The Role of Capillary Forces in the Natural State of Fractured Geothermal Reservoirs

Abstract

A lot of experiments into the natural state of geothermal reservoirs have been conducted using porous mediirm models, even though geothermal systems are usually highly fractured. It is unclear whether a porous niediirni model is adequate in describing the natural state of a fractured geothermal reservoir. Because of this, a dual yorositx model is ofteii invoked. The question of how heat and mass is transferred in fractures has been ,\*idel! investigated. The objective of this work was to further our understanding by investigating how heat and mass transfer is affected by capillaty forces. Also, the question of how capillary forces affect the stability of a nnter-saturated regiori overljitig a liquid-dominated two-phase zone was examined. The study was carried out 61 developing a two-dimensional numerical model representing a fractured geothermal reservoir. The nunierical sirnulariotis were carried to steady state with the use of a commercial simulator TETRAD (version 12). Results iiidicate that due to capillaty forces, the fractures act as heat pipes - transporting heat by the process of convection. The convection process was found to be enhanced if there is no capillaty pressure in the fractures. It was also determined that only if capillary forces are present can a system consist of a watersaturated ;otic overljitig a liquid-dominated two-phase zone remain stable.