基于二次电场的可控源电磁法三维矢量有限元正演模拟  

Three-dimensional controlled-source electromagnetic forward modeling by edge-based finite element using secondary electric field

作　　者：汤文武[1,2,3] 李耀国 柳建新[2,3] 刘春明[2,3] 

机构地区：[1]东华理工大学放射性地质与勘探技术国防重点学科实验室,江西南昌330013 [2]中南大学地球科学与信息物理学院,湖南长沙410083 [3]有色资源与地质灾害探查湖南省重点实验室,湖南长沙410083 [4]Center for Gravity,Electrical & Magnetic Studies,Department of Geophysics,Colorado School of Mines

出　　处：《石油物探》2015年第6期665-673,共9页Geophysical Prospecting For Petroleum

基　　金：国家自然科学基金项目(41174103);国家高技术研究发展计划(863计划)项目(2014AA06A615);湖南省自然科学基金项目(2015JJ2151)联合资助

摘　　要：可控源电磁法作为地震勘探的重要补充手段,可通过研究地下介质电性的变化达到监测油藏的目的。为了从理论上研究可控源电磁法在油藏监测方面的应用前景,在前人研究的基础上,对三维可控源电磁法的正演模拟算法开展了进一步的研究。为克服场源附近总场变化快、基于总场求解时难以精确模拟的问题,采用均匀半空间或水平层状介质模拟的一次场作为场源;针对传统的节点型有限元模拟电场时存在散度条件不满足的问题,采用矢量有限元对基于二次电场的偏微分方程进行离散求解;多频点正演时引入频率适应网格,可以在保持正演精度的同时提高计算速度。对比3层电导率模型的有限元数值解与解析解,验证了算法的正确性。通过一个简单的油藏模型正演模拟,从理论上证明了可控源电磁法应用于油藏监测的可能性。As an important complementary tool for seismic survey, the controlled-source electromagnetic （EM） method can be used to monitor reservoirs by detecting the subsurface electrical properties. In order to investigate theoretically feasibility of monitoring reservoirs by the controlled-source EM, a requisite component is to calculate the EM responses of three-dimen- sional conductivity model excited by the EM sources. Total fields varies rapidly and is difficult to simulate accurately for the region adjacent to the source locations, to this end, the primary field is calculated for a half-space or a layered-earth model as the source term. To bypass the problem that the divergence condition is unsatisfied when using traditional nodal element to model the electrical field, the partial deferential equation （PDE） for the controlled-source EM, based on the secondary electric field,is solved discretely by the edge-based finite element method. To model the responses at multiple frequencies, the fre-quency-adaptive mesh can be used to increase the speed of forward calculation while maintaining the accuracy. The algorithm is verified by comparing the analytic solution with the numerical solution for a three-layered conductivity model The modeling re- sults of a simple reservoir model demonstrate the possibility of the controlled-source electromagnetic method in reservoir monitoring.

关 键 词：二次电场 可控源电磁法 矢量有限元 正演模拟 油藏监测 

分 类 号：P631[天文地球—地质矿产勘探]