Numerical Modeling of Hydrothermal Reactions in Geothermal Reservoirs

Abstract

Although the corrosion and scaling problems associated with handling geothermal fluids are well known, the effects of hydrothermal reactions are often overlooked in geothermal reservoir modeling. Water-rock chemistry can be expected to affect the evolution of a reservoir in at least three ways: (a) the thermodynamic properties of water are affected by the dissolved solids - this is especially important in two-phase regimes, (b) the porosity and permeability change with time due to dissolving and precipitation as well as due to the volume change associated with alteration, and (c) the heats of reaction may contribute directly to the energy production.

Table 1 summarizes the important hydrothermal reactions in a granitic source rock together with the heats of reaction and associated volume changes. Note that the available chemical energy is comparable to the thermal energy while the associated volume changes are an order of magnitude larger than those due to thermal contraction.