## 2 Literature Review  
The performance and stability of proppants under THMC conditions have been studied over the years, with significant insights gained regarding their behaviour under elevated temperature and pressure. Ref. [26] conducted one of the earliest investigations into the conductivity of various proppants, including sand, RCS, intermediate-strength bauxite ceramic, intermediate-strength lightweight ceramic, and high-strength bauxite ceramic, at 135 \({}^{\circ}\)C and 55.2 MPa over 14 days. The study revealed a drastic reduction in conductivity, with a correction factor as severe as 0.3 under extreme conditions (for sand), emphasizing the singular effect of temperature on proppant performance. Ref. [27] assessed the stability of high and intermediate-strength proppants under temperatures ranging from 40 to 150 \({}^{\circ}\)C and confining pressures of 3-50 MPa over 36 days. Their findings indicated a significant permeability reduction (-50%) within the first four days, driven by chemical-mechanical interactions between the rock, fluid, and proppant. They also highlighted the pronounced impact of higher temperatures (150 \({}^{\circ}\)C) on permeability loss in long-term experiments. Ref. [28] explored sintered bauxite proppants' chemical and thermal stability under EGS conditions with temperatures of 200-230 \({}^{\circ}\)C over five weeks. The study documented dissolution textures on corundum mineral faces and the deposition of amorphous silicates, aluminiosilicates, and aluminum oxides/hydroxides, revealing significant geochemical alteration under such conditions. Ref. [29] investigated the influence of self-propping, time, and closure stress on the conductivity of a 30/60 sintered bauxite proppant at ambient temperature and at 90-95 \({}^{\circ}\)C under a confining pressure of 13.8 MPa (2000 psi) for 1-7 days. Their results showed that although temperature effects and granite fines generation influence fracture conductivity, proppants maintained adequate performance for geothermal energy production over time. Ref. [30] examined the geochemical interactions of bauxite-based proppants at 25 \({}^{\circ}\)C and 150 \({}^{\circ}\)C for 12-80 days under 2-bar conditions in NaCl and CaCl\({}_{2}\) brings. They observed that the resin coating had no significant effect on chemical stability, and high aluminum concentrations in brines indicated limited proppant stability at reservoir conditions. Ref. [31] conducted long-term tests at 300 \({}^{\circ}\)F (149 \({}^{\circ}\)C) and 450 \({}^{\circ}\)F (232 \({}^{\circ}\)C) for 180 days. They observed that diagenetic chemical reactions at high temperatures led to geochemical scaling, permeability loss, and proppant-strength deterioration. However, coating proppants with hydrophobic styrene-maleic anhydride (SMA) materials significantly reduced the effects of these reactions, mitigating fracture diagenesis. Ref. [32]  
Figure 2: Schematic illustration of (**a**) the coupled THMC processes affecting proppant stability in geothermal environments and (**b**) thermal cycling effects on a ceramic, resin- or polymer-coated proppant, showing micro-cracking and delamination. evaluated the thermal impact on fracture conductivity evolution in granite samples using mono-layered 40/70 mesh ceramic proppants at temperatures ranging from 25 to 500 \({}^{\circ}\)C under 5-55 MPa confining pressures. The study found that proppant embedding depth increased with higher thermal treatment levels, which alleviated proppant crushing but exacerbated embedment. Ref. [33] investigated the effect of a 30 MPa confining pressure and 60-90 \({}^{\circ}\)C temperatures on the conductivity of a proppant pack. Their findings demonstrated that proppants significantly improved hydraulic characteristics in rough fractures compared to unpropped fractures. Ref. [34] examined the performance of resin-coated proppants under temperatures ranging from 20 to 150 \({}^{\circ}\)C and pressures of 5-30 MPa.