Basic Principle And Method Study Of Electromagnetic Induction Remote Detection

As more and more oil fields enter the middle and later stage of development,drilling and logging techniques have been developed rapidly in order to detect more subtle reservoirs.At the same time,some new challenges have emerged,such as the analysis of induction logging response characteristics in highly deviated and horizontal wells and the influence of anisotropy and measurement of resistivity of anisotropy layer,the evaluation and design of new logging instruments are becoming more and more important.It was proved that the multi-component low-frequency electromagnetic induction detection method can effectively detect the abnormal conductivity area around the well,and its detection depth is also improved.In the process of detection,the instrument parameters are optimized continuously,and the results can provide effective reference for the design of detection instruments.The work of this paper is based on the above background.The research includes not only electromagnetic induction and electromagnetic wave propagation logging in heterogeneous media,but also the design of numerical calculation algorithm and different formation models.The numerical algorithms involved are mainly volume fraction equation and BCGS algorithm.The expression of the induction electromotive intensity and magnetic field intensity at the receiving coil are deduced based on the Maxwell equations.Then the expression of the volume component equation for the magnetic field intensity vector at the receiving coil is given.The derivation of dyadic green's function is given subsequently.Finally,the abnormal area of conductivity is discrete and iterated unceasingly,the magnetic field intensity and induced electromotive intensity in a single well are solved by using integral equation.In this paper,a long coil distance electromagnetic induction logging tool is used to detect the electrical conductivity abnormal body at a distance from the borehole.We present different formation models,including horizontal stratigraphic model,two-dimensional conductivity abnormal body model and three-dimensional conductivity abnormal body model.In particular,in the forward modeling of three-dimensional multi-component induction logging,not only the model of block conductivity abnormal body is considered,but also the model of fractured conductivity abnormal body is numerically simulated.By analyzing the response characteristics of various formation models,we find that the proportion of scattered signals in the received signals increases with the increase of coil spacing and detection depth.By analyzing the real and imaginary parts of different components,the existence of conductivity abnormal body can be preliminarily judged.However,as the total signal strength is also decreasing,accurate positioning cannot be achieved.Therefore,in order to detect the existence of the conductivity abnormal body,the appropriate frequency and coil distance should be selected according to the distance between the abnormal body and the borehole,and the scattering signal strength should be improved by improving the transmitting and receiving strength of the coil.Finally,the numerical results are analyzed comprehensively,and the feasibility and superiority of the method are discussed by comparing the results of different parameter designs.This paper provides a theoretical basis for instrument parameter design in oilfield development and makes a new theoretical contribution to electromagnetic induction logging theory.