Thermal Impacts on Induced Hydraulic Fracture Propagation in Complex Carbonate Reservoirs

Abstract Hydraulic fracturing is critical for complex geothermal and deep hydrocarbon reservoirs, such as the Brazilian Pre-salt carbonates. However, conventional fracturing models neglect the thermo-hydro-mechanical coupling process in hot rock formations subjected to cold waterflooding. This work investigates the thermal impacts on fluid-driven fracture propagation in heterogeneous permeable carbonate media, using a robust fully coupled thermo-hydro-mechanical (THM) finite element approach. The proposed numerical model is verified against relevant analytical and numerical solutions. Fracture propagation under isothermal and non-isothermal conditions was compared in all asymptotic propagation regimes. The results demonstrate that thermal effects impact fracture evolution, particularly in leak-off-dominated regimes. The numerical findings show the substantial influence of injection rate, initial stresses, and fluid viscosity on pore pressure evolution, fluid leak-off, temperature conduction, and fracture growth. A 3D case study of the heterogeneous Brazilian Pre-salt highlights the critical failure of isothermal analysis of cold injection in deep or hot formations. The isothermal model predicted excessive injection pressures with negligible fracture opening in layers with high permeability. On the other hand, the THM model forecast fracture propagation with higher aperture at significantly lower pressure thresholds. This analysis revealed a counterintuitive mechanism in which fracture growth was inhibited in layers with lower confining stress while being preferentially directed towards layers with higher permeability. This behavior is attributed to permeability-enhanced fluid leak-off and the resulting amplification of local cooling. These findings underscore the importance of fully coupled THM analysis for accurate fracture design and risk assessment in thermally sensitive heterogeneous reservoirs.