基于VTI各向异性介质的频率域海洋可控源电磁三维约束反演

近年来,海洋可控源电磁法(MCSEM)被引入油气勘探领域以降低勘探风险.在海洋环境中,受沉积因素所造成的电阻率各向异性的影响,地电模型往往会非常复杂.为更好地反映地下电性结构,本文实现了基于VTI各向异性介质的频率域海洋可控源电磁三维反演.其中,正演采用基于Yee氏交错网格的三维有限差分算法,所形成的离散线性系统通过大规模并行矩阵直接求解器(MUMPS)进行求解.反演采用基于不等式约束的有限内存BFGS(L-BFGS)算法.最后,利用VTI各向异性介质合成数据,分别进行了电阻率各向异性覆盖层和电阻率各向异性高阻层的三维反演,结果表明:(1)基于并行直接法的MCSEM非常适用于海洋电磁所特有的多场源问题;(2)针对各向异性覆盖层模型进行三维各向异性约束反演,提高了解的可靠性;(3)针对电阻率各向异性高阻层,Inline和broadside数据覆盖的反演结果对异常体位置有很好的反映.

3D frequency-domain MCSEM constrained inversion in VTI media

Recently, frequency domain marine controlled source electromagnetic method(MCSEM) plays an increasingly important role in the oil and gas exploration. The geoelectric model tends to be very complicated due to the influence of resistivity anisotropy caused by deposition. To correctly interpret the sub-surface structure with the observed MCSEM data, it is desirable to develop three-dimensional anisotropy inversion algorithm. In order to accelerate the modeling speed of 3D model, we solve the linear system of finite difference equation by using the massively parallel solver MUMPS. This paper adopts L-BFGS algorithm for inversion. Finally, three-dimensional inversion of anisotropic covering layer and resistivity anisotropy resistive formation was carried out by using VTI anisotropic media synthesis data. The results illuminate that: (1) MCSEM based on parallel direct method is very suitable for multi-field source problem; (2) Three-dimensional anisotropic constrained inversion for the anisotropic cover model improved the reliability of the solution; (3) For anisotropic high resistivity model, the inversion of all lines recovers the reservoir much better than inversion of inline.