Numerical Simulation For Low-frequency Near-field Problems Based On Volume Integral Equation

As an important part of geography exploration,electromagnetic measurement while drilling is a typical low-frequency near-field problem.In the application of oil drilling and coalbed meth ane exploration,EM-MWD signal wireless transmission technology is responsible for the downhole monitoring work and realising real-time communication between underground and ground which means a lot to the drilling control system.Because of the complicate and lossy layers,electronics waves fade very quickly,how to construct a reliable and accurate physical model is very important.To solve the EM-MWD modeling and numerical stimulation problem,this paper has done some work,which is divided into six parts:In the first chapter,the classification of MWD technology and the development history,present situation and research value of EM-MWD system is introduced.Also the main contents and structure of this paper is stated.The second chapter illustrates the principle of the VSIE and process of Mo M method,which includes geometry modeling,chosing basis functions,calculating the impedance matrix elements and finally solving the linear equations;the method of numerical integration,singularity processing and iteration methods are stated.The third chapter introduces the multi-layer adaptive crossing method,including it’s basic principles and process in details.MLACA is useful to solve the computer memory and iteration steps problem which are caused by the massive unknown number in Mo M.The fourth chapter is the key content of this paper, after the comparison of several commonly used EM-MWD numerical modeling methods,the new numerical model based on the integral equation method is set up. This paper choses the vertical asymmetric gap voltage excitation as feed mode,through theoretical derivation the Finite-Gap voltage source model is established.In the end, some numerical examples are presented to verify this new EM-MWD model.The fifth chapter is the numerical analysis part.By analysising some important parameters of EM-MWD technology,such as the formation conductivity,size of drilling pile and working frequency,some conclusions are presented.