石油实验地质2026，Vol.48Issue(4)：765-781,17.DOI:10.11781/sysydz2026040765
鄂尔多斯盆地吴起地区上三叠统延长组长71亚段砂质夹层孔喉结构及渗流主控因素
Pore-throat structure and major seepage-controlling factors of sandy interbeds in Chang 71 sub-member,Upper Triassic Yanchang Formation,Wuqi area,Ordos Basin
摘要
Abstract
The sandy interbeds in the Chang 71 sub-member of the Upper Triassic Yanchang Formation,Wuqi area,Ordos Basin,are characterized by strong heterogeneity of pore-throatstructure,ambiguous relationship between pore development and seepage capacity,and insufficient understanding of whether dissolution pores can be transformed into effective seepage spaces.To address these issues,this paper takes sandstone samples collected from shale-reservoir sandy interbeds of the Chang 71 sub-member,Yanchang Formation,at well A within the study area as the research object.Comprehensive methods including bulk-rock X-ray diffraction,porosity and permeability testing,scanning electron microscopy observation,rate-controlled high-pressure mercury intrusion experiments,and nano-CT three-dimensional pore network reconstruction are adopted to analyze the mineral com-position,pore-throat structure characteristics,and their controlling effects on seepage capacity.The results show that the sandy interbeds of the Chang 71 sub-member generally present low porosity and ultra-low permeability features.The porosity ranges from 0.60％to 7.92％,with an average of 2.01％,and permeability ranges from 0.004 84× 10-3 μm2 to 0.131× 10-3 μm2,with an average of 0.018 4× 10-3 μm2.Porosity shows a significant posi-tive correlation with permeability.The reservoir spaces are mainly residual intergranular pores,feldspar dissolu-tion pores,and clay intercrystalline micropores.Carbonate cements and clay minerals are widely developed with obvious heterogeneity.The displacement pressure of representative samples is 0.119-0.306 MPa,and there are remarkable discrepancies in the main throat interval and fine throat tailing characteristics.High-permeability samples have a high proportion of connected pores,large average coordination number,and well-connected pore networks,while low-permeability samples feature a low proportion of connected pores and sparse pore network branches,and are prone to connectivity interruption.The seepage capacity of sandy interbeds in the Chang 71 sub-member is mainly controlled by the development degree of dominant throats,throat threshold,and three-dimensional con-nected framework.Carbonate cementation-dissolution and clay filling exert remarkable coupled controlling effects over pore-throat structure.Early carbonate cementation and late re-precipitation can narrow and partition pore throats,and clay filling further aggravates throat refinement and weakens connectivity.The pore increment formed by feldspar dissolution can only be converted into seepage advantages under the condition of preserving an effec-tive connected framework.The research results can provide a basis for sweet spot identification of shale oil sandy interbeds and the optimization of fracturing intervals in the Chang 7 Member.关键词
页岩油/砂质夹层/碳酸盐胶结—溶蚀/孔喉结构/渗流能力/长71亚段/鄂尔多斯盆地Key words
shale oil/sandy interbed/carbonate cementation-dissolution/pore-throat structure/seepage capacity/Chang 71 sub-member/Ordos Basin分类
能源科技引用本文复制引用
王香增,高潮,钟志,郭超,石彬,杨潇,李颖,杨泽光,孙璐..鄂尔多斯盆地吴起地区上三叠统延长组长71亚段砂质夹层孔喉结构及渗流主控因素[J].石油实验地质,2026,48(4):765-781,17.基金项目
国家科技重大专项资助项目"中生界陆相湖盆油藏富集规律及增储领域研究(盆地东南部中生界非常规油气藏成因机制及控藏作用评价)"(2025ZD1400205)与陕西延长石油(集团)有限责任公司企事业横向项目"定边东仁沟、吴起铁边城地区陆相页岩油地质—工程'双甜点'智能表征与预测"(YCSY2025JCYJ-B-06)联合资助. （盆地东南部中生界非常规油气藏成因机制及控藏作用评价）
