Steam-Water Capillary Pressure

Steam-water capillary pressure is of central importance in geothermal reservoir engineering, however it is still poorly known due to the difficulty making direct measurements. To this end, we have conducted experimental and theoretical studies over the past five years and have made significant progress in understanding fundamental steamwater flow. In this paper, we summarize and discuss the results. Methods to measure steam-water and air-water capillary pressures were developed using an X-ray CT scanner. Both steam-water and air-water capillary pressures were measured and compared. It was found that there are significant differences between steam-water and air-water capillary pressures. So we may not substitute air-water capillary pressure data in steam-water flow calculations. Using data measured from steady-state steam-water flow, an empirical model was developed to calculate steam-water capillary pressure directly. The only required reservoir parameters are porosity, permeability, and temperature. Also developed was a generalized capillary pressure model from fractal modeling of a porous medium. The model encompasses the frequently used Brooks-Corey model and the Li-Horne model. This also demonstrates that the two models, both of which have been considered as empirical, have a solid theoretical basis. We also showed that steamwater relative permeability could be calculated from capillary pressure based on a generalized relative permeability model, which is derived from the generalized capillary pressure model.