Using Numerical Simulation of Electrokinetic Potentials in Geothermal Reservoir Management

Abstract

Software has recently been developed to calculate space/time distributions of electrokinetic potentials resulting from histories of underground conditions (pressure, temperature, vapor saturation, concentration of dissolved species, flow rate, etc.) computed by unsteady multidimensional geothermal reservoir simulations (Ishido and Pritchett, 1999). The ìEKP postprocessorî can be applied to ìhistory-matchingî of self-potential (SP) data since SP changes are caused principally by electrokinetic effects, particularly in the early stages of field exploitation. To assess the feasibility of using repeat SP surveys for reservoir monitoring, we carried out numerical simulations based on a mathematical model of a moderate-temperature two-phase reservoir. The results confirm the electrokinetic origin of production-induced changes in SP proposed by Ishido et al. (1989), and show that SP will respond to field-wide flow rate changes rapidly (within a month or so). This suggests that frequently-repeated SP surveys and/or continuous SP monitoring at times of flow rate changes will provide useful supplementary data for reservoir management.