Research On Forward Modeling And Inversion Of Vertical Line Source Borehole-Ground DC Method

Borehole-ground DC charged-body potential method refers to ground observing DC field produced by power supply line source in the exploitation well in order to prospect the boundary and orientation of hydrocarbon reservoir after analyzing DC field distribution. It found the method that can be used to dope out residual hydrocarbon and water boundary by researching the influence caused by the change of oil-water model.The numerical calculation software of 3D forward of vertical line source borehole-ground DC charged-body potential method uses steady current filed relation and finite difference principle. This work was developed based on Wang Zhigang's 3D forward of point source. Improving the older one, it adds some functions as followed: 1. Calculate vertical line source borehole-ground DC charged-body potential; 2. Split the simulation area irregularly; 3. Calculate several anomalous bodies'anomalous response; 4. Reduce the irregularity of the source. In addition, based on 3D forward algorithms, the Tarantola and Valette(1982)'s theory: the maximum likelihood inverse is introduced to our 3D resistivity inversion. Conjugate gradient relaxation technique is adopted to solve the maximum likelihood equations, then calculate the theory data and the field data respectively. It achieves the expectative results.After 3D numerical calculations, comparing the responses of low-resistivity anomalous bodies with different sizes at different depths and different time, it's found that the method can be used to dope out residual hydrocarbon and water boundary; comparing the responses of the lateral combined bodies and the vertical combined bodies, it's found that the method has a higher sensitivity of low-resistivity anomalous bodies than high-resistivity ones, and its lateral resolution is higher than vertical. Clearly, the sharp features of the conductive anomaly, such as the corners, cannot be resolved; however, the location, the average size, and the low-resistivity of the zone can be determined from the inversion.