In order to explore the strong heterogeneity of evaporite-carbonate symbolic system, based on core and logging data, this paper clarifies microfacies types of Arab Formation in B Oilfield of Abu Dhabi, and analyzes the reservoir characteristics of various microfacies and the main controlling factors of high-quality reservoirs. Twelve microfacies types (MF1–MF12) can be identified in the Arab Formation. Microfacies types and associations indicate that it is a sedimentary system of Sabha tidal flat-lagoon-barrier beach under the background of limited-evaporation. Microfacies control reservoir quality. MF2 and MF9–MF12 have thicker pore throats, better connectivity, and higher porosity and permeability, making them favorable microfacies types for reservoir development. MF2 and MF10 develop dolomite reservoirs, with the reservoir space mainly composed of intergranular pores, residual intergranular pores and intragranular dissolution pores. Grainstone reservoirs are developed in MF9, MF11 and MF12, with the reservoir space dominated by intergranular (dissolution) pores, mold pores and intragranular dissolution pores. The seismic change of relative sea level causes orderly stacking of sedimentary facies belts in longitudinal direction. The difference of microfacies types and diagenesis between different sedimentary facies belts and within the same sedimentary facies belt is the fundamental reason for the strong heterogeneity of the Arab Formation reservoir. The barrier beach and supratidal are favorable facies belts for the development of high-quality reservoirs. The primary intergranular pores of high-quality reservoirs in the barrier beach facies are well maintained and superimposed with significant early exposure and dissolution, resulting in the generation of secondary pores and the further improvement of pore structure. The development of high-quality reservoirs in the supratidal is controlled by early dolomitization and penecontemporaneous dissolution. Dolomitization improves pore structure, which is conducive to early pore preservation. The early dissolution of dispersed anhydrite produces a large number of secondary pores, significantly improving reservoir physical properties.

evaporite-carbonate symbolic system, Arab Formation, microfacies, reservoir characteristics, main controlling factors of reservoir

为探究膏盐岩–碳酸盐岩共生层系强非均质性问题, 基于岩芯及测井资料, 探究阿布扎比B油田Arab组岩石微相类型 , 分析各类微 相的储层特征及优质储层主控因素。Arab组可识别出12种微相类型(MF1~MF12), 微相类型及组合指示其为局限–蒸发背景下萨布哈潮坪–潟湖–障壁滩沉积体系。微相类型控制储层品质, 其中MF2及MF9~MF12孔喉较粗, 连通性好, 孔隙度和渗透率较高, 是储层发育有利微相类型。MF2和MF10发育白云岩储层, 储集空间以晶间孔、残余粒间孔及粒内溶孔为主; MF9, MF11和MF12发育颗粒灰岩储层, 储集空间以粒间(溶)孔、铸模孔及粒内溶孔为主。相对海平面的震荡性变化导致各沉积相带在纵向上的有序叠置, 不同沉积相带之间或同一沉积相带内微相类型及成岩作用的差异性是Arab组储层强非均质性的根本原因。障壁滩和潮上带是优质储层发育的有利相带, 其中障壁滩相优质储层原生粒间孔保持较好, 并叠加显著的早期暴露溶蚀, 导致次生孔隙的产生和孔隙结构的改善; 潮上带优质储层的发育受控于早期白云石化和准同生溶蚀作用, 白云石化改善孔隙结构, 有利于早期孔隙保存, 分散状硬石膏的早期溶蚀产生大量次生孔隙, 显著地改善了储层物性。