鄂尔多斯盆地延长探区长7油层组泥页岩孔隙结构定量表征与动态演化过程

Quantitative characterization and dynamic evolution of pore structure in shale reservoirs of Chang 7 oil layer group in Yanchang area,Ordos Basin

全孔径孔隙结构的定量表征与动态演化研究是认识泥页岩储层成储机理和明确孔隙与烃-岩相互作用关系的重要基础。通过场发射扫描电镜、高压压汞、N_(2)和CO_(2)吸附实验等技术,对鄂尔多斯盆地延长探区长7油层组不同成熟度的典型岩心,以及开展过生、排烃模拟实验的泥页岩样品进行了孔隙结构的定量表征。在此基础上,结合生、排烃模拟和X射线衍射全岩/黏土矿物含量的测试结果,研究有机质生排烃、矿物成岩与孔隙结构演化的相互作用,定量分析储层孔隙结构和分形特征的动态演化特征。结果表明:长7油层组泥页岩储层的微孔、小孔和中孔对孔体积贡献较大,而孔比表面积主要由微孔和小孔提供。随着有机质生排烃、无机矿物溶蚀和矿物间转化的发生,总孔体积具有先减小后增大的趋势,其中中-大孔占比先降低后增加,且微-小孔的非均质性总体增强,而中-大孔的非均质性具有先增加后降低的趋势。相关性分析表明:孔隙大小、矿物组成耦合于储层的非均质性,其中微-小孔的分形维数D_(1)与微孔占微-小孔的孔体积比例和黏土矿物含量均呈正相关,而中-大孔的分形维数D_(2)与大孔占中-大孔的孔体积比例呈负相关,与脆性矿物含量呈正相关。研究结果对以长7油层组泥页岩为典型代表的中国陆相页岩油甜点区优选具有重要的指导意义。

Quantitative characterization and dynamic evolution study of full-scale structure provides an important basis for understanding the forming mechanism of shale reservoirs and clarifying the relationship between pores and hydrocarbon-rock interactions.Using field emission scanning electron microscopy integrated with high-pressure mercury intrusion as well as N_(2) and CO_(2) adsorption experiments,representative core plugs of different maturity and corresponding samples subjected to hydrocarbon generation and expulsion simulation experiments from Chang 7 oil layer group in the Yanchang area,Ordos Basin,were quantitively characterized for their full-scale structure.Furthermore,combined with hydrocarbon generation and expulsion simulation and X-ray diffraction test results of whole rock/clay mineral content,the interaction of organic hydrocarbon generation and expulsion,mineral diagenesis and pore structure evolution was studied,and the dynamic evolution of reservoir pore structure and fractal characteristics was quantitatively analyzed.The results show that the micropores,small pores and mesopores in shale reservoirs of the Chang 7 oil layer group contribute more to the pore volume,while the micropores and small pores provide most pore specific surface area.With hydrocarbon generation and expulsion of organic matter,dissolution of inorganic minerals and transformation between minerals,the total pore volume first decreases and then increases,and the proportion of meso-macropores decreases first and then increases,and the heterogeneity of micro-small pores is generally enhanced,while the heterogeneity of meso-macropores has a trend of increasing first and then decreasing.The correlation analysis reveals that the pore size and mineral composition are coupled with the heterogeneity of the reservoir,in which the fractal dimension D_(1) value of micro-small pores is positively correlated with the proportion of micropores to micro-small pores and the content of clay minerals,while the fractal dimension D_(2) value of meso-macropores is negatively correlated with the proportion of macropores to meso-macropores,and positively correlated with the content of brittle minerals.This study provides an accurate determination of the full-scale structure and evolution of the shale in Chang 7 oil layer group,which is of great significance for identifying sweet spots in shale reservoirs of terrestrial facies.