Fine-Description Of Reservoirs And Favourable Areas Optimization Of The Shanxi Formation-He 8 Member In The Shan-186 Well Area,Southeast Sulige Gas Field

Shan 186 well area is located in the southeast area of Sulige gas field,with the main exploit layer being the Shanxi and Lower Shihezi Formation,which has the characteristics of low porosity,low permeability,and strong heterogeneity.Since the large-scale construction began in 2017,most of the geological reserves have been utilized,and there are fewer favorable areas available for deployment of development well locations.Therefore,it is of great significance to accurately describe the reservoir in the study area,establish 3D geological model and select favorable areas.Used core,well logging and other data,the sedimentary facies,reservoir characteristics and sand body distribution characteristics are studied and a three-dimensional geological model is established.On the basis of comprehensive research,favorable areas are selected and the following understandings are obtained:(1)The braided river delta plain subfacies is developed in the He 8 Member and sedimentary microfacies include braided distributary channel and interdistributary swamp.Shan 1 member is a meandering river delta plain subfacies,and sedimentary microfacies include four types:distributary channel,interdistributary swamp,natural levee and crevasse splay.The distribution of sand bodies is controlled by sedimentary facies,and overall presents a north-south striped distribution feature in the study area,with the sand bodies lower strata of H8 being the best developed.(2)Diagenesis affects reservoir physical properties in the study area.Compaction and cementation cause poor physical properties of the reservoir,resulting in the formation of a dense reservoir.Compaction has a greater effect than cementation on the reduction of reservoir primary pores,which is the main factor leading to the deterioration of reservoir properties in the study area.Dissolution is beneficial for improving reservoir properties.(3)Based on the research results of stratigraphic division,sedimentary facies and reservoir physical properties,construct stratigraphic-structure,lithology,porosity,permeability and saturation models in the study area.Analysis of the established model shows that the physical properties of the reservoir in the study area are controlled by sedimentary microfacies and sand body thickness,and the best physical properties are found in the area of thick layer sand overlapping in distributary channel.The gas saturation in lower strata of He8 is higher than that of other layers.(4)Based on the sedimentary microfacies distribution map,sand body thickness plane distribution map,effective sand body thickness plane distribution map,and 3D geological modeling results,two types of favorable areas are divided.Class I favorable area is mainly braided river distributary channel and distributary channel,with sand body thickness of10-15m,effective sand body thickness of 6-8m,porosity of more than 7.0%and permeability of more than 0.5μm~2,with a gas saturation greater than 55%.Class II favorable area is mainly distributary channel,natural levee,and crevasse fan,with sand body thickness of 5-10,effective sand body thickness of 4-6m,porosity is between 5.0-7.0%and permeability is between 0.3-0.5μm~2,the gas saturation is 40-55%.