Numerical Study on CO₂-Brine-Rock Interaction of Enhanced Geothermal Systems with CO₂as Heat Transmission Fluid

Abstract

Abstract. Enhanced Geothermal Systems (EGS) with CO 2 instead of water as heat transmission fluid is an attractive concept for both geothermal resources development and CO 2 geological sequestration. Previous studies show that CO 2 has lots of favorable properties as heat transmission fluid and also can offer geologic storage of CO 2 as an ancillary benefit. However, after CO 2 injection into geological formations, chemical reaction between brine and rock can change chemical characteristics of saline and properties of rock such as porosity and permeability. Is this advantage or disadvantage for EGS operating? To answer this question, we have performed chemically reactive transport modeling to investigate fluid-rock interactions and CO 2 mineral carbonation of Enhanced Geothermal Systems (EGS) site at Desert Peak (Nevada) operated with CO 2 . The simulation results show that (1) injection CO 2 can create a core zone fulfilled with CO 2 as main working domain for EGS, and (2) CO 2 storage can induced self-enhancing alteration of EGS.

Evaluation of CO2-Fluid-Rock Interaction in Enhanced Geothermal Systems: Field-Scale Geochemical Simulations

“…We elected to adopt a 5-spot well pattern because of its wide application in oil fields and geothermal reservoirs [3,9,[17][18][19][20][21][22]. The resulting 3D model domain with its 5-spot well pattern is illustrated in Figure 1.…”

“…Several recent experimental and numerical efforts quantify geochemical reactions associated with CO 2 injection in EGS reservoirs [2,3,[5][6][7][8][9][10]. Pruess [2,3] compared CO 2 and water with respect to heat extraction rate and mass flow rate in EGS reservoirs.…”

“…Na et al [7] performed laboratory experiments to study CO 2 -fluid-rock chemical reactions at high temperatures and pressures in geothermal systems and conducted batch simulations to analyze the experimental data. Wan et al [9] and Xu et al [10] simulated geochemical processes of fluid-rock interactions within CO 2 -EGS under high pressures and temperatures, and results suggest that significant CO 2 may be stored in EGS reservoirs by mineral trapping by precipitation of carbonate minerals. Xu et al [11] also performed batch geochemical simulations for three different aquifer lithologies to evaluate long-term CO 2 disposal in deep aquifers.…”

A review on heat transfer and energy conversion in the enhanced geothermal systems with water/CO2as working fluid

“…However, when considering the wellbore frictional pressure losses, the CO 2 -EGS would be less effective at energy extraction than a water-EGS for conditions used in past EGS trials. Xu et al numerically studied the fluid-rock interactions in the periphery using one-dimensional and twodimensional models and CO 2 as the EGS working fluid, and showed that the dissolved CO 2 diffusing to the periphery of the EGS zone dissolved primary minerals with precipitation of secondary carbonate and clay minerals, which resulted in significant CO 2 being trapped in the rock matrix, a condition that is favorable for geological storage [127,128]. Xu et al numerically studied the fluid-rock interactions in the periphery using one-dimensional and twodimensional models and CO 2 as the EGS working fluid, and showed that the dissolved CO 2 diffusing to the periphery of the EGS zone dissolved primary minerals with precipitation of secondary carbonate and clay minerals, which resulted in significant CO 2 being trapped in the rock matrix, a condition that is favorable for geological storage [127,128].…”

“…In addition, it was suggested that a CO 2 -EGS would be better than a water-EGS in lower permeability reservoirs and with the use of larger wellbores [125,126]. Xu et al numerically studied the fluid-rock interactions in the periphery using one-dimensional and twodimensional models and CO 2 as the EGS working fluid, and showed that the dissolved CO 2 diffusing to the periphery of the EGS zone dissolved primary minerals with precipitation of secondary carbonate and clay minerals, which resulted in significant CO 2 being trapped in the rock matrix, a condition that is favorable for geological storage [127,128]. Luo et al numerically investigated a doublet CO 2 -EGS system based on conditions at the European EGS site at Groβ Schönebeck using the CFD code FLU-ENT 6.3, including dramatic variations of the supercritical CO 2 properties and the thermal-hydraulic turbulence features of CO 2 in the wellbores [120].…”