Research On Forward And Inversion Method Of Electromagnetic Wave Resistivity Logging While Drilling

With the development of drilling wells into complex wells such as horizontal wells in high-angle wells,traditional wireline logging technology is far from meeting the development and demand of the petroleum industry.It has high measurement accuracy and more accurate and accurate measurement while drilling.Technology has become the trend today.This paper mainly studies the fast forward and inversion method of electromagnetic wave resistivity logging while drilling.Based on COMSOL finite element software,the different formation models are constructed,and the electromagnetic wave resistivity log response database is built.The response characteristics of different influencing factors are analyzed.The library's inversion method is verified using actual log curves.Provide theoretical support for electromagnetic wave resistivity logging interpretation while drilling.The main research results are divided into the following four parts:The first part studies the three-dimensional numerical calculation of the electromagnetic wave resistivity log while drilling.The parameters and calculation principle of the electromagnetic wave resistivity logging tool while drilling are analyzed.The three-layer model is constructed based on COMSOL finite element software.The data post-processing problem and the calibration problem are studied.The calculation formula of amplitude ratio and phase difference is given.The calculation of the conversion conductance is calculated.The scale method of the rate indicates that the depth and scale scale curves of the instrument based on the existing source distance and frequency are separated,and the phase scale curve separation is small.The second part studies the response characteristics of electromagnetic wave resistivity logging while drilling.Calculate and analyze the logging response when factors such as caliper,eccentricity,surrounding rock,depth of investigation,intrusion and dip angle change,and establish corresponding models for different influencing factors.Analyze the influence characteristics of electrical anisotropy in high dip formations.The results show that the influence of caliper and eccentricity is small.The thin layer of low-resistance surrounding rock is obviously separated,the thick layer is basically coincident;the high-resistance surrounding rock is opposite;the phase is ineffective in reflecting the contrast of the formationand intrusion conductivity;the intrusion effect of low-resistance surrounding rock is negligible,and the deeper the intrusion The more serious the impact;the angle of the "corner" is most obvious when the inclination is about 90 degrees;when the inclination is less than 20 degrees,it is mainly affected by the horizontal conductivity;when the inclination is greater than 80 degrees,it is mainly affected by the vertical conductivity;The third part establishes the information database and fast forward modeling of electromagnetic wave resistivity logging while drilling.The COMSOL model was constructed and verified to be reasonable,and the response characteristics of different target thicknesses,contrasts and dip angles were analyzed.The results show that when the layer thickness increases,the amplitude does not change much,the phase change is low,the surrounding rock increases,and the high-conducting surrounding rock decreases.When the contrast is less than1,the phase and amplitude decrease first and then decrease with the instrument motion,and the contrast is greater than 1.The time trajectory is opposite,and the greater the contrast,the more severe the "corner" effect.The fourth part studies the rapid inversion method of electromagnetic wave resistivity logging while drilling.The actual logging curve is used to verify the inversion method and the response characteristics of the actual logging curve are analyzed.The local layer resistivity is10 ?·m,and the response change is small;the local layer resistivity is 90 ?·m,and the phase difference does not reflect the surrounding rock information;the amplitude ratio can be used to identify the layer boundary.Long source distance amplitude changes can be used to invert layer boundaries.The measured signal varies approximately linearly with the resistivity of the target layer,which indicates that it is easy to find the optimal solution in the inversion.The inversion of the wellbore trajectory is from the center of the layer,and the result is consistent with the actual curve.