Well-ground Potential Modeling Constraint-based Electrical Logging

Through supplying power current to the underground from metal casing in the wells as the excitation source and measuring the potential distribution of surface or borehole, well-ground potential method is a geophysical exploration that study the influence the changes in underground geologic body on the distribution of the electric field on the ground or underground electric. This method is a technical means that study the residual oil distribution of high water-cut stage in an oilfield and concealed deposits exploration of crisis mines in the deep edge. In addition, well-ground method also has certain guiding meaning in hydrogeology, geological exploration and other fields. Resistivity logging is a kind of logging methods that measure the resistivity of the formation in a certain range of the underground by putting electrode system into the wells and recorde formation resistivity variations with depth continuously with automatic logging instruments. The recorded curve is called resistivity curve that study geological section where drilling crossed and the division of oil, gas and water layer. The main contents of this paper is based on modeling technology of well-ground potential constrained by electric logging. Providing some artificial constraints to the inversion work of well-ground potential is in order to improve the retrieval accuracy.In this paper, we took measured electric logging curve in the area to be studied as starting point. First, measured electric logging curve was denoised with EMD soft threshold. And then we made electric logging curve achieved computerized automatic zonation using variance analysis and extreme variance stratification, programed corresponding composition. On this basis, using bi-cubic B-spline interpolation surface, we formated surface reconstruction of hierarchical processed data based finite strip electric logs. Using inverse distance weighting interpolation method, We obtained the resistivity of surface reconstruction. Finally, target layer to be studied was subdivised of space grid. The subdivised grid and grid nodes were endowed initial resistivity according the resistivity of the upper and lower layers in the target layer. We modeled according to computerized automatic zonation of the electric logging curve in the area studied by well-ground potential method, and obtained three-dimensional resistivity distribution of the target area, what provided some artificial constraint to the inversion of well-ground potential. Research work provided some basis and research direction to improving the retrieval precision of well-ground potential method. It also had a certain significance in the production practice simultaneously.