Sedimentary And Reservoir Characteristics And Prediction Of Favorable Exploration Targets Of The First Member Of The Badaowan Formation In The Western Slope Of The Mahu Depression

The Mahu depression in the northwestern margin of the Junggar basin is rich in hydrocarbon resources,It has great exploration potential and has a long history of exploration.Recent exploration practice shows that the Badaowan formation in the west slope of the Mahu depression has become a hot spot for hydrocarbon exploration in the area.In order to deepen the understanding of the sedimentary system,the characteristics of reservoir development,and to build up the Jurassic hydrocarbon accumulation model,sedimentary facies composition,paleogeomorphology restoration,sediment sources and reservoir characteristics were studied using geological,logging and seismic data.The following progresses have been made:(1)The first member of the Badaowan formation is divided into four sand groups and the palaeogeomorphology in different periods responding the four stages of deposition of sand groups are restored based on the residual thickness.As a result,four kinds of paleogeomorphic units are identified,i.e.groove,low convex,slope break and platform,which are divided into two large sand body unloading areas of Xiazijie fan and Huangyangquan fan,which are divided into the frontline watershed of well Aihu15-well Aihu 9 and well Aihu 14 and the two big sand bodies of the Xiazijie fan and Huangyangquan fan.The sand bodies are transported by grooves and unloaded in the slope-platform area.Comparing the relationship between paleogeomorphic framework and sedimentary facies,it is known that palaeogeomorphology controls the distribution of provenance and sedimentary facies in this area.(2)The first member of the Badaowan formation in the study area is characterized by extensive development of the underwater distributary channel at the front of Braided River Delta.Based on the seismic sand map,paleogeomorphology,paleocurrent,sediment source and well sand,the J1b12 of the Badaowan formation in the oil layer is been studied in great detail.(3)Determine the types and causes of reservoir space in the study area.The pores of the reservoir are mainly the primary remaining intergranular pores(97.9%),only2.1% of the pores in the grain,and the cementation are not obvious.The pore throat connectivity is good,and the medium and small pore throats are the main.The average porosity of hydrocarbon reservoirs in this area is 13.4% and the average permeability is4.71 m D.According to the evaluation criteria of clastic reservoirs in Petro China,it is a medium low porosity and medium low permeability reservoir.The main reservoirs in this area are coal series sandstone and glutenite,which are rich in plastic debris.Compaction is the main geological control that restricts reservoir and seepage properties.The development of high quality reservoir is limited by the formation of diagenesis,and the grain size of the clastic rock controlled high quality reservoir.The coarse-grained sandstone and gravel and coarse sand rock are of the best quality,and then the reservoir classification evaluation template with grain size in this area is established by combining logging information.(4)The reservoir in the study area is characterized by lower generation and upper reservoir.The formation of the reservoir is controlled by the fracture,and the hydrocarbon accumulation is controlled by granularity.Based on the key reservoir forming conditions such as fracture,four favorable zones of hydrocarbon exploration are optimized,with a cumulative area of 19.1 km2,based on the seismic GR inversion.