Study On The Sedimentary Characteristics Of The Jurassic Sangonghe Formation Ⅱ Sandstone Reservoir In The South Slope Of The Mahu Depression

The Junggar Basin is located in the intersection of Kazakhstan Plate,Tarim Plate and Siberian Plate,and is rich in oil and gas resources with a long history of exploration.In recent years,insisting on the exploration idea of"going beyond the fracture zone to the slope area",the exploration work has gradually changed from the tectonic exploration of the fracture zone at the source to the lithological exploration of the main area within the source,especially the Mahu depression,as an important hydrocarbon producing depression,has gradually become a hot spot for finding hydrocarbon resources.With the deepening of geological understanding,under the guidance of sand and conglomerate fan-controlled large-scale reservoir formation model,industrial oil flow was firstly obtained in the Permian and Triassic formations in the south slope area of the Mahu Depression,and then important discoveries were made in the middle and shallow Jurassic formations by using old well review combined with exploratory well deployment and control.The Mahu Depression has multi-layer system three-dimensional formation characteristics,and there are more oil-bearing formations,and the geological characteristics are complex due to different formation backgrounds.The target reservoir of Jurassic Sangonghe Formation has the characteristics of shallow burial and good development efficiency,but due to the real problems such as thin oil-bearing sand body,rapid lateral change and difficulty in target prediction,no unified geological understanding has been formed and the research results are relatively scattered.In this paper,with geology,sedimentology and stratigraphic stratigraphy as the theoretical guidance,based on 3D seismic data,core data,logging and recording data,a detailed study of rock types,sedimentary structures and sedimentary micro-phase spreading characteristics of the second section of the Jurassic Sangonghe Formation has been conducted,combined with seismic inversion techniques to predict the distribution of sand bodies in favorable areas of the Mahu A and Mahu B blocks,and the following understanding has been achieved:（1）Through core observation,drilling and logging,the second section of the Jurassic Sankonghe Formation in the Manan slope area is divided into one long-term rotation,two medium-term rotations and six short-term rotations,and the target J₁s₂⁴sand formation is further subdivided into two small layers;vertically,the second section of the Sangonghe Formation to the third section of the Sangonghe Formation shows a regressive process from the subfacies of the front edge of the braided river delta to the front delta,with a clear evolutionary pattern.（2）According to the results of regional geological background survey,combined with logging interpretation and field core observation description,it is believed that Mahu A and Mahu B blocks mainly develop braided river delta front subphase sedimentation,which can be further subdivided into submerged divergent channels,matted sand,divergent inter-bay and other micro-phases;the sand body formed by frequent oscillation of submerged divergent channels is the main reservoir group,and the lithology is mainly fine-grained feldspathic clastic sandstone with rich sedimentary tectonic types.（3）The sedimentary micro-phases in the study area were delineated by using log-phase analysis and seismic inversion techniques.The sedimentary micro-phases delineated by this combination of well and seismic have more practical geological significance,and the dominant phase zone of the sedimentary micro-phases was delineated based on the distribution characteristics of the sedimentary phases delineated by the combination of well and seismic,which guided the expansion drilling in the northern part of the Mahu A block and made new discoveries.