Acta Petrolei Sinica ›› 2026, Vol. 47 ›› Issue (4): 791-813.DOI: 10.7623/syxb202604005

• PETROLEUM EXPLORATION • Previous Articles    

Carbon isotope fractionation mechanism of deep coalbed methane in Yan’an gas field of Ordos Basin and its indication significance

Wan Yongping1, Wang Zhenchuan1, Qiao Yu2, Han Shuangbiao2, Ma Dong1, Huang Jie2, Bian Jiang1, Liu Yu2, Qiao Liang2   

  1. 1. Gas Field Company, Shaanxi Yanchang Petroleum Group Co., Ltd., Shaanxi Yan'an 716000, China;
    2. College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China
  • Received:2025-03-31 Revised:2025-11-22 Published:2026-05-11

鄂尔多斯盆地延安气田深部煤层气甲烷碳同位素分馏机理及其指示意义

万永平1, 王振川1, 乔钰2, 韩双彪2, 马冬1, 黄劼2, 边疆1, 刘宇2, 乔良2   

  1. 1. 陕西延长石油(集团)有限责任公司气田公司 陕西延安 716000;
    2. 中国矿业大学(北京)地球科学与测绘工程学院 北京 100083
  • 通讯作者: 韩双彪,男,1987年9月生,2014年获中国地质大学(北京)博士学位,现为中国矿业大学(北京)地球科学与测绘工程学院教授、博士生导师,主要从事非常规油气地质评价工作。Email:bjcuphan@163.com
  • 作者简介:万永平,男,1981年9月生,2013年获中国地质大学(北京)博士学位,现为陕西延长石油(集团)有限责任公司气田公司总地质师、正高级工程师,中国石油学会常务理事、副秘书长、非常规油气专业委员会副主任委员,主要从事非常规油气勘探开发研究。Email:wanhunter@163.com
  • 基金资助:
    延长石油(集团)有限责任公司深部煤层气科技攻关项目"延安气田宜川区域深部煤层含气性评价"(2024207010243)资助。

Abstract: This study addresses the exploration and development requirements for deep coalbed methane (CBM) in Yan’an gas field on the southeastern margin of Ordos Basin. It focuses on the critical scientific issue regarding methane carbon isotope fractionation mechanisms under high-temperature and high-pressure conditions. Through the integration of various research methods, the study reveals the occurrence and migration patterns of methane in deep CBM, providing theoretical support for the evaluation and high-efficient development of deep CBM resources. Molecular simulation techniques were utilized to investigate the adsorption-diffusion behavior of methane across nanoscales under various temperature and pressure conditions, and thus clarify the microscopic mechanisms of isotope fractionation, such as differences in diffusion rates and adsorption energy barrier effects. Further, the study explores the occurrence state, enrichment characteristics, and flow and emission patterns of methane gas. The results show as follows. (1) Methane carbon isotope fractionation during the desorption process of deep coal is primarily controlled by the coal’s pore structure, gas occurrence, and the kinetic characteristics observed during the gas transport process. (2) In CBM liberated through on-site desorption of deep coal samples, significant 13C enrichment was commonly observed in methane carbon isotope value (δ13C1), and the isotope fractionation process presents three distinct patterns. (3) Molecular simulations confirm that carbon isotope fractionation is controlled by both the differential CH4 adsorption capacities in micropores and the kinetic-energy enhancement via thermal motion. (4) The slight variations (-31.46 ‰ to -30.68 ‰) in δ13C1 of gas samples from deep coal seam wells contrasts sharply with the strong fractionation characteristics as demonstrated by core desorption data, highlighting the coupling effects of multi-scale migration pathways within the reservoir. A comparison between the field-measured data and molecular simulation results reveals strong consistency in the carbon isotope fractionation characteristics. This finding not only validates the reliability of the molecular simulation model, but also introduces a new technical approach for the geological research of deep CBM.

Key words: deep coal seam, on-site desorption, wellhead gas sample, carbon isotope fractionation, Ordos Basin, Yan’an gas field

摘要: 面向鄂尔多斯盆地东南缘延安气田深部煤层气勘探开发需求,聚焦高温高压条件下甲烷碳同位素分馏机制这一关键科学问题,通过多方法融合研究,揭示了深部煤层气中甲烷的赋存与运移规律,为深层煤层气资源评价与高效开发提供理论支撑。利用分子模拟手段,探究了甲烷在不同纳米尺度及不同温压条件下的吸附-扩散行为,厘清了甲烷碳同位素分馏的微观机制(如扩散速率差异、吸附能垒效应),进一步探讨了甲烷的赋存状态、富集特征和流动产出规律。研究结果表明:①深部煤在解吸过程中的甲烷碳同位素分馏主要受控于煤的孔隙结构、气体赋存以及气体传输过程中的动力学特征;②在深部煤样品现场解吸的煤层气中,甲烷的碳同位素值(δ13C1)普遍较重,碳同位素分馏过程呈现3种模式;③分子模拟证实,微孔中的CH4吸附性能差异与热运动动能增强效应共同影响着碳同位素分馏;④深部煤层气井井口气样的δ13C1(-31.46 ‰~-30.68 ‰)的微弱变化与岩心解吸数据的强分馏特征形成鲜明对比,揭示储层内部多尺度运移路径的耦合效应。通过对比现场实测数据和分子模拟结果发现,二者在碳同位素分馏特征上具有高度一致性。这一结果验证了分子模拟模型的可靠性,同时也为深部煤层气的地质研究提供了新的技术手段。

关键词: 深部煤层, 现场解吸, 井口气样, 碳同位素分馏, 鄂尔多斯盆地, 延安气田

CLC Number: