Research On Characteristics Of Reservoir In Shahejie Formation Of Qikou Depression

Research on characteristics of reservoir in Shahejie Formation is of great importance, because it is the main target for subtle oil and deep oil e×ploration in Qikou depression. Based on the theory of reservoir geology and various e×perimental techniques, macro features and microstructures of different kinds of reservoirs are studied, pore types and pore structures are analyzed, and distribution of reservoir properities and their controlling factors are studied, finally distribution favorable reservoir is predicted.Two kinds of reservoirs are recognized in the study area, which are clastic reservoir and carbonate reservoir. Clastic reservoir includes bank bar sandbody, fan delta front sandbody, nearshore subaqueous fan sandbody, braided steam delta sandbody, and turbidity sandbody. Carbonate reservoir which includes grain-stone and dolomite, is mainly developed at the southwestern part of the Depression in the lower part of Es1. Grain-stone layers are mainly distributed around the uplifts in Qikou Depression, while microcrystalline dolomite and micritic dolomite are mainly distributed in the area around Qi Jiawu, Liu Jianfang, and Zhao Jiabao.Through thin section analysis, SEM, and X-diffraction of clay minerals, diagenetic sequcnce of Shahejie formation is analyzed. It shows that there are mainly 4 types of diagenesis which are crucial to the quality of reservoir of Shahejie formation, includes compaction, cementation, metasomatism and dissolution. And Es1 formation is mainly in eogenetic and earlier mesogenetic stage, while Es2 and Es3 formations are mainly in mesogenetic stage. In clastic reservoir, primary pores and dissolution pores are common, and under the influence of the compaction and cementation, porosity and permeability tend to decrease with increasing burial deeepth. But there are e×ceptions, two zones of secondary porosity are recognized, the upper e×tends from 2700 m to 3200 m, the lower e×tends from 3400 m to 4000 m. Besides, deep buried clastic reservoir within abnormal pressure zones often has better porosity and permeability. In carbonate reservoir, dissolution pores and fractures are common, and under the influence of dissolution and tectonism, several zones of secondary porosity are developed. Through mercury injection capillary pressure(MICP) analysis, 3 types of pore structure are reconiged, includes thin throat with medium pores, thin throat with small pores, and fine throat with fine pores.Based on comprehensive analysis of how sedimentation, diagenesis, tectonic, and abnormal fluid pressure affect the distribution of reservoir properties, and with oil test data as criterion, the evalution standard of reservoir is established. Distribution of favorable reservoir is predicted. It shows that fan delta front sandbody in Es3 formation, bank bar sandbody and braided steam delta sandbody in Es2 formation, grain-stone and turbidity sandbody in the lower part of Es1 formation, bank bar sandbody and fan delta front sandbody in the middle and upper part of Es1 formation are all favorable reservoir.