复杂场源形态的海洋可控源电磁三维正演  

Three-dimensional forward modeling of the marine controlled-source electromagnetic field with complex source geometries

作　　者：韩波[1,2] 胡祥云[1] Adam SCHULTZ 左博新[1] 李建慧[1] 蔡建超[1] 

机构地区：[1]中国地质大学(武汉)地球物理与空间信息学院,武汉430074 [2]俄勒冈州立大学地球与海洋与大气科学学院

出　　处：《地球物理学报》2015年第3期1059-1071,共13页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41274077;41474055);中国地质调查局项目(12120113101800)联合资助

摘　　要：在使用电偶极发射源的可控源电磁法(CSEM)勘探中,发射源的方位、长度、形状等对观测数据有重要的影响,然而现有的大部分三维数值模拟方法没有全面地将这些因素考虑进来,很多都只能应对非常简单的场源形态,例如单一方位的点电偶极子,这有可能显著降低模拟结果的准确性.本文实现了基于交错网格有限体积(FV)离散的海洋CSEM三维正演算法,能够模拟形态相对复杂的场源,包括任意方位的有限长直导线和弯曲导线发射源.该算法使用一次场/二次场方法,只需对二次场使用FV法求解,避免了场源的奇异性问题;一次场的计算为一维正演问题,使用准解析法求解,并且只要在计算一次场时考虑复杂的场源形态便可以实现同样场源的三维正演.通过与一维理论模型的解析解对比验证了三维程序的准确性,并针对三维理论模型进行了一系列正演测试,初步考察了场源形态对三维正演结果的影响.In controlled-source electromagnetic（CSEM）surveys that utilize electric dipole sources,observations can be greatly influenced by the orientation,length and the shape of the source.However,most of the current 3DCSEM modeling algorithms do not take all these factors into account,and many are only able to deal with very simple source geometries such as a point dipole with a fixed orientation,which may cause significant inaccuracies in the modeling result.A3 Dforward modeling code for marine controlled-source electromagnetic（CSEM）surveys has been developed,which permits simulations of complex source geometries.The solution is based on a staggered-grid finite volume（FV）discretization of the secondorder Maxwell′s equations.The primary/secondary field approach,in which only the secondary fields need to be solved using the FV method,is employed to avoid the source singularity problem.To accurately compute the primary fields over an 1Dlayered background model,theopen source software Dipole1 Dis integrated into the 3Dcode.Due to Dipole1D′s versatility and the fact that the primary field calculation is the only part of the 3Dmodeling that directly handles the source geometry,the 3Dcode is capable of simulating arbitrarily orientated finite-length wire sources.The resulting linear system of FV equations is solved by the quasi-minimum residual（QMR）method.To validate the 3Dcode,we first benchmarked FV solutions against quasi-analytic solutions for a canonical 1D reservoir model.The numerical solutions show excellent agreement with analytic solutions for various transmitter orientations for both a point dipole source and a 300 m wire source.Then we calculated responses of a 3Dreservoir model similar to a well-studied one,varying horizontal sizes of the resistor.Reasonable results for the 3Dmodel,which are consistent with published work,can be observed.Further,a suite of numerical experiments on the 3Dmodel were conducted to investigate the influences of source geometries,and the observations include：（1�

关 键 词：海洋可控源电磁法 三维正演 有限长线源 场源形态 

分 类 号：P631[天文地球—地质矿产勘探]