塔里木盆地西北缘上震旦统微生物碳酸盐岩储层特征与成因

Characteristics and origin of the Upper Sinian microbial carbonate reservoirs at the northwestern margin of Tarim Basin

通过野外露头地质观察、薄片鉴定与孔渗分析等,详细研究了塔里木盆地西北缘什艾日克剖面上震旦统微生物碳酸盐岩岩石学和储层特征,并简要分析了储层成因。研究认为该区上震旦统微生物碳酸盐岩以微生物白云岩为主,约占整个上震旦统碳酸盐岩的70.37%。根据是否具有叠层构造,将该区上震旦统微生物岩划分为叠层石和非叠层石两大类型,其中,叠层石类包括层状叠层石、丘状叠层石和小型孤立柱状叠层石,并以层状叠层石为主,结构以纹层球粒、泥晶为特征;而非叠层石包括非叠层蓝细菌球粒岩和非叠层蓝细菌泡沫绵层岩,结构以球粒、泡沫绵层为特征。根据储集性,可将该区上震旦统微生物岩储层划分为上、下两段,上段储层要优于下段。层状叠层石和非叠层蓝细菌球粒、泡沫绵层白云岩为有利储集岩石类型。微生物结构、白云石化和溶蚀作用为微生物岩储层形成的有利因素,其中微生物结构是基础,决定着微生物岩储层的孔隙类型及其孔隙结构特征,而白云石化和溶蚀作用则为微生物岩储层有效孔隙形成的关键因素,上段储层较好更得益于表生岩溶作用的影响。

Through outcrop observation,thin section examination and physical property analysis,this paper studied the petrological and reservoir characteristics of the Upper Sinian microbial carbonates on the Shiairike section at the northwestern margin of the Tarim Basin and briefly discussed the origin of the microbial carbonate reservoirs. The microbial carbonates are dominated by microbial dolomites,accounting for 70. 37% of the whole Sinian carbonates. Based on having stromatilithic structure or not,the microbial carbonates are divided into stromatolites and non-stromatolites. The stomatolites include stratiform,domal and small isolate columnar types,with the stratiform stromatolites as the main type and pelletoid and micritic lamination as their texture characteristics. In contrast,the non-stromatolites include non-stromatolic cynobactiarial pellet rock and cyanobacterial foam spongy rock,featuring in pelletoid and foam sponge textures. According to physical property,the Sinian microbial carbonate reservoir can be divided into two intervals,with the upper interval being better than the lower. Among the microbial carbonates,the stratiform stromatolites and non-stromatolitic cyanobacterial dolostones especially with foam sponge-like texture are the favorable reservoir rocks. The reservoirs are characterized by fenestal,pellet-associated,foam sponge-associated dissolved porosity as their main reservoir space. The formation and distribution of the microbial carbonate reservoirs are mainly controlled by microfabrics,dolomatization and dissolution. Of these influencing factors,the microfabicsisthe fundamental factor determining the types of the pore space and their texture; the dolomization and dissolution are the critical factors determining the formation of effective pore space. The higher quality of the upper microbial carbonate reservoirs is also attributed to the epigenetic kastification.