Calculation of borehole-to-surface electromagnetic responses on horizontal stratified earth medium
Cao Hui1, Wang Xuben1, He Zhanxiang2, Mao Lifeng1, Lv Dongwei1
1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu,Sichuan 610059,China;
2. GME and Geochemical Surveys,BGP Inc.,CNPC,Zhuozhou,Hebei 072751,China
Abstract：Borehole-to-surface electromagnetic forward modeling for 1D medium can be simplified as a calculation of electromagnetic response on earth surface exited by a vertical line current source with finite-length embedded in stratified medium.The field near the line current source cannot be seen as the response of a vertical electric dipole(VED) source.In order to calculate the electromagnetic fields on the earth surface,the integral formulation to calculate the fields of vertical fragmentation current source in each layer which contains current source is derived based on the Sommerfeld integral formal of magnetic potential of VED.Finally the electromagnetic fields of vertical line current source with arbitrary length can be obtained by way of superposing the electromagnetic fields of each fragmentation current source.The validity of the method is tested in this paper,and the computing time and the accuracy are compared with the results of the conventional approximate calculation method which discretizes the vertical finite-length current source into many small VEDs.The results show that this method is reliable and efficient.
