Physical Simulation Study On Sedimentary System Of Upper Wuerhe Formation,permian In Dongdaohaizi Sag

Dongdaohaizi Sag is one of the important oil and gas exploration fields in the Junggar Basin.Multiple exploration wells in the eastern slope area of the Dongdaohaizi Sag have been discovered by Petro China Xinjiang Oilfield in the sedimentary period of the Upper Wuerhe Formation in the Permian.The adjacent Sinopec Shengli Oilfield exploration area is located in the central part of the Dongdaohaizi Sag,and is there a developed sandstone reservoir? If so,how is it distributed;What is the sedimentary pattern.Due to the limited number of Permian exploration wells encountered in the exploration area of Shengli Oilfield and the lack of relevant seismic data,conventional methods are difficult to explore the above issues.Therefore,on the basis of clarifying the prototype geological characteristics of the eastern slope area of the Dongdaohaizi Sag,this article adopts the method of sedimentary physical simulation experiments to explore the distribution law of coarse debris,establish sedimentary models,predict the planar distribution characteristics of sedimentary facies,and guide the next exploration work.The ancient landform of the Upper Wuerhe Formation of the Permian in the eastern slope area of the Dongdaohaizi Sag before sedimentation is a slope with a northeast high and southwest low slope,overall with a relatively gentle slope.From northeast to southwest,it is divided into three secondary geomorphic units: trench area,platform area,and slope area.During the deposition period of the Upper Wuerhe Formation,Dongdaohaizi Sag has a warm and humid climate,the lake level rose,and the provenance was mainly from the northeast of Dinan Uplift.The lake transgressive and retrogressive braided river delta sediments were developed.Based on the prototype geological conditions,an experimental pool with a bottom shape of trench-platform-slope was designed,and sedimentary physical simulation experiments were carried out to obtain a braided river delta sedimentary body with obvious overlapping stages.The first stage braided river delta has the largest distribution area,the third stage braided river delta has the smallest distribution area,and the braided river delta has obvious retrogradation stages.After the analysis of the experimental results,it can be seen that:(1)the stage 1 has the most coarse debris,which mainly occurs in the platform area and slope area;the stage 2 is distributed in the trench area,platform area and slope area,which are mostly coarse and fine mixed coarse debris;the third stage has coarse debris developed in the platform area,which is mainly the progradation of the braided river delta front.From the experimental results,it can be seen that during the sedimentary period of the Upper Wuerhe Formation,coarse debris deposits developed in the exploration area of Sinopec Shengli Oilfield.(2)The flood period provides the material basis for the front coarse debris accumulation.The flood develops strong sheet flow in the upstream and strong distributary flow in the downstream.The strong flood transports the coarse debris forward to the front of the braided river delta and develops progradation blobs.During the middle flow period,the sand transport equilibrium is reached,and the stronger middle flow transports the fine-grained materials in the front edge of the flower to a further location,making the remaining coarse debris in the sediment more concentrated.(3)The closer the shoreline is to the source,the fewer the number of distributary channels and the fewer coarse debris clusters at the front edge;On the contrary,the farther the shoreline is from the source,the more distributary channels there are,and the more coarse debris clusters at the front edge,but the cluster size is smaller.Based on deposition physical simulation experiments,a sedimentary model was established.In the first member of the Upper Wuerhe Formation,the braided river delta plain subfacies extend from the trench area to the platform area,and the slope area develops the braided river delta front subfacies;In the second member of the Upper Wuerhe Formation,the braided river delta plain subfacies are distributed in the trench area and in the front of the platform area.The distribution range of the braided river delta front subfacies is generally from the rear of the platform area to the middle of the slope area;In the third member of the Upper Wuerhe Formation,the braided river delta plain subfacies are distributed in the trench area,and the braided river delta front subfacies extend from the rear of the trench area to the middle of the platform area.According to the sedimentary model,the sedimentary facies of single well and the profile facies of connected well are reinterpreted to predict the plane distribution of the depositional system.On the plane,in the Member 1 of Upper Wuerhe Formation,the trench filling deposits developed inside the trench,the middle and upper reaches of the platform area and the slope area were braided river delta plain,and the braided river delta front developed in the lower reaches of the slope area.Braided channel and interchannel microfacies of the delta plain are mainly developed in the Member 2 of Upper Wuerhe Formation,trench area and platform area,braided river delta front is developed in the middle and upper reaches of the slope area,and shore-shallow lake deposit is developed in the lower reaches of the slope area.Due to lake transgression,the sedimentary facies of the Member 2 of Upper Wuerhe Formation were indented towards the provenance.