柴西南地区下干柴沟组碳酸盐岩致密油储层特征

摘要

柴西南地区下干柴沟组发育大面积的碳酸盐岩,具有形成致密油藏的潜力,但目前对该地区碳酸盐岩致密储层研究较少.通过碳酸盐岩普通薄片鉴定、铸体薄片鉴定及扫描电镜观察等手段,结合物性测试和压汞资料,对柴西南地区碳酸盐致密储层岩性、物性、孔喉特征及孔隙类型进行分析.认为柴西南地区碳酸盐致密储层具有低—特低孔、低—特低渗特征,致密油储集空间类型为晶间溶孔、晶内溶孔和微裂缝等,发育在斜坡带碳酸盐岩致密储层与研究区滨浅湖—半深湖相发育的暗色泥质生油岩形成源储共生关系,致密储层发育受沉积作用、成岩作用和溶蚀作用影响.沉积作用中,斜坡带处于半深湖—深湖沉积环境有利微晶或泥晶灰(云)岩发育,利于形成致密储层;成岩作用中,压实作用、碳酸盐胶结作用是控制致密储层的主要因素;溶蚀孔和裂缝成为致密油的主要储集空间.该研究能够为预测柴西南地区下干柴沟组致密油有利区域提供依据,为今后该地区致密油的勘探提供理论支撑.%There is a set of carbonate rocks with large area in the Lower Ganchaigou Formation of the southwestern Qaidam Basin,which shows great potential for tight oil accumulation. However,there are few researches on the tight carbonate reservoir. The carbonate thin-section,cast thin-section,SEM and other test methods are used to analyze the lithology,physical properties,pore-throat properties and pore types of the carbonate tight reservoir in the southwestern Qaidam Basin by combining with physical property test and mercury intrusion data. The carbonate tight reservoir in the southwestern Qaidam Basin is characterized by low to ultra-low porosity and low to ultra-low permeability. The tight oil reservoir space consists of intercrystal dissolved pore,dissolved pore and micro-crack, etc. There is a source-reservoir relation between the carbonate tight reservoir in the slope zone and the dark muddy source-rock with well-developed shore-shallow lacustrine and semi-deep lacustrine facies. The tight reservoir de-velopment is influenced by sedimentation,diagenesis and dissolution. The slope zone within semi-deep lacustrine-deep lacustrine sedimentary environment is favorable to the development of micro-crystal or cryptite(dolomite)in sedimentation,which is beneficial to tight reservoir development.Tight reservoir is mainly controlled by diagenesis, compaction and carbonate cementation. The tight oil reservoir space is mainly dominated by dissolved pore and crack. This research could provide certain reference for the favorable tight oil area prediction in Ganchaigou Forma-tion of southwestern Qaidam Basin and also provide certain theoretical basis for the further tight oil exploration in this area.