考虑激电效应的三维时移大地电磁法正演研究  

Forward modeling study of three-dimensional time-lapse magnetotelluric method considering induced polarization effect

作　　者：代博帅 黄鑫[1] 曹晓月 严良俊[1] 谢兴兵[1] DAI BoShuai;HUANG Xin;CAO XiaoYue;YAN LiangJun;XIE XingBing(Key Laboratory of Exploration Technologies for Oil and Gas Resources,Ministry of Education,Yangtze University,Wuhan 430100,China)

机构地区：[1]油气资源与勘探技术教育部重点实验室(长江大学),武汉430100

出　　处：《地球物理学进展》2024年第4期1565-1585,共21页Progress in Geophysics

基　　金：国家自然科学基金(42374096,42030805,42274103);湖北省自然科学基金面上项目(2022CFB229);油气资源与勘探技术教育部重点实验室(长江大学)青年团队项目(PI2023-02)联合资助。

摘　　要：大地电磁法是一种广泛应用于油气资源领域的勘探方法,时移大地电磁法通过观测地下电性构造和界面,随时间的变化引起的时变大地电磁响应,进而实现对油藏动态分布和界面变化监测.传统时移大地电磁法监测模拟是基于各向同性理论和规则网格,然而储层的激电效应广泛存在,忽略激电效应会对油藏动态监测带来解释误差和困难,对复杂地形和油藏开发后期高含水具有激电效应的非常规油气储层适用性差.为了解决以上问题,本文首先引入Cole-Cole复电阻率模型表征储层介质的激电效应,结合基于非结构四面体单元的有限元实现了考虑激电效应的三维时移大地电磁算法.其次,通过考虑激电效应的一维模型解析解验证了本文三维算法正确性.然后,设置并分析了不同的激电参数变化对油气储层的特征响应,讨论了时移电磁监测的分辨能力.最后,设置理论模型和涪陵地区油藏模型分析储集油层驱替前后产生的时移电磁异常.研究表明:储层激电参数变化导致时移大地电磁测深响应差值明显,可用于推断出储集油层的时移变化过程.在油藏驱替的增进过程中不同模式的响应差值对驱替波及区边界的灵敏性不同,其中Δρaxy可以有效反映界面的x方向的变化,而Δρayx则反之.The Magnetotelluric(MT)method is widely used in the exploration of oil and gas resources.The time-lapse MT method can monitor reservoir dynamic distribution and interface changes by observing the time-lapse MT response caused by the change of underground electrical structures and interfaces.Traditional time-lapse MT methods monitoring simulation are based on isotropic theory and regular grids.However,the induced polarization(IP)effect is widely present in reservoirs,ignoring which can lead to interpretation errors and difficulties in time-lapse monitoring of reservoirs,especially for unconventional reservoirs with complex terrain and high water content in the later phases of development.First of all,in order to solve these problems,the Cole-Cole complex resistivity model is used in the vector Helmholtz equation to characterize the IP effect of the reservoir medium.Then,the vector Helmholtz equation discretized by the Galerkin finite element method with unstructured tetrahedral grids,has been implemented to a 3D time-lapse electromagnetic algorithm that considers the IP effect.Thirdly,the analytical solution of the ID model considering IP effect is used to verify the correctness of the 3D algorithm in this paper.Further,different IP parameter variations are set and analyzed to determine the characteristic responses of the reservoirs and discuss the resolution ability of the time-lapse electromagnetic monitoring.At last,a realistic reservoir model in the Fuling area is set up to analyze the time-lapse electromagnetic anomalies generated before and after the displacement of the reservoir.The results show that the significant differences in the time-lapse MT responses caused by changes in the IP parameters of the reservoir can be used to infer the time-lapse change process of the reservoir.In the process of reservoir displacement enhancement,the response difference is distinguished by the sensitivity to the boundary of the displacement swept region,where△ρxya can effectively respond to the change of the interface

关 键 词：时移大地电磁法 三维有限元法 激电效应 动态监测 

分 类 号：P631[天文地球—地质矿产勘探]