concen- temperatures of aqueous inclusions in the quartz over- tration of short-chain carboxylic acids is 75–90 C (a peak of growths was approximately dated to 42 Ma before the pre- kerogen releasing oxygen-containing groups), and the opti- sent, which is the same as the feldspar dissolution under an mum temperature for organic acid preservation is organic acid environment. A study by Wang (2010) sug- 80–120 C. At lower temperatures, organic acids may be gested that gypsum began to convert to anhydrite through decomposed by bacteria. When the temperature rose to dehydration as the formation temperature exceeded 90 C, 120–160 C, carboxylate anions were converted into and large-scale dehydration can be expected during hydrocarbons and CO by thermal decarboxylation, raising 100–150 C. Thus, at approximately 42 Ma, significant the concentration of CO in solution and reducing the con- amounts of gypsum started to dehydrate as the bottom tem- - 2? centration of organic acids. However, the presence of perature reached 100 C, with a portion of OH and Ca organic acids maintained the pH of the fluids at 5–6 during dissolving in the water from dehydration of gypsum. Depth, km Porosity lower limit Pet. Sci. (2016) 13:1–17 11 However, the concentration of organic acids in the strata evolution of formation pressure showed that this hydrocar- during this period reached a maximum, which caused the bon charging period was accompanied by fluid overpressure, formation water to remain acidic. Under conditions of acidic which protected the reservoir pores. The point contacts of 2? formation water, Ca does not precipitate as carbonate. As grains and abundant primary pores can still be identified in the temperature reached 100 C, smectite gradually trans- the Fengshen1 well (Wang 2007) (Appendix Fig. 10A). formed into illite through the middle state of the mixed-layer Carbonate cementation was significantly inhibited in reser- of illite/smectite (I/S) in alkaline potassium-rich solutions voirs with hydrocarbon charging, and the present reservoirs (Wang 2010). Although the temperature reached the con- are characterized by a lower amount of euhedral carbonate version temperature of smectite to I/S, and although the cements (Appendix Fig. 10B). However, reservoirs without ? 3? formation water was rich in K and Al because of feldspar hydrocarbon charging were intensely filled by carbonate dissolution, smectite was not converted to I/S because of the cements because of the long duration of the alkaline envi- presence of the acidic formation water. Although secondary ronment. A statistical analysis of the percentage of secondary pores were abundant during this stage, primary pores still pores after carbonate cementation showed that the reservoir dominated the reservoir spaces in the SPDZs in Es because spaces in the SPDZs were mainly primary pores, and the of the short dissolution time (only 3 Ma) and the develop- percentage of secondary pores was less than 15 % (Wang ment of primary pores (Fig. 6). From 41 to 24.6 Ma before 2010) (Fig. 6). the present (late depositional period of the Dongying For- The strata experienced uplift and then subsidence from mation), the top boundary of the strata was buried at 3090 m 24.6 to 7 Ma before the present (the end of the depositional at temperatures of 130 C, and the bottom boundary was period of the Guantao Formation). During this period, the buried at 3690 m at temperatures of 150 C. The decar- top boundary was uplifted to 2680 m and then subsided to boxylation of organic acids began during this period, which 2990 m, while the bottom was uplifted to 3280 m and then formed CO and hydrocarbons and significantly reduced the subsided to 3590 m. The temperature of the top boundary concentration of organic acids. Gypsum entered the large- fell to 110 C and then increased to 120 C, while the scale dehydration stage, during which the presence of alka- temperature of the bottom boundary fell to 135 C and then line water controlled the pH of the formation water. In this increased to 140 C. During this period, the organic matter alkaline environment, smectite quickly transformed into I/S, stopped producing hydrocarbons, but the evolution of the 2? ? 2? 2? which released metal ions such as Ca ,Na ,Fe ,Mg , organic matter still generated large amounts of organic 4? ? and Si . In this alkaline environment, which was rich in K , acids, which were preserved at a favorable temperature and 2? 2? Fe , and Mg , the early kaolinite was rapidly converted to caused the formation water to be acidic. The tectonic 2? illite and chlorite. Under alkaline conditions with Ca , movements of the Chennan Fault destroyed the initial 2? 2? Fe , and Mg , detrital quartz and the early stage over- hydrocarbon reservoirs and caused the loss of hydrocarbons growths dissolved to form secondary pores, and significant and release of fluid overpressure. Meanwhile, meteoric amounts of carbonate cements precipitated to fill primary freshwater penetrated deep formations using faults as con- x x pores and early feldspar pores. The reservoirs in Es exhibit duits. The strata in Es were thought to have been buried 4 4 three stages of hydrocarbon accumulation. The first stage relatively deeply during the uplift stage; thus, meteoric fresh occurred from the end of the depositional period of Es (or water had a weak effect on reservoir reconstruction. the early depositional period of Es ) to the late depositional During this stage, the organic acids primarily recon- period of the Dongying Formation, from approximately structed the reservoirs at the bottom of ‘‘paleo-reservoirs’’, 38 Ma (or 41 Ma) to 24.6 Ma before the present. The second which had been charged with fewer hydrocarbons, or in and third stages experienced continuous charging of hydro- reservoirs where hydrocarbons had leaked. The organic carbons, which occurred from the mid-late depositional acids dissolved carbonate cements and small amounts of period of the Guantao Formation to the present (Song et al. feldspars, which caused second phase quartz overgrowths to 2009a, b). A study by Sui et al. (2010) showed that when the develop in the reservoirs. This process occurred because nearshore subaqueous fans in the northern zone of the Min- these reservoirs were protected by overpressure and feng Sag were buried deeper than 3200 m, the inner fan sub- hydrocarbons, which made the early cementation relatively facies acted as lateral seals for the hydrocarbon reservoirs. weak and led to higher porosity and good fluidity in these Therefore, the middle fan could have formed lithologic traps reservoirs. However, acidic fluids had difficulty in flowing because of the lateral plugging of the inner fan and the nor- into reservoirs with strong carbonate cementation, which mal lacustrine mudstone seal. Thus, when the organic matter acted as an obstacle for reservoir reconstruction and effec- became highly mature, massive amounts of oil and gas tive reservoir formation. The degree of reservoir recon- migrated into the top part of the ‘‘fan-anticlines’’ and middle struction was limited during this stage; thus, the reservoir fan lithologic traps at depths greater than 3200 m, which spaces in the secondary pore development zones were formed early hydrocarbon reservoirs. A study on the mainly primary pores (Fig. 6). 123 12 Pet. Sci. (2016) 13:1–17 The strata subsided quickly from 7 to 2 Ma before the secondary pores to exceed that of primary pores (Fig. 2, present (the end of the depositional period of the Minghuazhen Fig. 6). According to the definition of the SPDZ, the Formation). The top boundary was buried at 3600 m, and the SPDZs in Es in the northern zone of the Minfeng Sag bottom was buried at 4200 m. The temperatures of the top and formed when many primary pores were filled with asphalt bottom boundaries were 140 and 165 C, respectively. and pyrite from oil cracking since 2 Ma. Organic matter reached the second hydrocarbon generation peak and produced large amounts of crude oil and associated gas. The center of the Minfeng Sag had already entered the 6 Conclusions condensate gas stage. Many organic acids began to decompose by thermal decarboxylation, which decreased the acidity of the (1) Secondary pore development zones can be defined in formation water. Later, the reservoirs were mainly charged three ways: (1) the percent of secondary pores is with oil and gas, which were further supplements to the ‘‘paleo- greater than 50 %; (2) the porosity of the reservoirs is reservoirs’’. Li et al. (2010a, b) showed that normal pressure higher than the effective reservoir porosity cutoff charging occurred during this period. When little formation because the absolute content of secondary pores is water was flowing, the degree of hydrocarbon charging was high; and (3) high porosity reservoirs concentrate to limited. Thus, the oil charging during this period was only a form belts at particular depth intervals in the porosity- supplement to early stage hydrocarbon reservoirs. According depth profile, with the porosity envelope curve bul- to Li et al. (2010a, b), the gas reservoirs in Es in the Fengshen1 ging toward higher porosities. Accordingly, two well were mainly gas from oil cracking, which demonstrated secondary pore development zones exist in Es in the that the contribution of later-stage charging to the present northern zone of the Minfeng Sag, which range from reservoirs was subordinate. During this period, the rocks had 4200 to 4500 m and from 4700 to 4900 m. basically consolidated and the emplacement of hydrocarbons (2) The secondary pore development zones in Es in the inhibited diagenesis, so compaction and cementation had little northern zone of the Minfeng Sag experienced the effect on reservoir reconstruction. At the same time, the for- following processes. Significant numbers of secondary mation temperature reached the threshold for the thermo- pores (although fewer than primary pores) formed from chemical sulfate reduction (TSR) reaction, and organic acids the dissolution of feldspar in an early organic acid and H S were formed from hydrocarbon and anhydrite reac- environment. During this stage, the burial depth of the tions. These acidic fluids could dissolve feldspars and car- reservoirs was shallow. The pore spaces were slightly bonates, forming third phase quartz overgrowths with fluid changed during strata subsidence—uplift—subsidence inclusions with homogenization temperatures from 140 to because of early hydrocarbon charging and overpres- 160 C (Table 2). However, the formation was a relatively sure protection. Finally, the present secondary pore closed geochemical system during this period, and large development zones formed when many primary pores amounts of water flow and material transport were impossible, were filled by massive asphalt and pyrite from oil so the amount of acidic fluids from the TSR reaction and the cracking in deeply buried paleo-reservoirs. amount of secondary pores from the dissolution of feldspar and carbonate were small. Therefore, primary pores still dominated in the reservoirs in the SPDZs (Fig. 6). Acknowledgments The research is co-funded by National Natural Science Foundation of China (Grant No. 41102058, Grant No. From 2 Ma to the present, the top boundary of the strata U1262203, and Grant No. 41202075), the National Science and was buried at 3890 m at temperatures of 150 C, and the Technology Special Grant (Grant No. 2011ZX05006-003), the Fun- bottom boundary was buried at 4490 m at temperatures of damental Research Funds for the Central Universities (Grant No. 170 C. During this stage, the organic acids had almost 14CX02181A, Grant No. 15CX08001A, and Grant No. 15CX0 5007A), and Shandong Natural Science Foundation (Grant No. been completely decomposed, which caused the formation ZR2011DQ017). The authors thank the Geological Scientific water to be weakly acidic with a pH of 6–7. Organic matter Research Institute of Sinopec Shengli Oilfield Company, the Explo- began generating condensate gas, and crude oil in the ration and Development Research Institute of Sinopec Zhongyuan ‘‘paleo-reservoirs’’ started to crack and form large amounts Oilfield Company, and the CNPC key laboratory of oil and gas reservoirs in China University of Petroleum for providing database of asphalt and H S. The TSR reactions also produced some 2? and technological assistance. H S. Later pyrite from the reaction between H S and Fe 2 2 in the reservoirs replaced the initial cements and filled the Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://crea pores. Evidence of petroleum cracking in the ‘‘paleo- tivecommons.org/licenses/by/4.0/), which permits unrestricted use, reservoirs’’ was discussed in detail as part of the diagenetic distribution, and reproduction in any medium, provided you give evolution sequence. The later cementation of asphalt and appropriate credit to the original author(s) and the source, provide a pyrite destroyed a large amount of primary porosity in the link to the Creative Commons license, and indicate if changes were ‘‘paleo-reservoirs’’, which caused the proportion of made. 123 Pet. Sci. (2016) 13:1–17 13 Appendix 1 See Appendix Fig. 7. Feldspar-boundary dissolved pores Feldspar intra-granular dissolved pores Quartz-boundary dissolved pores Dissolved pores of acid-extrusive rock debris C D Dissolved pores of ankerite cements Dissolved pores of dolomite cements Compacted crack in feldspar grains Dissolved pores of pyrite cements G H Fig. 7 A Fengshen1 well, 4321.9 m, intra-granular-dissolved pores in feldspar grains. B Fengshen1 well, 4321.9 m, dissolved pores along feldspar grain boundaries. C Fengshen1 well, 4321.9 m, dissolved pores in acid extrusive rock debris. D Fengshen1 well, 4321.9 m, dissolved pores along quartz grain boundaries. E Fengshen1 well, 4323.3 m, dissolved pores in ankerite cement. F Fengshen4 well, 4476.15 m, dissolved pores in dolomite cement. G Fengshen1 well, 4348.25 m, dissolved pores in pyrite cement. H Fengshen3 well, 4867 m, compacted cracks in feldspar grains 123 14 Pet. Sci. (2016) 13:1–17 Appendix 2 See Appendix Fig. 8. Halite Lumpy siderite cement Ankerite Quartz overgrowth Anhydrite C D Pyrite Quartz overgrowth Ankerite Feldspar dissolved pores Dolomite Feldspar overgrowth Asphalt G H Fig. 8 A Fengshen1 well, 4323.3 m, lumpy siderite cement. B Feng8 well, 4397.15 m, halite-filled pores (SEM). C Feng8 well, 4397.15 m, anhydrite that replaced ankerite. D Fengshen3 well, 4867 m, ankerite that replaced quartz overgrowths. E Fengshen3 well, 4867 m, pyrite that replaced quartz overgrowths. F Fengshen3 well, 4867 m, ankerite filling parts of the feldspar-dissolved pores. G Fengshen1 well, 4350 m, dolomite that replaced feldspar overgrowths. H Fengshen1 well, 4321.9 m, asphalt filling intra-granular-dissolved pores in feldspar grains (Li et al. 2010a, b) 123 Pet. Sci. (2016) 13:1–17 15 Appendix 3 See Appendix Fig. 9. Fig. 9 A Fengshen1 well, 4323.3 m, asphalt and star-like pyrite filling intergranular pores. B Fengshen1 well, 4323.3 m, reflected light, the same visual area as A. C Fengshen1 well, 4321.9 m, asphalt and pyrite filling quartz-dissolved pores. D Fengshen1 well, 4321.9 m, reflected light, the same visual area as C. E Fengshen1 well, 4321.9 m, asphalt filling dissolved pores in ankerite cement. F Fengshen1 well, 4321.9 m, reflected light, the same visual area as E. G Fengshen1 well, 4323.3 m, reflected light, pyrite cement. H Fengshen3 well, 4867 m, pyrite that replaced ankerite 123 16 Pet. Sci. (2016) 13:1–17 Appendix 4 See Appendix Fig. 10. Fig. 10 A Fengshen1 well, 4322.5 m, primary pores (Wang 2010). B Fengshen1 well, 4321.9 m, complete crystal ankerite filling intergranular pores Jiang ZX, Qiu LW, Chen GJ. 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