过成熟煤成气同位素异常和成因机制—以鄂尔多斯盆地东部地区为例

In recent years, researchers have continuously discovered large-scale carbon and hydrogen isotopic anomalies in the petroliferous basin that under the background of over-mature and hydrothermal fluids, and the genesis mechanism is still not fully understood. In particular, the study on the genesis and evolution mode of isotope anomalies (full isotopic reversal and abnormally light carbon isotope values of ethane) of the Carboniferous-Permian coal-derived gas in the eastern Ordos Basin is weaker. In this study, based on the detailed analysis of the actual geological conditions and a large number of natural gas components and isotope data in the area, and combined analysis of different series of hydrocarbon generation thermal simulation experiments, we intend to determine the evolution of carbon and hydrogen isotopes of coal-derived gas under different thermal evolution stages, control effects of various catalytic media such as clay mineral and transition metal and other factors on the isotope anomalies of coal-derived gas, and point out the genesis mechanism of isotopes anomalies, which has important theoretical and practical significance for the scientific understanding of the generation process and evolution of coal-derived gas, and the enrichment and development of natural gas genetic identification theory.

近年来随着勘探深入，国内外过成熟区和热液流体背景下的含油气盆地内出现规模性碳、氢同位素组成异常现象，其成因机制目前还没有确切认识，尤其针对鄂尔多斯盆地东部石炭-二叠系煤成气同位素异常（同位素完全倒转且乙烷碳同位素值异常偏轻）成因和演化模式的研究更为薄弱。本项目拟在详细分析该区实际地质条件，在大量天然气组分和同位素数据研究基础上，结合不同系列煤系热模拟实验分析，明确煤成烷烃气在不同热演化阶段条件下的碳、氢同位素演变规律，分析不同催化介质如黏土矿物、过渡金属等因素对煤成气同位素异常现象的影响和控制作用，指出过成熟煤成气碳、氢同位素异常的成因机制，这对于科学认识该区煤成气藏的形成过程，完善煤成气形成和演化规律、丰富和发展天然气成因鉴别理论等具有重要的理论和实践意义。

针对鄂尔多斯盆地东部石炭-二叠系煤成气同位素异常（同位素完全倒转且乙烷碳同位素值异常偏轻）和演化模式研究相对薄弱的情况，本项目通过系统总结前人成果，补充采集天然气样，系统分析了鄂尔多斯盆地东部，即从东北部大牛地气田，到盆地东南缘的宜川-黄龙产气区的石炭-二叠系煤成气地球化学特征，包括碳-氢同位素分布样式的演化规律；其次，采集鄂尔多斯盆地东北缘山西省河曲县的沙坪煤矿二叠系山西组低熟煤样进行多系列热模拟实验，在保证低熟煤有机组成与区内气源岩一致的基础上，分析不同温度点产物的碳同位素组演化趋势，包括不同催化介质对煤成气同位素异常现象的影响，指出过成熟煤成气碳、氢同位素异常的成因机制。综合上述研究，本项目尝试明确煤成烷烃气在不同热演化阶段条件下的碳同位素演变规律，这对于科学认识盆地东部煤成气藏的形成过程，完善煤成气形成和演化规律有着一定的理论和实践意义。项目资助发表申请人第一作者SCI论文2篇。培养硕士生2名。项目投入经费22万元，支出20.6848万元，各项支出基本与预算相符。剩余经费1.3152万元，剩余经费计划用于本项目研究后续支出。