INJECTION OF CO2 INTO LIQUID DOMINATED TWO-PHASE GEOTHERMAL RESERVOIRS

Abstract

Reinjection of CO2 into geothermal reservoirs is receiving increasing interest from many industries to minimize the emission of the greenhouse gas into the atmosphere. The CO2 could be injected in the form of gas dissolved in water or as super critical fluid. To understand the migration and impact of injected gases in the reservoir and forecast the effects on the reservoir pressure, production enthalpy and the potential breakthrough of reinjection fluid to the production wells, numerical reservoir simulation studies are required.
This work investigates the possible impacts of infield reinjection of CO2 in two-phase liquid-dominated geothermal reservoirs using an earlier computer model of the Wairakei-Tauhara system (O’Sullivan and Yeh 2007) as a representative case study. Various reinjection scenarios were applied to test alternative reinjection strategies. Different injection rates of CO2 were used along with the separated geothermal water and its effects on: reservoir pressure, temperature, production enthalpy, steam and CO2 production were investigated. The breakthrough of CO2 was also monitored since it can result in lower power recovery and higher gas (CO2) production, hence higher practice load. The modelling results showed that the injection of CO2 helps maintaining the reservoir pressure, but at the same time it suppresses boiling which results in reduction of the enthalpy of the produced fluid.