Access the full text.
Sign up today, get DeepDyve free for 14 days.
D. Müller, J. Mckenzie, P. Mueller (1990)
Abu Dhabi sabkha, Persian Gulf, revisited: Application of strontium isotopes to test an early dolomitization modelGeology, 18
G. V. Middleton (2003)
214
Y. S. Ma (2005)
861Acta Geologica Sinica., 79
R. C. Zheng (2007)
78Journal of Mineralogy and Petrology., 27
R. Pankhurst, P. Doyle, F. Gregory, J. Griffiths, A. Hartley, R. Holdsworth, J. Howe, P. Leat, A. Morton, N. Robins, J. Turner (2005)
Geological Society Special Publications
Z. Li (2006)
2151Acta Petrologica Sinica., 22
G. Davies, Langhorne Smith (2006)
Structurally controlled hydrothermal dolomite reservoir facies: An overviewAAPG Bulletin, 90
Wang Rui-hua, Mou Chuan-long (2006)
Diagenetic processes and environments of the reef shoal dolostones from the Changxing Formation in the Daxian-Xuanhan region,northeastern SichuanSedimentary Geology and Tethyan Geology
L. Zhong (2006)
Scientific problems and frontiers of sedimentary diagenesis research in oil-gas-bearing basinsActa Petrologica Sinica
F. Whitaker, P. Smart, Gareth Jones (2004)
Dolomitization: from conceptual to numerical modelsGeological Society, London, Special Publications, 235
Andrew Hogg (2003)
Encyclopedia of Sediments and Sedimentary RocksEncyclopedia of Sediments and Sedimentary Rocks
S. Mazzullo, G. Chilingarian (1996)
Dolomite reservoirs: Geochemical techniques for evaluating origin and distribution: by J.R. Allen and W.D. Wiggins. American Association of Petroleum Geologists, 1993, Continuing Education Course Note Series No. 36Journal of Petroleum Science and Engineering, 14
Huile Gao, Zhi Pang, Li Fan, K. Hu, Bing-xian Wu, Xin-guo Jiang (2010)
Effect of lactoferrin- and transferrin-conjugated polymersomes in brain targeting: in vitro and in vivo evaluations, 31
Liu Jia-qing (2009)
Key Problems and Research Trend of Diagenetic Geodynamic Mechanism and Spatio-Temporal Distribution in Sedimentary Basins
J. Veizer, Davin Ala, K. Azmy, P. Bruckschen, D. Buhl, F. Bruhn, G. Carden, Andreas Diener, S. Ebneth, Y. Goddéris, T. Jasper, C. Korte, Frank Pawellek, O. Podlaha, H. Strauss (1999)
87Sr/86Sr, δ13C and δ18O evolution of Phanerozoic seawaterChemical Geology, 161
D. Green, E. Mountjoy (2005)
Fault and Conduit Controlled Burial Dolomitization of the Devonian West-Central Alberta Deep BasinBulletin of Canadian Petroleum Geology, 53
J. R. Allan (1993)
129AAPG Continuing Education Course Note Series, 36
Z. hui (1988)
Acta geologica sinica
J. Veizer (1999)
58Chemical Geology., 161
J. R. Allan, W. D. Wiggins (1993)
Dolomite reservoirs: Geochemical techniques for evaluating origin and distributionAAPG Continuing Education Course Note Series, 36
(2006)
Probe into formation mechanism of H2S and high-quality reservoirs of Puguang large gas field in the Sichuan Basin
(2006)
22(8): 2113-2122 (in Chinese) Li Z, Han D L and Shou J F
T. Anderson, M. Arthur (1983)
Stable Isotopes of Oxygen and Carbon and their Application to Sedimentologic and Paleoenvironmental Problems
R. Worden, S. Burley (2009)
Sandstone Diagenesis: The Evolution of Sand to Stone
L. Hardie (1987)
Dolomitization: A Critical View of some Current Views: PERSPECTIVESJournal of Sedimentary Research, 57
S. Burley, R. Worden (2003)
SANDSTONE DIAGENESIS: Recent and Ancient
Z. Li (2006)
2113Acta Petrologica Sinica., 22
C. L. Mou (2005)
198Sedimentary Geology and Tethyan Geology., 25
L. A. Hardie (1986)
Perspectives on dolomitization: A critical review of some current viewsJournal of Sedimentary Petrology., 57
Huang Sijing, Zhou Shaohua (1997)
Carbon and Strontium Isotopes of Late Palaeozoic Marine Carbonates in the Upper Yangtze Platform, Southwest ChinaActa Geologica Sinica ‐ English Edition, 71
Lin Guoxiong (2005)
Basic Characteristics and Concentration of the Puguang Gas Field in the Sichuan BasinActa Geological Sinica
T. F. Anderson (1983)
1SEPM Short Course, 10
Xu Fabo (2010)
Diagenetic system of carbonate reservoir in Huanglong Formation from East Sichuan to North Chongqing areaActa Petrologica Sinica
Chen Shou-chun (2007)
GENESIS OF DOLOMITE RESERVOIR OF THE CHANGXING FORMATION OF UPPER PERMIAN,NORTHEAST SICHUAN BASINJournal of Mineralogy and Petrology
H. Deng (2006)
Diagenesis systems and their spatio-temporal attributes in sedimentary basins.Acta Petrologica Sinica
Z. Li (2009)
837Acta Sedimentologica Sinica., 27
S. J. Huang (1997)
45Acta Geologica Sinica., 71
G. Middleton (2003)
Encyclopedia of sediments & sedimentary rocks
Y. Qian (2005)
Diagenesis of the Upper Permian Panlongdong organic reefs in northeastern SichuanSedimentary Geology and Tethyan Geology
R. H. Wang (2006)
30Sedimentary Geology and Tethyan Geology., 26
S. C. Zhang (2006)
230Geological Review., 52
Pet.Sci.(2012)9:141-153 141 DOI 10.1007/s12182-012-0194-9 Geochemical characteristics and diagenetic systems of dolomite reservoirs of the Changxing Formation in the eastern Sichuan Basin, China 1 1 1 2 1 Zhang Bing , Zheng Rongcai , Wang Xuben , Zheng Chao , Wen Huaguo , 3 1 Luo Yuan and Chi Yuelong State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Engineering, Chengdu University of Technology, Sichuan 610059, China &KLQD&KRQJTLQJ&KRQJTLQJ*DV0LQH3HWUR&KLQD6RXWKZHVW2LODQG*DV¿HOG&RPSDQ\ Sichuan Science and Technology Worker University, Sichuan 610059, China © China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2012 Abstract: In order to discuss the relationship between dolomite reservoirs and diagenetic systems of the Changxing Formation, we studied carbon, oxygen and strontium stable isotopes, iron, manganese and strontium trace elements and the Mg/Ca (mol%) ratio, dolomite order degree, and determined that burial dolomitization is the key to controlling the distribution of high quality dolomite reservoir in the Changxing Formation in the eastern Sichuan Basin. The dolomite of the Changxing Formation is divided into four diagenetic systems: (1) penecontemporaneous stage syngenetic brine diagenetic system, (2) early diagenetic stage strata seal brine diagenetic system, (3) middle-late diagenetic stage mixed hot EULQHGLDJHQHWLFV\VWHPDQG WHFWRQLFXSOLIWVWDJHPL[HGK\GURWKHUPDOÀXLGGLDJHQHWLFV\VWHP1HZ understanding of the controlling factors and distribution of dolomite reservoir development is discussed. Reef shoal facies belts controlled regional reservoir distribution and the scale of development. Burial dolomitization of a strata seal brine diagenetic system is the foundation of reservoir development, mainly developing pore reservoir. Burial dolomitization of mixed hot brine diagenetic system expanded the reservoir distribution and improved the reservoir quality, mainly developing pore-vug reservoir. Fracturing DQGGLVVROXWLRQRIDPL[HGK\GURWKHUPDOÀXLGGLDJHQHWLFV\VWHPLVWKHNH\WRLPSURYLQJWKHUHVHUYRLU quality, mainly developing pore-vug-crack complex reservoirs. Key words: Eastern Sichuan Basin, Changxing Formation, dolomite reservoir, diagenesis, geochemical characteristics, diagenetic system in China think that the formation of dolomite reservoirs of 1 Introduction the Changxing Formation in the eastern Sichuan Basin is due The Changxing Formation in the eastern Sichuan Basin to infiltration reflux and mixed water dolomitization (Wang is an exploration target for marine carbonate rocks in South et al, 2006; Mou et al, 2005). Based on the rock structure, China. A series of large and medium gas fields such as trace elements and stable isotope geochemical characteristics, Huanglongchang, Datianchi, Gaofengchang, Puguang and Zheng et al (2010) demonstrated that the dolomite reservoirs Yuanba has been found in Changxing Formation reef shoal of Changxing reef shoal facies are independent of atmospheric facies. The proven reserves is over 200 billion m . The genesis, water or mixed water, they are the product of multi-stage distribution and controlling factors of the marine carbonate hydrothermal dolomitization during burial diagenesis. reservoirs in the Changxing Formation are very important (Ma Therefore, new understanding of the genesis of dolomite et al, 2005; Zhang et al, 2006). Previous researchers studied reservoirs extensively developed in the Changxing Formation the sedimentary facies, reservoir space, diagenesis type and in the eastern Sichuan Basin is needed, to increase the success gas accumulation characteristics and genesis, and there is rate of dolomite reservoir prediction. Based on the analysis of a considerable controversy about the genesis of dolomite rock structure–genesis, and the data of Mg/Ca (mol%) ratio, reservoirs (Hardie, 1986; Whitaker et al, 2004; Green and dolomite order degree, iron, manganese and strontium trace Mountjoy, 2005; Davies and Smith, 2006). Most researchers elements, and carbon, oxygen and strontium stable isotopes, we studied the geochemical characteristics of Changxing Formation dolomite and the water-rock reaction processes and *Corresponding author. email: zb4819890@qq.com Received June 23, 2011 properties and sources of dolomite (Middleton, 2003; Worden UHODWLRQVKLSVLQHDFKVWDJHRIGRORPLWL]DWLRQ$FFRUGLQJWRÀXL Interbank Interbank Study area Intraplatform trough Trough Interbank The slope of platform Interbank Interbank Interbank 142 Pet.Sci.(2012)9:141-153 and Burley, 2003; Li et al, 2006a; 2006b; Li and Liu, 2009; The Upper Permian Changxing Formation and the underlying Zheng et al, 2010), we divide the dolomitization process of Upper Permian Longtan Formation (locally known as the Changxing Formation into four diagenetic systems, further the Wujiaping Formation) were deposited continuously. discuss the relationships between the dolomite reservoirs of The Changxing Formation is unconformably overlain by Changxing Formation reef shoal facies and diagenetic systems, the lower Triassic Feixianguan Formation. From field and reveal the reservoir properties and type of every diagenetic profiling, drill core observation and thin section analysis, VWDJH7KLVVWXG\LVVLJQL¿FDQWIRUPDULQHFDUERQDWHUHVHUYRLU we conclude that the lithology of Changxing Formation is exploration in China. mainly limestone, secondly dolomite and occasionally thin layers of shale. The limestone can be subdivided into mud- 2 Characteristics of sedimentary geology microcrystalline limestone, calcarenite, bioclastic limestone, and reef limestone. Dolomite can be subdivided into mud- The study area is located in Xuanhan and Kaijiang counties of Dazhou city, east Sichuan and Wanzhou District microcrystalline dolomite, granular dolomite, reef dolomite, and crystalline dolomite. The type of sedimentary facies is of Chongqing. It is in the northeastern margin of the east Sichuan arc fold belt, including Wubaiti, Damaoping, various, and the favorable reservoir development facies in the study area is mainly platform margin reef and shoal facies Gaofengchang and Huanglongchang tectonic belts, striking northeast-southwest, and covers nearly 10,000 km (Fig. 1). dolomite (Fig. 1). Shoal Panlongdong 0 5 10km Hekou Reef Dukou Reef Puguang3 Shoal Manyue Shoal Kai Honghua Puguang4 Open Jiang Reef Shoal Liang Shoal Shoal Xuanhan Shoal Huanglong6 Reef Ping Tieshan9 Daxian Reef Tiandong23 The Kaixian Tiandong76 Platform Slope Intraplatform Tiandong10 ইĽ Kaijiang ইĻ Shoal of Tiandong65 Shoal ইļ Tiandong7 Tiandong63 Platform ইķ ইĸ ইĹ Trough ইĺ Menxi3 Reef Tiandong18 Wanzhou Shoal Tiandong4 Dazhu Shoal Reef Liangping Tiandong13 Open Shoal Tiandong14 Legend Fault Dolomite thickness Platform Favorable for Favorable for reef shoal The shoal in The reef in Open platform The reef in Intraplatform platform The slope of platform platform Open platform platform margin Open platform Tiandong13 shoal Tiandong14 margin Tiandong4 margin Tiandong18 Datian2Tiandong23 Menxi3 Tiandong 10 B Tiandong7 Study area Honghua 20m Lithofacies palaeogeography of the Changxing Formation in the eastern Sichuan Basin Fig. 1 Interbank Interbank 500m Pet.Sci.(2012)9:141-153 143 GHYHORSHGLQWKHVDENKDHQYLURQPHQWVXFKDVWKHWRSUHHIÀDW 3 Reservoir diagenesis characteristics of the of intermittent exposure evaporation, and the barrier protected Changxing Formation lagoon-tidal flat. Since this kind of dolomite is still very GHQVHLWJHQHUDOO\GRHVQRWKDYHWKHUHVHUYRLUVLJQL¿FDQFH Different diagenesis stages have different diagenesis Diagenetic burial dolomite HQYLURQPHQWVÀXLGSURSHUWLHVGLDJHQHVLVFRPELQDWLRQW\SHV According to the microscopic thin section identification, and reservoir formation processes. The Changxing Formation the dolomite which has reservoir significance in the has many reservoir diagenesis types. According to the relation Changxing Formation is most developed in geologic bodies between diagenesis and reservoir development, compaction, such as sponge reefs and shoal facies, but poorly developed pressure solution and cementation have the most destructive LQPXGPLFURFU\VWDOOLQHOLPHVWRQHDQGFODVWLFPXGPLFUR effect on reservoir properties, and dolomitization, dissolution crystalline limestone. So the rock fabric with better properties and recrystallization are constructive for the reservoir is more conducive to dolomitization occurrence. It can be development. determined that diagenetic burial dolomitization is the most 3.1 Destructive diagenesis important diagenesis for the Changxing Formation reservoirs. Dolomitization in the study area can be divided into four 3.1.1 Compaction and pressure solution stages: early diagenetic stage, middle diagenetic stage, late Compaction and pressure solution are common developed diagenetic burial dolomitization and tectonic uplift dolomite in the Changxing Formation, and are destructive to reservoir fragmentation. 1) early diagenetic stage, the granular and reef development. Compaction primarily acts as the compaction dolomites with the primary structure well preserved (Fig. and deformation of carbonate rock sediments. Pressure 2(b), (c)), the Mg/Ca (mol%) ratio and degree of order slightly solution acts as dissolution and suture line development. higher than penecontemporaneous dolomite, respectively 0.915 Compaction and pressure solution caused strong shrinkage DQG PLGGOHGLDJHQHWLFVWDJHWKHUHVLGXDOSRZGHU of primary pores, which is the main reason of bad reservoir fine grained dolomites with the primary structure damaged GHYHORSPHQW3UHVVXUHVROXWLRQPDGHVXWXUHOLQHV¿OOHGZLWK (Fig. 2(d), (e)), the Mg/Ca (mol%) ratio and degree of order clay interlayer or carbonaceous organic matter, and reservoir significantly higher than those in early diagenetic stage, porosity and permeability are poor. respectively 0.944 and 0.802. 3) late diagenetic stage, the 3.1.2 Cementation middle-coarse grained dolomites with the primary structure Cementation is common in the Changxing Formation. almost disappeared. The dolomites have good crystalline Most primary intergranular pores are filled with cements, form, and some have bright border of fog center and a strong which is unfavorable for reservoir development. Cementation recrystallization structure. The intercrystal pores, intercrystal has following types: early generation ring edge comb dissolved pores and large dissolved pores were well cementation, even grained powder–fine crystalline calcite cementation, medium-coarse crystalline and intergrowth and saddle-shaped dolomites with a ring structure (Fig. 2(f), calcite cementation, and coarse-macro crystalline calcite (g)), the Mg/Ca (mol%) ratio is a little higher and the degree cementation. of order is significantly higher than those in middle stage, respectively 0.946 and 0.928. 4) the fragmentation dolomites 3.2 Constructive diagenesis (Fig. 2(h), (i)) with strong dissolution, the dissolution cracks 3.2.1 Dolomitization and large pores are all well developed and the dissolved pores The Changxing Formation dolomitization is characterized by multiple stages and multiple genesis. It is divided into averaging 0.95, the Mg/Ca (mol%) ratio is 0.947. The degree penecontemporaneous dolomite and diagenetic burial of order and Mg/Ca ratio of different diagenetic stages have GRORPLWHDFFRUGLQJWRVWUXFWXUH±JHQHVLVFODVVL¿FDWLRQ7KHUH a weak positive correlation, the correlation index R is 0.1142 are many types of dolomite reservoir development. They are (Fig. 3). With increasing diagenetic strength, the dolomite PXGPLFURFU\VWDOOLQHGRORPLWHPLFURSRZGHUFU\VWDOOLQH crystallinity gets better. ELRORJLFDOUHHIGRORPLWHSRZGHUILQHFU\VWDOOLQHELRORJLFDO VKRDOGRORPLWHSRZGHU¿QHFU\VWDOOLQHELRFODVWLFGRORPLWH The statistics of X-ray diffraction analysis data of dolomite Table 1 SRZGHUILQHFU\VWDOOLQHGRORPLWHILQHPHGLXPFU\VWDOOLQH samples in the Changxing Formation dolomite, and fragmentation dolomite. Mg/Ca (mol%) Degree of order Penecontemporaneous dolomite Sample Sample type 3HQHFRQWHPSRUDQHRXVPXGPLFURFU\VWDOOLQHGRORPLWH number Variation Variation Average Average range range (Fig. 2(a)) is one of the common types of Changxing Penecontemporaneous 2 0.86-0.95 0.906 0.59-0.64 0.615 Formation dolomite. It is allotriomorphic-subhedral, and dolomite often with tides and exposed genesis signs such as clay Dolomite of early 16 0.86-0.98 0.915 0.36-0.85 0.618 bands, bird eye, gypsum false crystal, calcium crusts and diagenetic stage algal layers–algae aggregate structures. The degree of order Dolomite of middle 22 0.82-1.00 0.944 0.51-1 0.802 diagenetic stage of penecontemporaneous dolomite is lowest, averaging 0.615, Dolomite of late and the Mg/Ca (mol%) is also the lowest at 0.906 (Table 1). 12 0.86-1.03 0.946 0.73-1 0.928 diagenetic stage Its genesis is not controversial, and all researchers suggest Structural fragmentation an evaporation pumping dolomitization origin. It is mainly 3 0.91-0.98 0.95 0.93-0.96 0.947 dolomite W DUH¿OOHGZLWKDXWKLJHQLFTXDUW]WKHGHJUHHRIRUGHULVKLJKHV GHYHORSHG7KHSRUHVZHUHRIWHQ¿OOHGZLWKFDUERQL]HGDVSKDOW 144 Pet.Sci.(2012)9:141-153 a b de f Fig. 2 Photos of the dolomitization and evolution process of different diagenetic stages from the Changxing Formation in the eastern 6LFKXDQ%DVLQD3HQHFRQWHPSRUDQHRXVPXGPLFURFU\VWDOOLQHGRORPLWHGHYHORSLQJIUDFWXUHV¿OOHGZLWKGRORPLWHDQGFDOFLWH)HQJ 003-2 well, 4471.11 m, stained thin section, 10×20 (-); b: Clay-powder crystalline sponge limestone, early burial dolomitization occurred in the sponge, Tiandong 53 well, 4329.08 m, conventional thin section, 10×20 (-); c: Sponge barrier reef dolomitic OLPHVWRQHEXULDOGRORPLWL]DWLRQRFFXUUHGLQWKHVKHOOOLNHFHPHQW¿OOHGZLWKUHHIVNHOHWRQSRUHVLQWKHHDUO\GLDJHQHWLFVWDJHWKH JUDQXODUSRUHVZHUH¿OOHGZLWKFDOFLWH¿QHJUDQXODUJUD\GRORPLWHWKHELRORJLFDOFDYLW\KROHVDQGWKHLQWHU5HVLGXDOELRFODVWLFSRZGHU Tiandong 74 well, 4329.08 m, stained conventional thin section, 10×20 (-); e: Fine-grained gray dolomite, the dolomite intergranular JDQLFPDWWHURUDQGGLDJHQHWLFSRUHVFDOFLWH¿OOHGSDUWZHOOZLWKRILDQGRQJFOD\WKHGRORPLWHZDV7GHGRORPLWL]DWHG PVWDLQHGFRQYHQWLRQDOWKLQVHFWLRQî I5HVLGXDOELRFODVWLFSRZGHU¿QHJUDLQHGGRORPLWHWKHLQWHUJUDQXODUSRUHVZ HUH ¿OOHGZLWKFDOFLWHDQGFDUERQL]HGDVSKDOWLDQGRQJ7ZHOOPVWDLQHGFRQYHQWLRQDOWKLQVHFWLRQî J0XG FU\VWDOOLQHVSRQJHGRORPLWH¿OOHGZLWKGRORPLWHFDOFLWHDQGELWXPHQLDQGRQJ7ZHOOPVWDLQHGFRQYHQWLRQDOWKLQ VHFWLRQî K)UDJPHQWDWLRQ¿QHFU\VWDOOLQHGRORPLWHFUDFNVIUDFWXUHGWKHURFNLQWREUHFFLDVVKDSHWKHIUDFWXUHVDU H¿OOHG ZLWKLDQGRQJDVSKDOWZHOO7PFDVWLQJWKLQVHFWLRQî L)UDJPHQWDWLRQ¿QHFU\VWDOOLQHGRORPLWHWKHFUDFNV LDQGRQJZHOOPFDVWLQJWKLQVHFWLRQî 7DUH¿OOHGZLWKFRDUVHFU\VWDOOLQHGRORPLWH 3.2.2 Recrystallization Number: 55 y=1.2209ln(x)+0.8558 R =0.1142 Recrystallization is the most common diagenesis of 1.0 the Changxing Formation. The dolomite recrystallizes from micro, powder, fine crystals to medium-fine crystals. This causes the destruction of the internal structure of 0.8 bioclastics and recrystallization residual bioclastic structure is well developed. The strength of recrystallization has a 0.6 big influence on the reservoir properties. Some granular limestones and dolomites were transformed by strong recrystallization, which increased the intercrystal pores of the 0.4 original rock and provided a dissolution space for diagenetic ÀXLGV*HQHUDOO\WKHVWUXFWXUHRIWKHPHGLXPUHFU\VWDOOL]DWLRQ 0.2 SRZGHU¿QHFU\VWDOOLQHGRORPLWHLVZHOOGLVWULEXWHGDQGWKH 0.700 0.750 0.800 0.850 0.900 0.950 1.000 1.050 intercrystal pores are well developed, which improve the MgCO /CaCO 3 3 URFNSURSHUWLHV7KHUHFU\VWDOOL]DWLRQRIWKHPLFURSRZGHU crystalline dolomite is weak, so its porosity and permeability Fig. 3 The relation between degree of order and MgCO / CaCO of dolomite 3 3 are low, unfavorable for reservoir development. Degree of order G UHPDLQLQJSRUHVRIVNHOHWRQZHUH¿OOHGZLWKFDOFLWHLDQGRQJZHOOPVWDLQHGFRQYHQWLRQDOWKLQVHFWLRQî Di agenesi s- por osi t y ev ol ut i on cur v e Compaction Early cementation Hydrothermal dissolution and filling cementation Pet.Sci.(2012)9:141-153 145 3.2.3 Dissolution 4 Dolomite geochemical characteristics Dissolution occurred commonly in the Changxing REHWWHUXQGHUVWDQG7WKHÀXLGSURSHUWLHVRULJLQHYROXWLRQ Formation, including middle stage medium-deep burial history and the influence on the reservoir development of dissolution and late stage deep burial dissolution. The former the diagenesis systems in the Changxing Formation, we usually occurred in the fine-medium crystalline dolomite, studied the Fe, Mn, Sr trace elements and C, O, Sr isotopic and intercrystal and intragranular dissolution pores were geochemical characteristics. The samples were taken GHYHORSHGZKLFKZHUHSDUWLDOO\¿OOHGZLWKFDOFLWHGRORPLWH from fresh drill cores by micro-drilling. After microscopic and celestite. Although the filling has some influences on thin section detection and decontamination, ensuring the the quality of the reservoir, generally it is favorable for the reliability and representativeness of samples classified by reservoir development. The latter usually occurred in the structure genesis, the selected samples were ground to 200 coarse crystalline dolomite, and extra-large dissolution pores, mesh, and split into four sub-samples. One was for standby intercrystal dissolution pores, moldic pores and karst caves application, and the other three were respectively used for were mainly developed, which were not completely filled 13 18 PHDVXUHPHQWVRI)H0Q6UFRQWHQWVį &į O values and with celestite, ferroan calcite, unusual shape dolomite and 87 86 Sr/ Sr ratio. Sample numbers, distribution and analysis carbonized asphalt. The reservoir space was preserved, so this results are shown in Table 2. Fe, Mn, Sr contents were stage is the most favorable for reservoir development. analyzed by Chengdu Minerals Complex Utilization Institute of Chinese Academy of Geological Sciences, using a Perkin 3.3 Diagenetic evolution modes Elmer 2000DV ICP-AES (identifier: 1-44-40), test basis is Based on the diagenesis characteristics analysis, referring JY/T105-1996 (inductively coupled plasma atomic emission to the national standard of carbonate rocks diagenesis (SY/ spectrum general method). The analysis results are shown as T5478-2003), we divided the evolution process of the single element content, limit of detection is 0.001%, and error Changxing Formation dolomite reservoir into five stages: is 0.002%. C and O isotopes were analyzed by Exploration penecontemporaneous stage, early diagenetic stage, middle and Development Research Institute Geology Laboratory of diagenetic stage, late diagenetic stage and tectonic uplift PetroChina Southwest Oil and Gasfield Company, using a stage (Fig. 4). The diagenetic stage division and evolution Finnigan MAT 252 isotope ratio mass spectrometer, test basis characteristics can provide a basis for the study of diagenesis is SY/T 6039-94, working standard is TTB-2. The analysis 13 18 systems. HUURURIį &UDQJHVLQDQGWKDWRIį O ranges 87 86 in 0.009-0.043. Sr/ Sr was analyzed by Professor Yin Guan The division of Penecontem Early diagenetic Middle diagenetic Late diagenetic Tectonic uplift from Isotope Laboratory of State Key Laboratory of Oil and diagenetic stage -poraneous stage stage stage stage stage Near surface Shallow burial Middle burial Deep burial Gas Reservoir Geology and Exploitation Engineering in Uplift diagenetic diagenetic diagenetic diagenetic Diagenetic environment diagenetic environment environment environment environment environment Chengdu University of Technology, also using a Finnigan Diagenetic fluid Mixed property Syngenesis brineStrata seal brine Mixed hot brine hydrothermal Diagenesis MAT 252 isotope ratio mass spectrometer, experiment Same thickness ring edge cementation condition is 22°C, humidity 50%, test basis is standard Equal-granular calcite cementation Crystal stock sample NBS987 of American National Standards Institute, calcite cementation measurement error is less than 0.02%. Gypsification Penecontemporaneous dolomitization 4.1 Geochemical characteristics of iron, manganese, Neomorphism Compaction strontium trace elements Pressure dissolution In the 46 analysis samples (Tables 2 and 3), 38 are Recrystallization dolomite, six are marine mud microcrystalline limestone, Shallow burial dolomitization Medium-deep burial and two are calcite. The results showed that the contents of dolomitization Hydrothermal ferroan Fe, Mn and Sr trace elements in various types of dolomite calcite filling Hydrothermal unusual shaped dolomite filling are very similar (Fig. 5). The content of Fe is high, followed Dedolomitization by Sr, and Mn is the lowest. However, the late diagenetic Silicification stage dissolution vugs and cracks filled with calcites Anhydrite have high content of Sr, and the next are Fe and Mn. The Celestite content and distribution of Fe, Sr and Mn of dolomite in Fluoritization Deep hydrothermal different diagenetic stages are very similar, indicating that dissolution Diagenesis Tectonic Fracturation dolomitization fluids of different diagenetic stages have the Accumulation effect Interparticle Primary Remaining Extra large dissolved dissolved pores, intergranular pore, primary pore holes, diagenesis Tectonic fractures Pore combination intergranular of Fe and Sr in dolomite show that the diagenetic fluid had organism cavity pore, and intergranular karst fractures and tectonic types dissolved pores, pore and filled remaining dissolved fractures reef framework pore diagenetic pressure pores cracks strong reducibility and was not affected by continental fresh water, that is, dolomitization is independent of atmospheric 30% water, a closed diagenetic environment. The fluid in open 25% 20% conditions can only precipitate calcite with medium Sr 15% 10% content, while the late dolomitization coexisting calcite has an 5% unusually high Sr content (up to 0.614‰), so it can be inferred Strong cementation Destructive diagenesis Constructive diagenesis that the dolomitization occurred in a relatively closed system Fig. 4 The diagenesis stages and evolution models of the Changxing Formation in the eastern Sichuan Basin is independent of atmospheric water and mixed water. Tectonic fracturation Pressure dissolution dolomitization hydrothermal dissolution and fracturation GRORPLWL]DWLRQWKDWDJDLQFRQ¿UPVZKLFK DOHW=KHQJ VDPHÀXLGVRXUFH7KHORZFRQWHQWRI0QDQGWKHKLJKFRQWHQW 146 Pet.Sci.(2012)9:141-153 The content of Fe, Mn, Sr and the distribution of C, O, and Sr isotopes of carbonate rocks in the Changxing Formation Table 2 Depth 13 18 87 86 Well number Lithology Genetic type Ȧ(Fe), ‰ Ȧ(Mn), ‰ Ȧ(Sr), ‰ į C, ‰ į O, ‰ Sr/ Sr number Datian 002-1 3942.59 Micrite 0.1911 0.00789 0.5043 4.847 -4.71 0.709062 Microcrystalline bioclastics Feng 003-2 4498.09 2.621 0.0612 0.7852 2.706 -5.947 0.709609 limestone Microcrystalline bioclastics Tiandong 10 3896.3 0.2544 0.0103 0.469 1.881 -4.183 0.710847 limestone Marine limestone Tiandong 53 4329.18 Micritic reef limestone 0.5495 0.0654 0.278 2.827 -5.857 0.709303 Huanglong 5 4315.29 Micritic-crystallite limestone 0.9462 0.0956 0.265 1.762 -6.216 0.709254 Yunan 1 3565.72 Micritic-crystallite limestone 3.091 0.0151 2.409 3.517 -4.396 0.708825 Granophyric mud-powder Feng 003-2 4470.26 6.1 0.4418 0.1982 1.771 -5.11 0.7091 Penecontemporaneous crystalline dolomite dolomite Puguang 6 5-38/101 Micritic-crystallite dolomite 3.7 0.08 0.14 2.186 -2.979 0.7095 Fine medium crystalline residual Feng 003-2 4488.21 2.79 0.3179 0.2298 1.393 -5.989 0.707334 sponge reef dolomite Tiandong 021-3 4259.17 Fine crystalline powder dolomite 2.182 0.2004 0.2016 2.298 -4.179 0.707163 Tiandong 10 3748.65 Fine crystalline powder dolomite 4.9 0.2251 0.4419 1.961 -4.651 0.707023 Tiandong 10 3756.5 Fine crystalline powder dolomite 6.9 0.4347 0.2393 2.387 -3.664 0.708201 Tiandong 10 3761.55 Fine crystalline powder dolomite 43.1 0.2069 0.4498 4.292 -7.056 0.708408 Tiandong 10 3824.73 Fine crystalline powder dolomite 0.7636 0.0847 0.221 3.804 -4.698 0.70969 Early diagenetic burial Tiandong 21 4308.93 6SLQHV¿QHFU\VWDOOLWHGRORPLWH dolomite 1.777 0.1869 0.1401 2.916 -6.64 0.708622 Fine crystalline powder residual Tiandong 53 4286.06 1.842 0.197 0.7352 2.638 -5.699 Abnormally sponge reef dolomite Huanglong 5 4362.63 Powder crystalline dolomite 0.708 0.1223 0.1291 3.648 -5.905 0.708112 Huanglong 5 4380.46 Powder crystalline dolomite 2.309 0.1067 0.1191 2.251 -3.643 0.71275 ¿QH*UDQRSK\ULFSRZGHU Puguang 6 11-128/148 3.5 0.11 0.24 2.76 -4.066 0.707372 crystalline dolomite Puguang 6 10-51/137 Powder crystalline gravel dolomite 2.3 0.09 0.13 2.965 -4.017 0.709327 Dissolved pore powder Feng 003-2 4484.14 3.419 0.3036 0.2535 1.572 -5.781 Abnormally crystalline dolomite Tiandong 002-21 3857.65 ¿QHFU\VWDOOLQHGRORPLWH3RZGHU 0.9303 0.092 0.4601 3.155 -5.396 0.707348 Tiandong 10 3733.79 Fine crystalline dolomite 0.8082 0.0798 0.861 2.178 -4.082 0.708097 Tiandong 10 3801.59 Fine crystalline dolomite 1.36 0.0803 0.3626 2.591 -5.902 Abnormally Tiandong 10 3839.96 Fine crystalline dolomite 0.525 0.0806 0.119 4.048 -5.999 0.709677 Tiandong 53 4353.17 ¿QHFU\VWDOOLQHGRORPLWH3RZGHU 0.7335 0.0809 0.2696 3.471 -6.822 0.709686 Tiandong 53 4356.88 Fine crystalline dolomite 0.3858 0.0854 0.1933 3.609 -6.097 0.707492 Middle diagenetic 'LVVROYHGSRUHFODVWLF¿QH burial dolomite Tiandong 74 4129.36 0.7151 0.0794 0.1523 2.369 -5.738 Abnormally crystalline dolomite ¿QH'LVVROYHGSRUHSRZGHU Tiandong 74 4146.92 0.6039 0.0754 0.1078 1.501 -6.525 0.709041 crystalline dolomite ¿QH5HVLGXDOVSLQHVSRZGHU Huanglong 5 4390.2 0.6384 0.0833 0.1274 2.814 -7.205 0.711328 crystalline dolomite Dissolved pore spherulite unequal Maoba 3 14-10/34 2.8 0.08 0.18 3.064 -4.484 0.706592 crystalline dolomite Dissolved pore residual sand Puguang 6 8-88/130 2.1 0.1 0.22 2.584 -4.42 0.706635 coarse crystalline dolomite 'LVVROYHGSRUH¿QHFU\VWDOOLQH Puguang 6 9-105/121 2.1 0.08 0.44 2.921 -3.652 0.70667 reef dolomite (To be continued) Pet.Sci.(2012)9:141-153 147 (Continued) Depth 13 18 87 86 Well number Lithology Genetic type Ȧ(Fe), ‰ Ȧ(Mn), ‰ Ȧ(Sr), ‰ į C, ‰ į O, ‰ Sr/ Sr number Feng 003-2 4478.17 ¿QHFU\VWDOOLQHGRORPLWH3RZGHU 2.141 0.2834 0.22 -0.647 -6.732 0.70757 Residual sponge powder Tiandong 002-11 3831.8 0.7285 0.0858 0.2764 1.463 -6.558 0.707397 crystalline dolomite Coarse crystalline residual Tiandong 10 3795.5 0.7461 0.0768 0.1548 3.15 -6.913 0.708831 sponge reef dolomite 5HVLGXDOVSLQHV¿QH Tiandong 10 3874.86 0.5281 0.0624 0.1513 4.581 -5.561 0.708386 mesocrystalline dolomite Late diagenetic burial dolomite Pore powder-coarse crystalline Tiandong 21 4337.21 0.6035 0.0974 0.2392 3.437 -4.526 0.708297 dolomite ¿QH5HVLGXDOJUDLQSRZGHU Tiandong 74 4141.18 0.8698 0.0705 0.1704 2.337 -5.401 0.706599 crystalline dolomite Huanglong 5 4396.54 Mesocrystalline dolomite 0.1998 0.078 0.1587 3.184 -6.611 0.708392 Residual maerl coarse crystalline Maoba 3 19-35/41 1.8 0.08 0.26 2.535 -4.044 0.706755 dolomite Tiandong 10 3782.55 1.441 0.0952 0.3072 3.211 -5.525 0.706013 crystalline dolomite Tectonic )UDJPHQWDWLRQGLVVROYHGSRUH¿QH fragmentation Puguang 6 6-24/96 2 0.05 0.1 2.61 -4.473 0.707488 mesocrystalline dolomite dolomite )UDJPHQWDWLRQUHVLGXDO¿QH Puguang 6 7-67/147 1.9 0.05 0.12 2.021 -4.001 0.708821 mesocrystalline dolomite Huanglong 1 2-35 Calcite 0.1691 0.0325 0.5715 2.687 -7.289 0.70994 Filling calcite Tiandong 002-3 4396.69 Calcite 0.6693 0.0147 0.6567 -0.513 -6.942 0.708721 Table 3 The content of Fe, Mn, Sr and the composition characteristics of C, O, and Sr isotopes of each diagenetic stage of the Changxing Formation dolomites Trace elements Carbon and oxygen isotopes (PDB) Strontium isotope *HQHWLFFODVVL¿FDWLRQRIFDUERQDWHURFNV Total number Ȧ(Fe) Ȧ(Mn) Ȧ(Sr) Total number Total number 13 18 87 86 į C, ‰ į O, ‰ Sr Sr ratio of samples ‰ ‰ ‰ of samples of samples Ordinary marine mud-micrite 6 1.28 0.043 0.785 6 2.923 -5.218 6 0.7094 Penecontemporaneous dolomite 2 4.90 0.261 0.169 2 1.98 -4.045 2 0.7093 Early diagenetic stage dolomite 12 6.09 0.190 0.273 12 2.776 -5.017 11 0.7085 Middle diagenetic stage dolomite 13 1.32 0.101 0.288 13 2.760 -5.546 10 0.7083 Late diagenetic stage dolomite 8 0.95 0.104 0.203 8 2.505 -5.793 8 0.7078 Structural fragmentation dolomite 3 1.78 0.065 0.176 3 2.614 -4.666 3 0.7074 /DWHGLDJHQHWLFVWDJH¿OOLQJFDOFLWH 2 0.42 0.024 0.614 2 1.087 -7.116 2 0.7093 Marine mud-micro crystalline limestone 4.2 Geochemical characteristics of carbon and Penecontemporaneous dolomite oxygen isotopes Early diagenetic stage burial dolomite Middle diagenetic stage burial dolomite The carbon and oxygen isotopic compositions of the Late diagenetic stage burial dolomite samples have the following characteristics. Tectonic fragmentation dolomite Late diagenetic stage filling calcite 7KHį C (PDB) values are all in the corresponding period global ancient seawater variation range. Compared with QRUPDOPDULQHPXGPLFURFU\VWDOOLQHOLPHVWRQHÅ DQGSHQHFRQWHPSRUDQHRXVGRORPLWHÅ WKHį C (PDB) 0.1 average of burial dolomites and tectonic uplift dolomites is between them, with small variation range and high value (2.505‰-2.776‰). It proved that this type is the product of diffusion burial dolomitization of normal marine sediments. 0.01 7KHį 2YDOXHYDULDWLRQUDQJHLVÅÅ Sr Mn Fe generally consistent with the data from Veizer and other VFKRODUVWKDWWKHį O (PDB) value of the late Paleozoic Fig. 5 Cross plots of Sr, Fe and Mn contents in the Changxing Formation )UDJPHQWDWLRQUHVLGXDOSRZGHU¿QH 148 Pet.Sci.(2012)9:141-153 (Changxing Formation sedimentary period) global ancient the isotopic fractionation principle, the isotopic evaporation VHDZDWHUUDQJHVLQÅÅ,Q)LJWKHį O made the relatively light isotopic water evaporate, and the of carbonate rocks has a trend that with the diagenetic relatively heavy isotopic water remained in the evaporation intensity increasing, the negative bias values increase. The water. This isotope fractionation dynamic process ultimately penecontemporaneous dolomite has the lowest negative bias made the stable isotope in evaporation sea water more value, with an average of -4.045‰. The late stage calcite has positive than that in normal sea water. Therefore the oxygen the highest negative bias value, with an average of -7.116‰. stable isotope values of penecontemporaneous dolomite The other types of diagenetic dolomites fall in between them, should be more positive than those of the sea cements and indicating burial metasomatism characteristics. According to burial dolomite. Marine mud-micro crystalline limestone Penecontemporaneous dolomite Early diagenetic stage burial dolomite Middle diagenetic stage burial dolomite Late diagenetic stage burial dolomite Tectonic fragmentation dolomite Late diagenetic stage filling calcite Penecontemporaneous Burial dolomite dolomite Late Triassic Temperature brine Evaporation effect effect į O į O (‰) -6 -8 PDB -4 0 -2 13 18 Fig. 67KHį &į O plot for different carbonate rocks and cements of the Changxing Formation in the eastern Sichuan Basin. Marine facies mud-microcrystalline limestone; Penecontemporaneous dolomite; Burial dolomite; /DWHSHULRG¿OOLQJFDOFLWH A number of foreign studies, divided burial dolomitization 0.7068-0.7079, averaging 0.7075) established by Veizer et al into two stages, the relatively low temperature early stage (1999) and that of the same period marine carbonate rocks in and the relatively high temperature late stage (Anderson the Yangtze platform area (ranging 0.7066-0.7077, averaging and Arthur, 1983). The statistical results from Allan and 0.7071) established by Huang (1997). This is because in LJJLQV: IXUWKHUVKRZHGWKDWWKHį O (PDB) of early the last stage of the late Permian the eastern Sichuan Basin low-temperature dolomite was distributed between -6.5‰ platform margin experienced a large regressive event, and due and -9.0‰, and that of the late high-temperature dolomite to strong erosion, a large amount of terrestrial strontium was was between -2.5‰ and -16.0‰. The former overlapped in added to sea water. Penecontemporaneous dolomite inherited 87 86 87 the latter. Because with the diagenetic intensity increasing, similar Sr/ Sr ratio, and a lot of Sr-rich marine source the negative bias values of the oxygen isotope composition water was trapped in the formation, which means the study 87 86 of carbonate rocks in the Changxing Formation increase, area has high Sr/ Sr values. the burial dolomitization of early-middle diagenetic stage The dolomite Sr isotope characteristics of different RFFXUUHGLQUHODWLYHO\ORZWHPSHUDWXUHÀXLGDQGWKHGRORPLWH diagenetic stages vary. The penecontemporaneous dolomite 87 86 recrystallization and tectonic fragmentation of middle-late Sr/ Sr value (average 0.7093) was higher than that of GLDJHQHWLFVWDJHRFFXUUHGLQUHODWLYHO\KLJKWHPSHUDWXUHÀXLG the diagenetic stage burial dolomite, and was the highest in all samples. This can be explained by the same reason 4.3 Geochemical characteristics and comparison of 87 86 why the Sr/ Sr ratio of penecontemporaneous dolomite strontium isotope caused by brine metasomatism was higher than that of the Table 2 and Table 3 list the structure type and analysis corresponding period normal marine sediment in the Abu results of strontium isotopes from 42 samples. The strontium Dhabi sabkha environment. The value is close to the marine isotope ratio in alteration carbonate minerals primarily PXGPLFURFU\VWDOOLQHOLPHVWRQHLQWKH&KDQJ[LQJ)RUPDWLRQ 87 86 depends on the Sr/ Sr ratio in the diagenetic fluid, so the DYHUDJH LOOXVWUDWLQJWKDWWKHWZRÀXLGVKDYHDFORVH strontium isotope ratio of the Changxing Formation dolomite relationship. 87 86 in the study area has the following important features. The Sr/ Sr ratio of the late dissolved vugs and The ordinary marine limestone in the study area has a FUDFNILOOLQJFDOFLWHLVORZHUWKDQWKDWRIWKHPDULQHPXG 87 86 high Sr/ Sr ratio (Fig. 7), 0.7088-0.7108, and the average microcrystalline limestone and penecontemporaneous is 0.7094, higher than that of global late Permian (ranging dolomite while higher than that of the diagenetic dolomite. CPDB (‰) Pet.Sci.(2012)9:141-153 149 This is because the lower Triassic Feixianguan Formation Triassic Feixianguan Formation sealed penecontemporaneous 87 87 Sr-rich sea source water and the Sr-poor hydrothermal sea source pore water with high Mg and Sr contents and high ÀXLGIURPGHHSVWUDWDLQWHUPLQJOHG salinity. The fluid migrated downward and mixed with the The diagenetic dolomites in the Changxing and Sr-rich sea water in the Changxing Formation, and then 87 86 Feixianguan formations have similar Sr/ Sr ratio dolomitization occurred to the surrounding rocks, resulting 87 86 distribution and evolution (Table 4). This shows that the in the Changxing Formation dolomite having higher Sr/ Sr ratio than the Feixianguan Formation. With the decrease formations have similar properties, and provides the basis for of Sr in the early dolomitization process, the greater the 87 86 determining that the Changxing Formation dolomitization diagenesis strength, the lower the Sr/ Sr ratio of burial ÀXLGVLQWKHVWXG\DUHDZHUHGHULYHGIURPWKHRYHUO\LQJORZHU dolomite (Table 3, Fig. 7). 87 86 Table 4 Comparison of Sr/ Sr ratios in the Changxing Formation and Feixianguan Formation 87 86 87 86 Sr/ Sr of Changxing Formation Sr/ Sr of Feixianguan Formation *HQHWLFFODVVL¿FDWLRQRIFDUERQDWHURFNV Sample number Variation range Average Sample number Variation range Average Ordinary marine mud-micrite 6 0.7088-0.7108 0.7094 11 0.7064-0.7075 0.7073 Penecontemporaneous dolomite 2 0.7091-0.7095 0.7093 2 0.7068-0.7093 0.7080 Early diagenetic stage dolomite 11 0.7070-0.7093 0.7085 5 0.7070-0.7085 0.7079 Middle diagenetic stage dolomite 10 0.7067-0.7097 0.7083 10 0.7066-0.7089 0.7075 Late diagenetic stage dolomite 8 0.7068-0.7088 0.7078 4 0.7068-0.7076 0.7073 Structural fragmentation dolomite 3 0.7060-0.7088 0.7074 3 0.7069-0.7075 0.7073 /DWHGLDJHQHWLFVWDJH¿OOLQJFDOFLWH 2 0.7087-0.7099 0.7093 11 0.7077-0.7087 0.7081 87 86 The burial dolomite Sr/ Sr ratios of different diagenetic 5 Diagenetic system in the Changxing stages have a slight difference. The variation range of early Formation 87 86 diagenetic dolomite Sr/ Sr ratio is large (0.7070-0.7093), and the average is 0.7085. The variation range of medium 5.1 Diagenetic system division 87 86 diagenetic dolomite Sr/ Sr ratio is larger (0.7067-0.7097), The Changxing Formation dolomite in the eastern and the average is 0.7083, close to that of early diagenetic Sichuan Basin is divided into four relatively independent dolomite (Fig. 4). The variation range of late diagenetic 87 86 and successive evolving diagenetic systems: (1) syngenesis dolomite Sr/ Sr ratio is the smallest (0.7068-0.7088), and 87 brine diagenetic system of the penecontemporaneous stage; the average is also small (0.7078). This is because the Sr (2) strata seal brine diagenetic system of the early diagenetic consumption increased in the early dolomitization process, 87 stage; (3) mixed hot brine diagenetic system of the middle- and the concentration of Sr in fluid gradually decreased, late diagenetic stage and (4) mixed hydrothermal diagenetic thus showing the variation tendency that with the diagenetic 87 86 system of the tectonic uplift stage. Each system has its own strength increasing, the Sr/ Sr ratio of burial dolomite independent diagenetic fluid sources and fluid properties, decreased (Table 3, Fig. 7). physical-chemical environment and water-rock interaction sequences, and the corresponding diagenetic combination. 0. 7090 5.2 Fluid properties and diagenetic evolution rules of each diagenetic system 0. 7085 IHUHQW'LIGLDJHQHWLFVWDJHVKDYHIHUHQWGLIÀXLGSURSHUWLHV and different diagenetic systems have different diagenetic 0. 7080 features, diagenetic product characteristics, fluid properties and the ancient hydrological conditions, which correspond to Marine limestone 0. 7075 Penecontemporaneous dolomite various dolomites with different genesises. Early diagenetic stage burial dolomite 5.2.1 The syngenesis brine diagenetic system of the Middle diagenetic stage burial dolomite 0. 7070 penecontemporaneous stage Late diagenetic stage burial dolomite The penecontemporaneous stage dolomitization in the Tectonic fragmentation dolomite Late diagenetic stage filling calcite Changxing Formation occurred in a near-surface syngenetic 0. 7065 Changxing Formation 87 86 87Sr/86Sr Sr / Sr average evaporation concentrated high salinity sea source pore 87 86 range Sr / Sr Oarboniferous Silurian PermianTriassic Jurassic Cretaceous water diagenetic system, that is, under dry and hot climatic Cambrian Ordovician Devonian Tertiary 0. 7060 600 400 200 0 conditions, it developed on the top of reef and shoal or Age, million the barrier protection lagoon-tidal flat environments. 87 86 This is penecontemporaneous dolomitization caused Fig. 7 Sr/ Sr ratio distribution of carbonate by the evaporation-concentrated high magnesium brine rocks in the Changxing Formation 87 86 Sr/ Sr EXULDOGRORPLWL]DWLRQÀXLGVRIWKH&KDQJ[LQJDQG)HL[LDQJXDQ 150 Pet.Sci.(2012)9:141-153 metasomatizing limestone. The dolomitization fluid and WKHGLVVROYHGSRUHVDQGYXJV,WDOVRFRQ¿UPHGWKHH[LVWHQFH diagenetic environments have syngenetic origins and low RIDQRWKHUVLOLFDULFKK\GURWKHUPDOÀXLGWKDWLVIURPDGHHS temperature and high salinity, and the main products are hydrothermal source. J\SVXPDQGKDOLWHPXGPLFURFU\VWDOOLQHGRORPLWHVLPLODU 3) The dissolved pores, vugs and cracks were generally to the extremely dry and hot conditions of the modern Abu filled with carbonized asphalt, showing that the spaces had Dhabi sabkha and penecontemporaneous dolomitization RQFHEHHQ¿OOHGZLWKOLTXLGK\GURFDUERQ,WFDQDOVREHXVHG environment (Müller et al, 1990). for proving that in the oil and gas migration period deep 5.2.2 The strata seal brine diagenetic system of early K\GURWKHUPDOÀXLGSDUWLFLSDWHGLQWKHGLDJHQHVLV diagenetic stage 5.2.4 The mixed hydrothermal diagenetic system of The early diagenetic stage dolomitization in the tectonic uplift stage Changxing Formation occurred in a shallow burial strata seal The tectonic uplift and fault activity of the Changxing brine diagenetic system. The main products of the diagenetic Formation occurred in the late period of the early Himalayan. V\VWHPDUHJUD\SRZGHU¿QHFU\VWDOOLQHSDUWLFOHVZLWKZHOO Folding and faulting caused widespread fragmentation of preserved primary structure or biological reef dolomite and dolomite, and made SO SDUWLFOHVGXHWRVOLJKWGLVVROXWLRQ7KHGRORPLWL]DWLRQÀXLGLV move along the dissolved holes, vugs, cracks and fractures derived from the high salinity sea source pore brine, and the of the fragmented dolomite. This is mixed hydrothermal evidence is as follows. diagenesis system with deep discharge and transport along the 1) The geochemical characteristics of iron, manganese, cracks. Hydrocarbon and SO have thermochemical sulfate strontium trace elements and carbon, oxygen, strontium reduction (TSR) reaction. On one hand hydrocarbon in gas isotopes are similar to those of the penecontemporaneous reservoirs and SO in fluid were consumed, on the other dolomite (Zheng et al, 2007). hand large amounts of acid gas H S and CO were produced, 2 2 2) The strontium isotope characteristics are between the forming a high efficiency gas reservoir with high contents penecontemporaneous dolomite in the Feixianguan Formation of H S and CO in the Changxing Formation. The diagenetic 2 2 and the diagenetic burial dolomite, but are different from the system can be divided into strong recrystallization, dissolution penecontemporaneous dolomite in the Changxing Formation, and the most important tectonic fragmentation. The primary showing that the early diagenetic stage dolomitization rock structure completely disappeared, filled with unusual fluid was related to the Feixianguan penecontemporaneous shape dolomite due to mixed hydrothermal action and a small dolomite and burial dolomite, and the Feixianguan burial amount of authigenic quartz and carbonized asphalt, usually GRORPLWL]DWLRQÀXLGKDVEHHQVKRZQWREHGHULYHGIURPWKH developing tectonic fractures. fourth member of the Feixianguan Formation trapped sea 5.3 The control of diagenetic system on the reservoirs source high salinity pore brine (Zheng et al, 2007). 5.2.3 The mixed hot brine diagenetic system of middle-late Through analysis of the carbonate reservoir space and diagenetic stage different reservoir characteristics and distribution of the The middle-late diagenetic stage of the Changxing Changxing Formation, it is shown that the contribution of Formation belongs to the pressure release mixed hot brine different diagenetic systems to the Changxing reservoir diagenesis system under the deep burial environment. development has a big difference (Fig. 8, Table 5). The In the middle diagenetic stage dissolution and burial reservoir quality is the result of multi-stage overlaying of UHFU\VWDOOL]DWLRQHXKHGUDOSRZGHUILQHFU\VWDOOLQHGRORPLWH different diagenetic systems. Not all facies belt development with residual primary particles or biological reef structure, areas experienced the four diagenetic systems, for example, and medium-coarse crystalline dolomite formed. In the late inland ocean trough facies did not experience diagenesis, diagenetic stage strong recrystallization and dissolution, front slow slope belt, restricted platform and open platform medium-coarse crystalline dolomite with almost no residual facies experienced two or three stages. Only the platform primary structure formed, and dissolved pores were often edge reef, shoal facies belt and fracture zones experienced ¿OOHGZLWKFDOFLWHDXWKLJHQLFTXDUW]XQXVXDOVKDSHGRORPLWH four diagenetic systems. DQGDVSKDOW7KHGRORPLWL]DWLRQÀXLGZDVVWLOOPDLQO\GHULYHG The syngenesis brine diagenetic system of the from the high salinity sea source pore water released in the penecontemporaneous diagenetic stage mainly has deeply buried environment of the Feixianguan Formation, compaction and cementation. Most primary intergranular and and some intragranular pores were filled in the penecontemporaneous strata, so it was mixed hot brine. The evidence is as follows. period and the pores were not well developed. For example, 87 86 1) The Sr/ Sr ratio of the late dissolved vugs and WKHPXGPLFURFU\VWDOOLQHOLPHVWRQHDQGWKHPLFURFU\VWDOOLQH FUDFNILOOLQJFDOFLWHLVORZHUWKDQWKDWRIWKHPDULQHPXG dolomite were very compacted, and the porosity is extremely microcrystalline limestone and penecontemporaneous low. The porosity of microcrystalline dolomite ranges from dolomite while higher than that of the diagenetic dolomite. 0.92% to 6.46%, and the average is 1.76%, so it generally It is shown that as well as from the high salinity sea source GRHVQRWKDYHUHVHUYRLUVLJQL¿FDQFH pore water, the dolomitization fluid also had another deep In the strata seal brine diagenetic system of the early hydrothermal source. Their interaction caused the decrease of diagenetic stage, due to compaction, pressure solution and 87 86 the Sr/ Sr ratio. further cementation, most primary pores were completely 2) Accompanied by the dolomitization and dissolution in destroyed. However, the wide range of burial dolomitization this stage, secondary quartz precipitation began to occur in and recrystallization was in favor of the development of 6UGH¿FLHQWK\GURWKHUPDOÀXLGUHOHDVHGIURPGHHS ULFKK\GURFDUERQÀXLGFRQWLQXRXVO\ Pet.Sci.(2012)9:141-153 151 intragranular pores. For example, the porosities of weak evolution characteristics that the burial dolomitization dolomitization calcareous dolomite and crystalline dolomite intensity increasing is gradually beneficial for the reservoir are favorable. The former ranges from 0.46% to 12.52%, development. averaging 3.06%, and the latter ranges from 0.53% to In the mixed hot brine diagenetic system of the 14.33%, averaging 4.41%. These have the diagenetic middle-late diagenetic stage, the burial dolomitization, 60 60 Fragmentation dolomite 32 Granular dolomite 349 40 40 30 30 10 10 0 0 <2 266 12 >12 <2 2 66 12 >12 Porosity, % Porosity, % Reef dolomite 93 Crystalline granular dolomite 683 60 60 50 50 30 30 20 20 0 0 <2 2 66 12 >12 <2 2 66 12 >12 Porosity, % Porosity, % Calcareous dolomite 89 Dolomicrite 44 <2 266 12 >12 <2 2-6 6-12 >12 Porosity, % Porosity, % Histogram of porosity distribution of the Changxing Formation in the eastern Sichuan Basin Fig. 8 recrystallization and pressure solution were strong, and oil and gas in a short time, so they are effective fractures. The GHYHORSHGIUDFWXUHVKDYHDVLJQL¿FDQWLQÀXHQFHLQLPSURYLQJ played an extremely important role in reservoir creation. reservoir properties. Finally pore-vug-fracture type reservoirs Granular dolomite and biological reef dolomite with almost were formed. The porosity of fractured dolomite ranges from no remaining primary structure formed. The former porosity 3.20% to 19.7%, averaging 12.3%. It is the best lithology for is high, ranges from 1.65% to 18.92%, averaging 8.82%, and reservoir development, and has the largest contribution to the the latter ranges from 1.06% to 16.95%, averaging 6.56%. In Changxing Formation reservoirs. WKHODWHGLDJHQHWLFVWDJHVRPHHDUO\IRUPHGSRUHVZHUH¿OOHG Therefore, burial dolomitization of the strata seal brine with anhydrite, celestite, silica and other secondary minerals, diagenetic system is the basis for the reservoir development, so that the physical properties got worse. The reservoir is and pore type reservoirs developed. The burial dolomitization mainly pore-vug type. of mixed hot brine diagenesis system expanded the reservoir The tectonic stage mixed hydrothermal diagenetic distribution and improved the reservoir quality, and pore- system mainly had the regional tectonic uplift in the vug type reservoir developed. The cataclasis and dissolution early Himalayan. Fracturing and dissolution were strong, of the mixed hydrothermal diagenetic system is the key to increasing the primary pores and vugs. The fractures were improving the quality of reservoirs and developing pore-vug- VHOGRP¿OOHGZLWKVHFRQGDU\PLQHUDOVDQGZHUHFKDUJHGZLWK fracture type reservoirs. Frequency, % Frequency, % Frequency, % Frequency, % Frequency, % Frequency, % 152 Pet.Sci.(2012)9:141-153 Table 5'LDJHQHWLFV\VWHPFODVVL¿FDWLRQDQGHYDOXDWLRQRIFDUERQDWHUHVHUYRLURIWKH&KDQJ[LQJ)RUPDWLRQLQWKHHDVWHUQ6LFKXDQ%DVLQ Diagenetic system type Syngenesis brine Strata seal brine Mixed hot brine Mixed hydrothermal Calcareous dolomite, Granular dolomite, Main lithology Dolomicrite Fragmentation dolomite crystalline granular dolomite reef dolomite Mesopore and Pore-throat combination 0LFURSRURXVPLFURWKURDW +ROHV²¿QHWKURDW 0HVRSRUH²¿QHWKURDW PDFURSRUH²¿QHWKURDW Dissolved pore, Dissolved pore, Dissolved pore, Pore type Crack intercrystal pore, dissolved hole, dissolved hole, crack casting membrane pore intercrystal pore Representative types Platform margin shoals, Platform margin biological Platform margin biological Restricted platform of sedimentary facies open platform reef and shoal reef and shoal overlap Medium and high porosity, Very low porosity, Low porosity, Medium porosity, Property comprehensive medium and high very low permeability reservoir low permeability reservoir medium permeability reservoir evaluation permeability reservoir ( 2, 0.1) (2-6, 0.1-1) (6-12, 1-10) ˘ ˘ (>12, >10) Reservoir types Fractured reservoir Pore reservoir Pore-vug reservoir Pore-fracture complex reservoir Development Characteristics at Kaijiang-Liangping East 6 Conclusions Trough” (Number XNYQT-XNS02-2007-TS-5777). 1) The main reservoir rocks of the Sichuan Basin Changxing Formation reservoirs are granular dolomite, reef References dolomite and intercrytalline dolomite. The main destructive All an J R and Wiggins W D. Dolomite reservoirs: Geochemical effect is compaction, pressure solution and cementation. techniques for evaluating origin and distribution. AAPG Continuing The main construction effect is burial dolomitization, Education Course Note Series. 1993. 36: 129 recrystallization and dissolution. The more thorough the burial And erson T F and Arthur M A. Stable isotopes of oxygen and carbon dolomitization of the early and medium-late diagenetic stage, and their application to sedimentologic and paleoenvironmental the better the developed dolomite porosity and permeability problems. SEPM Short Course. 1983. 10: 1-151 and the more favorable the reservoir development. Dav ies G R and Smith Jr L B. Structurally controlled hydrothermal 2) The main diagenetic systems and modes which are dolomite reservoir facies: An overview. AAPG Bulletin. 2006. closely related with reservoir development are: burial 90(11): 1641-1690 Gre en D G and Mountjoy E W. Fault and conduit controlled burial dolomitization and recrystallization of early diagenetic sealed dolomitization of the Devonian west-central Alberta Deep Basin. brine diagenetic system, burial dolomitization, dissolution and Bulletin of Canadian Petroleum Geology. 2005. 53(2): 101-129 recrystallization of medium-late diagenetic mixed hot brine Har die L A. Perspectives on dolomitization: A critical review of some diagenetic system and tectonic fracturing and dissolution of current views. Journal of Sedimentary Petrology. 1986. 57: 166-183 tectonic stage mixed hydrothermal diagenetic system. Hua ng S J. Carbon and strontium isotopes of Late Palaeozoic marine 3) According to the time-space relationship of the carbonates in the Upper Yangtze platform, Southwest China. Acta diagenetic system and reservoirs, the controlling factors and Geologica Sinica. 1997. 71(3): 45-53 (in Chinese) distribution of the Changxing Formation high quality reef Li Z and Liu J Q. Key problems and research trend of diagenetic ÀDWGRORPLWHUHVHUYRLUVFDQEHGHPRQVWUDWHGDVIROORZV5HHI geodynamic mechanism and spatio-temporal distribution in shoal facies belts controlled regional reservoir distribution sedimentary basins. Acta Sedimentologica Sinica. 2009. 27(5): 837- and the scale of development. Burial dolomitization of 848 (in Chinese) Li Z, Chen J S and Guan P. Scientific problems and frontiers of the strata seal brine diagenetic system is the foundation of sedimentary diagenesis research in oil-gas-bearing basins. Acta reservoir development, mainly developing pore reservoirs. Petrologica Sinica. 2006a. 22(8): 2113-2122 (in Chinese) Burial dolomitization of mixed hot brine diagenetic system Li Z, Han D L and Shou J F. Diagenesis systems and their spatio- expanded the reservoir distribution and improved the reservoir temporal attributes in sedimentary basins. Acta Petrologica Sinica. quality, mainly developing pore-vug reservoirs. Fracturing 2006b. 22(8): 2151-2164 (in Chinese) and dissolution of a mixed hydrothermal fluid diagenetic Ma Y S, Cai X Y and Li G X. Basic characteristics and concentration of system is the key to improving the reservoir quality, mainly the Puguang Gas Field in the Sichuan Basin. Acta Geologica Sinica. developing pore-vug-crack complex reservoirs. 2005. 79(6): 861-865 (in Chinese) Mid dleton G V. Encyclopedia of Sediments and Sedimentary Rocks. Acknowledgements London: Kluwer Academic Publishers. 2003. 214-219 Mou C L, Ma Y S, Wang R H, et al. Diagenesis of the Upper Permian This study is funded by PetroChina Southwest Oil and Panlongdong organic reefs in northeastern Sichuan. Sedimentary HFKQRORJLFDO3URMHFWV³7KH7*DV¿HOG&RPSDQ\6FLHQWL¿FDQG Geology and Tethyan Geology. 2005. 25(1-2): 198-202 (in Chinese) Research of Changxing Organic Reef Bioherm and Reservoir Mül ler D W, Mckenzie J A and Mueller P A. Abu Dhabi sabkha, Persian Pet.Sci.(2012)9:141-153 153 Gulf, revisited: Application of strontium isotopes to test an early 2003. 1-44 dolomitization model. Geology. 1990. 18(7): 618-621 Zha ng S C, Zhu G Y and Liang Y B. Probe into formation mechanism 87 86 13 18 Vei zer J, Ala D, Azmy K, et al. Sr/ 6Uį &DQGį O evolution of of H S and high-quality reservoirs of Puguang large gas field in Phanerozoic seawater. Chemical Geology. 1999. 161(1-3): 58-88 the Sichuan Basin. Geological Review. 2006. 52(2): 230-235 (in Wan g R H, Mou C L, Tan Q Y, et al. Diagenetic processes and Chinese) environments of the reef shoal dolostones from the Changxing Zhe ng R C, Dang L R, Zheng C, et al. Diagenetic system of carbonate Formation in the Daxian-Xuanhan region, northeastern Sichuan. reservoirs in Huanglong Formation from the east Sichuan to North Sedimentary Geology and Tethyan Geology. 2006. 26(1): 30-36 (in Chongqing area. Acta Petrolei Sinica. 2010. 31(2): 237-245 (in Chinese) Chinese) Whi taker F F, Smart P L and Jones G D. Dolomitization: From Zhe ng R C, Hu Z G, Feng Q P, et al. Genesis of dolomite reservoir of conceptual to numerical models. Geological Society Special the Changxing Formation of the Upper Permian, northeast Sichuan Publications. 2004. 235: 99-139 Basin. Journal of Mineralogy and Petrology. 2007. 27(4): 78-84 (in Wor den R H and Burley S D. Sandstone diagenesis: the evolution of Chinese) sand to stone. In: Burley S D and Worden R H (eds.). Sandstone Diagenesis: Recent and Ancient. Cahaba Heights: Blackwell Pub.. (Edited by Hao Jie)
Petroleum Science – Springer Journals
Published: Jul 28, 2012
You can share this free article with as many people as you like with the url below! We hope you enjoy this feature!
Read and print from thousands of top scholarly journals.
Already have an account? Log in
Bookmark this article. You can see your Bookmarks on your DeepDyve Library.
To save an article, log in first, or sign up for a DeepDyve account if you don’t already have one.
Copy and paste the desired citation format or use the link below to download a file formatted for EndNote
Access the full text.
Sign up today, get DeepDyve free for 14 days.
All DeepDyve websites use cookies to improve your online experience. They were placed on your computer when you launched this website. You can change your cookie settings through your browser.