Geochemical characteristics, generation, and evolution mechanism of coalbed methane in the south-western Ordos Basin, China

Abstract

The south-western Ordos Basin is rich in low-middle rank coalbed methane (CBM) resources; while the geochemical characteristics and genetic mechanism of CBM are not clear. Herein, according to geological and geochemical test data from gas and coal seam water from CBM wells in Bingchang, Jiaoxun, Huangling, Yonglong, and Longdong minging areas, we systematically studied the geochemical characteristics, generation, and evolution mechanism of CBM in Jurassic Yan’an Formation in the south-western Ordos Basin. The results show that the CH₄ content of whole gas is in the range of 42.01%–94.72%. The distribution ranges of the δ¹³C-CH₄ value is −87.2‰ to −32.5‰, indicating diverse sources of thermogenic gas and biogenic gas. The microbial methane is mainly generated by a CO₂ reduction pathway, with certain methyl-type fermentation spots. The δ¹³C-CH₄ has a positive correlation with burial depth, indicating the obvious fractionation of CBM. The relationship between the genetic types and burial depth of the CBM reservoir indicates that the favorable depth of secondary biogenic gas is less than 660 m. The Late Cretaceous Yanshanian Movement led to the uplift of the Ordos Basin, and a large amount of thermogenic gas escaped from the edge of the basin. Since the Paleogene Period, the coal reservoir in the basin margin has received recharge from atmospheric precipitation, which is favorable for the formation of secondary biogenic methane. The deep area, generally under 1000 m, mainly contains residual thermogenic gas. The intermediate transition zone is mixed gas. Constrained by the tectonic background, the genetic types of CBM in different mining areas are controlled by the coupling of burial depth, coal rank, and hydrogeological conditions. The Binchang mining area contains biogenic gas, and the development of CBM has achieved initial success, indicating that similar blocks with biogenic gas formation conditions is key to the efficient development of CBM. The research results provide a scientific basis for searching for favorable exploration areas of CBM in the south-western Ordos Basin.

Graphical abstract

Keywords

coalbed methane / stable isotopes / geochemistry / generation and evolution mechanism / Ordos Basin

References

[1] Bao Y, Wang W, Ma D, Shi Q, Ali A, Lv D, Zhang C (2020). Gas origin and constraint of δ¹³C(CH₄) distribution in the Dafosi mine field in the southern margin of the Ordos Basin, China.Energy Fuels, 34(11): 14065–14073

[2] Chen Y, Qin Y, Ji M, Duan H, Wu C, Shi Q, Zhang X, Wang Z (2020). Influence of lamprophyre sills on coal metamorphism, coalbed gas composition and coalbed gas occurrence in the Tongxin Minefield, Datong Coalfield, China.Int J Coal Geol, 217: 103286

[3] Conrad R (2005). Quantification of methanogenic pathways using stable carbon isotopic signatures: a review and a proposal.Organic Geochem, 36(5): 739–752

[4] Dai J, Qi H, Song Y, Guan D (1986). The components and carbon isotopes of coal bed gases in China and origin. Sci China Series B-Chem, Bio, Agri, Med Earth Sci, 16(12): 1317–1326 10.1360/zb1986-16-12-1317 (in Chinese)

[5] Dong J (2010). The rule of the coal accumulation and coal-bed methane accumulation in Jurassic Yan’an Formation of Ordos Basin. Dissertation for Master’s Degree. Qingdao: China University of Petroleum

[6] Fu H, Tang D, Pan Z, Yan D, Yang S, Zhuang X, Li G, Chen X, Wang G (2019). A study of hydrogeology and its effect on coalbed methane enrichment in the southern Junggar Basin, China.AAPG Bull, 103(1): 189–213

[7] Fu H, Yan D, Su X, Wang J, Li Q, Li X, Zhao W, Zhang L, Wang X, Li Y (2022). Biodegradation of early thermogenic gas and generation of secondary microbial gas in the Tieliekedong region of the northern Tarim Basin, NW China.Int J Coal Geol, 261: 104075

[8] Fu H, Yan D, Yang S, Wang X, Wang G, Zhuang X, Zhang L, Li G, Chen X, Pan Z (2021). A study of the gas-water characteristics and their implications for the coalbed methane accumulation modes in the southern Junggar Basin, China.AAPG Bull, 105(1): 189–221

[9] Green M S, Flanegan K C, Gilcrease P C (2008). Characterisation of a methanogenic consortium enriched from a coalbed methane well in the Powder River Basin, USA.Int J Coal Geol, 76(1–2): 34–45

[10] Gutsalo L K (2008). Isotope fractionation in the systems CH₄−H₂O and CH₄−CO₂ during microbial methane genesis in the Earth’s crust.Russ Geol Geophys, 49(6): 397–407

[11] Jin X, Zhang H (2014). Evolution of Jurassic low rank coal CBM system in Ordos basin.Coal Geol Explor, 42: 17–24

[12] Ju W, Yang Z, Shen Y, Yang H, Wang G, Zhang X, Wang S (2021). Mechanism of pore pressure variation in multiple coal reservoirs, western Guizhou region.Front Earth Sci, 15(4): 770–789

[13] Kotarba M J, Rice D D (2001). Composition and origin of coalbed gases in the Lower Silesian Basin, southwest Poland.Appl Geochem, 16(7): 895–910

[14] Lan F, Qin Y, Wang A, Li M, Wang G (2020). The origin of high and variable concentrations of heavy hydrocarbon gases in coal from the Enhong syncline of Yunnan, China.J Nat Gas Sci Eng, 76: 103217

[15] Li G, Qin Y, Shen J, Wu M, Li C, Wei K, Zhu C (2019). Geochemical characteristics of tight sandstone gas and hydrocarbon charging history of Linxing area in Ordos Basin, China.J Petrol Sci Eng, 177: 198–207

[16] Li Q, Ju Y, Bao Y, Li X, Sun Y (2015). Composition, origin, and distribution of coalbed methane in the Huaibei Coalfield, China.Energy Fuels, 29(2): 546–555

[17] Li Q, Ju Y, Bao Y, Yan Z, Li X, Sun Y (2014). Origin types of CBM and their geochemical research progress.J China Coal Soc, 39(5): 806–815

[18] Li Y, Fu H, Yan D, Su X, Wang X, Zhao W, Wang H, Wang G (2022b). Effects of simulated surface freshwater environment on in situ microorganisms and their methanogenesis after tectonic uplift of a deep coal seam.Int J Coal Geol, 257: 104014

[19] Li Y, Pan S, Ning S, Shao L, Jing Z, Wang Z (2022a). Coal measure metallogeny: metallogenic system and implication for resource and environment.Sci China Earth Sci, 65(7): 1211–1228

[20] Li Y, Tang D, Fang Y, Xu H, Meng Y J (2014). Distribution of stable carbon isotope in coalbed methane from the east margin of Ordos Basin.Sci China Earth Sci, 57(8): 1741–1748

[21] Li Y, Zhang C, Tang D, Gan Q, Niu X, Wang K, Shen R (2017). Coal pore size distributions controlled by the coalification process: an experimental study of coals from the Junggar, Ordos, and Qinshui basins in China.Fuel, 206: 352–363

[22] Lin Y (2021). Geological controls and high productivity model of low-rank coalbed methane reservoir in the Huanglong Coalfied, Shaanxi, China. Dissertation for Doctoral Degree. Xuzhou: China University of Mining and Technology

[23] Lin Y, Qin Y, Duan Z, Ma D, Chen L (2021b). In-situ stress and permeability causality model of a low-rank coalbed methane reservoir in southwestern Ordos Basin, China.Petrol Sci Technol, 39(7–8): 196–215

[24] Lin Y, Qin Y, Ma D, Duan Z (2021a). Pore structure, adsorptivity and influencing factors of high-volatile bituminous coal rich in inertinite.Fuel, 293: 120418

[25] Lin Y, Qin Y, Ma D, Zhao J (2020). Experimental research on dynamic variation of permeability and porosity of low-rank inert-rich coal under stresses.ACS Omega, 5(43): 28124–28135

[26] Meng Z, Yan J, Li G (2017). Controls on gas content, carbon isotopic abundance of methane in Qinnan-east coalbed methane block, Qinshui Basin, China.Energy Fuels, 31(2): 1502–1511

[27] Milkov A V, Etiope G (2018). Revised genetic diagrams for natural gases based on a global dataset of >20000 samples.Organ Geochem, 125: 109–120

[28] Milkov A V, Faiz M, Etiope G (2020). Geochemistry of shale gases from around the world: composition, origins, isotope reversals and rollovers, and implications for the exploration of shale plays.Organ Geochem, 143: 103997

[29] Moore T A (2012). Coalbed methane: a review.Int J Coal Geol, 101(1): 36–81

[30] Ni Y, Dai J, Zou C, Liao F, Shuai Y, Zhang Y (2013). Geochemical characteristics of biogenic gases in China.Int J Coal Geol, 113: 76–87

[31] Qin S, Tang X, Song Y, Wang H (2006). Distribution and fractionation mechanism of stable carbon isotope of coalbed methane.Sci China Earth Sci, 49(12): 1252–1258

[32] Qin Y, Moore T A, Shen J, Yang Z, Shen Y, Wang G (2018). Resources and geology of coalbed methane in China: a review.Int Geol Rev, 60(5–6): 777–812

[33] Qin Y, Tang X, Ye J, Jiao S (2000). Distribution and genesis of stable carbon isotope of coalbed methane in China.J China Univ Min Technol, 29: 113–119

[34] Rice D D (1993). Composition and origins of coalbed gas. In: Law B E, Rice D D, eds. Hydrocarbons from Coal.AAPG Studies in Geology, 38: 159–184

[35] Rice D D, Claypool G E (1981). Generation, accumulation and resource potential of biogenic gas.AAPG Bull, 65: 5–25

[36] Schoell M (1980). The hydrogen and carbon isotopic composition of methane from natural gases of various origins.Geochim Cosmochim Acta, 44(5): 649–661

[37] Scott A R, Kaiser W R, Ayers J W B (1994). Thermogenic and secondary biogenic gases, San Juan Basin, Colorado and New Mexico–implications for coalbed gas producibility.AAPG Bull, 78: 1186–1209

[38] Smith J W, Pallasser R J (1996). Microbial origin of Australian coalbed methane.AAPG Bull, 80(6): 891–897

[39] Strąpoć D, Schimmelmann A, Mastalerz M (2006). Carbon isotopic fractionation of CH₄ and CO₂ during canister desorption of coal.Organ Geochem, 37(2): 152–164

[40] Tang Y, Gu F, Wu X, Ye H, Yu Y, Zhong M (2018). Coalbed methane accumulation conditions and enrichment models of Walloon Coal measure in the Surat Basin, Australia.Nat Gas Indus, 5(3): 235–244

[41] Tao M, Chen X, Li Z, Ma Y, Xie G, Wang Y, Wei L, Wang Z, Tang X (2021). Variation characteristic and mechanism of carbon isotope composition of coalbed methane under different conditions and its tracing significance.Fuel, 302: 121039

[42] Tao S, Chen S, Pan Z (2019). Current status, challenges, and policy suggestions for coalbed methane industry development in China: a review.Energy Sci Eng, 7(4): 1059–1074

[43] Tian W, Shao L, Zhang J, Zhao S, Huo W (2015). Analysis of genetic types of the coal bed methane of Jurassic formation, southern Ordos Basin.China Min Mag, 24: 81–85

[44] Vinson D S, Blair N E, Martini A M, Larter S, Orem W H, Mcintosh J C (2017). Microbial methane from in situ biodegradation of coal and shale: a review and reevaluation of hydrogen and carbon isotope signatures.Chem Geol, 453: 128–145

[45] Wang Q, Xu H, Tang D, Yang S, Wang G, Ren P, Dong W, Guo J (2022). Indication of origin and distribution of coalbed gas from stable isotopes of gas and coproduced water in Fukang area of Junggar Basin, China.AAPG Bull, 106(2): 387–407

[46] Whiticar M J (1996). Stable isotope geochemistry of coals, humic kerogens and related natural gas.Int J Coal Geol, 32(1–4): 191–215

[47] Whiticar M J (1999). Carbon and hydrogen isotope systematic of bacterial formation and oxidation of methane.Chem Geol, 161(1–3): 291–314

[48] Whiticar M J, Faber E, Schoell M (1986). Biogenic methane formation in marine and fresh water environment: CO₂ reduction vs. acetate fermentation-isotopic evidence.Geochim Cosmochim Acta, 50(5): 693–709

[49] Xin F, Xu H, Tang D, Cao C (2022). Differences in accumulation patterns of low-rank coalbed methane in China under the control of the first coalification jump.Fuel, 324: 124657

[50] Xing L T, Li Z P, Xu L, Li L W, Liu Y (2022). Application of chromium catalysis technology to compound-specific hydrogen isotope analysis of natural gas samples.Talanta, 239: 123133

[51] Xu H, Tang D, Liu D, Tang S, Yang F, Chen X, He W, Deng C (2012). Study on coalbed methane accumulation characteristics and favorable areas in the Binchang area, southwestern Ordos Basin, China.Int J Coal Geol, 95: 1–11

[52] Zhang J, Zhao J, Chen D, Li S, Lin H (2020). Sedimentary environment characteristics and genesis of H₂S-bearing coal seam in Binchang Mining Area, Ordos Basin.Nat Gas Geosci, 31(1): 100–109

[53] Zhang K, Meng Z, Wang X (2019a). Distribution of methane carbon isotope and its significance on CBM accumulation of No. 2 coal seam in Yanchuannan CBM block, Ordos Basin, China.J Petrol Sci Eng, 174: 92–105

[54] Zhang S, Zhang X, Li G, Liu X, Zhang P (2019b). Distribution characteristics and geochemistry mechanisms of carbon isotope of coalbed methane in central-southern Qinshui Basin, China.Fuel, 244: 1–12

[55] Zhao J, Zhang Q, Zheng K, Li C, Chen D (2018). Disaster-causing mechanism of surrounding rock gas flowing underground in the Huangling coal mine and prevention measures.J Nat Gas Indust, 38(11): 114–121

[56] Zhou B, Qin Y, Yang Z (2020). Ion composition of produced water from coalbed methane wells in western Guizhou, China, and associated productivity response.Fuel, 265: 116939

Acknowledgment

This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 42130802 and 42372200), China Postdoctoral Science Foundation (No. 2022M713792), Key Science and Technology Program of Shaanxi Province (No. 2023YBGY-083), and Open Fund of Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process of the Ministry of Education (China University of Mining and Technology) (No. 2022-007).

Competing interests

The authors declare that they have no competing interests.

RIGHTS & PERMISSIONS

2024 Higher Education Press

审图号：GS京（2024）1341号