Transient thermo-poroelastic analysis of drilling-induced mechanical damage in nonfractured rocks

Abstract

Permeability variations in reservoirs and around boreholes are of great interest in petroleum engineering due to the fact that they can significantly affect reserve estimates, reservoir development, well production or injection rate, and the likely success of remedial actions of near-wellbore damage. A fully coupled transient thermo-poroelastic concept with and without rock mechanical damage models is employed to evaluate stress distribution and permeability variation around the boreholes and breakouts. The anisotropy concept is applied to permeability, rock modulus, and uniaxial compressive strength using Weibull distribution. The Mogi-Coulomb failure criterion is employed to model breakout initiation and propagation around the borehole. Strain-based stress-permeability equation and stress-permeability models based on the experimental results and correlations are used to evaluate permeability changes near the borehole. Two cases of overbalanced and underbalanced drilling conditions are employed. The simulations for medium with isotropic and anisotropic physical properties result in varied effective stress distribution, breakout geometries, and consequently different distributions of tangential and radial permeability. Generally, in isotropic medium, permeability reduces to less than 70 % of its original value in the overbalanced condition and 80 % in underbalanced operations; however, there are differences between permeability along x and y directions. For anisotropic medium, permeability increases to more than 150 % all over the borehole periphery in the overbalanced operations; moreover, permeability enhancement is essentially larger along maximum in situ springline. In the underbalanced condition, permeability decreases to less than 70 % along minimum in situ stress direction and increases to more than 200 % in a limited area near the borehole along maximum in situ stress springline.

Pore pressure and stress distribution analysis around an inclined wellbore in a transversely isotropic formation based on the fully coupled chemo-thermo-poroelastic theory

“…Ghassemi et al (2001) and Ghassemi and Zhang (2004) applied the boundary element method to determine the distribution of the stress and pore pressures of a well in a poroelastic medium. Gomar et al (2015Gomar et al ( , 2014aGomar et al ( , 2014b) adopted a twodimensional finite element method to study wellbore stability based on the thermo-poroelastic theory, which takes into account conductive and convective transport processes. Roshan and Aghighi (2012) developed a finite element model based on chemo-poroelascity and found that a threshold in the formation permeability exists that can determine when the convection influence cannot be ignored.…”