井间视电阻率的几何成像方法

Geometry image method of crosshole apparent resistivity

基于非全空间直流电场的原理,采用镜像法推导出有别于半空间和全空间的视电阻率计算公式,求出与所有电位对应的视电阻率;以观测井深为纵坐标、供电井深为横坐标绘制视电阻率等值线图,由此得出井间异常体的影像图;应用三维三线性插值有限单元正演模拟方法,计算并分析几种典型的地质模型。研究结果表明:由视电阻率等值线形态能够判断异常体的空间形态和正确位置,但井间低阻体表现为高视电阻率异常,井间高阻体表现为低视电阻率异常;采用该方法所得垂向分辨率较高,确定深度较准确,但不能得出地层真电阻率。

Based on the theory of direct-current electric field in non-full space,the apparent resistivity formula that is different from half space and full space was deduced by the image method,and all apparent resistivities were determined,then the apparent resistivity isopleth map was drawn,in which observation hole depth was ordinate and power-supply hole depth was abscissa. At last,several typical geologic models were simulated by three-dimensional finite element method. The results show that the space shape and precise position of abnormity body can be judged from apparent resistivity isoline shape,but crosshole low resistivity body reflects high apparent resistivity abnormity and crosshole high resistivity body reflects low apparent resistivity abnormity. This method has high resolution in perpendicular direction,and can accurately ascertain the depth,but real resistivity of stratum can＇t be obtained.