The Effects of Adsorption and Desorption on Production and Reinjection in Vapor-Dominated Geothermal Fields

Abstract

Adsorbed water on the rock surfaces in vapor-dominated geothermal fields has long been thought to provide a major source of fluid within the reservoir. Over the past several years, the Stanford Geothermal Program has conducted a series of experimental, theoretical and numerical investigations into the phenomena of water adsorption in geothermal systems, and their effects on reservoir performance. The results and conclusions of the most recent studies will be summarized in this paper. It has been found through these studies that the amount of (liquid) water adsorbed in vapor-dominated geothermal fields is very considerable, even at pressures well below the boiling point pressure. Adsorbed water represents the major fraction of fluid stored in the reservoir and can he the most important source. Reservoir performance forecasts are strongly governed by amount, and the rate of release of adsorbed water. Based on the experimental results it can be inferred that water adsorbs more easily during reinjection than it subsequently is able to desorb, which results in a reduction in the efficacy of reinjection.