Research On Sedimentary Facies Of Triassic Reservoirs In Lunnan And Its Peripheral Areas,Tarim Basin

The Lunnan area is located in the Lunnan low uplift of the Tabei uplift in the Tarim Basin.It has two fault systems in the Lunnan fault zone and the Santam fault zone.The Triassic oil and gas resources are very rich and it is the key stratum for many years of exploration and development.However,the Triassic sand bodies in the study area are widely developed laterally and stacked vertically,and the oil layer distribution is complex.Only through careful study of the sedimentary microfacies,predicting the distribution range of favorable sand bodies can helps to properly deploy well locations and improve oil recovery.This paper comprehensively uses the core,well logging,and seismic data to systematically classify and contrast the Triassic in the Lunnan and surrounding areas,and then combine the phase signature and source information of core,logging,seismic data,paleontology and so on.The single well phase,the profile phase characteristics and the plane distribution of the sand body are analyzed,and the plane phase is studied on this basis.Through stratigraphic division and comparison,the Triassic is divided into five sequences of S1-S5.The three sequences of S2,S3 and S4 have obvious positive rhythm characteristics,and the bottom develops T3,T2 and T1 oil groups respectively.The T1 oil group includes three sand layer groups;the T2 oil group includes two sand layer groups;the T3 oil group includes five sand layer groups.The main lithologies of the Triassic development in the Lunnan area are mudstone,sandstone and conglomerate.The mudstone is mainly located in the upper part of the S1,S5 sequence and the S2-S4 sequence,and the mudstones in the three oil groups are limited in layers;the sandstones are mostly distributed in the T1,T2 and T3 oil groups,and the particle size varies widely;The rocks are all distributed in the lower part of the three oil groups T1,T2 and T3.The T3 oil group has the most conglomerate,the T1 oil group is the second,and the T2 oil group has less development of the conglomerate.A variety of sedimentary structures are developed in the oil group and are easily identified in the core.Logging curves are mostly box type,bell type,type,finger type,straight type and so on.In the seismic section,the upper part of the T1 oil group showed strong amplitude continuous reflection,and the lower part showed moderate amplitude continuous reflection;the T2 oil group mostly showed medium amplitude intermittent reflection;the T3 oil group showed weak amplitude intermittent reflection characteristics.The sandstones of the three oil groups in the study area are widely developed.The combination of large thick sandstone stacks or sand-shale interbeds can be seen in the section,with positive rhythm from bottom to top.In the plane,there are many strips or contiguous distributions,which are generally characterized by the southeast thick and thin northwest.The source is mainly from the Luntai fault uplift,the direction is from north to south;the northeast of the study area has secondary sources.The Triassic system in the Lunnan area developed the braided river delta plain,the braided river delta front and the coastal shallow lake sub-facies.Among them,the lower part of the T3 oil group is the sub-facies of the braided river delta plain,and the upper part gradually transitions to the the braided river delta front sub-facies.The front of the braided river delta of the T2 oil group develops in the north and southeast of the study area,and the shallow lake facies is developed in the central part.The lower part of the T1 oil group mainly develops the the braided river delta front sub-facies,and the plain subfacies only develops in the north;the upper water body is relatively deepened,and the southwestern part has evolved into the shallow lake sediment.Finally,the seismic waveform indication inversion is combined with the plane distribution of the sedimentary facies,and the favorable sand body is finely characterized on the plane.