柴达木盆地西部地区古近系湖相碳酸盐岩储层特征

柴达木盆地西部地区古近系下干柴沟组上段(E32)至上油砂山组(N22)广泛发育湖相碳酸盐岩.为研究其分布及储层发育特征,开展岩心观察、薄片鉴定、扫描电镜及X射线衍射分析等工作.结果表明:①研究区湖相碳酸盐岩具有岩石类型多、相变快、陆源碎屑发育、普遍白云石化等特点;主要岩石类型有块状碳酸盐岩、纹层状碳酸盐岩、藻灰岩、颗粒...

Reservoir characteristics of Paleogene lacustrine carbonate rocks in western Qaidam Basin

Lacustrine carbonate rocks are widely developed in the upper member of Xiaganchaigou Formation(E₃²)and upper Youshashan Formation(N₂²)of Paleogene in the western Qaidam Basin.In order to study its distribution and reservoir development characteristics,core observation,thin section identification,scanning electron microscope analysis and X-ray diffraction analysis were carried out.The results show that:(1)The lacustrine carbonate rocks in the study area have the characteristics of many rock types,rapid phase transformation,terrigenous clastic development and general dolomitization.The rocks are mainly composed of massive carbonate rocks,laminar carbonate rocks,algal limestones and granular carbonate rocks,which are closely related to sedimen-tary microfacies and paleoenvironment.(2)The massive carbonate reservoir space in the study area is mainly composed of intergranular pores,and fractures are locally developed.The bedding microfractures of laminar carbonate rocks are developed,the algal limestone reservoir space is mainly composed of algal framework pores with strong heterogeneity,and the granular carbonate rocks are significantly affected by cementation.(3)The average porosity of massive carbonate rocks is 10.6%,the average matrix permeability is 0.03 mD,the displacement pressure is 10.0 MPa,and the average pore throat radius is 0.038μm.The average porosity of laminar carbonate rocks is 7.4%,the average permeability is 0.76 mD,the displacement pressure is 11.5 MPa,and the average pore throat radius is 0.071μm.The average porosity of algal limestones is 10.1%,the average permeability is 9.09 mD,the displacement pressure is 3.2 MPa,and the average pore throat radius is 0.117μm.The average porosity of granular carbonate rocks is 7.1%,the average permeability is 0.01 mD,the displacement pressure is 15.0 MPa,and the average pore throat radius is 0.026μm.(4)The Paleogene high-quality reservoirs in Gasi area are mainly algal limestones,the carbonate rocks in Yingxi-Ganchaigou area develop fracture system,which is a high-yield“sweet spot”area,and Mangya Sag is an exploration potential area.The research results can be used as a reference for oil and gas exploration of lacustrine carbonate rocks in Qaidam Basin.