Study on response characteristics of well ground induced polarization method in electrical anisotropic media based on unstructured finite element method
The method of stimulated polarization in wells has been widely used in deep-searching,oil and gas resources exploration and water resources exploration because it possesses high working efficiency and good exploration effect.At present,the well-ground excitation polarization method of the relevant studies are the subsurface medium is assumed to be isotropic,but the actual electrical characteristics of the earth medium is anisotropic is the existence of anisotropy,this time based on the isotropic model of the traditional imaging and inverse imaging technology is no longer applicable to the anisotropic data processing and interpretation.In order to analyze the influence law of anisotropic features on the well-surface excited polarization method,In this paper,we carry out the research on the anisotropic orthogonal algorithm of conductivity and polarizability in different main axis directions based on the finite cell method.Marginal and variational problems for the steady current field under the anomalous potential method are derived from the partial differential equations and boundary conditions satisfied by the point-source field to realize three-dimensional orthogonal simulations of the well ground excitation polarization method for anisotropic media.The effectiveness and correctness of the algorithm is verified by testing and comparing the complex 3D isotropic model and 3D anisotropic model.A typical anisotropic geological model was constructed to analyze the effect of anisotropic anomalies of conductivity and polarizability in different principal axis directions on the polarization response of well-surface excitation.The results show that x-spindle conductivity anisotropy leads to an increase in the apparent resistivity response and an enhancement of its apparent polarizability response.Both y-and z-axis conductivity anisotropy show strong sensitivity in visual polarizability,x-axis polarizability anisotropy results in a diminished apparent polarizability response of the anomaly while polarizability anisotropy changes in the y-and z-axis directions are insensitive.When the conductivity and polarizability are anisotropic in the y-axis and z-axis directions,the sensitivity of the response change in the apparent polarizability is low,and the response change in the x-axis direction is more sensitive.This study not only facilitates the understanding of the law of the influence of anisotropy on the excitation in wells,but also can provide theoretical support for the data interpretation of the excitation data in wells considering anisotropy.
Well ground induced polarization methodAnisotropyFinite element analysisAbnormal potential method3D forward modeling
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