Study On Correction Of Influencing Factors Of Oil-based Mud Logging

The Xihu Sag is located in the East China Sea Shelf Basin and has abundant natural gas resources.However,due to the long interval of the underground target layer in the Xihu Depression and the large difference in formation conditions,the selection of the proportion of conventional water-based mud is uncertain,which brings great difficulties to the drilling work,and the drilling cost is relatively high.Therefore,the oil-based mud was tried to be used in the drilling process.And then the drilling time and logging efficiency have been greatly improved,and the drilling cost has also been effectively controlled.However,the widespread use of oil-base mud will have a series of effects on logging data,which will bring certain difficulties to the evaluation of reservoir physical properties and fluid properties.The target horizon selected for this study is the Pinghu Formation in the Xihu Sag,which belongs to the eastern depression zone of the East China Sea Shelf Basin and has abundant natural gas reservoirs.This thesis carried out the analysis and research on the influence mechanism of oil-based mud on conventional logging data,gas logging data,and nuclear magnetic resonance logging data,and proposed practical and feasible correction methods.Make it to the extent that it can be compared with logging data obtained under water-based mud from adjacent wells.The identification chart of fluid properties under oil-based mud conditions has also been improved.Firstly,the statistical comparison method is used to analyze the influence of oil-based mud on conventional logging,gas logging and nuclear magnetic resonance logging,so as to judge whether each logging method needs correction.For the gas logging correction,the general idea is normalization correction,and the gas logging data under oil-based mud condition is corrected by the component expansion method based on mudstone section.According to the NMR logging data,the reservoirs in the study area are divided into six types according to the classification standard of permeability.Taking the T₂ spectrum of water-based mud drilling as the criterion,the correction coefficient matrix of each type of reservoir is determined,and the T₂ spectrum of NMR is corrected by matrix inversion method,so that the T₂ spectrum of NMR is fully corrected,and the permeability calculation by NMR is more accurate.Utilizing the corrected gas logging data,introducing resistivity while drilling,and establishing a triangular pattern of combined logging and logging recognition technology,the accuracy of fluid identification in oil-based mud drilling is improved,and the fluid property identification chart under oil-based mud conditions is improved.