Optimizing Reinjection: Evaluating Temperature-Driven Mineral Reactions and Well Performance in Lithuania’s Cambrian Reservoirs

This study explores the optimization of reinjection strategies in Lithuania’s Cambrian geothermal reservoirs, focusing on temperature effects on mineral interactions and long-term reservoir performance. Western Lithuania contains significant geothermal potential, especially in the Cambrian sandstone reservoirs, which reach temperatures up to 96°C at 2000 meters depth. These reservoirs, once used for oil production, are now being reconsidered for geothermal energy, particularly district heating. Using reactive transport modelling (RTM) with TOUGHREACT, the study evaluates the impact of reinjecting saline water at 40°C—a temperature historically aligned with district heating return flows—on mineral dissolution and precipitation.

Simulations reveal that porosity and permeability around the injection well change over time due to geochemical reactions. Near the well, permeability increased by 53%, while it decreased by 83% at 20 meters distance. However, the 40°C reinjection temperature does not significantly impact reservoir quality, making it a viable option for sustained operations. The results suggest that careful reinjection temperature control, combined with horizontal well technologies, can enhance geothermal energy extraction while maintaining reservoir integrity. This research contributes to geothermal field development planning in Lithuania and supports sustainable energy transition efforts.