Application of MT and WFEM two-dimensional joint inversion in Datong geothermal area, Shanxi Province
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摘要:
地热能凭借其稳定性、经济性等优势已成为新型清洁能源体系构建的关键方向。电磁法作为解析地热系统电性结构的核心地球物理手段，其方法体系呈现显著互补特征：大地电磁法（magnetotelluric，简称MT）利用天然交变电磁场，具有探测深度大、对深部低阻异常体灵敏等特点，但极易受到电磁环境噪声的影响；广域电磁法（wide-field electromagnetic method，简称WFEM）采用人工场源，抗干扰性能强、对浅部异常体及细小断裂分辨率较高。为充分发挥MT和WFEM的优势互补效应，采用二维联合反演方法，探讨了MT与WFEM联合反演在地热勘探过程中的可行性和有效性。理论模型合成数据测试表明，相比于单独反演结果，MT与WFEM二维联合反演能够更为清晰地刻画地热系统的盖层及热储层分布特征。最后，对山西大同地热区实测MT及WFEM数据分别单独反演和联合反演，并进行了对比分析。研究结果显示联合反演结果要显著优于MT或WFEM单独反演结果，有助于圈定出地热系统的重要组成部分。根据联合反演所得的电阻率分布结构，结合测区地质及其他资料，推断出了该地区地热系统的概念模型。
Abstract:Objective Geothermal energy, owing to its stability and economic advantages, has become a crucial direction in the construction of new clean energy systems.
Methods Electromagnetic methods are core geophysical techniques for resolving the electrical structure of geothermal systems and exhibit distinct complementary features. The magnetotelluric (MT) method uses natural alternating electromagnetic fields with the advantages of high detection depth and sensitivity to deep low resistance bodies, but it is susceptible to the influence of electromagnetic environmental noise. Wide-field electromagnetic method(WFEM) utilizes artificial field sources, exhibiting strong anti-interference capabilities and showing higher resolution for shallow anomalous bodies and small fractures. This study explores the complementarity and effectiveness of MT and WFEM in geothermal exploration through a two-dimensional joint inversion method.
Results Theoretical models and synthetic data tests have shown that two-dimensional joint inversion combines the respective advantages of MT and WFEM, and can more clearly characterize the cap rock and thermal reservoir structure of geothermal systems. This paper conducted a joint inversion study on the measured data of MT and WFEM in a geothermal area in Datong, Shanxi, China. The results showed that the resistivity distribution obtained from the joint inversion clearly characterized shallow fault channels and deep thermal reservoirs.
Conclusion Based on the resistivity structure model obtained from joint inversion and other geological data, a conceptual model of the geothermal system in the region was constructued, providing a reference basis for the precise exploration of geothermal resources in the future.
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图 2 单独反演与联合反演的数据RMS收敛曲线
Figure 2. RMS convergence curve of data for individual inversion and joint inversion
图 5 2个代表性点的大地电磁观测数据视电阻率和相位曲线
Figure 5. Apparent resistivity and phase curve of MT observation data from two representative points
图 6 2个代表性点的广域电磁观测数据振幅−频率曲线图
Figure 6. Amplitude-frequency curve of WFEM observation data from two representative points
图 8 大地电磁单独反演时TE极化模式视电阻率拟断面图
Figure 8. Apparent resistivity pseudo section of TE polarization mode during MT individual inversion
图 9 大地电磁单独反演时TM极化模式视电阻率拟断面图
Figure 9. Apparent resistivity pseudo section of TM polarization mode during MT individual inversion
图 10 广域电磁单独反演时电场数据拟断面图
Figure 10. Pseudo section of electric field data during WFEM individual inversion
图 11 实测数据单独反演与联合反演平均拟合误差分布曲线图
Figure 11. Distribution curves of average fitting error for individual inversion and joint inversion of measured data
图 13 研究区地电解译模型
Q. 第四系；N2. 上新统；Ar. 太古宇；下同
Figure 13. Geoelectric and geological model of the study area
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