Vapor Pressure Lowering in Brines and Implications for Formation of a High Temperature Reservoir

Introduction That a “high temperature reservoir” (HTR) underlies a “typical” vapor-dominated reservoir under certain circumstances is well known (Drenick, 1986; Pruess et al., 1987; Walters et al., 1988). However, formation and behavior of such a feature is poorly understood. Recent theories regarding the behavior of the HTR fall into one of two broad categories: transient and steady state. In the transient models (e.g., Drenick, 1986; Walters et al., 1988; Truesdell, 1991), the HTR is a component of the typical vapordominated reservoir for a relatively short period of time.. These models generally assume either a recent boiling of a liquid system (a fossil liquid system; Drenick, 1986; Walters et al., 1988), or downward extension of the ‘4 pical” reservoir into hot dry rock (Truesdell, 1991 Steady state models (Shook, 1993a; Lai et al., 1994) consider the HTR as a steady component of the geothermal reservoir. As in the case of the transient theories, several different explanations are given for the formation of the HTR. For example, Shook (1993a) used vapor pressure lowering in a fractured domain to develop an HTR, whereas Lai et al. (1 994) used non-uniform heating in a porous media in forming the HTR.