Goethermal Reservoir Engineering: Performance Matching and Predicting

The initial conditions (physical and chemical state) of a geothermal reservoir and its fluids are important information needed in geothermal reservoir engineering for determining the future productivity of the reservoir. An optimization scheme was employed to minimize the least-squares function and determine the optimum initial conditions. Using the mass, energy, and volumetric balance equations, the initial parameters were obtained by matching the production data plot of average reservoir pressure versus cumulative mass produced for a compressed liquid, saturated liquid-steam, and superheated steam reservoir. Once a good curve match was attained, the performance projection of the geothermal reservoir was made at different production rates. A successful curve match was found to be highly dependent on the constraints chosen in the optimization scheme. Mass influx, as well as porosity also proved to be an influencing factor in the determination of the initial conditions. The computer prediction model is presently being used to assess reservoir conditions for the Hawaii Geothermal Project Well A, believed to be the hottest producing geothermal well in the world.