Influence of cold waterflooding on reservoir geomechanics in Brazilian pre-salt reservoirs

ABSTRACT: Oil is the main energy source used in the world, even with the strong development of the energy transition to renewable sources. Therefore, oil production will continue in the next years to meet the population's energy demand. Enhanced oil recovery (EOR) methods are used to change the rock and oil conditions inside the reservoir to recover additional oil content. However, it can have a strong impact on reservoir geomechanics. This work investigates the thermo-hydro-mechanical (THM) effect of cold waterflooding in a Brazilian pre-salt reservoir. The analysis evaluates how the constitutive model adopted for the caprock impacts the global response. A fully coupled THM finite element model describes the rock formation behavior, involving poroelasticity, single-phase fluid flow, and convection/diffusion heat transfer. The numerical results show that the thermal effect has a stronger impact on the mechanical behavior than the hydraulic effect in the cooled region. The instantaneous temperature drop induces significant changes in the reservoir stress states, mainly in the horizontal stresses. Different constitutive models are adopted in the caprock to highlight the influence of elastic, plastic, and viscoelastic models. The lower interval of the caprock is the most critical region that can compromise reservoir integrity. Finally, the work provides valuable findings that can be used to guide the cold fluid injection process.