Forward Numerical Simulation Of 2.5D DC Resistivity Between Wells

The electrical resistivity tomography technique is an important geophysical tool to detect the underground structure and widely applies in all kind of geophysical prospecting,such as mineral resource,oil-gas,engineering,hydrology,,archeology exploration,etc.Compared to the conventional resistivity method,the cross-hole resistivity image has a better resolution for the target with a certain depth because its current electrode is located below the surface. This method especially meets with the requirements of deep depth and high resolution of energy and resource exploration at present.Resolution of cross-hole electrical resistivity tomography technique is much better than surface technique for deeper objective, because the method of cross-hole was placed the current electrodes to the hole. But response apparent resistivity of cross-hole configuration relate with electrode array, depth and property of objective, and distance between the objective and the hole. Response apparent resistivity has the inherent complexity, and lead to many difficuties for processing and interpreting the information accurately.By using 2D cross hole finite element forward modeling and inversion on high resistivity horizontal tabulate body, low resistivity horizontal tabulate body,the response apparent resistivity characteristic are investigated detailedly and obtained important conclusions.There is great influence for observational result to choose the device type.The three-dimensional problems can be translated to the two-dimensional problems by the Fourier transform. By using the method of 2D bilinear interpolation and the Finite Element Method to calculate a series of model and analysis the effect of different geological spatial. From the result of forward modeling, when has two or more hole, single measurement can get a higher potential value and bipolar measurement can get more location information with lower potential value because of the value of potential difference.Besides,compared with condition of electric single-source-excited bipolar-source-excited has batter resolution capability about resistivity change.In theory, the method of polo-polo has the smallest observation data but can obtain maximum observation information.Meanwhile, through the geometry image method of cross-hole apparent resistivity to deal with the forward modeling date.The results show the space shape and precise position of abnormity body can be judged form apparent resistivity isoline shape. This method has high resolution in perpendicular direction, and can accurately ascertain the depth, but the transverse position of abnormity body can't be recognized.