基于全岩半封闭热模拟实验的页岩排烃效率与孔隙及裂隙演化特征  

Hydrocarbon expulsion efficiency and pore and fracture evolution characteristics of shale based on whole rock semi-closed thermal simulation experiments

作　　者：孙宇 王云鹏[1,2,3] 刘金钟[1,2] 史树勇[1,2,3] 何志华 SUN Yu;WANG Yunpeng;LIU Jinzhong;SHI Shuyong;HE Zhihua(State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,有机地球化学国家重点实验室,广东广州510640 [2]中国科学院深地科学卓越创新中心,广东广州510640 [3]中国科学院大学,北京100049

出　　处：《地球化学》2024年第6期815-826,共12页Geochimica

基　　金：国家自然科学基金项目(42273053、42203054);中国科学院战略性先导科技专项(XDA14010103)联合资助。

摘　　要：页岩排烃发生在岩石物理介质中,传统基于页岩粉末样品的热模拟实验结果主要反映岩石中有机质的生烃过程,很难反映烃类在岩石中生成和排出的微观特征。基于页岩全岩样品的模拟实验保留了岩石完整的孔隙和裂隙结构,模拟结果更加接近实际地质过程。但目前针对页岩全岩样品的排烃与孔隙、裂隙演化特征的研究报道很少。本文通过半封闭系统高压热模拟实验,获取鄂尔多斯盆地东南部延长组长7段岩心两组不同尺寸圆柱样品的排烃效率,并利用低压气体吸附实验和X射线计算机断层(CT)扫描技术,表征了排烃过程中页岩微观孔隙和宏观裂隙特征。结果表明,页岩的排烃效率受热成熟度和几何特征影响,21 mm页岩圆柱的排烃效率整体高于27 mm页岩圆柱,两组样品间排烃效率的差值随热成熟度升高呈现先增加后减小的趋势。R_(o)=0.73%时,排烃效率差值为5.41%;R_(o)=1.08%时,差值(13.09%)达到最大,随后不断降低。页岩样品的中孔和宏孔体积比例受排烃效率影响,21 mm页岩圆柱的中孔体积比例随温度增加不断降低,而宏孔体积比例不断增加。页岩裂隙受残留烃裂解生气体积膨胀所积累的热应力影响,27 mm页岩圆柱整体排烃效率更低,残留烃裂解产生的气体更多,最终导致大量裂隙产生。本研究结果为页岩热演化过程中排烃效率与孔隙及裂隙演化研究提供了新的思路。Shale hydrocarbon expulsion occurs in the rock matrix;traditional thermal simulations based on shale powder samples mainly reflect the hydrocarbon generation process and ideal hydrocarbon migration,and it is difficult to reflect the microscopic characteristics of hydrocarbon generation and expulsion in the rock.The whole-rock sample-based simulation retained the structures,including pores and fractures,of the whole rock,and the simulation results were closer to those of the actual geological processes.However,there are few reports on the hydrocarbon expulsion and pore-fracture evolution characteristics of whole rock samples.In this study,we obtained the hydrocarbon expulsion efficiency of two sets of shale samples of different sizes from the core of the Upper Triassic Chang 7 Shale in the southeastern Ordos Basin through high-pressure thermal simulation in a semi-closed system and used low-pressure N_(2)/CO_(2) adsorption experiments and CT scanning to characterize the microporosity and microfracture characteristics of shale during hydrocarbon expulsion.The results show that the expulsion efficiency of whole-rock samples is determined by thermal maturity and sample size.The expulsion efficiency of the 21 mm sized column is higher than that of the 27 mm sized column,and the difference in expulsion efficiency shows a first increase and then decrease trend with increase in maturity.The difference in expulsion efficiency increases from 5.41% to 13.09% when R_(o) increases from 0.73% to 1.08%.Mesopore and macropore volume percentages are influenced by expulsion efficiency.With increasing temperature,the mesopore volume percentage of the 21 mm sized shale column decreased,and the macropore volume percentage increased.The fractures of shale are influenced by thermal stress generated by rapid volume expansion when residual hydrocarbons crack into gas mount.The 27 mm sized shale column has a lower expulsion efficiency and generates more gas from residual hydrocarbons,which causes more fractures.This study provides a novel

关 键 词：页岩 全岩半封闭模拟 排烃效率 孔隙和裂隙 CT扫描 

分 类 号：P618.13[天文地球—矿床学]