柴西地区属于柴达木盆地咸化湖盆沉积中心,柴西咸化阶段持续时间长、湖盆分布范围广,渐新统湖相混积岩具有重要勘探潜力.通过对狮子沟地区样品进行岩心观察、岩石薄片鉴定及扫描电镜、电子探针分析,研究储层岩性、物性及储集空间特征,分析储层影响因素及形成机理.狮子沟地区储层具有混合沉积的特征,岩石矿物成分主要为碳酸盐岩和碎屑颗粒,但两者的相对含量均未超过50%;混积岩成因类型为相混合,以组构混合岩为主,见层系混合岩及少量生物混合岩,样品普遍含有盐类矿物.储层为特低渗-特低孔储层,连通性差,X衍射成分分析碳酸盐岩含量为10.9% ~47.0%,平均为32.1%,同时孔隙度与碳酸盐岩含量具有很好的正相关关系;样品的储集空间主要为盐类矿物溶蚀孔、白云石晶间孔及裂缝;影响储层发育的主要成岩作用为胶结作用和白云石化作用,尤其盐类矿物胶结抑制了后期成岩作用,形成局部高压;灰质含量高及咸化环境为白云石化作用发生的重要条件,压实弱,先后两期的胶结作用,特别是晚期胶结的盐类矿物为溶蚀作用发生的主要部位.
Western Qaidam Basin belongs to the sedimentary center of the saline lake basin in Qaidam Basin.Salinization stage of the western Qaidam Basin lasts for a long time,and the lake basin is widely distributed.Therefore the Oligocene lacustrine carbonate rock has great exploration potential.Based on core observation,rock slice identification,and the analysis of scanning electron microscope and electron spectrum of the samples of Shizigou area,the features of reservoir lithology,reservoir physical property and reservoir space are studied,and reservoir influential factors and forming mechanism are analyzed.The main conclusions are as follows.(1) The reservoir has characters of mixed deposit.The mineral composition is mainly carbonate and clastic grain,but neither of relative content is over 50%.The genetic type of mixed carbonate-siliciclastic rock or sucession is facies mixed.Fabric mixed is the main type,layer series mixed is the second type,and a few biological mixed type is found.The samples generally contain saline minerals.(2) The results of physical property analysis and X diffraction components testing show that the reservoir is super-low permeable and super-low porous,and its connectivity is poor.The content of carbonate rock composition is in the range of 10.9% to 47.0%,with an average of 32.1%.At the same time,porosity and carbonate content have a good positive correlation.(3) The reservoir space of the samples is mainly saline mineral dissolved pore,dolomite intercrystal pore and fracture.(4) The diagenesis of the reservoir is mainly cementation and dolomitization.Especially the cementation of the saline minerals suppresses the later diagenesis,forming local high pressure.The important conditions of dolomitization are high carbonate content and saline environments.The compaction of reservoir is weak.The reservoir experiences two cementation periods.The saline minerals which cementated in the later period are the main dissolution parts.