四川盆地西北部栖霞组碳酸盐岩储层特征及主控因素

摘要

四川盆地西北部中二叠统栖霞组已成为近期重点及热点勘探领域之一.针对该地区栖霞组碳酸盐岩储层特征和主控因素不清的问题,通过露头及岩心观测、岩石薄片鉴定、储层物性测试等方法,系统分析了栖霞组储层岩石学、储集空间及物性特征,并利用三维地震资料,通过古地貌恢复,讨论了储层发育的主控因素.结果表明:栖霞组储集层岩石类型主要为晶粒白云岩、豹斑状灰岩/白云岩以及少量颗粒灰岩;储集空间以晶间孔、晶间溶孔为主,溶孔(洞)及裂缝次之,具有中—低孔渗特征,其中中—粗晶白云岩储层物性最佳.栖霞组储层分布受沉积相和沉积古地貌控制,其中台缘滩、台内滩等高能沉积相带是储层形成的物质基础;沉积古地貌高地不但控制了高能相带的分布,而且还有利于后期白云石化作用和溶蚀作用的发生.位于栖霞组沉积古地貌高地的中坝—双鱼石构造带,台缘滩相白云岩储层发育,是该区最重要的勘探区带.在该区首次提出的沉积古地貌控制优质储层分布这一重要认识为该区储层地震预测提供了新的思路.%The Middle Permian Qixia Formation in NW Sichuan Basin has become the important and hot explo-ration field in Sichuan Basin.To clear the reservoir characteristics and main controlling factors of Qixia Forma-tion in this area,the field outcrops and drilling core observation,rock thin section examination and reservoir physical property testing were used to analyze the characteristics of petrology,reservoir space and physical prop-erties,three-dimensional seismic data were used to recover the ancient geomorphology,and then the main control-ling factors of the reservoir were discussed.The result shows that the reservoir rocks are mainly crystalline dolo-mite,dolomitic leopard-spot limestone/dolomite and a small amount of grainstone.A variety of reservoir spaces are developed in Qixia Formation,and different reservoir rocks develop different reservoir space types.Intercrystal-line pores,intercrystalline dissolved pores,and nonselective dissolved pores and cavities are mainly developed in the dolomite reservoir.A small amount of intragranular and intergranular dissolved pores are developed in the part of grainstone. Fractures can be developed in all types of reservoir rocks.The reservoir physical properties show the characteristics of middle-low porosity and permeability,and medium-macro-crystalline dolomite has the best reservoir property. The reservoir development is controlled by multiple factors,and the high-energy shoals in the platform-margin and intra-platform are the material foundation for the formation of reservoirs.Pa-leogeomorphology of sedimentary period of Qixia Formation was restored by the method of the residual thick-ness.The result shows that the sedimentary highland not only controls the high-energy facies belt distribution but also the main development area of the late dolomitization and dissolution,thus controlling the reservoir distribu-tion of Qixia Formation.The Zhongba-Shuangyushi structure belt(Jiange-Jiangyou region)is in the highland of Qixia Formation paleogeomorphology,and develops platform-margin shoal facies dolomite reservoir with superi-or physical properties and a bigger reservoir thickness and a wider area,which shows a good exploration pros-pect.The important viewpoint put forward for the first time that the paleogeomorphology controls the distribution of high quality reservoir provides a good way of thinking of reservoir seismic prediction.