Geolchemical calculation workflow to estimate fluid chemistry of water dominated geothermnal reservoir

Abstract

Sampled aqueous chemistry at surface, is altered from reservoir chemistry due to boiling, degassing of non-condensable gases (mostly CO2), and conductively or adiabatically cooling in wellbore at water dominated geothermal field. Geochemical modelling studies, from reservoir to surface or reinjection, begin by computing the initial equilibrium state of the system at temperature and pressure of geothermal reservoir. Practically, however, physical and chemical properties of fluid in reservoir cannot be measured. Therefore, in such cases, fluid chemistry is calculated from chemical analysis of surface samples. Consequently, some geochemical calculation steps should be combined to estimate reservoir chemistry.
Aqueous chemical analysis reveals just bulk composition of the solution. In order to distribute bulk composition among concentrations of ionic and molecular species, speciation step should be conducted. This process is the first step of the geochemical calculation workflow. Following steps are; mixing, increasing temperature, dissolution and equilibration. In this paper, governing equations that used in geochemical calculations and computation sequence of geochemical models are introduced to estimate reservoir fluid chemistry.