1D Forward Modeling And Inversion Of The CSAMT Signal Incorporation IP Effect

Controlled source audio-frequency magnetotelluric method(CSAMT) which is an artificial source method of frequency domain exploration, can effectively complete the detailed survey of underground electrical structure, so it has been widely used in the oil and gas exploration, metal ore prospecting, geothermal development, hydrological environment, and so on.Effects of induced polarization(IP), also known as IP effect, which is a inherent electrochemical properties of different rock, ore in the ground, is a kind of phenomenon, when is excited by the time domain or frequency domain source produced by people. CSAMT, as a kind of frequency domain and artificial active source exploration method, mainly observes electromagnetic effects in the practical field measurement, so the influence of the IP effects have not been taken into account. And in the basic theory of controlled source audio-frequency magnetotelluric method, the uniform layer resistivity of the formation is regarded as real numbers ignoring the frequency. Actually, considering IP effect, the resistivity of the various rock and mineral composition in the formation is a complex resistivity that is related to the frequency, rock ore,chemical composition and so on. Using a real number resistivity instead of a complex number resistivity in the calculation of the apparent resistivity and phase, will surely lead to a deviation in contrast to the actual situation, and the detection accuracy is reduced. In this paper, we adopt the Cole-Cole model for the IP effects research.First of all, according to the maxwell's equations, we deduce the electromagnetic field excited by the electric dipole in the uniform horizontal layered earth, select the appropriate digital filter coefficients for implementing one-dimensional procedure of the CSAMT forward modeling, and analyze the influence of the different model parameters on the results of the CSAMT forward modeling based on the Cole-Cole model. By the forward modeling, the response characteristics of the different horizontal layered geoelectric models containing the IP effects is analyzed and summarized. Using the adaptive regularization inversion method, we has realized the one-dimensional inversion in order to get the IP information in the CSAMT, and analyze and discuss the inversion results of different models.Studying the IP effects in the CSAMT, can obtain the IP information in the deep layers contrast with the conventional induced polarization method. Then according to the electrical structure characteristics of the layers, we can get multiple parameter information for the later explanation in the deep prospecting and petroleum gas exploration, and it is helpful to improve the CSAMT interpretation accuracy and resolution in the practical application. To study the influence of the IP effect in the CSAMT, can provide some references to get the IP information for the MT, AMT and TEM method, and expand the application scope of the electromagnetic methods.