A Study On The Tight Oil Reservoir Description Of Da'anzhai Member Of Gongshanmiao Oilfield In Central Sichuan

The reservoir,at Gongshanmiao oilfield in the Da'anzhai formation of Lower Jurassic,is located in the central of Sichuan basin,among which oil production decrease severely after years of exploitation because formation pressure drops.guided by reservoir geology,logging geology,rock physics and theories of petroleum geology,in combination with regional tectonic,sedimentary background,the results of previous studies,geophysical logging and the analysis of cores and samples,the dissertation establishes the three-dimensional geological modes by using the latest Petrel 2015 geological modeling software,on a basis of reservoir lithology,physical property and oil-bearing features.The main contents are listed as follows:(1)Reservoir lithology in the da'anzhai formation is characterized by coquina,which is defined as the dense limestone reservoir with the porosity at 1%on average and permeability of matrix(0.0197mD).(2)The well-log interpretation models are established,based on the material and oil-bearing property respectively,by which the coincidence rate of the model and the measured result is above 80%.Part of the physical and oil-bearing properties of the fractures is available by using routine analysis and empirical methods.(3)The 3D geological models in the study area are obtained by using the random modeling method of physical property controlled by lithology and fractures,on a basis of the characteristics of the tight reservoir.The size of the model grid is 50m×50m;the vertical step length of the fracture-developed zones(0.5m);the longitudinal step length is 2m in the fracture-undeveloped zones;it is 16004140 grids in total.(4)The results of model analysis show that the heterogeneity of the reservoir is dominant in tabulate,and the zones with good physical properties are mainly distributed in the main fault and the interlayers of thin limestone.(5)The result of the models shows that there are nine favorable areas of crude oil enrichment in the industrial area,including Dayishang substrata and the limestone layer of Dasan subsegment in the lower part of the area near the G8 to G14 well,the limestone layers of Dayi and Dasan subsegment in the lower positon of the Gong103,G63-G47-G35,G003-X10-G67-G58,G3-G60-G45 and G39-G24-G003-X5,the limestone layer of Dasan subsegment in the part of the G57 to G62,the limestone layer of Dayisan subsegment in the high spot of the G46,and Dayishang limestone layer in the flat zone which lies in the southeastern part of the industrial area,and the favorable ones is in accordance with the oil testing conclusion.