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W. Hao (2011)
Genetic Types and Accumulation Conditions of Biogas in Bohaiwan BasinNatural Gas Geoscience
X Luo (2008)
13Nat Gas Ind, 28
HX Lin (2011)
195Nat Gas Geosci, 22
Xianzheng Zhao, Q. Jin, Fengming Jin, P. Ma, Quan Wang, Jing Wang, Chunling Ren, Qiuling Xi (2013)
Origin and accumulation of high-maturity oil and gas in deep parts of the Baxian Depression, Bohai Bay Basin, ChinaPetroleum Science, 10
DZ Tang, HX Liu, XM Li (2002)
Probe into deep-seated structural factors of abiogenic gas accumulation and storage in Jiyang DepressionEarth Sci: J China Univ Geosci, 27
Li Jin, G. Hu, Ying Zhang, Gui-Peng Yang, Huiying Cui, Hongming. Cao, Xülong Hu (2008)
Application of Carbon Isotope Fractionation during the Reduction Process from CO2 to CH4Earth Science Frontiers, 15
W. Stahl (1980)
Compositional changes and 13C12C fractionations during the degradation of hydrocarbons by bacteriaGeochimica et Cosmochimica Acta, 44
A. James, B. Burns (1984)
Microbial Alteration of Subsurface Natural Gas AccumulationsAAPG Bulletin, 68
L. Pi (2003)
The present research status and progress of petroleum exploration in the Jiyang DepressionPetroleum Exploration and Development
ML Sun (1996)
475Geochimica, 25
H. Tian, X. Xiao, Liguo Yang, Zhong-yao Xiao, Liguo Guo, Jiagui Shen, Yuhong Lu (2009)
Pyrolysis of oil at high temperatures: Gas potentials, chemical and carbon isotopic signaturesChinese Science Bulletin, 54
D. Leythaeuser, R. Schaefer, C. Cornford, B. Weiner (1979)
Generation and migration of light hydrocarbons (C2C7) in sedimentary basinsOrganic Geochemistry, 1
PL Li (2003)
1Pet Explor Dev, 30
SF Lu (2006)
825J Jilin Univ (Earth Science Edition), 36
Yunpeng Wang, J. Dai, Changyi Zhao, Jinzhong Liu (2010)
Genetic origin of Mesozoic natural gases in the Ordos Basin (China): Comparison of carbon and hydrogen isotopes and pyrolytic resultsOrganic Geochemistry, 41
Lin La-mei (2009)
Study on kinetics for generating natural gas of Shahejie Formation in deep-buried sags of Dongying DepressionActa Petrologica Sinica
W. Yu-lin (2008)
ORIGIN OF GAS IN DEEP JIYANG DEPRESSIONNatural Gas Industry
Zhou Jian-lin (2004)
Gas accumulation analysis of upper Paleozoic coal in Jiyang depressionJournal of Earth Science and Enivronmental
JX Dai (1993)
1Nat Gas Geosci, 2
J. Dai, Y. Ni, C. Zou (2012)
Stable carbon and hydrogen isotopes of natural gases sourced from the Xujiahe Formation in the Sichuan Basin, ChinaOrganic Geochemistry, 43
MS Song (2004)
646Nat Gas Geosci, 15
Xu Li-heng (2006)
Chemical Kinetics of Carbon Isotope Fractionation of Oil-Cracking Methane and Its Initial ApplicationJournal of Jilin University
Yan Song, Shaobo Liu, Qun Zhang, Mingxin Tao, Mengjun Zhao, F. Hong (2012)
Coalbed methane genesis, occurrence and accumulation in ChinaPetroleum Science, 9
R. Burruss, C. Laughrey (2010)
Carbon and hydrogen isotopic reversals in deep basin gas: Evidence for limits to the stability of hydrocarbonsOrganic Geochemistry, 41
LY Zhang (1991)
Identifying criteria of natural gases in the Jiyang DepressionPet Geol Exper, 13
AT James (1984)
957AAPG Bull, 68
GQ Song (2009)
672Acta Petrolei Sinica, 30
GY Hu (2005)
23Nat Gas Ind, 25
Peng-Fei Wang, Zhongmin Shen, Sibing Liu, Z. Lv, Tong-xing Zhu, Yajun Gong (2013)
Geochemical characteristics of noble gases in natural gas and their application in tracing natural gas migration in the middle part of the western Sichuan Depression, ChinaPetroleum Science, 10
Zhonghong Chen, Shouchun Zhang, M. Zha (2014)
Geochemical evolution during the cracking of crude oil into gas under different pressure systemsScience China Earth Sciences, 57
JL Zhou (2004)
Gas accumulation analysis of upper Paleozoic coal in the Jiyang DepressionJ Earth Sci Environ, 26
Y Gao (2011)
407Nat Gas Geosci, 22
Yang Gao, Q. Jin, G. Zhu (2010)
Genetic types and distribution of shallow-buried natural gasesPetroleum Science, 7
Jin Qiang (2011)
Fractionation Mechanism of Natural Gas Components and Isotopic Compositions and Sample AnalysisNatural Gas Geoscience
JX Dai (1993)
The carbon and hydrogen isotope characteristics and identification of different kinds of natural gasesNat Gas Geosci, 2
ML Sun, JF Chen, YS Liao (1996)
Helium isotopic characteristics, genesis of CO2 in natural gases and distribution of Tertiary magamatite in the Jiyang DepressionGeochimica, 25
DZ Tang (2002)
30Earth Sci: J China Univ Geosci, 27
Zhang Xue-cai (2004)
DISCUSSION ON DEEP GAS GEOCHEMICAL CHARACTERISTICS AND GENESIS OF BONAN SAG, JIYANG DEPRESSIONNatural Gas Geoscience
G. Hu, Xiaoting Luo, Zhisheng Li, Ying Zhang, Chun Yang, Jin Li, Y. Ni, X. Tao (2010)
Geochemical characteristics and origin of light hydrocarbons in biogenic gasScience China Earth Sciences, 53
M. Schoell (1980)
The hydrogen and carbon isotopic composition of methane from natural gases of various originsGeochimica et Cosmochimica Acta, 44
GY Hu, ZY Xiao, X Luo (2005)
Light hydrocarbon composition difference between two kinds of cracked gases and its applicationNat Gas Ind, 25
A. Hunt, T. Darrah, R. Poreda (2012)
Determining the source and genetic fingerprint of natural gases using noble gas geochemistry: A northern Appalachian Basin case studyAAPG Bulletin, 96
Pet. Sci. (2015) 12:81–95 DOI 10.1007/s12182-014-0003-8 OR IGINAL PAPER Genetic types and geochemical characteristics of natural gases in the Jiyang Depression, China • • Wen-Tao Li Yang Gao Chun-Yan Geng Received: 21 July 2014 / Published online: 22 January 2015 The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Natural gases were widely distributed in the Deep gases (3,500–5,500 m) are mainly kerogen thermal Jiyang Depression with complicated component composi- degradation gas, oil-cracking gas, and coal-type gas. tion, and it is difficult to identify their genesis. Based on investigation of gas composition, carbon isotope ratios, Keywords Genetic types Natural gases Jiyang light hydrocarbon properties, as well as geological ana- Depression Light hydrocarbon properties Carbon isotope lysis, natural gases in the Jiyang Depression are classified ratios Identification factors into two types, one is organic gas and the other is abiogenic gas. Abiogenic gas is mainly magmatogenic or mantle- derived CO . Organic gases are further divided into coal- 1 Introduction type gas, oil-type gas, and biogas according to their kero- gen types and formation mechanisms. The oil-type gases The Jiyang Depression is located in the north part of Shan- are divided into mature oil-type gas (oil-associated gas) dong Province in China, on the fluvial plain and the delta and highly mature oil-type gas. The highly mature oil-type where the Huanghe River runs into the Bohai Sea. Tectoni- gases can be subdivided into oil-cracking gas and kerogen cally, the Jiyang Depression is located in the southeast part of thermal degradation gas. Identification factors for each the Bohai Bay Basin. It is a big terrestrial depression and kind of hydrocarbon gas were summarized. Based on ranks as one of the most prolific petroliferous area (Li et al. genesis analysis results, the genetic types of gases buried in 2003). Since the discovery of the Shengli Oilfield in 1960, 8 8 3 different depths were discussed. Results showed that 50 9 10 t of OOIP and 2,500 9 10 m OGIP have been shallow gases (\1,500 m) are mainly mature oil-type proved, at the same time, 10.7 9 10 tons of oil and 8 3 gases, biogas, or secondary gases. Secondary gases are rich 460 9 10 m gases have been produced. in methane because of chromatographic separation during Five sets of source rocks were developed in the Jiyang migration and secondary biodegradation. Secondary bio- Depression, and they are distributed in the Carboniferous- degradation leads to richness of heavy carbon isotope ratios Permian, the second member of the Kongdian Formation in methane and propane. Genesis of middle depth gases (Ek ), and the fourth, third, and first members of the Eogene (1,500–3,500 m) is dominated by mature oil-type gases. Shahejie Formation (Es ,Es , and Es ). The kerogen in those 4 3 1 source rocks is mainly sapropelic type, and some of them are humic type. After a series of tectonic movements, these W.-T. Li source rocks vary greatly in depth and evolution histories School of Energy Resources, China University of Geosciences, which influence gas generation and accumulation in many Beijing 100083, China aspects, such as gas components, genesis, etc. (Zhang 1991). W.-T. Li Y. Gao (&) C.-Y. Geng Thirteen commercial gas bearing layers have been discov- Geoscience Research Institute, Shengli Oilfield Company ered in the Neogene Minghuazhen and Guantao Formations, SINOPEC, Dongying 257015, Shandong, China the Eogene Shahejie Formation, and the Paleozoic Carbon- e-mail: swap124@163.com iferous-Permian and Ordovician in the Jiyang Depression (Fig. 1). Gas reservoirs occurred widely at a depth from 192 Edited by Jie Hao 123 82 Pet. Sci. (2015) 12:81–95 to 4,750 m. In these reservoirs, gas compositions vary hydrocarbon properties, combined with geological analysis, greatly from hydrocarbon gas to abiogenic gas. As for natural gases in the Jiyang Depression are divided into two hydrocarbon gas, the paraffin hydrocarbon composition and categories namely organic gas and abiogenic gas. Organic gas carbon isotope ratios varied dramatically. There are several was further divided into coal-type gas, oil-type gas, and biogas different genesis models such as oil-type gas, coal-type gas, according to kerogen type and formation mechanism. The oil- biogas, and inorganic mantle source gas, etc. (Gao et al. type gases were finally divided into mature oil-type gas (oil- 2011; Zhou 2004; Luo et al. 2008). Natural gases usually associated gas) and highly mature oil-type gas (including oil- occur as normal gas reservoirs, tight sandstone gas reser- cracking gas and kerogen thermal degradation gas) (Schoell voirs, shale gas reservoirs, and coal-bed methane. 1980). The geochemical properties of each kind of natural gas To make a thorough investigation of the gas genesis in the were discussed, respectively. Jiyang Depression, the authors collected abundant data from exploration wells with commercial gas flow including 472 sets of natural gas composition data, 293 sets of carbon isotope 2 Abiogenic gas ratio data (both hydrocarbon gas and carbon dioxide), and 69 sets of light hydrocarbon properties data (Fig. 2). According Abiogenic gas in the Jiyang Depression is mainly CO , and to gas component contents, carbon isotope ratios and light its distribution is controlled by great deep faults (Tang Fig. 1 Strata histogram and gas R , % Kerogen carbon isotope Source Gas bearing o System Group Lithology Member 13 2 24 28 32 36 rock bearing layers in the Jiyang formation Q Qp Depression Oil type Nm Coal type Ng Ed Es Es Es Es Es Ek Ek Ek C-P Art Silt Sand Mud Conglomerate Limestone Dolomite Gyprock Salt Andesite Lamprophyre Gneiss Coal 123 Chengbei Uplift Huanghekou Sag Pet. Sci. (2015) 12:81–95 83 Fig. 2 Structural framework and typical gas producing wells 0 2 4km Zhuangxi in the Jiyang Depression Oil Field North Chb301 Chbg5 Gas well Chb16 Lao31 Da802 Organic Gas Field Zhuang14 Feiq2 Che660 Zhuang11 Bonan Gudong Abiogenic Gas Field Cheng3 Cheg201 Zhuang202 Oil Field Oil Field Yi155 Gudao Kend48 Gbg1 Bog4 Zhan29 Oil Field Bos8 7 4 Shao24 Gug8 Ken622 Gun20 Kenxi Ken23 Shao2 Oil Field Chenq20 Gunan Chenjiazhuang Oil Field Uplift Gas Field 3 Yanjia Yangxin 3 Gas Field Oil Field Cheng8 Shanjiasi Ming3 Yang5 Tuo165 Yang101 Fs1 Gas Field Balipo Yang16 Ning8 Ls101 Yong33 Gas Field Dong2 Qd11 Linfanjia Shan66 Sq17 Dongxin Uplift Binnan Linfanjia Oil Field Liang61 Shi101 Oil Field Oil Field Bin16 Shanghe BinG11 Cao23 Linpan Oil Field Mian1 Pingnan Oil Field Weibei Lin104 Yuhuangmiao Gas Field 8 Cao13 Uplift Xia8 Oil Field Hua16 GaoQ3 Fan54 2 Huagou Jinjia Hua17 Qudi Gas Field Jin8 Oil Field Qug1 Tong59 Oil Field Luxi Arched Structure 1 1-Shouguang Uplift; 2-Guangrao Uplift; 3-Chenjiazhuang Uplift; 4-Gudao Uplift; 5-Bonan Uplift; 6-Yihezhuang Uplift; 7-Qingyun Uplift; 8-Gaoqing Uplift; -6 -5 -8 et al. 2002). This type of gas is mainly found in Pingf- respectively, 1.4 9 10 , 1.1 9 10 , and 2 9 10 (Sun 3 4 angwang, Pingnan, and Huagou gas fields in the western et al. 1996). As shown in Table 2, the He/ He value of part of the Dongying Sag and the Balipo gas field in the CO reservoirs in the Pingfangwang, Huagou, and Yangxin northern part of the Huimin Sag. Vertically, CO is mainly gas fields in the Jiyang Depression was high -6 distributed in the Shahejie Formation of Eogene (Es for (3.55–4.49 9 10 ), and R/Ra was 2.5–3.2, indicating a short), Neogene, and Ordovician. The CO content of such mixed He origin of mantle genesis and crust genesis (Wang reservoirs ranges from 55.5 % sto 100 % and averages et al. 2013). The isotopic analysis of rare gases and CO 82.4 %. Hydrocarbon gases were mixed into CO reser- indicated that the highly concentrated CO gas reservoir in 2 2 voirs in varying degrees. The methane content in those the Jiyang Depression originated from magma–mantle reservoirs ranges from 0 % to 37.2 % with an average of degassing (Hunt et al. 2012). 13.3 %, while the heavy hydrocarbon (C ) content was 2? low with an average value of 1.4 % (Table 1). 3 Organic gases There are usually three genetic types of natural CO , namely magma degassing, decomposition of carbon rich Organic hydrocarbon gases are produced from sedimentary crustal rock, and decomposition of organic matter. Studies organic matter due to a series of biological-geochemical have confirmed that d C can be used to identify its CO2 reactions. Organic matter of different types and in different genesis. It is generally believed that d C [ -8 % CO2 thermal evolution stages will produce hydrocarbon gases indicates inorganic genesis, and d C \ -10 % indi- CO2 with different component compositions and isotopic com- cates organic genesis (Zhang 1991; Dai 1993). In the Jiy- positions. C /C and d C of hydrocarbon gases in the 1 1-5 1 ang Depression, gas reservoirs with high CO content Jiyang Depression changed regularly with depth, and could ([60 %) usually have heavy carbon isotope ratios ranging be divided into three categories according to the reservoir from -9.8 % to -3.4 % (PDB). The d C of most CO2 depth (Fig. 4): samples was higher than -7 %, and this can be classified as inorganic genesis. The CO content in hydrocarbon gas (1) Buried less than 1,500 m: the C /C value is 2 1 1-5 reservoirs was usually lower than 10 % with d C less usually high and ranges from 0.8 % to 1.0, 90 % of CO2 than -8 %, and it can be deduced that the CO came from the natural gases are dry gas (C /C [ 0.95) with a 2 1 1-5 decarboxylation of organic matter (Fig. 3). methane content more than 95 %, while the values of Previous studies have shown that helium of different d C can be separated into two groups: the values of genesis has different isotopic compositions, and the group one are between -40 % and -50 %, and the 3 4 He/ He values of atmosphere, earth mantle, and crust are, values of group two are less than -55 %. Laohekou Oil Field Chezhen Sag Shaojia Oil Field Pingfangwang Gas Field Huimin Sag Chengning Zhanhua Sag Dongying Sag Bamianhe Oil Field Structure Wudi Qingcheng Uplift Arched 84 Pet. Sci. (2015) 12:81–95 Table 1 Geochemical characteristics of CO in the Jiyang Depression 13 13 Area Well Formation Depth, m d C , % d C , % CH ,% C ,% N ,% CO ,% CO2 1 4 2? 2 2 (PDB) (PDB) Pingfangwang Gas Field Bin1 E 1890.0–1898.0 -6.1 -45.8 3.53 2.09 0 94.13 Ping13-2 E 1453.6–1483.2 -4.7 -52.7 26.43 2.79 1.07 68.85 Ping13-4 E 1450.8–1486.4 -4.4 -51.7 19.04 4.85 1.21 74.92 Ping14-3 E 1467.0–4684.6 -4.3 -51.8 18.17 3.30 0.61 77.93 Ping4 E 1459.4–1461.4 -5.4 -50.9 20.89 3.33 0.46 75.33 Ping9-3 E 1462.6–1489.2 -4.5 -51.6 22.46 3.40 0.25 73.87 Pingq12 E 1470.5–1472.5 -4.4 -51.9 21.63 3.39 0.63 74.2 Pingq12-61 E 1452.4–1487.6 -4.5 -51.8 17.13 3.19 0.38 79.17 Pingq4 E 1459.4–1474.5 -5.4 -51.7 20.89 3.32 0.46 75.33 Pingnan Gas Field Bin11 E 1980.2–2250.0 -5.9 -47.6 1.31 1.06 0 97.31 Bing11 O 2301.0–2307.0 -6.3 -47.6 1.52 0.74 0.25 97.06 Binnan Oilfield Bin4 E 1510.0–1568.0 -9.8 -49.4 32.62 4.91 0 60.72 Bin4-13-1 E 1453.0–1455.0 -5.1 -52.4 22.71 3.76 0.85 72.68 Bin4-6-6 E 1469.7–1474.7 -4.6 -51.7 23.52 3.53 0.33 72.5 Huagou Gas Field Gao10 N 824.3–838.9 -5.2 0 0 0 99.99 Gao3 N 833.4–834.8 -4.4 -35 0.07 0 0 97.87 Gao53 N 811.4–818.0 -6.8 0.04 0 0 99.96 Hua17 E 1965.1–1980.0 -3.4 -54.39 7.47 0.51 2.05 89.70 Hua17 E 2000.0–2009.6 -3.4 -54 10.99 0.35 9.03 79.56 Balipo Gas Field Yang25 E 2793.9–2805.0 -4.4 -42.51 0.52 0 3.83 95.64 Yang5 O 2380.4–2386.0 0.76 0 0 99.24 E Eogene, N Neogene, O Ordovician Organic CO natural gas buried between 1,500 and 3,500 m, the Inorganic CO Mix of organic and inorganic CO 2 2 −40 value of C /C is higher, and the d C is also 1 1-5 1 CO in hydrocarbon gas in the Jiyang Depression heavier with a value of -30 % to -50 %. Neogene CO in Huagou the Gas Field −30 Ordovician CO in Balipo Gas Field The carbon isotope composition can be used to deter- Paleogene CO in Binnan Oil Field mine the natural gas genesis as concluded below. Under Ordovician CO in Pingfangwang Gas Field −20 2 conditions of similar maturity, hydrocarbon gases gener- ated from sapropelic-type kerogen usually had heavier −10 d C than gases generated from humic kerogen; under the condition of similar kerogen type, the natural gases of high thermal evolution degree tend to have heavy d C . Due to multiple reasons such as various kerogen types, different thermal evolution degrees, and secondary changes, the 06 20 40 0 80 100 13 13 distribution characteristics of d C show that d C values 1 1 CO , % of natural gases at middle depth are much lower, but those at shallow and deep depths are higher (Fig. 4). Fig. 3 Identifying inorganic and organic CO with d C —CO 2 CO2 2 relationships (Dai 1993) To identify the genesis of natural gases, the three cate- gories of natural gases (shallow gas \1,500 m, middle gas 1,500–3,500 m, and deep gas [3,500 m) were put into the (2) Buried between 1,500 and 3,500 m: the heavy hydro- genesis identification template built by Dai (1993). As carbon content is usually high, and C /C ranges shown in Fig. 5, the genesis of shallow gas is complicated 1 1-5 from 0.4 to 0.9. Most gases are associated with oil, and with biogas and oil-associated gas dominating, while there 13 13 their d C ranges from -45 % to -52 %. is still a small portion of shallow gas having a d C value 1 1 (3) Buried between 3,500 and 5,500 m: the value of C / of -40 % to -55 % with high C /C and C /C 1 1 1-5 1 2?3 C ranges from 0.6 to 1.0. Compared with the values higher than 500, which indicate secondary changes. 1-5 δ C , ‰ (PDB) CO2 Pet. Sci. (2015) 12:81–95 85 Table 2 Characteristics of rare gas isotope in CO gas reservoirs in the Jiyang Depression 3 4 -8 40 36 4 20 Area Well Depth, m He/ He, 10 R/Ra Ar/ Ar He/ Ne Binnan Oilfield Bin4-6-6 1469.7–1474.7 387 2.76 1,791 934 Huagou Gas Field Hua17 1965.1–1980 445 3.18 770 Hua17 2000–2009.6 449 3.18 1,054 Pingfangwang Gas Field Ping13-2 1453.6–1483.2 359 2.56 1,220 493 Ping13-4 1450.8–1486.4 355 2.54 1,722 Ping14-3 1467–1484.6 447 3.19 1,378 110 Ping9-3 1462.6–1489.2 387 2.76 317 467 Pingq12 1470.5–1472.5 385 2.75 1,051 Pingq12-61 1452.4–1487.6 361 2.58 1,478 495 Pingq4 1459.4–1474.5 385 2.75 1,758 221 Yangxin Oilfield Yang25 2793.9–2805 412 2.94 In general, hydrocarbon gases in the Jiyang Depression 13 C /C δ C (PDB), ‰ 1 1-5 include biogas, oil-associated gas, highly mature oil-type -70 -60 -50 -40 -30 -20 0 0.2 0.4 0.6 0.8 1.0 gas, coal-type gas, and their geochemical characteristics are separately discussed below. 3.1 Biogas Biogas is defined as hydrocarbon gas or nonhydrocarbon gas that is produced due to biochemical reactions of fer- mentative bacteria and methanogens in the process of degradation of organic matter in source rocks or crude oil (Gao et al. 2010). Naturally existed biogas was formed due to two kinds of processes: one is methyl-type fermentation (CH COOH ? CH ? CO ) and the other is carbonate 3 4 2 reduction (CO ? 4H ? CH ? 2H O). Limited by the 2 2 4 2 survival temperature of methanogens (0-75 C) (Li et al. 2008), biogas was mainly developed in shallow-middle buried horizons. The present geothermal gradient in the Fig. 4 Variation of d C and C /C of hydrocarbon gases with 1 1 1-5 Jiyang Depression is about 3 C/100 m, and the surface depth in the Jiyang Depression temperature was about 17 C, so biogas in the Jiyang Depression tends to occur above 2,000 m. Biogas reser- voirs have already been discovered and they are scattered The genesis of middle gas is comparatively simple and in the Huagou and Yangxin gas fields. dominated by oil-associated gas. As for deep gas, there are The composition of biogas is fairly simple and is mainly several genesis options such as highly mature oil-cracking methane. Heavy hydrocarbon (C ) contents are extremely gas, associated gas with condensate oil, coal-type gas, and 2? low (usually less than 0.5 %), the value of C /C is the mixture of two or more of them (Fig. 5). 1 1-5 higher than 0.995, and there are also low levels of non- Carbon isotope ratios of methane, ethane, and propane can also be used to identify the genesis of natural gases hydrocarbon components (mainly N ,CO ). d C ranged 2 2 1 from -55 % to -60.9 % (Table 3) (Hu et al. 2010). Since (Lin et al. 2011). As shown in Fig. 6, shallow buried hydrocarbon gases in the Jiyang Depression were located in very little ethane and propane exist in biogas, it is difficult to measure their corresponding carbon isotope ratios. the area of oil-associated gas, but the ethane and propane Biogas is mainly developed in the first member of the carbon isotope ratios of some samples were abnormally Eogene Shahejie Formation (Es for short) in the Yangxin heavy, which might be caused by secondary changes such and Huagou gas fields. Source rocks in Es were buried in as biodegradation. The middle buried hydrocarbon gases less than 2,000 m, and were at an immature stage with an are mainly oil-associated gas mixed with a small amount of R value of 0.3 %–0.6 %, the formation temperature was coal-type gas. The deep natural gases were coal-type gas, about 55–75 C, which provided favorable conditions for oil-type gas, as well as a mixture of the both. Depth, m 86 Pet. Sci. (2015) 12:81–95 Fig. 5 Genesis identification 4 template for hydrocarbon gas in Shallow gas the Jiyang Depression (Dai a. Biogas Middle gas 1993) Deep gas e. Cracked gas b. Biogas and sub-biogas h. Inorganic gas & coal type gas i. Coal type gas c. Sub-biogas f. Cracked gas & coal type gas g. Condensate associated gas d. Oil associated & coal type gas gas –80 –70 –60 –50 –40 –30 –20 –10 0 δ C (PDB), ‰ Fig. 6 Characteristics of d C , Shallow gas Middle gas Deep gas 13 13 d C , and d C in the Jiyang 2 3 -80 Depression (Dai 1993) -70 -60 -50 -40 -30 -20 13 13 δ C (PDB), ‰ δ C (PDB), ‰ 3 -10 2 -40 -35 -30 -25 -20 -15 -20 -25 -30 -35 -40 -45 -50 Table 3 Geochemical properties of biogas in the Jiyang Depression Area Formation Well Depth, m CO ,% N ,% CH ,% C ,% d C , % (PDB) 2 2 4 2? 1 Yangxin Gas Field Es Yang101 1504.2–1529.6 0.39 1.04 98.4 0.17 -60.6 Es Yang16 1319.0–1325.0 2.98 2.17 94.66 0.19 -56.5 Es Yang21 1412.0–1415.6 0.1 1.69 97.16 0.08 -60.9 Huagou Gas Field Es Hua4 1276.0–1307.0 0.17 7.38 89.25 0.17 -55.4 Es Hua171 1453.0 13.9 6.68 79.10 0.14 -55.0 C /C 1 2+3 δ C (PDB), ‰ 1 Pet. Sci. (2015) 12:81–95 87 survival of methanogens. Anaerobes and methanogens which means that sapropel-type kerogen degrades into have already been detected in the formation water in this natural gas at high temperature; and the other is oil- area, and this confirmed that natural gas occurring in this cracking gas which means that oil cracks into natural gas at interval is biogas. high temperature (Lu et al. 2006). Compared with mature oil-type gas, kerogen thermal 3.2 Mature oil-type gas (oil-associated gas) degradation gas usually has a higher value of C /C , 1 1-5 13 13 and heavier d C and d C . Methane comprises 1 2 Mature oil-type gas is generated by sapropelic-type source 70.78 %–88.6 % of kerogen thermal degradation gas and rocks in mature stage (R = 0.6 %-1.3 %). Since sa- heavy hydrocarbons about 5 %–29 %, usually in the range propelic-type source rocks tended to generate more oil than of 10 %–15 %. The value of C /C ranged from 0.7 to 1 1-5 gas during its mature stage, this kind of gas usually 0.9 and was a little higher than that of mature oil-type 13 13 occurred as dissolved gas in oil reservoirs. Sometimes gas gas. d C ranged from -43.9 % to -33.9 %, d C 1 2 would exsolve from oil due to changes in temperature and ranged from -27.6 % to -28.7 %, d C ranged from pressure, and a gas cap would be formed. -23.3 % to -25.9 %, and d C ranged from -25.0 % Mature oil-type gas is the most important kind of natural to -26.6 %. There was an apparent reversal of d C and gas in the Jiyang Depression. Most shallow gases and d C (Table 5). There are multiple reasons for the iso- middle gases as well as part of deep gases are of this kind, tope reversal such as mixture of gases from different and the reserves of this kind of gas resource account for 3/4 kerogen types, mixture of gases from the same kerogen of all the proved gas reserves in place. Mature oil-type gas type but of different maturities, inorganic originated usually occurred in the third member and the fourth hydrocarbon gas, and biodegradation gas (Burruss and member of the Eogene Shahejie Formation (Es ,Es ), and Laughrey 2010). Analysis of the reservoir forming pro- 3 4 sometimes in buried hills in the Paleozoic Carboniferous or cesses indicated that the discovered highly mature oil-type Ordovician (e.g., Zhuangxi Oilfield). This kind of gas gases originated from the same source rocks, i.e., the always occurred associated with oil reservoirs and gas was fourth member of the Eogene Shahejie Formation (Es ), produced together with oil. which was deeply buried with little chance of undergoing The methane content of mature oil-type gas varied biodegradation. Therefore, it can be inferred that the 13 13 greatly and ranged from 25.6 % to 99.6 %. The methane reversal in d C and d C was caused by the mixing of 3 4 content of most oil-associated gas (81 %) was about gases of different maturities. 60 %–90 %, the heavy hydrocarbon content ranged from Only oil-cracking gas was discovered in the Minfeng 0 % to 70.9 %, and C /C ranged from 0.6 to 0.99. d C area (Chen et al. 2014), where the fourth member of the 1 1-5 1 of mature oil-type gas in the Jiyang Depression ranged Shahejie Formation (Es ) was deeply buried, and the from -38 % to -55 %, d C ranged from -26.3 % to temperature might exceed 210 C in its maximum depth. 13 13 -34.9 %, d C ranged from -25.6 % to -32.1 %, d C According to the experiment carried out by Luo et al. 3 4 ranged from -25.6 % to -32.1 %, and they were arran- (2008), crude oil would crack into gases when the tem- 13 13 13 13 ged in the order of d C \ d C \ d C \ d C perature exceeded 160 C. Compared with kerogen thermal 1 2 3 4 13 13 (Table 4). degradation gas with the similar maturity, d C and d C 1 2 13 13 d C and d C of mature oil-type gas in the Jiyang of oil-cracking gas were fairly light and, respectively, 1 2 Depression correlated well with depth, so it is possible to ranged from -48.4 % to -50.4 % and from -33 % to calculate the maturity using gas carbon isotope ratios. -34 % (Song et al. 2009; Tian et al. 2009). Comparison between gas samples and source rock samples Based on comparison of light hydrocarbon compounds was carried out, and the relationship between d C and R in oil-cracking gas and kerogen thermal degradation gas, 1 o was established: Hu et al. (2005) put forward that MCC /nC and (2- 6 7 MC ? 3-MC )/nC of oil-cracking gas were higher than 6 6 6 d C = 6.942 ln R 45.254ðÞ R = 0.4 1.3 ; ð1Þ 1 o o those of kerogen thermal degradation gases (MCC where d C is the methane carbon isotope ratios of mature means methylcyclohexane, 2-MC means 2-methylhexane, 1 6 oil-type gas, %; R is vitrinite reflectance, %. 3-MC means 3-methylhexane, nC means n-heptane, nC 6 7 6 means n-hexane). Based on simulation experiments, Wang 3.3 Highly mature oil-type gas (2005) discovered that there were differences in MCC / CC ,MCC /nC , and (2-MC ? 3-MC )/nC between 6 6 7 6 6 6 Highly mature oil-type gas was generated by sapropel-type these two kinds of highly mature oil-type gases (CC source rock in highly mature stage (R [ 1.3 %) (Zhao means cyclohexane). The content of thermally stable et al. 2013). There are two options for the genesis of highly compounds in kerogen thermal degradation gas was higher mature oil-type gas, one is kerogen thermal degradation gas than that in oil-cracking gas. In the Jiyang Depression, 123 88 Pet. Sci. (2015) 12:81–95 Table 4 Geochemical characteristics of typical mature oil-type gases in the Jiyang Depression 13 13 13 13 Area Formation Well Depth, d C , d C , % d C , % d C , % CH , C , N ,% CO , 1 2 3 4 4 2? 2 2 m %(PDB) (PDB) (PDB) (PDB) % % % Chengdao N Chengbs19 1308.2 -53.9 -36.2 -34.9 -32.1 98.03 1.2 0.37 0.2 Oilfield E Chengb12 2144.5 -38.0 -28.3 -27.8 -27.1 60.63 38.79 0.62 0.63 Pz Chengb242 2936.6 -45.7 -31.2 -28.9 -28.1 70.97 26.37 0.29 2.26 Linpan Oilfield N Lin2-6 1582.8 -44.5 -32.5 -26.7 -27.7 96.6 2.728 0.594 0.177 Yanjia Gas E Yan22 1573.0 -47.4 -33.5 -29.2 -27.7 70.77 25.39 0.39 3.45 Field Dongfenggang E Che57 4067.0 -44.2 81.8 11.86 0.06 6.28 Oilfield Shengtuo E Ning3 1805.6 -45.8 -35.6 -29.4 -28.4 83.79 13.98 0 0.4 Oilfield E Tuo113 1948.6 -53.8 91.86 6.18 0 0.34 E Tuo165 3391.1 -50.3 -35.1 -30.5 -29.0 65.95 19.02 2.79 12.24 Gubei Oilfield E Gub1 2138.5 -47.1 75.36 17.03 0.77 6.84 Bonan Oilfield E Xiny12 2454.9 -52.3 -33 -31.2 -29.8 74.78 20.5 0 4.3 E Yi37 3220.3 -45.6 -31.7 -32.9 -28.3 66.2 22.45 0 9.55 E Yi170 3817.6 -52.6 -31.2 -27.3 -27.2 84.44 12.4 0.14 2.72 E Bos4 3911.5 -52.7 -30.8 -28.2 -28.1 83.38 14.59 1.53 1.4 Gudong Oilfield E Gud9 2506.4 -48.7 -27.4 -27.3 -25.6 60.05 20.99 24 2.52 Guangli Oilfield E Lai10 2665.1 -50.6 81.35 15.39 0 0.46 Liangjialou E Liang60 2844.8 -52.3 73.12 20.23 0 3.61 Oilfield E Ling35 3119.9 -50.8 89.84 5.93 0 1.28 Lijin Oilfield E Li54 2904.3 -49.5 70.11 22.23 0 5.93 Xianhe Oilfield E Niu23 3289.8 -52.1 73.2 20.13 0 4.05 E Wang53 3389.0 -50.4 67.63 23.94 0 4.99 Dawangzhuang O Dag23 1738.3 -44.4 90.18 7.23 0 2.04 Oilfield Chengdong P Chengk1 2588.0 -51.5 -34.1 -31.7 -29.8 73.92 25.53 0.18 0.71 Oilfield Yong’anzhen E Yong12-21 -47.6 -39.9 -31.3 -28.5 98.55 1.28 1.109 0.663 Oilfield Zhuangxi E Zhuang202 2644.5 -51.6 -34.9 -31.7 -29.4 86.22 7.49 0 1.13 Oilfield E Zhuang50 3228.2 -49.7 -33.5 -30.1 -28.2 89.44 7.47 0 1.73 E Zhuang74 3634.5 -47.6 -33.3 -28.9 -27.5 68.44 23.49 0 4.81 O Zhuangg10 3627.2 -44.1 63.74 28.75 0 3.56 O Zhuangg21 3929.1 -42.4 -27.9 -27.7 -26.4 67.15 25.73 0 3.13 O Zhuangg4 4013.5 -45.4 77.5 16.97 0 4.55 [-Anz Zhuangg25 4277.6 -43.2 -29.7 -26.3 -27.7 71.34 25.48 0 1.36 O Zhuangg14 4318.5 -46.1 -32.0 -29.6 76.77 13.21 0 9.24 O Zhuangg13 4367.5 -42.2 -29.5 -28.1 -27.2 69.54 27.75 0 1.87 O Zhuangg18 4582.4 -44.4 71.18 24.65 0.59 3.08 [ Zhuangg17 4886.2 -45.8 -31.9 -29.2 -28.5 85.99 10.25 0.58 3.09 MCC /nC of oil-cracking gas was higher than 1.0, (2- 3.4 Coal-type gas 6 7 MC ? 3-MC )/nC of oil-cracking gas was higher than 6 6 6 0.4, which were higher than those of kerogen thermal Coal-type gas is defined as natural gas generated by coal or humic kerogen due to biochemical and chemical action. degradation gas and mature oil-type gas, while MCC /nC 6 7 of oil-cracking gas was less than 0.8 which was lower than Coal-type gas discovered in the Jiyang Depression was mainly developed in the Paleozoic Ordovician and Car- that of kerogen thermal degradation gas and mature oil- type gas (Fig. 7). boniferous—Permian in the Gubei buried hill belt, the 123 Pet. Sci. (2015) 12:81–95 89 fourth member of the Shahejie Formation in the Bonan deep sag, and the Shahejie Formation in the Qudi Oilfield in the Huimin Sag. Coal-type gas in the Gubei buried hill and Qudi Oilfield was generated by coal and humic kero- gen in the Shanxi Formation and Taiyuan Formation in Carboniferous—Permian, while that in the Bonan Sag (Well Yi115 and Yi121) was generated by humic kerogen in the upper part of Es . The methane content of coal-type gas ranged from 75 % to 92 %, and the heavy hydrocarbon content varied greatly from 0.51 % to 19.5 %. C /C ranged from 0.8 to 0.99 1 1-5 and the value of most samples exceeded 0.9. C /C of 1 1-5 coal-type gas is usually higher than that of oil-type gas with a similar maturity. d C of coal-type gas in the Jiyang Depression ranged from -32.6 % to -41.0 %, d C ranged from -22.0 % to -27.6 % (Table 6). There was a 13 13 slight reversal in d C and d C and this might be caused 3 4 by mixing with oil-type gas. It is pointed out that d C of coal-type gas in China is usually higher than -28 % (Song et al. 2012; Dai et al. 2012; Wang et al. 2010), and in the Jiyang Depression, the carbon isotope ratios of coal-type gas are located in the ‘‘I’’ area of the ‘‘V’’ shaped d C - 13 13 d C -d C template (Fig. 6). 2 3 C light hydrocarbon information can also be used to distinguish coal-type gas from oil-type gas. The C system is composed of three kinds of compounds: normal heptane (nC ), methylcyclohexane (MCC ), and multi-structured 7 6 dimethylcyclopentane ( DMCC ). MCC mainly came 5 6 from higher plants and was a major component of C system in coal-type gas, and DMCC mainly came from aquatic organisms and was a major component of C sys- tem in oil-type gas (Song and Zhang 2004). As shown in Fig. 8, coal-type gas differed significantly from oil-type gas. MCC / C of the coal-type gas 6 7 P P exceeded 50 %, while DMCC / C was less than 5 7 40 %; as for oil-type gas, nC / C exceeded 30 %, 7 7 MCC / C ranged from 20 to 40 %. 6 7 4 Secondary changes of natural gas Most shallow gas in the Jiyang Depression was originally dissolved gas that escaped from oil when temperature and pressure changed due to migration of oil along faults or sand bodies. This kind of natural gas was located in the ‘‘d’’ area (oil-associated gas) of ‘‘d C -C /(C ? C ) tem- CH4 1 2 3 plate’’ in Fig. 5, and in ‘‘II’’ area of ‘‘V’’ shaped ‘‘d C - 13 13 d C -d C template’’ in Fig. 6, and was typical mature 2 3 oil-type gas. There is a kind of shallow gas whose hydrocarbon car- bon isotope ratios are similar to mature oil-type gas, but its heavy hydrocarbon content is extremely low, the methane content is very high ([95 %), C /C is higher than 0.95, 1 1-5 Table 5 Geochemical properties and genesis of typical highly mature oil-type gas in the Jiyang Depression 13 13 13 13 Area Formation Well Depth, m d C , % d C , % d C , % d C , % C /C CH ,% C ,% N ,% CO , % Genetic type 1 2 3 4 1 1-5 4 2? 2 2 (PDB) (PDB) (PDB) (PDB) Bonan Oilfield O Bo601 5007.0–5009.0 -43.8 -28.7 -25.8 -26.1 0.716 70.78 29.22 Kerogen thermal degradation gas E Bos5 4491.9–4587.3 -38.0 0.859 79.55 13.07 0.43 7.03 O Bos6 4165.5–4246.0 -40.8 -27.6 -24.5 0.799 74.98 19.27 0.51 4.77 Laohekou Oilfield Pz Chengb39 4173.0–4320.0 -41.3 -27.6 -25.9 -25.7 0.835 75.02 15.47 2.04 7.48 Shengtuo Oilfield E Tuo765 4354.1–4386.0 -43.9 -28.6 -24.9 -26.6 0.880 87.82 12.03 0 0.15 Lijin Oilfield E Xinlis1 4271.2–4371.0 -41.8 0.905 87.82 9.27 0.04 2.87 Zhuangxi Oilfield O Zhuangg23 3897.0–3988.5 -38.3 -27.6 -23.3 -26.2 0.890 86.38 10.65 1.14 1.53 Dongxin Oilfield E Feng8 -49.0 0.798 62.92 16.61 1.25 19.16 Oil-cracking gas E Fengs1 4314.0–4316.0 -48.4 -33.0 -26.8 -25.0 0.862 46.73 8.12 0.39 44.76 E Fengs1 4316.0–4343.0 -50.4 0.876 81.01 11.59 1.6 5.74 E Fengs1 4400.0–4402.0 -48.0 -34.0 -27.3 -25.6 0.860 71.39 11.75 0.53 16.28 40 60 100 20 80 90 Pet. Sci. (2015) 12:81–95 Table 6 Geochemical properties of typical coal-type gas in the Jiyang Depression 13 13 13 13 Area Formation Well Depth, m d C , % d C , % d C , % d C , % CH ,% C ,% N ,% CO ,% 1 2 3 4 4 2? 2 2 (PDB) (PDB) (PDB) (PDB) Gudao Oilfield C–P Bo93 3230.0–3249.4 -38.1 -22.7 -21.25 -21.8 88.99 7.81 2.29 O BoG4 4375.0–4460.0 -38.2 -24.9 -22.5 -23.6 85.32 10.02 0 4.66 O BoG403 3850.5–3889.3 -37.1 -24.2 -22.0 -23.5 85.16 8.68 0.83 5.31 Es BoS3 4450.1–4472.4 -39.1 -26.7 -23.4 -23.9 83.15 10.8 0.73 5.05 P GBG1 4020.6–4139.5 -35.9 -23.1 -21.2 -21.2 88.44 6.48 0.55 4.54 C–P GBG1 4120.6–4139.0 -35.8 -22.9 -21.5 -20.8 82.52 10.09 0.74 6.66 C–P GBG2 3689.0–3731.0 -41.0 -25.8 -23.6 -23.6 75.87 19.52 0.96 3.65 Mz Yi132 3374.0–3387.0 -37.0 -25.3 -25.0 -25.5 87.01 7.9 1.98 2.18 P Yi155 4696.3–4706.7 -32.7 -22.0 -21.5 -21.0 87.64 4.85 6.64 Bonan Oilfield Es Yi115 5110.4–5164.4 -35.9 -24.9 -21.8 80.18 0.51 0.05 19.27 Es Yi121 4426.1–4438.4 -38.0 -22.0 -19.3 -20.6 91.36 1.46 0 7.09 O BoS6 4165.5–4246.0 -40.8 -27.6 -24.5 74.98 19.27 0.51 4.77 Qudi Oilfield Es QuG1 1514.0–1520.0 -32.6 -23.9 -20.3 -20.2 77.25 9.53 11.99 0.93 0.55 1.80 Oil cracking gas 1.60 Kerogen thermal degradation gas 0.45 Oil associated gas 1.40 1.20 0.35 1.00 0.80 0.25 0.60 0.15 0.40 0 0.5 1.0 1.5 00.5 1.0 1.5 MCC /nC MCC /nC 6 7 6 7 Fig. 7 Light hydrocarbon property differences between oil cracking gas and kerogen thermal degradation gas and is located above the ‘‘d’’ area of the ‘‘d C -C / CH4 1 Kerogen thermal degradation gas nC Oil associated gas (C ? C ) template’’ (Table 7; Fig. 5). Such characteris- 2 3 Oil cracking gas Coal type gas tics are caused by composition changes during long Biodegradation secondary gas distance migration of natural gas. Gas migration experi- ments in porous sandstone core samples indicated that, with increasing migration distance, the methane content tended to increase while the heavy hydrocarbon content (C ) decreased correspondingly. Furthermore, the car- 2? bon isotopes of hydrocarbon differentiated slightly and this means that carbon isotopes became lighter with an increase of migration distance (variation range usually less than -2 %). Therefore, it is believed that this kind of natural gas with a high content of methane was dis- solved gas that escaped from oil after long-distance 100 80 60 40 20 0 migration. ΜCC ΣDMCC 6 There is another kind of shallow gas whose methane carbon isotope ratios are heavier than those of mature oil- Fig. 8 Triangular template of C light hydrocarbon in different kinds 13 13 13 type gas, and d C and d C are extremely heavy. d C of of natural gases in the Jiyang Depression 2 3 3 20 40 80 100 (2-MC +3-MC )/nC 6 6 6 MCC /CC 6 6 Pet. Sci. (2015) 12:81–95 91 Table 7 Geochemical properties and genesis of shallow gas (part) in the Jiyang Depression 13 13 13 13 Area Well Formation Depth, m d C , % d C , % d C , % d C , % CH ,,% N , % Genesis 1 2 3 4 4 2 (PDB) (PDB) (PDB) (PDB) Caoqiao Oilfield Cao104 Es 1258–1265.6 -46.4 -35.7 -23 -22.12 97.87 0.4 1.23 0.42 High methane secondary Huagou Gas Field Hua16 N 828.1–831.1 -46.6 -30.4 -22.64 -26.1 98.99 0.31 0.71 0 gases Hua6-4 N 790–830 -44.7 -25.2 96.5 0.43 \ 1.93 Gudong Oilfield Gud22-3 N 1214.8–1219.6 -43.7 -30.6 -23.3 -22.4 97.17 2.41 0.26 0.13 Gud29-416 N 1246–1270.4 -45.9 -29.1 -23 -21.1 94.99 1.6 1.52 1.83 Gud3-015 N 1203.7–1207.4 -45.4 -30.7 -26.1 -23.3 95.19 3.92 0.33 0.54 Gud31-15 N 1196.2–1238.2 -45.6 -30.3 -25.6 -23.6 93.51 5.01 0.83 0.51 Gud3-517 N 1303.4–1315.4 -49.9 -31.4 -28.8 -29.2 96.79 0.37 2.26 0.49 Gud13-N11 N 1252.8–1263.6 -41.9 -32.1 -27.7 -24.8 93.57 5.2 0.45 0.71 Biodegradation secondary Gud13- N 1380.5–1562 -42.2 -31.9 -27.5 -25 88.25 10.59 0.5 0.56 gases P513 Gud2-2 N 1191–1204 -41.9 -31.1 -27.8 -25.5 90.42 8.1 0 1.27 Gud22-N3 N 1261.6–1294 -42.3 -31.3 -26 -23.9 83.12 5.42 0.28 1.15 Gud2-5 N 1175.2–1204.2 -41.8 -31.4 -27.7 -25.2 73.28 12.42 12.41 1.63 Chenjiazhuang Oilfield Chenq11 N 935–942 -52.9 -33.11 -20.08 -18.49 95.02 0.152 4.706 0.122 Chenq8 N 945–948 -53.87 -25.7 -27.14 -29.03 88.436 0.315 10.49 0.752 Shanjiasi Oilfield Shan66 Anz 1076–1100 -46.79 -29.89 -18.92 -24.11 95.85 0.41 0 1.61 Huagou Gas Field Gao41-5 Mz 1965.1–1984 -41.8 -25.14 -8.52 -22.13 97.384 3.592 0.82 Gao42 Es 945–952 -42.95 -32.03 -16.49 -23.09 89.138 5.328 3.096 5.1 Hua6 N 818–819.6 -44.28 -25.24 -20.33 -27.3 99.26 0.44 0.28 0.02 Hua6-2 N 743.8–783.4 -44.35 -24.91 -20.11 -24.85 96.7 0.43 1.92 Linpan Oilfield Lin2-4 N 1398.8–1426 -47.57 -29.27 -16.18 -20.81 96.624 0.719 2.496 0.16 Yuhuangmiao Oilfield Xia8 Ed 1457.7–1464 -46.95 -32.48 -22.03 -22.76 98 0.9 0 0 92 Pet. Sci. (2015) 12:81–95 normal mature oil-type gas ranged from -26 % to -34 %, 2.0 while d C of this kind of natural gas might as heavy as 1.0 -8.5 %. d C of most natural gas ranged from -8 % to -22 %, and carbon isotope ratios of light hydrocarbons 0.5 13 13 13 13 arranged in the order of d C \ d C \ d C [ d C . 1 2 3 4 0.3 d C of some samples was about 2 %–7 % heavier than 0.2 that of mature oil-type gas. Take the Gudong Oilfield as an example, d C of mature oil-type gas (Well Gud3-517) was 0.1 13 13 about -49.9 %, d C was about -31.4 %, but d C and Biodegradation secondary gas 2 1 Oil associated gas d C of the sample from the same horizon and similar depth 0.05 Kerogen thermal degradation gas (Gud2-2) were, respectively, -41.9 % and -31.1 %, that is Oil cracking gas to say d C was about 8 % heavier than that in Well Gud3- 0.02 Coal type gas Analysis indicated that the main reason that caused abnormal carbon isotope ratios was biodegradation. James 0.2 0.5 1.0 5.0 10 20 30 40 50 Heptane index and Burns (1984) analyzed the carbon isotope ratios of light hydrocarbons of biodegradation natural gases in Fig. 9 2,4-DMC /nC –heptane index template of natural gases in the 13 5 6 Australia and Canada, and discovered that d C was Jiyang Depression (Zhang 1991) abnormally heavy. They deduced that since propane is soluble in water, it is readily biodegradable. Secondary biodegradation shallow gas in the Jiyang Depression exhibited the similar characteristics. Stahl (1980) carried out bacterial degradation experi- ments, and pointed out that long-chained paraffin hydro- and with the help of gas compositions, carbon isotope carbon is more easily degradable than short-chained ones, ratios of paraffin hydrocarbon and CO , and light hydro- and normal paraffin hydrocarbon is more easily degradable carbon index, it is feasible to identify the genesis of natural than isomeric ones. As shown in Fig. 8, nC / C of bio- 7 7 gases in the Jiyang Depression. degradation shallow gas was less than 20 %, and was obvi- Take mature oil-type gas as reference, biogas has a high ously less than that of mature oil-type gas. methane content, and d C was less than -55 %; highly Leythaeuser et al. (1979) studied biodegradation of oil mature oil-type gases are divided into kerogen thermal using light hydrocarbon data, and summarized typical degradation gas and oil-cracking gas. They both have a high characteristics: the content of normal paraffin hydrocarbon value of C /C and heavy methane carbon isotope ratios, 1 1-5 was low, while the contents of isomeric ones (such as 3,3- and they can be distinguished by the (2-MC ? 3-MC )/ 6 6 DMC ; 2,3,3-TMC ; 2,2-DMC ; 2,4-DMC and 2,2- 5 4 5 5 nC –MCC /nC template. Ethane carbon isotope ratios of 6 6 7 DMC ) were high (DMC means dimethylpentane, TMC 4 5 4 coal-type gas in the Jiyang Depression are usually higher means triptane, DMC means dimethylbutane). Based on than -28 % and the compositions of C can be used to analysis of light hydrocarbons in shallow gas in the Jiyang effectively distinguish coal-type gas from oil-type gas. Depression, Zhang (1991) pointed out that the relationship Heavy hydrocarbons usually reduce in the process of between 2,4-DMC /nC and the heptane index can be 5 6 gas migration. The C /C value of methane rich sec- 1 2?3 used to distinguish biodegradation oil-type gas from other ondary gas might exceed 280, and its carbon isotope oil-type gases. As shown in Fig. 9, the value of 2,4- compositions and light hydrocarbon compositions are DMC /nC for biodegradation gas was usually higher than 5 6 similar to those of mature oil-type gas. Secondary bio- 0.5, and the heptane index was usually less than 5; in degradation gas is featured by heavy carbon isotope ratios contrast, the heptane index usually ranged from 20 to 50, 13 13 of d C or d C , and light hydrocarbon isotope ratios 1 3 and 2,4-DMC /nC for other oil-type gases was less than 5 6 13 13 13 13 arrange in the order of d C \ d C \ d C [ d C . 1 2 3 4 0.1. Influenced by biodegradation, the normal paraffin hydro- carbon content is low. The triangular template of C and 5 Identification factors 2,4-DMC /nC —heptane index template can be used to 5 6 distinguish the secondary biodegradation gas from other Based on discussion above, the identification factors for different kinds of natural gases are summarized in Table 8, natural gases. 2,4-DMC /nC 5 6 Pet. Sci. (2015) 12:81–95 93 Table 8 Identification factors of hydrocarbon gases with different genesis in the Jiyang Depression Genetic types Gas composition Isotope composition Light hydrocarbon characteristics 13 13 13 13 CO , C /C C / d C , d C , d C , d C , Isotope series 2 1 1-5 1 1 2 3 4 % C % % % % 2?3 CO gas [50% / / / // // / Hydrocarbon Biogas \10 % [0.995 \-55 // // / 13 13 13 13 gases Biodegradation 0.95–1 17–207 -38 to -20 to -13 to -14 to d C \ d C \ d C [ d C nC / C \ 0.2; 2,4-DMC /nC \ 0.5; heptane 1 2 3 4 7 7 5 6 secondary gas -48 -34 -24 -25 index \5; P P 13 13 13 13 High methane [0.95 [280 -42 to -29 to -26 to -25 to d C \ d C \ d C \ d C nC / C = 30-60; MCC / C = 20-40; 2,4- 1 2 3 4 7 7 6 7 secondary gas -55 -38 -34 -32 DMC /nC \ 0.1; heptane index = 30-40; 5 6 P P 13 13 13 13 Oil-associated 0.6–0.99 2–39 -42 to -29 to -26 to -25 to d C \ d C \ d C \ d C nC / C = 30-60; MCC / C = 20-40; 2,4- 1 2 3 4 7 7 6 7 gas -55 -38 -34 -32 DMC /nC \ 0.1; heptane index = 30-40; 5 6 13 13 13 13 Kerogen thermal 0.7–0.95 5–46 -33 to -27 to -23 to -26 to d C \ d C \ d C \ d C MCC /nC \ 1.0; (2-MC ? 3-MC )/nC \ 0.4; 1 2 3 4 6 7 6 6 6 degradation -44 -33 -26 -28 MCC /CC [ 0.8; 6 6 gas DMCC / C = 40-60; 5 7 13 13 13 13 Oil-cracking gas 0.7–0.9 2–55 -44 to -28 to -24 to -24 to d C \ d C \ d C \ d C MCC /nC [ 1.0; (2-MC ? 3-MC )/nC [ 0.4; 1 2 3 4 6 7 6 6 6 -52 -34 -28 -26 MCC /CC \ 0.8; DMCC / C = 30-40; 6 6 5 7 P P P 13 13 13 13 Coal-type gas 0.8–0.99 10–190 -29 to -17 to -19 to -20 to d C \ d C \ d C \ d C MCC / C [ 50 %; DMCC / C \ 40 %; 1 2 3 4 6 7 5 7 -41 -25 -24 -25 2,4-DMC /nC = 0.03-0.1; heptane 5 6 index = 30-50 94 Pet. Sci. (2015) 12:81–95 Dai JX. The carbon and hydrogen isotope characteristics and 6 Conclusions identification of different kinds of natural gases. Nat Gas Geosci. 1993;2:1–40 (in Chinese). 1) Based on analysis of gases compositions, carbon Dai JX, Ni YY, Zou CN. Stable carbon and hydrogen isotopes of isotope ratios, light hydrocarbon properties, combined natural gases sourced from the Xujiahe Formation in the Sichuan Basin, China. Org Geochem. 2012;43:103–11. with geological analysis, natural gases in the Jiyang Gao Y, Jin Q, Zhu GY. Genetic types and distribution of shallow- Depression were classified into two categories namely buried natural gases. Pet Sci. 2010;7(3):347–54. hydrocarbon gas and abiogenic gas. The abiogenic Gao Y, Jin Q, Shuai YH, et al. Genetic types and accumulation gas was mainly magmatogenic or mantle derived conditions of biogas in Bohaiwan Basin. Nat Gas Geosci. 2011;22(3):407–14 (in Chinese). CO . Hydrocarbon gases were further divided into Hu GY, Luo X, Li ZS, et al. Geochemical characteristics and origin of coal-type gas, oil-type gas, and biogas according to light hydrocarbons in biogenic gas. Sci China: Earth Sci. the kerogen types and formation mechanisms. The 2010;53(6):832–43. oil-type gases were divided into mature oil-type gas Hu GY, Xiao ZY, Luo X, et al. Light hydrocarbon composition difference between two kinds of cracked gases and its applica- (oil-associated gas), highly mature oil-type gas. tion. Nat Gas Ind. 2005;25(9):23–5 (in Chinese). Highly mature oil-type gases were subdivided into Hunt AG, Darrah TH, Poreda RJ. Determining the source and genetic oil-cracking gas and kerogen thermal degradation gas. fingerprint of natural gases using noble gas geochemistry: A 2) Analysis results showed that shallow gases (buried northern Appalachian Basin case study. AAPG Bull. 2012;96(10):1785–811. less than 1,500 m) are mainly mature oil-type gases, James AT, Burns BJ. Microbial alteration of subsurface natural gas secondary gas is rich in methane after chromato- accumulations. AAPG Bull. 1984;68(8):957–60. graphic separation during migration and secondary Leythaeuser D, Schaefer RG, Cornford C, et al. Generation and mature oil-type gas after biodegradation is featured by migration of light hydrocarbons (C -C ) in sedimentary basins. 2 7 Org Geochem. 1979;1(4):191–204. rich in C in methane and ethane. Meanwhile, biogas Li J, Hu GY, Zhang Y, et al. Study and application of carbon isotope is another kind of shallow gas. The genesis of middle fractionation during the reduction process from CO to CH . 2 4 gases buried in the depth of 1,500–3,500 m was Earth Sci Front. 2008;15(5):357–63 (in Chinese). simple and was dominated by mature oil-type gases. Li PL, Jin ZJ, Zhang SW, et al. The present research status and progress of petroleum exploration in the Jiyang Depression. Pet Deep gases buried in the depth of 3,500–5,500 m Explor Dev. 2003;30(3):1–4 (in Chinese). were usually kerogen thermal degradation gas, oil- Lin HX, Cheng FQ, Jin Q. Fractionation mechanism of natural gas cracking gas, and coal-type gas. components and isotopic compositions and sample analysis. Nat 3) Due to chromatographic effects, the methane content Gas Geosci. 2011;22(2):195–200 (in Chinese). Lu SF, Li JJ, Xue HT, et al. Chemical kinetics of carbon isotope increases and heavy hydrocarbons decrease during the fractionation of oil-cracking methane and its initial application. progress of migration. Secondary biodegradation gas J Jilin Univ (Earth Science Edition). 2006;36(5):825–9 (in was featured by heavy carbon isotope ratios of d C Chinese). or d C , and light hydrocarbon isotope ratios Luo X, Wang YB, Li J, et al. Origin of gas in deep Jiyang Depression. 13 13 13 Nat Gas Ind. 2008;28(9):13–6 (in Chinese). arranged in the order of d C \ d C \ d C [ - 1 2 3 Schoell M. The hydrogen and carbon isotopic composition of d C . Influenced by biodegradation, the normal methane from natural gases of various origins. Geochim paraffin hydrocarbon content was low. Triangular Cosmochim Acta. 1980;44(5):649–61. template of C and 2,4-DMC /nC —heptane index 7 5 6 Song GQ, Jin Q, Wang L, et al. Study on kinetics for generating natural gas of Shahejie Formation in deep-buried sags of template can be used to distinguish secondary Dongying Depression. Acta Petrolei Sinica. 2009;30(5):672–7 biodegradation gas from other natural gases. (in Chinese). Song MS, Zhang XC. Discussion on deep gas geochemical charac- teristics and genesis of Bonan Sag, Jiyang Depression. Nat Gas Open Access This article is distributed under the terms of the Geosci. 2004;15(6):646–9 (in Chinese). Creative Commons Attribution License which permits any use, dis- Song Y, Liu SB, Zhang Q, et al. Coalbed methane genesis, occurrence tribution, and reproduction in any medium, provided the original and accumulation in China. Pet Sci. 2012;9(3):269–80. author(s) and the source are credited. 13 12 Stahl WJ. Compositional changes and C/ C fractionations during the degradation of hydrocarbons by bacteria. Geochim Cosmo- chim Acta. 1980;44(11):1903–7. References Sun ML, Chen JF, Liao YS. Helium isotopic characteristics, genesis of CO in natural gases and distribution of Tertiary magamatite Burruss RC, Laughrey CD. Carbon and hydrogen isotopic reversals in in the Jiyang Depression. Geochimica. 1996;25(5):475–80 (in deep basin gas: evidence for limits to the stability of hydrocar- Chinese). bons. Org Geochem. 2010;41(12):1285–96. Tang DZ, Liu HX, Li XM, et al. Probe into deep-seated structural Chen ZH, Zhang SC, Zha M. Geochemical evolution during the factors of abiogenic gas accumulation and storage in Jiyang cracking of crude oil into gas under different pressure systems. Depression. Earth Sci: J China Univ Geosci. 2002;27(1):30–4 (in Sci China: Earth Sci. 2014;57(3):480–90. Chinese). 123 Pet. Sci. (2015) 12:81–95 95 Tian H, Xiao XM, Yang LG, et al. Pyrolysis of oil at high Zhang LY. Identifying criteria of natural gases in the Jiyang temperatures: gas potentials, chemical and carbon isotopic Depression. Pet Geol Exper. 1991;13(4):355–69 (in Chinese). signatures. Chin Sci Bull. 2009;54(7):1217–24. Zhao XZ, Jin Q, Jin FM, et al. Origin and accumulation of high- Wang G L. Accumulation conditions of natural gas in cratonic area, maturity oil and gas in deep parts of the Baxian Depression, Tarim Basin. Ph.D. Thesis. Chengdu: Southwest Petroleum Bohai Bay Basin, China. Pet Sci. 2013;10(3):303–13. University. 2005. 43–47. Zhou JL. Gas accumulation analysis of upper Paleozoic coal in the Wang P, Shen ZM, Liu SB, et al. Geochemical characteristics of Jiyang Depression. J Earth Sci Environ. 2004;26(2):47–50 (in noble gases in natural gas and their application in tracing natural Chinese). gas migration in the middle part of the western Sichuan Depression, China. Pet Sci. 2013;10(3):327–35. Wang YP, Dai JX, Zhao CY, et al. Genetic origin of Mesozoic natural gases in the Ordos Basin (China): comparison of carbon and hydrogen isotopes and pyrolytic results. Org Geochem. 2010;41(9):1045–8.
Petroleum Science – Springer Journals
Published: Jan 22, 2015
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