Geomechanical Analysis of Hot Fluid Injection in Thermal Enhanced Oil Recovery

Hot-fluid injection in thermal enhanced oil recovery (TEOR) imposes temperature-driven volumetric strains that can substantially alter in-situ stresses, fracture geometry, and wellbore/reservoir integrity, yet existing TEOR modeling has not fully captured coupled thermo-poroelastic effects on fracture aperture, fracture-tip behavior, and stress rotation within a displacement discontinuity method (DDM) framework. This study develops a fully coupled thermo-poroelastic DDM formulation in which fracture-surface normal and shear displacement discontinuities, together with fluid and heat influx, act as boundary sources to compute time-dependent stresses, pore pressure, and temperature, while internal fracture fluid flow (Poiseuille-based volume balance), heat transport (conduction–advection with rock exchange), and mixed-mode propagation criteria are included. A representative scenario considers an initially isothermal hydraulic fracture grown to 32 m, followed by 12 months of hot-fluid injection with temperature contrasts of ΔT = 0-100 °C and reduced pumping rate. Results show that hydraulic fracture aperture increases under isothermal and modest heating (ΔT = 25 °C) and remains nearly stable near ΔT = 50 °C, but progressively narrows for ΔT = 75-100 °C despite continued injection, indicating potential injectivity decline driven by thermally induced compressive stresses. Hot injection also tightens fracture tips, restricting unintended propagation, and produces pronounced near-fracture stress amplification and re-orientation: minimum principal stress increases by 6 MPa for ΔT = 50 °C and 10 MPa for ΔT = 100 °C, with principal-stress rotation reaching 70–90° in regions above and below the fracture and markedly elevated shear stresses that may promote natural-fracture activation. These findings demonstrate that thermo-poroelastic coupling can govern fracture stability, containment, and injectivity during thermal EOR, motivating temperature-aware geomechanical risk assessment and design for long-term hot-fluid injection operations.