Half-space Response And Calibration Of An Array Induction Logging Tool

The formation resistivity is an important paraeter in distinguishing the lithologicalcharacters and estimating the hydrocarbon saturation of the reservoir. Owing to a series ofcharacteristics like the high resolution，deep investigation depth and the intrusive invasion，theArray induction logging tool is a main tool for detecting the formation resistivity at present.The direct measured value of the array induction logging tool is the voltage signal. It must beinverted to the conductivity signals through calibration to eliminate the influences of theelectronic circuit and the sonde error. Whether the calibration is accuracy concerns theaccuracy rating of the logging information. The existing calibration method has a limitation toeliminate effectively the influence of the earth environment. Taking the array induction loggingtool MIT as the study objection, the dissertation investigates a three dimensional numericalcalculating method which can compute the response of the MIT in half-space based on theComsol Multiphysics, an Finite Element numerical calculation software. A new calibrationcorrection method based on the database is put forward. The results have a practicalsignificance to calibrate accurately the measurement signal of the MIT.Firstly，the induction logging theory is introduced. The analytic solutions of the electricfield and the magnetic field in the orthogonal coordinate which are generated by the magneticdipole source in the homogeneous formation are derived. It can verify the effectiveness of the3D numerical calculation method studied in follow. The tool calibration theory is studied，including the calibration environment and the calibration method.Secondly，a3D numerical calculation method to calculate the half-space response of theMIT based on the Comsol Multiphysics is studied. The design of the physical model，thedetermination of the solving regional，the addition of the material parameter，the boundarycondition and the reasonable the mesh generation，all of these works make sure the latercomputation is accuracy. The half-space responses are calculated in three statements: the tool ishorizontal，vertical and bias. The different heights，different earth conductivities and differentsource frequencies are considered. The distribution characters of the electromagnetic field areexplained. The horizontal statement is emphasized. Finally，the half-space response data base of the MIT is built. According to the feature ofthe data base，we put forward a new calibration correction method to eliminate the influence ofthe earth conductivity. Its effectiveness is verified by the actual measuring and comparing withthe result of the experiment.