Sedimentary System And Reservoir Characteristics Of The Xishanyao Formation In Malang Depression,Santanghu Basin

The Malang Sag is located in the south-central part of the Santanghu Basin in Xinjiang.During the exploration and development of the oil and gas reservoirs in the study area,several wells found low-yield oil flows in the Xiluyao Formation of the Jurassic,indicating a large exploration potential.Therefore,the study on the sedimentary system and reservoir characteristics of the Xishanyao Formation in the Malang Depression Block is of great guiding significance for the next step of oil and gas exploration.The main research contents and results of this paper are as follows:Under the guidance of sequence stratigraphy and sedimentology theory,the stratigraphic division of the Xishanyao Formation was finely divided by the traditional stratigraphic division method.The west of the Xishanyao Formation in the Malang Sag was selected by selecting six marker layers in the study area.One section is divided into three sand layers,and the second section is divided into two sand groups and the stratigraphic framework of the Malang depression is established.On the basis of establishing the stratigraphic framework,the sedimentary facies distribution and sedimentary system of the Malang Sag in the Santanghu Basin are studied through core observation,log response characteristics and heavy mineral analysis.The study shows that the braided river delta facies is mainly developed during the sedimentary period of the western section of the Xishanyao Formation（J₂x₁）in the Malang Sag,which can be divided into two sub-facies such as the delta front and the front delta,as well as the underwater distributary channel,the estuary sand dam,and the mat.4 kinds of microphases such as sand and diversion bay.The sedimentary period of the west section of the Xishanyao Formation（J₂x₂）is dominated by lacustrine facies deposition,and a small amount of braided river delta deposits are developed.Based on the lithology observation and the statistics of the slice data,it is believed that the Xishanyao Formation sandstone in the study area is dominated by lithic sandstone and feldspar lithic sandstone,and the reservoir cementation is not strong,mainly compacted and reduced.The main residual intergranular pores are developed.The study of microscopic characteristics of reservoir shows that the pore structure of Xishanyao Formation is poor,and the pore throat is mainly fine-microporous,which is generally medium-low porosity,low permeability or ultra-low permeability reservoir.Based on the study of the sedimentary system and reservoir characteristics of the Xishanyao Formation,the reservoirs of the three sand strata in the western section of the Xishanyao Formation are evaluated.The hydrocarbon reservoirs in the target interval are mainly Ⅲ₁ and Ⅲ₂.Partially a type Ⅱ reservoir.