Restoration Method of Closed Evolution History of Fractured Mudstone Cap Rock and Its Application

Fu Guang; Li Shizhao

doi:10.3799/dqkx.2017.514

Abstract：The failure degree of mudstone caprock was not considered in the previous study,and the study on the evolution history of the sealing characteristics of fractured mudstone caprock has not been reported in the literature,however,these problems are very important for oil and gas exploration in fault development area of petroliferous basin.On the basis of the study of the sealing mechanism and the closed evolution characteristics of fractured mudstone cap rock,by comparing the relative size of the fault contact thickness of the mudstone cap rock and the minimum fault contact thickness required for sealing oil and gas,the fractured mudstone cap rock sealling type is divided into 2 kinds,including non-fractured and fractured mudstone cover.And the mudstone cap rock sealing formation time,fault rock compaction time and sealing capacity formation time were determined by recovering the ancient displacement pressure of mudstone cap rock and fault rock.A restoration method of the closed evolution history of fractured mudstone cap rock is established,then it was applied on the restoration of closed evolution history of the fractured mudstone cap rocks damaged by f2 fault of Ed2,Nanpu 5 structure,Bohai Bay basin.The results show that fault f2 did not destroy the Ed2 mudstone cap rock sealing ability in L1,L3,L4,L5,L6,L7 and L9 test line,and is still mudstone cap rock sealling of Ed2,its closed evolution has experienced non-closed and closed phases.At present,it has strong sealing ability.The Ed2 mudstone cap rock sealing in L2 and L8 test lines was destroyed by fault f2,its sealing ability comes from f2 fault rock,the evolution of its sealing ability has experienced 3 stages:compaction period not closure,diagenetic period not closure and diagenetic period closure.At present,it has a strong ability of closure,which is favorable for the accumulation and preservation of oil and gas in the reservoir under the mudstone caprock of Ed2.The prediction results are consistent with the discovered oil and gas distribution in the reservoir under the Ed2 mudstone cap rock,which shows this method is feasible to restore the closed evolution history of mudstone cap rock.