Study On Log Evaluation Of Clay Mineral And Water Sensitivity For Shale Gas Reservoirs

During the exploration and development of shale gas reservoirs,the formation characteristics of the dense shale throat,high clay mineral content,etc.would produce water swelling,lead to blockage of pore channels and reduce reservoir permeability,thus increase the difficulty of production.Therefore,it is necessary to study water sensitivity assessment with shale gas reservoir log and core analysis.The thesis focuses on the shales in Wufeng Formation and Longmaxi Formation of the Jiaoshiba shale gas field in Chongqing,quantitatively calculates different types of clay based on the improved plate method and data mining method with the natural gamma-ray spectroscopy and XRD analysis.The effect of different clay mineral content on the water sensitivity of shale gas reservoirs was studied by using artificial core and natural core experiments.The results show that the shale mineral components is complex and the content of clay minerals is high;the chart correction method is simple in calculation and has certain applicability;the multiple linear regression method is relatively stable,and the clay mineral content value could be calculated in the whole well section;the decision tree regression is abnormal,and the value is not sensitive and the applicability is not strong;in the low porosity and low permeability reservoirs,the content of illite/smectite formation is the main factor of water sensitivity;combining the multiple linear regression and the relationship between the water sensitivity and the content of illite/smectite formation,a water sensitivity log evaluation curve was obtained.Although shale water sensitivity is affected by many factors,the method has certain applicability and provides ideas for further improving the clay minerals evaluation with logs for shale gas.