The Structure And Dynamic Process Of The Underlying Interface Of The Sinian Stratum In Tarim Basin

Tarim Basin is an important petroliferous basin in China,which is rich in oil and gas resources.In recent years,the industrial oil and gas flow of Lower Cambrian has been drilled in Tazhong uplift for the first time.With the progress of exploration technology,the exploration trend in the future is to explore the deep and advance to the oil source.The sedimentary sequence of Nanhua-Sinian is a non-metamorphosed rock system which contains sandstone,mudstone and carbonate and has good hydrocarbon generation and accumulation conditions.The contact surface between the Nanhua and Sinian systems is an unconformity surface and it plays an important role in controlling hydrocarbon accumulation.Based on the seismic data,drilling data and field outcrop data,combined with the previous excellent exploration experience,the structure,interface contact relationship,evolution and dynamic genesis of the Sinian underlying interface in Tarim are studied,the influence of the structure and unconformity distribution of the T100 interface on hydrocarbon accumulation is analyzed by seismic data interpretation,field outcrop observation,balance profile,etc.The results show that the Sinian stratum is located in the north and southwest of the Tarim Basin,pinched out in the southeast,and has the same distribution trend as Nanhua stratum rift trough.The contact relationship between the upper and lower layers of the underlying interface T100 of the Sinian stratum includes conformity,parallel unconformity,heterolithic unconformity and overlap unconformity.The conformity and parallel unconformity distribute in the contact area between Sinian stratum and Nanhua stratum.Heterolithic unconformity distributes in the contact area between Sinian stratum and basement,and overlap unconformity distributes around the paleouplift of basement.Deep seismic data and stratigraphic thickness maps show that the Nanhua stratum is a rift graben type deposit and the Sinian stratum is a depression type deposit.They have the same thickness distribution direction.Therefore,T100 interface is a break-up unconformity surface,which is the structural interface formed by post rift thermal subsidence.Evolution process and buried depth of interface after its formation have a good response to the plate tectonic activities around the Tarim Basin.According to seismic data and distribution of sedimentary facies,lacustrine source rocks developed in the Nanhua-Sinian stratum.The platform facies dolomite of Qigbulak Formation of Upper Sinian stratum is a good reservoir,and the shale of Yuertus Formation of Cambrian stratum is a good caprock.There is a complete combination of source,reservoir and cap.At the structural high points such as the Tazhong paleouplift,Tabei paleouplift and Southwest paleouplift,the underlying unconformity interface of Sinian stratum and stratigraphic combination form traps.The trap is a favorable area for oil and gas accumulation.It is of great significance to explore the distribution of the unconformity for the exploration of favorable areas in Tarim Basin.