An Accurate PVT Model for Geothermal Fluids as Represented by the H2O-CO2-NaCl Mixtures

Abstract

Estimates for the pressure decline in high TDS geothermal fluids containing dissolved gases are extremely sensitive to the PVT representation of the reservoir fluid. Significant errors in predicted pressures will occur if the geothermal fluid is represented by one or two pseudo components with modified water properties. As a result, we have developed a PVT model to predict the thermodynamic properties of a prototype geothermal fluid as represented by three-component H20-C02-NaC1 mixtures. The range of applicability of the model is: Temperatures from 75 to 700+"F, pressures from 14.7 to 5000 psi, carbon dioxide content from 0 - 5 wt%, and salt concentrations to 30 wt%. The model has been implemented into Unocal's version of a commercially available reservoir simulator and is currently being used to study one of Unocal's high salinity reservoirs located in the Imperial Valley of Californa.