开江—梁平海槽西侧中东段长兴组台缘储层特征及差异性

Characteristics and Differences of the Platform Margin Reservoir,Changxing Formation,Central Eastern Region,West of the Kaijiang-Liangping Trough

将开江—梁平海槽西侧中东段长兴组台缘划分为龙岗主体和龙岗东两个地区来探讨其储层基本特征、成因、演化模式及差异性。龙岗主体为陡坡型台缘,礁滩体呈山脊线状、紧靠台缘外带生长,垂向呈多期次加积;龙岗东为缓坡型台缘,礁滩体宽缓,垂向侧积为主。储集空间类型前者以组构选择性的粒内溶孔、粒间溶孔等和非组构选择性的溶蚀缝洞和构造裂缝并存为特征,后者以晶间孔、晶间溶孔、粒间溶孔、构造溶蚀缝等为主;前者为低孔低渗的孔隙型储层,后者为特低孔特低渗的裂缝型—孔隙型储层。龙岗主体台缘礁滩储层受准同生期大气淡水溶蚀、回流渗透白云化、早成岩近地表岩溶及埋藏溶蚀、埋藏白云化等的综合控制;龙岗东地区由于水体相对较深,同生阶段的大气淡水溶蚀和早成岩期近地表溶蚀较弱,优质储层更受裂缝及埋藏溶蚀作用控制。

In this study,the margin platform in the central eastern region to the west of the Kaijiang-Liangping Trough was divided into two areas:(1)the main central Longgang area,and(2)the eastern Longgang area,to determine the properties,genesis,patterns and differences of the reservoir.The main Longgang area is a steep-slope platform margin type.The reefshoal complex growth close to the outer edge of the platform margin has a ridgeline shape,with multiple stages apparent in the vertical direction.The eastern part of the Longgang area is a gently sloping platform margin;the reefshoal complex is the product of broad horizontal and vertical development.The former type of reservoir space contains constitutively selective intragrain dissolution pores,intergrain dissolution pores and non-constitutively selective dissolution fractures and structural fractures,producing low porosity and low permeability.The latter type consists mainly of intercrystal pores,intercrystal dissolved pores,intergrain dissolved pores and structural dissolution joints,resulting in a fracture-type reservoir possessing extremely low porosity and low permeability.Development of the reefshoal complex reservoir was completely controlled by atmospheric freshwater dissolution,reflux infiltration and dolomitization,together with early diagenetic near-surface karstification,burial dissolution and buried dolomitization.The water body in the eastern Longgang area was relatively deep,resulting in weak atmospheric freshwater dissolution in the syngenetic stage,and weak near-surface dissolution in the early diagenetic stage.The highquality reservoir is influenced by fractures and buried dissolution.