Evaluation Of Sedimentary System And Reservoir-cap Assemblage Of Fault Ascent Plate On The West Slope Boundary Of Xihu Sag

Based on the theory of modern sedimentology and petroleum geology,this paper selects the Longjing Formation and Huagang Formation in the boundary area of the western slope of Xihu Sag,which are relatively less studied at present,to systematically carry out the evaluation of sedimentary system and reservoir-cap assemblage.The purpose is to enhance the basic understanding of the upper strata of Xihu Sag and provide some geological basis for future exploration work.In this paper,the existing drilling wall core test data,logging data and seismic data are fully applied,and combined with the previous research results of the lower strata,it is considered that the study area is a river-delta sedimentary system,including meandering river deposits,braided river deposits and braided river delta deposits.The distribution characteristics are as follows : the northern part of the study area is braided river deposition,and the southern part is meandering river deposition;the whole area of the lower section of Longlong is braided river deposits;the western part of the study area is braided river deposition,and the eastern part is braided river delta deposition.The lower section of the lower section is braided river delta deposition.According to the physical properties,particle characteristics,formation thickness and sedimentary facies of the reservoirs,the reservoirs in the study area are divided into four categories:(1)high-quality reservoirs:good physical properties,large thickness and best reservoir properties,which are distributed in the upper part of the Longshang Formation and the upper part of the Longxia Formation in the Baowu area.(2)good reservoirs: physical properties and thickness are not as good as high-quality reservoirs,with good reservoir properties,mainly distributed in the Longjing Formation in the study area.(3)medium reservoirs:physical properties are medium-poor,mainly located in the upper part of the study area.(4)poor reservoirs:its physical properties are the worst in the study area,located in the lower part of the study area.According to the characteristics of breakthrough pressure,formation thickness,physical properties,shale content and regional connectivity of the caprock,the caprock in the study area is divided into three categories:(1)high-quality caprock:its breakthrough pressure,formation thickness and shale content are the highest in the study area,with good regional connectivity and extremely high sealing,which is located at the top of the upper section and the top of the lower section of the Tiantai block.(2)Good cap rock : the relevant parameters are slightly lower than the high-quality cap rock,with good sealing,located in the upper section of the Tiantai block.(3)Medium cap rock : in contrast,its parameters are low,with a certain cap rock sealing,located in the northern part of the study area,the upper section of the Pinghu block and the lower section of the Huagang Formation.According to the relationship between reservoir and cap rock thickness,the reservoir-cap rock assemblages are divided into three types :(1)Type A : the cap rock thickness is much larger than the reservoir ’s reservoir-cap rock assemblage,with high sealing,but the reservoir is general,mainly distributed in the upper section of the Huagang Formation;(2)Type B :the reservoir-cap rock assemblage with similar thickness of reservoir and cap rock has good sealing and reservoir,mainly distributed in the Longjing Formation of the study area;(3)Type C : the reservoir thickness is much larger than the cap rock ’s reservoir-cap rock assemblage,with good reservoir,but the cap rock sealing is poor,mainly distributed in the lower section of the Longjing Formation and the lower section of the Huagang Formation.