Mixed CO2-Water Injection Into Geothermal Reservoirs: A Numerical Study

Abstract

Heat recovery from deep/ultra-deep geothermal reservoirs and CO2 storage in geologic formations are promising techniques for reducing CO2 emissions. Both techniques involve injection of fluid into deep saline aquifers, oil/gas reservoirs, or stimulated fractured crystalline formations. A potential alternative to storing CO2 in aquifers involves dissolution of CO2 in the return (cold) water stream of geothermal doublets. The efficiency of injection and sweep, as well as the safety of operations highly depends on reservoir physical, thermal, and compositional properties, which may change following CO2 and/or cooled water injection and potential reaction. However, although there is convincing evidence that thermal, flow, and chemical processes are strongly coupled, the nature of the coupling is not yet fully understood. In order to understand the spatial and temporal hydrothermal and chemical effects on targeted geologic media of CO2 injection, a geometrically flexible approach for solving reactive non-isothermal density–viscosity-dependent flow and reactive transport in low-enthalpy geothermal systems is utilized. The method is applied to simulate the non-isothermal reactive flow transport in a doublet geothermal system. Several injection scenarios are analyzed. The overall heat recovery and CO2-storage capacity are calculated for different formations. Furthermore, the influence of both the induced viscosity and porosity changes on flow and heat transfer in such systems are investigated.