Numerical analysis of a caprock integrity during oil production by steam-assisted gravity drainage method

Abstract

The work is devoted to the investigation of a caprock integrity during oil production by steam-assisted gravity drainage method. An originally proposed thermo-hydro-mechanical model was used for the evaluation of mechanical loading acting on the over-burden. The model includes mass conservation laws, the energy conservation law and the linear momentum balance. Filtration of each phase of the three-phase flow (steam, oil and water) is described by Darcy�s law. Effective stress concept is used to take into account the effect of pore pressure on the stress-strain state. Inelastic deformations are described by the phenomenological viscoplastic model based on Drucker-Prager yield criterion. Two qualitatively and quantitatively different scenarios of porosity evolution are considered. The first scenario corresponds to the case of the pore compression while the second one describes increase in porosity induced by the volumetric strains. The obtained stress-strain state in the reservoir was used for the assessment of the caprock integrity for both cases of porosity evolution. In addition, the effect of the porosity evolution on the oil production rate is studied. It has been shown that the oil production rate strongly depends on the prevailing physical mechanism of the porosity evolution.

Keywords

• Coupled problems
• Steam-assisted gravity drainage
• Caprock integrity
• Rock failure.