The Origin of Tx2 Low Resistivity Gas Reservoirs in the Yuanba Area and Their Logging Evaluation Method

Due to the fact that gas reservoir identification is difficult in the Tx2 formation in the Yuanba Area,and the interpretation coincidence rate is lower by conventional logging evaluation methods,the origin of low-resistivity gas reservoirs and its logging evaluation methods have been studied.On the basis of analysis of sedimentary microfacies,reservoir characteristics,the data of well logging,mud logging,testing and experiment in Tx2x gas reservoirs,a conclusion was drawn that the main factors influencing the resistivity value in gas reservoirs are reservoir mineral composition,pore structure,grain size and cementation type,and quartz content had a positive correlation with logging resistivity. The logging mode for lithology subdivision and identification in reservoir was established,and determined the comprehensive lithology, resistivity and water saturation,etc.,so it was possible to form the evaluation criteria for gas reservoir with different lithology and logging evaluation method for gas reservoir with low resistivity. This method has been applied in multiple exploration wells in Yuanba Area to evaluate continental tight sandstone gas reservoirs,and as a result,the success rate of logging evaluation was improved significantly,and a breakthrough was made in the exploration of continental tight sandstone gas reservoir in the Yuanba Area. Research and application showed that the success rate of logging evaluation on tight sandstone gas reservoirs could be increased by establishing the logging evaluation method for low resistivity gas reservoirs,which thus could solve the problems of overlooking low resistivity gas reservoirs and accompanying errors in judgment.