Title

Magnetotelluric modeling based on a two-dimensional induced-polarization geothermal reservoir model and its response characteristics analysis

单位

(1.中国石油化工股份有限公司石油物探技术研究院,江苏南京211103;2.中国地质大学地球物理与空间信息学院,湖北武汉430074;3.长江大学油气资源与勘探技术教育部重点实验室,湖北武汉430100)

Organization

(1.Sinopec Geophysical Research Institute,Nanjing 211103,China;2.Institute of Geophysics and Geomatics,China University of Geosciences,Wuhan 430074,China;3.Key Laboratory of Exploration Technologies for Oil and Gas Resources,Yangtze University,Wuhan 430100,China)

摘要

储层岩石在低频电磁场作用下,会同时发生电磁感应和激电效应。为解决目前深层地热大地电磁(MT)勘探以单一电阻率作为解释参数的局限性,以及温度与激电参数间关系不明确等问题,有必要开展基于深层热储激电模型的MT响应特征研究。从Maxwell方程组出发,基于MT正演理论,引入Cole-Cole复电阻率模型,实现了二维激电介质的有限差分MT正演。对比二维MT有限差分正演与一维解析解结果,验证了算法的正确性。结合岩石电阻率与温度经验关系,开展了不同激电模型条件下二维MT正演模拟。分析不同激电参数对深层热储视电阻率与相位的响应特征,发现极化率参数引起的激电响应比时间常数和频率相关系数明显,且H偏振(TM)模式对激电参数的反应灵敏度优于E偏振(TE)模式。建议在实际深层地热MT勘探中,采用TM极化模式进行资料反演,并以电阻率和极化率两种参数联合解释,有助于提高地热勘探与热储评价效果。

Abstract

Electromagnetic induction and induced polarization (IP) effects occur simultaneously in reservoir rocks in response to a low-frequency electromagnetic field.Owing to the limitations of the current deep geothermal magnetotelluric (MT) exploration technique (which only uses resistivity as the interpretation parameter) and the unclear relationship between temperature and IP parameters,research on the characteristics of the MT response based on deep geothermal reservoir IP models is warranted.In this study,based on the Maxwell equations and the MT forward theory,finite-difference MT forward modeling was realized for an IP two-dimensional (2D) medium by introducing the Cole-Cole complex resistivity model.The accuracy of the proposed algorithm was verified by comparing the model results with one-dimensional analytical solutions.With the aid of an empirical relationship between rock resistivity and temperature,2D MT forward modeling was also performed for different IP models.By analyzing the response characteristics of the apparent resistivity and phase,it was found that the IP response caused by the polarizability parameter was more evident than those caused by the time constant and the frequency correlation coefficient,and the sensitivity of the TM mode to the IP parameters was higher than that of the TE mode.It is suggested that the TM mode should be used for data inversion in actual deep geothermal MT exploration,and the resistivity and polarizability should both be accounted for during data interpretation to improve the effectiveness and reliability of geothermal reservoir prospection and evaluation.

关键词：

大地电磁; 地热储层; 激电模型; 电阻率; 极化率; 正演; 响应特征;

Keywords:

magnetotellurics;; geothermal reservoir;; IP model;; resistivity;; polarizability;; forwarding;; response characteristics;

基金项目

国家自然科学基金项目(41774082)和国家重点研发计划项目(2019YFC0604902)共同资助。

DOI

10.3969/j.issn.1000-1441.2021.06.016

二维热储激电模型的大地电磁模拟及其响应特征分析