川中地区须家河组致密砂岩电成像测井裂缝张开度校正方法OA

The central Sichuan basin has abundant tight gas reserves in Xujiahe formation,and the development degree of natural fractures has a significant impact on the gas production of individual wells.Electrical imaging logging is one of the core methods for evaluating fractures.However,the calculated fracture width by the conventional electrical imaging logging equations generally too high,which severely limits the practical application of tight sandstone fracture width.This research aims to establish a correction method for the fracture width of electrical imaging logging to improve the accuracy of fracture parameter evaluation of Xujiahe formation tight sandstone.Firstly,based on core samples,electrical imaging log and conventional logging data,the fracture types of tight sandstone from Xujiahe formation are analyzed,and the characteristics of fracture logging responses are clarified.Then,based on the principle of the electrical imaging logging tool,the reason for the large deviation of the fracture width calculated by the logging software is analyzed.On this basis,a correction method for fracture width based on image processing and core calibration is proposed.The research results show that tight sandstone from Xujiahe formation is widely developed with unfilled fractures.The characteristics such as increased acoustic wave time difference,decreased amplitude of bilateral resistivity,and dark sinusoidal bands in electrical imaging logging can accurately identify fractures,but the quantitative calculation of fracture width has a large error.The main reason is that the fracture current anomaly area measured by the electrical imaging logging button electrode can be divided into two levels of anomalies.The external current abnormal area is the relatively lighter color fracture shadow,whose width is significantly larger than the actual fracture width.The internal current abnormal area is the darker color fracture core,whose width is significantly closer to the actual fracture width.The traditional formula typically identifies the entire current abnormal area as a fracture,resulting in significantly inflated calculated values for the fracture width.The proposed two-level fracture width correction method based on image processing and core calibration can sequentially reduce the error in calculating the fracture width.The average absolute error is reduced from 5.26 mm using the traditional formula to 0.13 mm with core-scale correction,and the average relative error decreased from 674.74%using the traditional formula to 16.63%with core-scale correction,ultimately yielding results close to the actual fracture width of the core.The research results provide more accurate parameters for quantitative evaluation of fractures based on electrical imaging logging,can be used to optimize the calculation process of electrical imaging logging fracture parameters,and also have important reference value for the study of fractures in tight sandstone reservoirs.