Sedimentary Characteristics And Favorable Sandbodies Prediction Of Permian Wutonggou Formation In Dixi Area, Junggar Basin

The Dinan bulge of the Junggar basin has a north-south dual source for hydrocarbon potential and abundant source of oil.At present,the north side has found the KeLaMeiLi gas field with over 100 billion cubic meters,however,its south side is relatively small.Based on previous studies,synthesized core,thin section,well logging and seismic data and so on,this research thoroughly investigated the stratigraphic distribution characteristics,types and distribution of sedimentary facies,reservoir characteristics,rock physical characteristics as well as the sensitive parameters of the Dixi area of Wutonggou Formation,forecasted and evaluated favorable zones of sand body distribution.The main achievements of the thesis are as follows:Based on the regional geological background,rock electrical characteristics and seismic reflection characteristics,the Dixi area of Wutonggou Formation can be divided into two parts from the bottom up,namely,the first Member of Wutonggou Formation and the second Member of Wutonggou Formation.Among them,the first Member of Wutonggou Formation is mainly composed of gray-brown pebbly sandstone,coarse sand and silty sand,with a thickness of the strata between 0 to 100 meters.The second Member of Wutonggou Formation is mainly composed of reddish-brown mudstone,silty mudstone and argillaceous siltstone with a thickness of strata between 50 to 100 meters.Based on the petrological characteristics,sedimentary facies and conventional logging of the researching area,the Dixi area of Wutonggou Formation is considered to developing fan delta and lacustrine depositional system mainly.The first Member of Wutonggou Formation is considered to be the main lake-delta sedimentary system,from bottom to top,which can be subdivided into shore shallow lake and fan delta front,sand body is mainly distributed in underwater distributary channel and mouth bar sand body,then the frontal sand sheet;Vertically the first Member of Wutonggou Formation can be roughly divided into two sets of sand bodies.The second Member of Wutonggou Formation are mainly the mudstone deposits of the large shallow lake,locally there are front edge sheet sand of the fan delta.According to the type and division of sedimentary facies,and the vertical and horizontal development characteristics,the distribution of the sedimentary facies of the upper and lower sets of sand bodies in the first Member of the Wutonggou Formation in the study area was defined.It is considered that the sand bodies in the study area are mainly controlled by the north source area and favorable sands are formed.The body enrichment zone is located near Dixi 179 well area.The southern sand body is spreading in the east-west direction,the sand body has a smaller extension range,and it quickly turns westward into lake-phase and diversionary bay deposits,making it a potentially favorable exploration area.The reservoirs of the Wutonggou Formation in the Permian are mainly distributed in the middle and upper parts of the first member of the braided section.The lithology of the reservoir is mainly unequal sandstone,fine-fine-grained sandstone and siltstone,and the sandstone composition is tuff and diagenesis.Rock debris is the main,followed by feldspar,quartz content is low.Intergranular interstitials mainly consist of chlorite and turbidite,and the particles are mainly embedded in press-fit.The pore types are mainly intragranular dissolution pores,residual intergranular pores,and casting mold pores.In addition,they contain a small amount of intergranular dissolved pores and Interparticle dissolution pores.The analysis results of the sandstone and mudstone intersection in the Wutonggou Formation in the study area show that the resistivity of the sandstone mudstone is more distinct,so it is preferable that the resistivity curve is the sensitive parameter of the effective reservoir in the area.Through the deep resistivity inversion,the upper and lower sets of sand bodies in the Member of the Wutonggou Formation were identified and predicted.It was found that the relationship between the upper and lower sets of sand bodies was clearly defined vertically.The upper sandbody of the first Member of the last Member is mainly concentrated in the underwater distributary channel and the sand bed of the mat-like sand estuary in the Dixi 179 well area and the northern area,and in the Dixi 32 well area and the south area;Located in the underwater distributary channel and estuary bar sandbody of Dixi 179-Dixi 402 well area and northern area,the favorable area is about 83km~2.