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 medium models, even though geothermal
systems are usually highly fractured. It is unclear whether a porous medium model is adequate in describing the natural state of a fractured
geothermal reservoir. Because of this, a dual porosity model is often invoked. The question of how heat and mass is transferred in fractures has
been widely investigated. The objective of this work was to further our understanding by investigating how heat and mass transfer is affected
by capillary forces. Also, the question of how capillary forces affect the stability of a water-saturated region overlying a liquid-dominated two-
phase zone was examined. The study was carried out by developing a two-dimensional numerical model representing a fractured geothermal
reservoir. The numerical simulations were carried to steady state with the use of a commercial simulator TETRAD (version 12). Results indicate
that due to capillary 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 capillary pressure in the fractures. It was also determined that only if capillary forces are present can a system consist of
a water-saturated zone overlying a liquid-dominated two-phase zone remain stable.