川中南部下二叠统栖霞组白云岩储层特征及主控因素

针对川中南部下二叠统栖霞组台内白云岩储层特征及控储因素不清的科学问题，通过岩心观察、薄片鉴定、孔渗和地球化学测试以及测井资料等综合分析，取得以下地质认识：(1)白云岩类主要发育于栖二a、栖二b段的上部，并以晶粒化颗粒云岩和豹斑状云质灰岩或灰质云岩为主；储集空间主要为晶间(溶)孔、溶洞，辅以裂缝；晶粒云岩平均孔隙度和渗透率分别为3.16%和0.137×10^-3μm²；而豹斑状云质灰岩或灰质云岩则分别为3.4%和0.383 7×10^-3μm²，总体具有低孔低渗特点；与岩心、成像测井及生产曲线一起揭示储层主要为裂缝—孔隙型和裂缝—孔洞型2类。(2)储层主控因素分析表明，台内生屑滩沉积是储层形成的物质基础，2类白云岩均发育于向上变浅序列上部的滩相颗粒岩中；准同生期白云石化作用交代滩相颗粒岩形成的2类白云岩，提供了晶间孔和抗压骨架，δ¹³C、δ¹⁸O数据指示栖霞组准同生期白云石化可能与海水有关；向上变浅序列顶部常具有暴露面、溶洞等早成岩期暴露岩溶特征，且早期白云岩受...

Characteristics and main controlling factors of dolomite reservoirs in the Lower Permian Qixia Formation in south of central Sichuan Basin

Aiming at the scientific problem of unclear characteristics and reservoir control factors of dolomite reservoir in the Lower Permian Qixia Formation platform in south of central Sichuan Basin， this paper obtained the following geological understanding through the comprehensive analysis of core observation， thin section identification， pore permeability and geochemical testing and logging data. （1） The dolomites are mainly developed in the upper part of the Qi II A and B members， and mainly consist of grainy granular dolomite and leopard porphyritic limestone or calcareous dolomite； the main reservoir spaces are inter-crystalline （dissolved） pores and karst caves supplemented by fractures.The average porosity and permeability are 3.16% and 0.137×10^-3 μm²，respectively. The values of leopard porphyritic limestones and calicitic limestones were 3.4% and 0.383 7×10^-3 μm²， respectively， with low porosity and low permeability. Together with core， imaging logs and production curves， it revealed that the reservoir is mainly divided into two types：Fracture-pore type and fracture-cave type.（2） The analysis of the main controlling factors of the reservoir shows that the internal clastic bank deposition is the material basis for the formation of the reservoir， and the two kinds of dolomites are developed in the shoal facies granular rocks in the upper part of the upward shallow sequence. Two kinds of dolomites formed from beach facies granulocyte metasomatised by dolomitization during the quasi-syngenetic period provide intercrystalline pores and compressive framework. The δ¹³C and δ¹⁸O data indicate that the quasi-syngenetic dolomitization in the Qixia Formation may be related to seawater. The top of the upward shallower sequence often has the characteristics of exposed karst in early diagenesis， such as exposure surface and karst cave， and the early dolomite is cut by karst fabric to form small karst cave， which indicates that the early diagenesis karst is the key to the formation of the dolomite reservoir in Qixia Formation， and the formation time of the dolomite in the platform is earlier than the early diagenesis karst or near the same period. The hydrothermal emplacement related to the extensive activity of the basaltic magma in the Late Permian of Emei Mountain resulted in dolomite recrystallization and saddle-shaped dolomite filling in the pores. Combined with the geochemical results， the dolomite reservoirs in Qixia Formation were influenced and transformed by high temperature hydrothermal during the burial period， but their contribution to reservoir formation was limited. In conclusion， the “quasi-syngenetic facies， dolomitization and dissolution” three-unit reservoir model of the two types of dolomites in Qixia Formation is proposed， which indicates that this kind of dolomite reservoir is largely controlled by favorable sedimentary facies zones related to large-scale microgeomorphic highland. Therefore， the exploration idea may need to change to the direction of “reservoir control in sedimentary period”.