深部煤层游离气形成机理及资源意义

Formation mechanism and resource significance of free gas in deep coalbed

何发岐,董昭雄,赵兰,马超,范明,王小彩

1．中国石化华北油气分公司，河南 郑州 450006 2．中国石化华北油气分公司勘探开发研究院，河南 郑州 450006
3．中国石化石油勘探开发研究院无锡石油地质研究所，江苏 无锡 214126 中国石化中原油田分公司天然气产销厂，河南 濮阳 457001

North China Oil and Gas Company, SINOPEC, Zhengzhou 450006, China Research institute of Exploration and Development, North China Oil and Gas Company, SINOPEC, Zhengzhou 450006, China Wuxi Research Institute of Petroleum Geology, Petroleum Exploration and Production Research Institute, SINOPEC, Wuxi 214126, China Natural Gas Production and Marketing Plant, Zhongyuan Oilfield Company, SINOPEC, Puyang 457001, China

落实我国分布广泛、规模巨大的深部（埋深在2 000 m以上）煤岩地质体中的煤层气资源具有重要意义。文中以鄂尔多斯盆地8#煤为对象开展了系统研究，通过岩心含气量检测和等温吸附实验发现，深部煤层含气量高（平均高达20 m3/t），且大于地层条件下的理论吸附量；利用煤岩物性、压汞、吸附/脱附等实验结果分析认为，深部煤层含气量高是因煤系（煤）岩性圈闭中聚集了游离气。综合地层埋藏演化史和煤岩孔隙结构特征等资料研究认为：煤岩微孔吸附甲烷达到饱和后，裂隙之中聚集了大量游离态甲烷；围岩封盖能力和后期煤岩吸附增量决定了现今煤层中游离气饱和度。研究指出，深部煤层气资源通过有效储层改造后，较浅层有降本优势，是一个具有经济价值的天然气勘探开发新领域。

 It is important to find out the coalbed methane resources in the widely distributed and large-scale deep (the buried depth is more than 2, 000 m) coal geological bodies in China. Taking 8# coalbed of Ordos Basin as an example, a systematic evaluation is carried out. Through core gas content detection and isothermal adsorption experiment, it is found that the gas content of deep coal seam is high (up to 20 m3/t average) and greater than the theoretical adsorption capacity under formation conditions. Based on the experimental results of coal physical properties, mercury injection and adsorption/desorption, it is considered that the high gas content in deep coal seam is due to the accumulation of free gas in lithological traps of coal measures (coal). According to the data of strata burial evolution history and pore structure characteristics of coal-rock, it is considered that a large amount of free methane is accumulated in the fissures after the micro-pores of coal-rock reach saturation by methane adsorption. The sealing capacity of surrounding rock and the adsorption increment of coal-rock in later stage determine the present free gas saturation in coalbed. It is pointed out that the deep coalbed methane resources have the advantage of cost reduction after effective reservoir transformation, which is a new field of natural gas exploration and development with economic value.

10.6056/dkyqt202105005