鄂尔多斯盆地陆相页岩油富集条件及有利区优选

Enrichment conditions and favorable area optimization of continental shale oil in Ordos Basin

中国石油长庆油田公司在鄂尔多斯盆地三叠系延长组7段(长7段)湖相烃源岩层系探明十亿吨级庆城页岩油大油田,盆地累计提交页岩油探明地质储量11.53×108t,并在陇东地区建成中国第一个百万吨级整装页岩油开发示范区。系统回顾了鄂尔多斯盆地长7段页岩油勘探开发历程,总结页岩油富集条件及甜点区优选,分析了页岩油勘探开发的资源前景。长7段沉积期,鄂尔多斯盆地为宽缓的大型内陆坳陷湖盆,高生产力、强还原的湖盆环境利于富有机质泥页岩沉积,多级坡折带的发育和频繁的地震火山活动利于多种深水重力流沉积的发育,细粒砂岩与泥页岩盆地范围内大面积接触,页岩油源储共生富有机质烃源岩的强生、排烃作用为长7段页岩油源内运移、富集提供动力;由粒间孔、溶蚀孔、黏土矿物晶间孔和微裂缝构成的微—纳米级孔喉—缝网耦合系统是页岩油的主要富集单元,控制了页岩油的最终富集。烃类由泥页岩运移至砂岩夹层的过程中,泥页岩的层析作用使砂岩夹层富集油质轻、黏度小、流动好的优质烃类,形成长7段低压页岩油效益开发的关键甜点。湖盆中部可效益开发的运移型页岩油是页岩油增储上产的现实目标,湖盆边缘可效益开发的运移型页岩油是长7段页岩油稳产上产的后备领域。围绕庆城油田及其外围,扩大运移型页岩油勘探成果,并积极探索滞留型页岩油开发潜力,是助推长庆油田二次加快发展和保障国家能源安全的重要举措。

PetroChina Changqing Oilfield Company has discovered Qingcheng oilfield in the source rock stratum of Member 7 of Triassic Yanchang Formation in Ordos Basin;it is a billion-ton-level shale oilfield with the proven geological reserves totalling 11.53×108 t,and has built China’s first development demonstration zone of megaton monoblock shale oil in Longdpng area.This paper systematically reviews the exploration and development history of shale oil of Member 7 of Yanchang Formation in Ordos Basin,summarizes the enrichment conditions of shale oil and sweet-spot optimization,and analyzes the resource prospects for shale oil exploration and development.During the deposition period of Member 7 of Yanchang Formation,Ordos Basin was a large,wide and gentle inland depression lake basin,where the lake basin environment with high productivity and strong reductivity was conductive to the deposition of organic matter-rich shale,the development of multi-stage slope break belt and frequent seismic and volcanic activities were conductive to the development of various deep-water gravity flow deposits,and the large-area contact between fine-grained sandstone and shale basin as well as the strong hydrocarbon generation and expulsion of the organic matter-rich source rocks of shale oil co-existing with reservoirs provided an impetus for the intra-source migration and enrichment of shale oil of Member 7 of Yanchang Formation;the micro-nano-scale pore throat-fracture network coupling system composed of intergranular pores,dissolved pores,clay mineral intercrystalline pores and micro-fractures is the main enrichment unit of shale oil,which controls the final enrichment of shale oil.In the migration process of hydrocarbons from shale to sandstone interlayer,the chromatographic action of shale urges the sandstone interlayer to be enriched with high-quality hydrocarbons,which have the characteristics of light oil,low viscosity and good fluidity,thus forming the key sweet spots for the efficient development of low-pressure shale oil of Member 7 of Yanchang Formation.In addition,the migrating shale oil that can be beneficially developed in the central lake basin is the realistic target of increasing the reserve and production of shale oil,while the migrating oil that can be beneficially developed at the edge of the lake basin is the stand-by exploration field for stabilizing and increasing the production of shale oil of Member 7 of Yanchang Formation.Focusing on Qingcheng oilfield and its periphery,to expand the exploration achievements of migrating shale oil and actively explore the development potential of retained shale oil are important measures to accelerate the secondary development of Changqing oilfield and guarantee national energy security.