The Research Of Joint Inversion Of Marine Controlled Source Electromagnetic And Seismic

In the exploration and exploitation of oil and gas,accurate estimation of reservoir parameters based on geophysical data are very important.Seismic data can be used to get geological structural image and prediction of reservoir porosity accurately,but it is difficult to determine the fluid characteristics.On the contrary,although marine controlled source electromagnetic(CSEM)method cannot solve the problems related to geological structures.The resistance is very sensitive to the saturation of different fluid.Therefore,the marine controlled source electromagnetic method and seismic exploration can provide complementary information.This paper carried out the research of joint inversion in the both marine controlled source electromagnetic(CSEM)method and seismic full waveform inversion method constrained by reservoir structure to get the saturation and porosity of reservoir.Marine controlled-source electromagnetic method and seismic method obtain different kinds of geophysical properties data respectively.When these data apply to joint inversion they are supposed to be the same geophysical properties through petrophysical modeling.Due to the uncertainties of petrophysical model,we built petrophysical model based on statistical analysis.The relationship between porosity and resistivity can be given by Archie formula.linear relationships between the velocity of P-and S-wave and resistivity are derived and the impact of different pressure values on petrophysical models is also analyzed.The results show that velocity and resistivity of each sample increases with the increasing of pressure;and velocity and resistivity also have an approximate linear relationship under different pressure.According to petrophysical model,we established an adaptive regularization factor for objective function for joint inversing marine controlled source electromagnetic and seismic data,which is aimed to reservoir.The target function includes the model fitting item and model constraint item.So they make the regularization factor only relates to the last iteration value of the objective function.Then the weighted factor Q is introduced into controlling the proportion of regularization factor and model constraint in order to making the joint inversion process more stable.Based on 1D theoretical model we compare the advantages and disadvantages of the simulated annealing particle swarm algorithm and nonlinear conjugate gradient algorithm.The compared results showing that nonlinear conjugate gradient method can improve the retrieval speed effectively,thus this paper focuses on the research of joint inversion based on the nonlinear conjugate gradient method.Seismic wave filed gradient and the electromagnetic field gradient are derived.Well-logging constraint and the convergence criteria are also discussed.The results of separate inversion and joint inversion are compared based on the 2D theoretical model.The comparison results show that the joint inversion results are better than the separate inversion.Joint inversion can reflect the geophysical characters of reservoir accurately,which can reduce ambiguity in a large scale.Finally,we choose the practical data from the East China area to examine the joint inversion method,and the results prove that the joint inversion method of this paper can accurately determine reservoir parameters and improve the success rate of drilling.