A comparison of electric power output of CO2 Plume Geothermal (CPG) and brine geothermal systems for varying reservoir conditions

Brine displacement by CO2, energy extraction rates, and lifespan of a CO2-limited CO2-Plume Geothermal (CPG) system with a horizontal production well

“…Operating an EGS typically involves hydraulically, thermally, and/or chemically stimulating naturally low-permeability rock to increase the bulk formation permeability, a process that has a significant likelihood of inducing seismicity (e.g., Evans et al, 2005;Majer et al, 2007;Giardini, 2009). In contrast, CO 2 -Plume Geothermal (CPG) systems (Randolph and Saar, 2011a,b;Saar et al, 2012Saar et al, -2015Buscheck et al, 2013) involve injection of CO 2 that comes from a CO 2 emitter, as a subsurface working fluid to extract heat and pressure energy (enthalpy) from naturally high-permeability sedimentary or stratigraphic basins. Formations in these basins are typically bounded by low-permeability formations such as base rocks and caprocks, although more complex trapping structures may exist.…”

“…Furthermore, supercritical CO 2 has a high mobility (i.e., low kinematic viscosity) and high thermal expansibility compared to water, resulting in the formation of a strong thermosiphon, a physical effect which circulates a fluid without the necessity of a mechanical pump (Atrens et al, 2009(Atrens et al, , 2010Adams et al, 2014). This thermosiphon eliminates the need for parasitic Randolph and Saar, 2011b;Saar et al, 2012Saar et al, -2015, implemented in a deep saline aquifer. Shown are both a direct (left side) and an indirect, i.e., binary Organic Rankine Cycle (ORC) implementation (right side).…”

“…The injected CO 2 forms a large subsurface CO 2 plume that permanently sequesters CO 2 underground and absorbs heat from the geothermal reservoir. The CO 2 plume can be "tapped" for thermal and/or electric power production in a geothermal power system (Randolph and Saar, 2011a,b;Saar et al, 2012Saar et al, -2015Adams et al, 2014Adams et al, , 2015 as illustrated in Fig. 1.…”

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

“…However, currently, geothermal power production is limited to distinct geological conditions, where fluid flow rates in geothermal reservoirs carry sufficient heat (Saar, 2011) and/or pressure for economic power generation (Randolph and Saar, 2011a;Breede et al, 2013;Adams et al, 2015). It is widely agreed that the earth's crust holds substantially more geothermal re-116 F. Amann et al: The seismo-hydromechanical behavior during deep geothermal reservoir stimulations sources than are presently being exploited (e.g., Tester et al, 2006).…”

“…The artificially enhanced permeability needs to be high enough to reach flow rates that are commercially relevant for power production, depending on the subsurface working fluid. Larger permeability enhancements are required for water or brine than for CO 2 , as the latter can utilize lower temperatures and lower permeabilities for economic geothermal power generation, due to its higher energy conversion efficiency (Brown, 2000;Pruess, 2006Pruess, , 2007Randolph and Saar, 2011a, b;Adams et al, 2014Adams et al, , 2015Garapati et al, 2015;Buscheck et al, 2016). Moreover, fluid flow should occur within a large number of permeable fracture pathways that sweep a large surface area of the rock, thereby providing longevity to the system and avoiding early thermal breakthrough, such as occurred at the Rosemanowes Project (Parker, 1999) and the Hijiori Project (Tenma et al, 2008).…”