1. School of Earth Science, Institute of Disaster Prevention Science and Technology, Langfang 065201, China 2. Data Processing Interpretation Center of Well-Tech, China Oilfield Services Limited, Langfang 065201, China 3. Department of Geological Survey, No. 203 Research Institute of CNNC, Xianyang 712000, China 4. Geophysics and Information Technology Academy, China University of Geosciences, Beijing 100083, China
The time-lapse resistivity method can be applied to engineering and environmental problems such as monitor groundwater contaminant transport, measure slope stability. In this paper, the normalized data inversion result of the time-lapse resistivity method was used to identify the subsurface structure of small resistivity changes. First, the data ratio normalization was adopted in which the initial data serve as the background data to normalize the data at other times. Next, the separate nonlinear conjugate gradients (NLCG) inversion result of initial data, time-lapse data and normalized time-lapse data were implemented. The same inverted parameters and homogenous half space model that was taken as the reference model were applied in all synthetic data examples. The inversion results show that the normalized data inversion results can effectively distinguish the small changes of resistivity relative to the background, but the conventional resistivity inversion almost cannot recognize it.
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