Logging Evaluation Technology In Tight Reservoir Of Shaximiao Formation,Eastern Slope,Western Sichuan

Tight gas resource is abundant in china.A set of practical exploration and development technologies has been formed with exploring a large number of gas fields,such as Xinchang,Luodai,Bajiaochang and majin.In recent years,there are significant breakthroughs made in Jurassic of East slope,which turned out to be the second largest gas field in the middle-shallow layers of Southwest Oil and Gas Company,Sinopec.The shaximiao gas reservoir on the Eastern Slope of Western Sichuan Depression is characterized by low porosity and permeability of tight sandstone,complex gas-water relations and enrichment,as well as material sources,multiple gas-producing layers,and narrow river channels.Reservoir geological characteristics and differences in the intricacy river system lead to diverse logging responses in different gas reservoirs and river channels of the Shaximiao Formation.Therefore it is hard to establish a unified electric standard and make a low reliability of reservoir logging evaluation model.In the previous study,a quantitative reservoir logging evaluation method based on porosity,saturation,and resistivity was established.It is considered that the resistivity of the gas layer is higher than the value of the evaluation standard which is obviously no longer appropriate in this case.The correct evaluation of these low resistivity reservoirs has become the focus of logging interpretation.The factors that influence the resistivity value are the key to establishing an effective logging evaluation technique.In addition,well logging evaluation techniques for horizontal wells also need further studyBased on the different reservoir geological characteristics such as reservoir rock type,grain size,cement type,pore structure and well trajectory,the paper has focused on reservoir logging response characteristics and four properties of reservoirs.It is suggested that reservoir logging response is mainly due to the difference in well patterns and reservoir geological characteristics with no direct correlation of gas reservoirs and river channels.Difference correction standard for horizontal wells and vertical wells has been established.According to the comprehensive study of the “low-resistance” gas reservoir genesis and reservoir geological characteristics,it is clear that the resistivity of the reservoir is affected not only by the fluids contained in the reservoir but also by the porosity and pore structure of the reservoir.Additional conductivity of clay minerals,its relatively poor pore structure and high bound water content are the main reasons for the low resistance in Eastern slope.Fluid identification methods of neutron slope,multifactor radar image,and resistivity slope have established for this low resistance reservoir.Through the comprehensive study of reservoir geological and logging response characteristics,a set of reservoir parameter evaluation model and its supporting model parameters have been established,which effectively improves the accuracy of reservoir logging evaluation and is more conducive to the discovery of potential low-resistivity reservoirs.