Background to the Study

The aim of the study is to provide a dispassionate review and overview of scenarios where geothermal energy and CO2 utilisation and storage technologies can be combined for mutual benefit and contribute to Net Zero targets. Sourced from a rich body of literature from global research institutes and some demonstration projects many of the concepts identified have been conceptualised over the past 20 years and are still in the early concept stage. These concepts have been categorised, described and evaluated using qualitative and quantitative methods. And a map based screening exercise useful for initial evaluation of areas suitable for combined synergies has been undertaken.

Key Messages

• The use of subsurface resources will play a central role among the many solutions necessary for climate-change mitigation and to keep the Paris Agreements on track. These can comprise both shallow (near surface) and deep geological (>0.8km) resources. The hybrid use of the subsurface to produce renewable heat or electricity that could largely be decarbonised and /or in conjunction with Carbon Capture and Storage (CCS) of an external industrial CO2 source opens up promising solutions.
• Most of the concepts described in this work developed over the past 20 years are at conceptual stages and sourced from a rich body of literature (over 150 papers) these concepts largely need to be tested before demonstrating their potential for deployment.
• Concepts are grouped into main themes:oUse of supercritical CO2 as a heat vector for geothermal energy production – this includes CPG (CO2 Plume Geothermal), CO2-EGS (Enhanced Geothermal Systems), Heat production from former oil and gas reservoirs, CPG-ES (Energy Storage), and Earth Battery.oWater-driven geothermal concepts with CO2 injection or re-injection generally dissolved in the geothermal brine. The source of the CO2 is either from an external source, e.g. CO2-Dissolved and Geothermal BECCS, or from the geothermal fluid e.g. CarbFix, CLEAG-AATG and CO2-reinjection concepts. Of these, pilots are in preparation in France, operational in Iceland or about to start in Croatia, Italy, New Zealand and Turkey.oOther synergetic uses - CCS with improved efficiency in the capture process by using geothermal energy, synergy through dual non-competitive use in the same reservoir, and synergetic use through pressure management.oBorderline concepts were also discussed in brief, but otherwise deemed out of scope for the study.
• Key criteria are identified and where possible used as comparisons between concepts made, for example, total CO2 stored, energy produced, overview of research and path to commerciality, and subsurface features.
• The most ambitious concepts in terms of high energy delivery and high CO2 storage potential- (CO2-EGS, CPG-ES, Earth Battery, Hybrid Energy Systems) rely on high technological complexity that needs to be proven to confirm feasibility.
• Lower capacity systems, such as most of the water-driven geothermal concepts with CO2 reinjection, have the advantage of using simpler and more mature technologies, making technical feasibility more likely to be achievable or already proven by existing demonstrators (CarbFix, CLEAG, CO2 re-injection). These concepts require high level of replicability if they are going to have a measurable environmental impact on reducing CO2 emissions, but are potentially easier to manage permitting and gain social acceptance.
• First level screening is possible with the use of publicly available data to produce maps that co-locate the most favourable areas to combine geothermal power and some form of CCS while being in relative close proximity to an industrial CO2 emission source or within reach of a transportation network. A broad brush approach for France highlights the Paris and Marseilles areas as being most ideal.
• Future work on the economic evaluation will need to accompany pilot projects to assess the economic feasibility, a feature lacking in many desk based studies to date.
• Engagement across multiple stakeholders are necessary to move concepts to development.