A Study On Sealing Effectiveness Of The Fault-Cap Configuration In The Es1~x Of Beidagang Area,Qikou Sag

To study the role of sealing effectiveness of fault-cap configuration in the lower first member of Shahejie Formation(Es1~x)of the Beidagang area in controlling the accumulation and distribution of oil and gas.Based on the oil and gas exploration information available in the study area,through the characterization of the development and distribution characteristics of the caprock and its internal faults,analyzed the degree of destruction of faults to the caprock of the middle first member of Shahejie Formation(Es1~z)and determined the type of sealing mechanism of the fault-cap configuration.Afterward,by comparing the differential displacement pressure between the fault rock or mudstone and the reservoir rock,the sealing capacity of the fault-cap configuration and its distribution characteristics in different periods were determined.Finally,the space effectiveness of the sealing of the fault-cap configuration in different periods was evaluated by combining the distribution characteristics of oil and gas in the Es1~x,and the time effectiveness of the sealing of its fault-cap configuration was evaluated through the relationship between the sealing formation period of the Es1~x fault-cap configuration and the main hydrocarbon generation and expulsion periods of the source rocks.The main research results are as follows:(1)The sealing mechanism of the fault-cap configuration in the Es1~x of Beidagang area can be divided into the mudstone-sealing mechanism and fault rock-sealing mechanism.The fault rock-sealing mechanism parts of the current fault-cap configuration in the Es1~x of the Beidagang area are distributed in the north,middle,and south of this area,and the rest parts are the mudstone-sealing mechanism of fault-cap configuration in the Es1~x;The fault rock-sealing mechanism parts of oil and gas accumulation phase fault-cap configuration are mainly distributed in the central and southern parts,and the rest parts are all mudstone-sealing mechanism.(2)The mudstone-sealing mechanism parts of the current fault-cap configuration of the Es1~x in the Beidagang area are not sealed only in the northwestern edge and some parts of the central and western regions,and the rest of the parts are sealed;The unsealed parts of the fault rock-sealing mechanism parts of the current fault-cap configuration in the Es1~x of the Beidagang area are mainly distributed in the central and southern border regions,and the sealed parts are mainly distributed in the northern central,eastern central and southwestern border regions.The unsealed parts of the mudstone-sealing mechanism parts of the oil and gas accumulation phase fault-cap configuration mudstone of the Es1~x in the Beidagang area are distributed in the northeast,northwest,and parts of the central and western regions.The rest parts are all sealed;The fault rock-sealing mechanism parts of the oil and gas accumulation phase fault-cap configuration were not sealed.(3)The unsealed parts of the current fault-cap configuration are not consistent with the oil and gas in the northwestern part,central southern,and southern parts of the Es1~x in the Beidagang area,and the sealing space effectiveness of the fault-cap configuration is poor.The rest of the sealing parts are consistent with the oil and gas distribution,and the sealing space effectiveness of the fault-cap configuration is good.The sealed parts of the oil and gas accumulation phase fault-cap configuration are not consistent with the oil and gas in the northwestern part,northeast,central south,and southern part of the Es1~x in the Beidagang area.The sealing space effectiveness is poor.The remaining parts are in good agreement with the oil and gas distribution,and the sealing space effectiveness of the fault-cap configuration is good.(4)The mudstone-sealing of the Es1~x fault-cap configuration in the Beidagang area was formed in the middle and late stages of the deposition of the second member of the Dongying Formation(Ed2),it’s earlier than the massive hydrocarbon expulsion phase of the third member of the Shahejie Formation(Es3)source rocks—the end of the deposition period of the Guantao Formation(Ng).The sealing time effectiveness of the fault-cap configuration is good,which is conducive to the accumulation and preservation of oil and gas in the Es1~x.The fault rocks-sealing of the Es1~x fault-cap configuration in the Beidagang area was formed in the late depositional period of the upper Minghuazhen Formation(Nm).Although later than the period of massive hydrocarbon expulsion of the Es3 source rocks,the sealing time effectiveness of the fault-cap configuration is relatively poor,it is still in the period of hydrocarbon expulsion of source rocks.It can also seal a certain amount of oil and gas,which is relatively favorable for oil and gas aggregation and preservation in the Es1~x.The sealing of the Nm caprock in the Beidagang area was formed in the late depositional period of the upper Nm,still in the hydrocarbon expulsion period of the Es3 source rocks,it is also possible to seal a certain amount of oil and gas.