Resistivity tomography with a vertical line current source and its applications to the evaluation of residual oil saturation

The forward and inversion methods of resistivity tomography with a vertical line current source (RTVLCS) were introduced in this paper. The technique was applied to the evaluation of residual oil saturation of the reservoir studied in an old oil region. The observed water saturation during the course of the measurement of RTVLCS and subsequent drilling records proved the reliability of our result. However, our model has not included the influence of all factors such as electrical contact resistance between the metal casing and surrounding rocks and of the size of the metal cased well taken as a vertical line current source (VLCS). In addition, RTVLCS was carried out after the well had been in use for many years, while the initial resistivity values used in the inversion were obtained from the resistivity curve logged upon the completion of the well. Therefore, the residual oil saturation obtained by RTVLCS is relative and has not complete consistency with real situations, and can only be used as reference for adjusting a plan for oil production in the mid- or post-phase of an oilfield.