Thermal Effects on the Wellbore Stability

Abstract

Thermal-mechanical behaviour plays an important role in wellbore stability of enhanced geothermal systems (EGS). Based on the thermo-poro-elastic model proposed by Coussy (1989) and by using Laplace transformation methods, analytical solutions for the temperature, pore pressure and stresses around a vertical well are obtained in the Laplace space. Then the solutions in the time domain are obtained via numerical Laplace inverse transformation. The results show that the cooling of the wellbore has a considerable effect not only on the pressure, in-plane radial and hoop stresses, but also on the vertical stress. It reduces the compressive radial and hoop stresses along the maximum horizontal stress direction. When the wellbore temperature is low enough, the hoop stress has a tendency to become tensile leading to the wellbore breakdown and the lower vertical stress implies the generation of an in-plane fracture. The possibility of wellbore shear failure is found to exist at places with higher compressive hoop stress.