Three-dimensional Induction Logging Borehole Correction

Formation resistivity is a key parameter in determining hydrocarbon saturation in formation evaluation,so obtaining accurate resistivity is particularly critical for accurate formation evaluation.The resistivity of natural formations is anisotropically distributed,but conventional induction logging cannot effectively determine the anisotropy of formation resistivity.3D induction logging instruments can measure the nature of anisotropic reservoirs such as thin interbedded sand mudstone,however,3D induction logging instruments are susceptible to environmental factors in the wellbore when logging due to the complexity of the formation media and wellbore,and short array measurement data is influenced by these factors The short array measurements are more strongly influenced by these factors.Wellbore environmental factors include well diameter,formation inclination,mud conductivity,instrument eccentricity and instrument eccentricity.If these factors are not eliminated,the true formation conductivity values will not be obtained in the subsequent 1D inversion,and the quality of the log data processing and log interpretation will be reduced.This thesis improves the efficiency of wellbore correction by establishing a wellbore correction library,using a finite difference algorithm for the forward simulation.Firstly,the forward simulation results of three sets of models are selected and compared with the results of COMSOL modelling software to verify the reliability of the algorithm.Then,suitable model parameter values are selected to build a wellbore correction library and analyse the variation of apparent conductivity under the influence of wellbore environmental parameters.The wellbore environmental parameters are inverted by the Gaussian Newton method,and the wellbore response is quickly calculated by an interpolation algorithm during the inversion,while a linear search algorithm is added to the algorithm in order to improve the efficiency of the Gaussian Newton algorithm.A multi-step inversion method is used to perform sensitivity analysis on the logging data,select the components affected by each parameter,invert each parameter separately and achieve the purpose of eliminating the wellbore environmental factors by calculating the difference between the response subject to the wellbore environmental factors response and the response not subject to the wellbore environmental factors response as the wellbore correction amount.To verify the reliability of the algorithm,two sets of straight wellbore models and two sets of inclined wellbore models were selected to invert the wellbore parameters and to calculate the wellbore corrections.The results show that the method used in this thesis improves the speed and reduces the complexity of the wellbore correction,eliminates the influence of the wellbore environmental parameters to a certain extent,and provides important technical support for obtaining the true conductivity of the formation and the accurate interpretation of the 3D induction logging data.