3D FEM Forward Modeling Research Of Borehole-to-surface DC Method Drived By The Arbitray Linear Current Source

Borehole-surface DC method is a effective technique to predict and analyze the distribution of the residual oil in high water cut oil field, it can solve some problems that can't be solved by traditional well logging and seismic methods.furthermore it play a important role in the exploration of the metalmine, hydrologic geology,engineering geology and environmental geology. There are three key problem in the research on the borehole-surface DC method: the instrument research , the 3D forward modeling research and the 3D inversion imaging research. In this thesis, it mainly focus on the studying process of the 3D finite element forward model of borehole-surface DC method about arbitrary shape linear current sources.We elaborate the basic theory on 3D geo-electric field of arbitrary shape linear current sources, after that, the normal potential formula of any point in the semi-underground space drived by the arbitrary shape linear current sources has been fetched, and this formula is more perfect than the achievements obtained by predecessors. In the course of simulation, the influence of singularity in vicinity of linear current source was eliminated through decomposing total potential into two part: abnormal potential and normal potential. Through a series of deduction and transformation, the energy functional expression on the variation problem of the arbitrary shape linear current sources abnormal potential can be obtained which is the foundation of the finite element numerical calculation. Furthermore,we discuss the 3D finite element numerical calculation of arbitrary shape linear current sources whose the conductivity varies continuously in each block. In view of the features of the linear equations coefficient matrix formed in the finite element method, the effective and stable solving method can be obtained through applying SSOR-PCG (the symmetrical super relaxation preconditioned conjugate gradient method and the compressed sparse row technique ) combined with CSR (compressed sparse row) technique. The arbitrary shape casings of the pumping well or injection well exist in oil field, such as vertical, inclined, horizontal, ( herringbone) multiple branch well, water injection steel tube and petroleum pipeline et al, especially, the multiple branch well has been widely applied in the oil field in recent years, we have researched the forward modeling of many arbitrary shape casing and some typical oil&gas accumulation geological model and the influence of the nonhomogeneous discharge at cement bonding and perforated interval ,then get the corresponding abnormal response with the respective characteristic. These results shows it is necessary to select the real linear source and fellow the actual situation of the nonhomogeneous discharge to design survey system and to carry out the forward modeling. We also discuss an impact of the model parameters (bury depth , scale size , thickness , resistivity difference)over result. All of these result can help to design the scientific and economical exploitation plan and establish a basis for the inversion imaging. We implemented some operators on the contour diagram and get some useful result, this method is able to make the abnormal characteristic especially notable , it is able to make abnormal border especially distinct. These results can help us to confirm the bound and position of oil&gas accumulation geological anomalies more easily.