Research On 2-D Inversion Of Marine Controlled-source Electromagnetic Method

The appliacation of marine controlled-source electromagnetic(CSEM)to oil exploration has become the hotspot overseas.The CSEM method can be used to study the oceanic crust,the bottom of the ocean sediment distribution and exploration of offshore oil and gas.The CSEM method can detect the anomalies associated with hydrocarbon reservoir effectively utilizing the resistivity differences.The research of marine controlled source electromagnetic method is relatively mature in foreign countries,but the research of China's marine electromagnetic is lagging behind in our countries.Therefore,we should strengthen the research on numerical simulation and inversion method of CSEM.This paper analyzes the current development at home and abroad of CSEM forward and inversion in detail,and on this basis we obtained two-dimensional finite difference formation,described the difference principle under two-dimensional point source coordinate,the method of area discrete method and mesh generation method.Finally we completed marine CSEM 2D forward modeling.By using the 2D finite-difference forward modeling program,we simulate the different response of groundwater model.We contrast the different electromagnetic response under different depth,different emission frequency,different field components and different resistivity.We also contrast the electromagnetic response of the anticline,fault and buried hill oil reservoirs.On the basis of 2D forward modeling,we achieved nonlinear conjugate gradient inversion of CSEM method.Firstly,the nonlinear conjugate gradient method of CSEM is introduced,then achieve marine CSEM 2D inversion using nonlinear conjugate gradient method.We designed single prism model and anticline model,the results show that using the real and imaginary parts of horizontal electric field,we can inverse the specific location and resistivity of oil and gas reservoir,but the thickness deviation is a little big.We also do the inversion of the controlled source electromagnetic data,the results show that,the result of this paper consistent with the results of log and seismic.