The structure characteristics and major controlling factors of platform margin microbial reef reservoirs in the Lower Cambrian Xiaoerbulak Formation in the Aksu area,Tarim Basin were analyzed based on 5 outcrop sections,162 thin sections,12 SEM samples,52 sets of porosity and permeability data.Macroscopically,small-scale microbial reefs form the platform margin.A single microbial reef has several microbial reef progradation complexes,including reef front,fore reef,reef crest,and back reef,but microscopically,they have different kinds of microstructures.The reservoir spaces in the reefs can be divided into microbial structure reservoir space,including fenestral,frame,moldic,and oversized dissolution pores,and non-microbial structure reservoir space,including microcracks and stylolites.The statistical results of porosity and permeability show that in the Yutixi Section,porosities and permeability of the microbial reef reservoirs are generally below 5％ and 1.0×l0-3 μm2 respectively,characteristics of extremely low porosity and permeability reservoirs;while the reef reservoirs in the Sugaitebulake Section have a wide porosity range between 3％ and 10％,and permeability range between 0.1×10-3 μm2 and 50×10-3 μm2,and strong heterogeneity,are low-medium porosity,low-medium permeability reservoirs.This demonstrates different microbial reefs have big differences in physical properties,and even the reservoir in the same reef has obvious heterogeneity.Paleotopography controls the formation of microbial reefs and sedimentation controls the facies distribution and the primary porosity development.Dissolution,controlled by the former two factors,finally decides evolution of reservoir pores.%基于5条野外露头剖面、162块薄片、12块扫描电镜(SEM)样品及52套孔渗物性数据等资料,分析塔里木盆地阿克苏地区下寒武统肖尔布拉克组台缘微生物礁的结构特点及储集层主控因素.台缘由小型微生物礁群组成,单一礁体可分为前礁相、礁前相、礁脊相、礁后相,镜下可见礁岩具有不同的显微结构.微生物礁发育微生物结构储集空间和非生物结构储集空间,前者包括窗格孔、格架孔、铸模孔及超大溶孔,后者包括微裂缝和缝合线.孔渗数据统计结果表明:于提希剖面微生物礁孔隙度基本小于5％,渗透率一般小于1.0× 10-3 μm2,主要为特低孔特低渗储集层,而苏盖特布拉克剖面孔隙度多为3％～10％,渗透率为(0.1～50.0)×10-3 μm2,整体跨度较大,且礁内物性非均质性较强,主要为低—中孔、低—中渗储集层.说明不同微生物礁的物性特征具有较大的差异,同一微生物礁内亦具有明显的储集非均质性.古地貌特征控制微生物礁的发育,沉积作用控制相带的展布及原生孔隙的发育,而溶蚀作用受控于古地貌特征和沉积作用,最终决定微生物礁储集层孔隙的演化.
展开▼
