Draft:CO2-Plume Geothermal

CO₂-Plume Geothermal (CPG) combines Carbon Capture and Storage (CCS) with geothermal energy extraction, utilising CO₂ itself as a geothermal energy extraction fluid.

Technology

First, liquid-like CO₂ is injected in deep and naturally permeable reservoirs, just like in CCS, where the CO₂ is heated up by the surrounding hot rocks. At a nearby location, production wells then extract the geothermally heated supercritical CO₂ back to the land surface, where it is expanded in a CO₂ turbine to generate electricity. The CO₂ is then cooled and condensed back to a liquid state and re-injected into the reservoir, closing the cycle and enabling all CO₂ to be permanently sequestered. CPG has the potential to generate over twice the power of conventional, water-based geothermal systems for similar conditions: while the specific heat capacity of CO₂ is less than that of H₂O, the significantly lower dynamic viscosity of CO₂ enables higher overall energy extraction rates.

16 peer-reviewed publications have been published on CPG as of 2024, since its invention by Martin Saar and Jimmy Randolph in 2011.

Relation to CCS projects

As the subsurface reservoir cools due to geothermal heat extraction, the density of CO₂ in the subsurface increases, enabling a larger mass to be stored for a given formation. Other identified impacts of CPG on CCS include increased control over CO₂ volumetric sweep, reduced carbon intensity of storage due to renewable energy production, additional monitoring data from production wells, flexibility to repurpose producer wells to injectors, avoiding injector downtime with associated halite deposition risks, and providing communities with power produced using CO_2.

Research needs

While existing equipment from CO₂ EOR and CCS projects can be repurposed for CPG, new equipment is required, primarily lower temperature supercritical turbines and high-pressure CO₂ cooling and condensing units.