World Geothermal Congress 2020+1
March - October, 2021

Modelling of the Non-Condensable Gases Re-Injection for Geothermal Emission Control (GECO Project)


[IFP Energies nouvelles, France]

High enthalpy geothermal systems, including vapour-dominated reservoirs, may contain non-condensable gases (NCGs). Thus, the steam production is accompanied with emissions of geothermal gases (CO2, H2S, H2….) initially dissolved in the liquid phase or mixed in a vapour phase at depth in the reservoir. In order to reduce the environmental impact of geothermal exploitation resources and avoid emission of greenhouse or toxic gases in the atmosphere, NCGs have to be captured and re-injected. This approach leads to an environmentally friendly exploitation, pressure support and geothermal resource sustainability. For low NCG content, the gases can be fully dissolved at the surface in the condensed water and re-injected. However, for high concentration of NCG, the dissolution is only partial and a two-phase flow (gaseous NCGs and condensed water) needs to be re-injected. We focus here on presenting the fluid flow model of a completion configuration ensuring the simultaneous re-injection of NCGs and condensed water in the same well. A specific geothermal site was selected as base case, main characteristics of which are the high concentration of NCGs on the production geothermal fluid (mainly vapour) and the low injection reservoir pressure. The objective of the current work is to study the complete operation of reinjection under non-isothermal steady state conditions and to demonstrate its efficiency. The prototype well completion consists in an annulus completion with water circulating in one part and non-condensable gases in the other. The two fluids are mixed at a given depth and through several injection points. A part of the non-condensable gases is then progressively dissolved into the liquid phase within the flow and the mixture flow is re-injected into the reservoir at the bottom hole. The recompression occurring in the two-phase flow section of the well allows reduction of NCG compression at the surface improving the overall efficiency and the cost of the system. The model takes into account the single phase flows of water and NCGs, the hydrodynamics of the two-phase downward flow with two major components (H2O and CO2) in the injected fluid, constitutive laws for the mixtures, the dissolution of gas into water, and the evaporation of the aqueous phase into the gaseous phase. Finally, the heat exchange between the surrounding ground, the annulus and the central part of the well is modelled.

        Topic: Injection Technology Paper Number: 23003

         Session 36C: Injection Technology [Tuesday 15th June 2021, 04:00 pm] (UTC-8)
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