Quantifying the Benefit of NCG Reinjection on Geothermal Production Performance

Abstract

Non-condensable gases (NCGs) occur naturally in geothermal systems, presenting an opportunity and challenge for geothermal operators. In self-flowing/artesian production wells, NCGs can support production by reducing density of fluid in the wellbore, which is a particular benefit in low and moderate enthalpy systems. In an operating geothermal field, NCGs may be vented to atmosphere or reinjected. Without NCG reinjection, reservoir concentrations of NCGs will decline over time, reducing production well outputs. NCG reinjection is feasible over a wide range of production NCG rates, injecting gases along with reinjected brine with or without compression required. Reinjecting NCGs reduces the rate of NCG decline in the production reservoir, therefore reducing the rate of production decline. At fields with higher NCG content, parasitic load may be required for NCG reinjection, partially offsetting this benefit. A combined reservoir engineering and plant process analysis demonstrates that NCG reinjection is beneficial to long-term reservoir sustainability and project performance across a wide range of initial reservoir conditions.