湖相碳酸盐岩—混积岩储层有利相带分析——以柴达木盆地古近系为例

Analysis of favorable facies belts in reservoir of lacustrine carbonate rocks-hybrid sediments:Case study of Paleogene in Qaidam Basin

湖相碳酸盐岩广泛发育于中国各陆相含油气盆地,与海相碳酸盐岩相比,湖相碳酸盐岩沉积规模较小,受多物源陆相碎屑体系干扰,易于发育湖相碳酸盐岩-混积岩。近年来,随着油气勘探的深入,湖相碳酸盐岩-混积岩作为一种致密油储层得到重视。干旱气候封闭-咸化湖盆碳酸盐岩致密油储层分布区,以青海古近系、四川侏罗系为典型,称之为内源沉积湖相碳酸盐岩储层沉积有利相带。通过野外露头剖面和钻井岩心、测井资料,对柴达木盆地柴西南地区上干柴沟组进行了横向、纵向的层序地层学和沉积相研究,探索了湖相碳酸盐岩-混积岩的沉积模式及其石油地质意义。研究认为湖侵体系域-高位体系域的演化为湖相碳酸盐岩-混积岩致密油储层提供了有利相带,从滨浅湖到半深湖-深湖区,存在湖相混积滩坝、滨湖白云岩化泥灰坪/泥云坪、浅湖叠层石礁滩和半深湖相裂缝性泥灰岩有利微相带,对柴达木盆地及其相类似盆地湖相碳酸盐岩-混积岩致密油储层油气勘探具有一定的参考价值。

Lacustrine carbonate rocks are widely developed in various continental petroliferous basins in China.Compared with marine carbonate rocks,lacustrine carbonate rocks have a smaller sedimentary scale and are easily developed with lacustrine carbonate rocks-hybrid sediments.In recent years,with the development of oil and gas exploration,lacustrine carbonate rocks and hybrid sediments have been paid more attention as a tight oil reservoir.The distribution area of tight oil reservoirs of carbonate rocks in arid climate sealed-saline lake basin is characterized by Sichuan and Qinghai,which is called the sedimentary favorable facies zone of internal sedimentary lacustrine carbonate reservoir.Based on outcrop profile,drilling core and logging data,the horizontal and longitudinal sequence stratigraphy and sedimentary facies of Upper Ganchaigou Formation in southwestern Qaidam Basin and Da’anzhai and Dongyuemiao members in Jurassic Sichuan Basin were studied.The genetic mechanism of lacustrine carbonate rocks to hybrid sediments is explored.It is considered that the evolution of lacustrine transgressive systems tract-highstand systems tract provides favorable facies zone for lacustrine carbonate rock-hybrid sediments tight oil reservoir.From littoral-shallow lake to semi-deep to deep lake area,there exists lacustrine hybrid sedimentation beach and bars,dolomited mudstone and limestone flat/mudstone and dolomite flat,semi-deep lake reef and lacustrine fissured muddy limestone microfacies zone.It has certain guiding significance for oil and gas exploration of lacustrine carbonate rocks-hybrid sediments tight oil reservoirs in Qaidam Basin and its similar basins.