Accounting for the Effect of TDS and NCG on Salton Sea Reservoir Response

Abstract

The Salton Sea reservoir, located in Imperial County, Ca., is unique in several ways from most liquiddominated geothermal reservoirs that have been developed to date. One of these differences is the presence of hyper-dine brines containing up to 28% TDS (Total Dissolved Solids) and up to 0.2% NCG (Non-Condensible Gas). A simple material and energy balance model has been developed to study the effect of TDS and NCG on Salton Sea reservoir response. This study demonstrated that during the development of a two-phase system the partitioning of the NCG into the vapor phase and the consequential concentration of the TDS in the brine drastically alters the reservoir fluid properties. In modeling pressure depletion of hyper-saline reservoirs, such as the Salton Sea, these changes in reservoir fluid composition were shown to seriously affect the simulation results. As a result of these findings, a compositional fluid property package was developed using published data on H20-C02-NaCI mixtures. This fluid property package was then incorporated into the simulation program used by Unocal. Validation of the fluid property package in this simulation program was made using measured reservoir temperature, surface enthalpy, and surface flash data.