Research On Fast Forward And Inversion Algorithms For 2.5D MCSEM Data

In the 21 st century,more and more attention has been paid to the development of marine resources,and the exploration of petroleum resources by energy-powered countries has shifted from land to sea.Three-dimensional seismic exploration is one of the important methods to understand the submarine stratum structure,but people are not satisfied with obtaining an accurate understanding of the submarine structure and want to know the nature of the fluid in the reservoir.In order to improve the success rate of drilling and save costs,the marine controlled source electromagnetic method has attracted people's attention due to its unique advantages.It can effectively detect the difference in resistivity between the reservoir and the surrounding rock.Now the equipment and methods of the marine controlled electromagnetic method have made many achievements,especially in the forward simulation and inversion interpretation,many researchers have done research on it.At present,China's research in these fields is still relatively backward.This paper mainly studies the forward and inversion of the marine controlled source electromagnetic method,and analyzes the results of forward and inversion.In the forward part,the potential field function in the layered medium excited by the horizontal electric dipole source is derived,and a one-dimensional forward simulation is performed.Based on this,it can be concluded that when the offset is twice the depth of the oil and gas layer,the receiver mainly receives the target echo.Expand Maxwell's equations to derive the coupled equations of electric and magnetic fields under 2.5D.Then use Galerking weighted residual method to get the finite element equations.The2.5D forward modeling was performed using the finite element method.Based on this,the influencing factors affecting the forward response characteristics of the marine controlled source electromagnetic method are analyzed.The high-resistance model and the low-resistance model are designed separately to analyze the forward response characteristics of the ocean's controllable source electromagnetics,and at the same time analyze the influence of the graben terrain on the electromagnetic field of high-resistance oil and gas reservoirs.The inversion part mainly grasps the basic theory of inversion and commonly used inversion methods.Finally,the Gauss-Newton method is used to inverse the high-resistance thin-layer oil and gas reservoirs and low-resistance reservoirs and analyze the results.Through inversion,the morphological distribution and resistivity values of the submarine target body can be roughly obtained.It is believed that the inversion code can achieve the effect of preliminary application.