Reinjection of greenhouse gases into geothermal reservoirs

Abstract

This work addresses the feasibility of reinjecting H2S and CO2, captured and dissolved in effluents from the geothermal field, back into the geothermal reservoir. A series of numerical modelling scenarios was used to assess the effect of NCG (non-condensable gases) reinjection on energy recovery, understand permanent trapping, and forecast potential NCG breakthrough into production wells.Although the gas species from geothermal systems typically have moderate solubility in water, formation of gas phases at lower pressures and/or the shallow subsurface requires careful consideration of the injection rate and composition of NCG. Possible fluid paths and distribution of gas components were investigated to estimate the NCG storage capability of a reservoir, and evaluate the potential risk of the reinjected NCG growing into fingers that may lead to an early breakthrough or potential leakage to the ground surface.Modified versions of benchmark geothermal reinjection models were constructed with initial conditions of a liquid-dominated geothermal system. The results obtained show that the effects of injection depend on the reinjection and production wells arrangement and the recharge conditions. The risk of leakage to the surface is very limited since the injected NCG remain in the liquid phase.