Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Permeability Evolution in a CO₂-Circulated Geothermal Reservoir

Abstract

The meager availability of water as a heat transfer fluid is sometimes an impediment to enhanced geothermal system (EGS) development in semi-arid regions. One potential solution is in substituting CO2 as the working fluid in EGS. However, complex thermo-hydro-mechanical-chemical (THMC) interactions may result when CO2 is injected into the geothermal reservoir. We present a novel numerical model to describe the spatial THMC interactions and to better understand the process interactions that control the evolution of permeability and the heat transfer area. The permeability and porosity evolution accommodate changes driven by thermo-hydro-mechanical compaction/dilation and mineral precipitation/dissolution. Mechanical and hydraulic effects are demonstrated to exert a small and short-term influence on permeability change, while the thermal effects are manifest in the intermediate and short-term influence. The most significant and long-term influence on permeability change is by chemical effects, where decreases in fracture permeability may be of the order of 10-5 due to calcite precipitation in fracture throats, which causes the overall permeability to reduce to 70% of the initial permeability. The initial pressure and temperature of the injected CO2 exerts an overriding influence on permeability. In particular, an increased temperature reduces the mineral precipitation in the fracture and enhances mineral dissolution within the matrix and pore but results in mechanical closure of the fractures. Optimizing injection pressure and temperature may allow the minimization of precipitation and the maximization of heat recovery.

A semianalytic time‐resolved poro‐elasto‐plastic model for wellbore stability and stimulation

“…Important effects can happen due to chemical reactions, precipitation, dissolution, and swelling . This can be related to the high temperatures and large temperature differences manifest in geothermal applications, and the chemical response of different minerals and solutes present.…”

“…Criticality develops in a similar fashion as the case above; the permeability is not more than completely reversed to the starting values-this is due to the elastic part of the response of the strain to the stresses [Colour figure can be viewed at wileyonlinelibrary.com] Important effects can happen due to chemical reactions, precipitation, dissolution, and swelling. 38,39 This can be related to the high temperatures and large temperature differences manifest in geothermal applications, and the chemical response of different minerals and solutes present. One can also think about the use of fluids different from water.…”

Laboratory Investigation and Modelling of the Thermal-Mechanical Properties of Soil in Shallow Mineralized Groundwater Area

“…Figure 3. It can be observed that the maximum dry density ranged from 1.68 g/cm 3 to 1.83 g/cm 3 , where the corresponding optimum 3 Geofluids moisture contents are 21.2% to 17.4%, respectively. This phenomenon can be explained by the theory of electric double layer (EDL).…”

“…According to the United Nations Educational, Scientific and Cultural Organization (UNESCO), over 1 billion hectares of saline soils or salt-affected soils are widely distributed in nearly 100 countries and regions, especially in arid and semiarid areas [1]; many of these areas are facing severe challenges of substantial air pollution and energy shortage caused by consuming fossil fuels for heating and cooling of the buildings [2]. Therefore, the renewable geothermal energy becomes a promising alternative to achieve thermal comfort due to its low cost, high availability, stability, and minimal environment impact and can be utilized by various geothermal subsurface earth structures such as geothermal energy piles (GEP), ground source heat pumps (GSHP), earth-air tunnel heat exchangers (EATHE), borehole thermal energy storage (BTES), geological carbon dioxide sequestration and storage, and geothermal heated pavement [3][4][5][6][7]. The basic principle of these projects is simple: a cold fluid (CO 2 or water) is injected into the buried pipe, absorbs heat from hotter surrounding soil, and then is pumped out [8].…”

The influence of coupled physical swelling and chemical reactions on deformable geomaterials

“…To simplify the discussion, the swelling coefficient is assumed to be ω s S f ρ w f = 0:2. The strain resulting from dissolution can be expressed by considering the volumetric strain 40 as…”