Features Analysis of Borehole-surface Electromagnetic Monitoring in Shale Gas Reservoir Utilization Model
In order to meet the strategic demand of high efficiency and low cost development of shale gas resources in China,we need to develop a wide range of applications at low cost and high reliability of the reservoir subsurface electromagnetic monitoring technology.Bore-hole-surface electromagnetic monitoring technology helps to obtain and analyze potential a-nomalies caused by the electrical changes of underground media by supplying the power in borehole and monitoring the signal on the surface,and also contributes to understanding the features of surface potential distribution for borehole-surface electromagnetic monitoring.Therefore,this paper constructs several groups of shale gas reservoir models and uses the fi-nite element method to calculate and analyze the distribution features of surface potential a-nomalies under different models.The numerical experimental results show that:① the sur-face maximum potential anomaly center does not correspond to the surface projection position of the center of the low resistance body;② With the increase of burial depth,the anomaly contour changes,and the low value zone in the measuring area also changes,and the overall anomaly amplitude gradually decreases;③ Low-resistivity bodies with different electrical features cause different surface potential abnormal response features after entering the reser-voir.The smaller the relative background resistivity of low-resistivity bodies,the higher the amplitude of surface anomalies,and the more favorable it is for electromagnetic monitoring.@The features of surface potential anomalies are significantly affected by the changes in the size and location of the low-resistance body.When the size of the low-resistance body is small,the abnormal contour line is approximately circular.As the size of the low-resistance body increases,the amplitude of the potential anomaly increases and the contour line shape changes.After analyzing the abnormal distribution characteristics of surface pure potential in borehole-surface electromagnetic monitoring of shale gas reservoir,this paper verifies the feasibility of borehole-surface electromagnetic monitoring method of shale gas reservoir pro-duction to a certain extent,and provides theoretical support for shale gas reservoir produc-tion monitoring in China.
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