Systematic study of steam–water capillary pressure

Although steam–water capillary pressure is of central importance in geothermal reservoir engineering, it is nevertheless still poorly understood because of the difficulties involved in making direct measurements. To this end, we have conducted some experimental and theoretical studies. Unique methods have been developed to measure capillary pressures in order to overcome the complications in laboratory procedures associated with mass transfer as temperature and pressure changes. Both steam–water and air–water capillary pressures were measured and compared. Significant differences were found; in the cases studied, the steam–water capillary pressures were smaller. The drainage capillary pressure was greater than the imbibition capillary pressure, as was expected. Using experimental data, an empirical model was derived to calculate steam-water capillary pressure directly. Also developed was a generalized capillary pressure model based on fractal modeling of a porous medium; it encompasses the frequently used Brooks–Corey model (Brooks, R.H., Corey, A.T., 1964. Hydraulic Properties of Porous Media. Colorado State University, Hydro paper No. 3, Fort Collins, CO, USA, 24 pp.) as well as others. Recent studies on the topic are summarized and reviewed.