时移可控源音频大地电磁法三维反演研究

doi:10.19657/j.geoscience.1000-8527.2021.156

摘要/Abstract

摘要：

时移地球物理监测是观测地下物性参数随时间动态变化的有效方法。地球物理反演结果会受到测量误差、测量环境的噪声污染以及地球物理反演多解性等系统性因素的影响。如果对时移地球物理数据进行不同时刻数据的单独反演,可能会导致不同时刻的反演结果可对比性差,从而影响时移地球物理的监测效果。针对可控源音频大地电磁法在监测领域的实际需求,将不同时刻的观测数据放在一起反演,不同时刻的电阻率模型相互约束,实现了时移可控源音频大地电磁法三维反演。设计三种类型模型进行合成数据的单独反演和时移反演对比试算,验证了时移反演算法的有效性。反演结果表明:通过加入相邻时刻模型约束,时移反演可以更好地聚焦异常体的位置,降低噪声以及测量环境变化对反演结果的影响,防止反演伪影掩盖真实的地下变化。研究成果为时移可控源音频大地电磁法的实际应用奠定了良好基础。

关键词: 时移可控源音频大地电磁法, 有限内存拟牛顿反演, 时移约束

Abstract:

Time-lapse monitoring is an effective way to observe underground dynamic changes. Geophysical inversion results could be affected by systemic factors, including measurement errors, noise pollution in the studied environment, and the inversion ambiguity. If time-lapse geophysical data is inverted separately at different times, the results may have poor comparability, which would affect the monitoring of time-lapse geophysics. For the actual needs of the controlled-source audio frequency magnetotelluric (CSAMT) in the monitoring field, we integrated the observation data at different moments for inversion, and constructed resistivity models at different moments (mutually constrained) for three-dimensional inversion of the time-lapse CSAMT. Three types of models were designed to perform without time-lapse constraint inversion and time-lapse inversion comparison trial calculations of synthetic data, which verified the inversion algorithm and its effectiveness. The inversion results show that by adding adjacent time model constraints, the time-lapse controllable source inversion can better focus on the anomaly locations, reduce the noise impact and local environment changes, and minimize the impact of inversion artifacts. Our findings have laid a good foundation for the application of time-lapse CSAMT.

Key words: controlled-source audio-frequency magnetotellurics, limited-memory quasi-Newton method, time-lapse constraint

中图分类号:

P631.3

胡琪璇, 谭捍东, 于翠. 时移可控源音频大地电磁法三维反演研究[J]. 现代地质, 2023, 37(01): 90-98.

HU Qixuan, TAN Handong, YU Cui. 3D Inversion of Time-lapse Controlled Source Audio-frequency Magnetotellurics[J]. Geoscience, 2023, 37(01): 90-98.

图/表 10

图1 单网格剖分示意图

Fig.1 Schematic diagram for the single grid division

图2 时移反演流程示意图

Fig.2 Flow chart of the time-lapse inversion algorithm

图3 观测系统示意图

Fig.3 Schematic diagram for the observation system

图4 棱柱体电阻率随时间变化模型

Fig.4 Resistance variation model with changing time

图5 不同 β 值反演结果

Fig.5 Inversion results for the different β values

图6 t1/t2/t3 模型反演结果 (a) 反演结果电阻率值XOZ切片图,从上到下依次为时刻t1/t2/t3电阻率值示意图,左侧为单独反演,右侧为时移反演;(b) 反演结果电阻率值YOZ切片图,从上到下依次为时刻t1/t2/t3电阻率值示意图,左侧为单独反演,右侧为时移反演;(c) 反演结果电阻率差值XOZ切片图,从上到下依次为(t2-t1)/(t3-t2)/(t3-t1)电阻率差值示意图,左侧为单独反演,右侧为时移反演;(d) 反演结果电阻率差值YOZ切片图,从上到下依次为(t2-t1)/(t3-t2)/(t3-t1)电阻率差值示意图,左侧为单独反演,右侧为时移反演

Fig.6 Inversion results for the t1/t2/t3 model

图7 单个棱柱体延伸随时间变化模型

Fig.7 Model showing the height changes over time

图8 t2模型反演结果 (a) 单独反演t2模型的结果示意图,左图为XOZ切片图,右图为YOZ切片图;(b) 时移反演t2模型的结果示意图,左图为XOZ切片图,右图为YOZ切片图;(c)左图为XOZ切片深度100 m的电阻率折线图,右图为YOZ切片深度100 m的电阻率折线图

Fig.8 Inversion results for the t2model

图9 t2模型观测系统示意图

Fig.9 Schematic diagram for the t2 model observation system

图10 t2模型反演结果 (a)单独反演t2模型的结果示意图,左图为XOZ切片图,右图为YOZ切片图;(b) 时移反演t2模型的结果示意图,左图为XOZ切片图,右图为YOZ切片图;(c)左图为XOZ切片深度100 m的电阻率折线图,右图为YOZ切片深度100 m的电阻率折线图

Fig.10 Inversion results for the t2 3D time-lapse data

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