Analysis of models for porosity evolution in reservoir during steam injection

Depletion of traditional hydrocarbon reserves leads to the development of extracting methods for heavy crude oil and bitumen characterized by extremely high viscosity. The most effective technology is the steam-assisted gravity drainage. The aim of this method is to decrease oil viscosity by injection of hot steam into the reservoir. Increase of temperature, pore pressure and change of stress-strain state during this process significantly affect porosity which is the key storage parameter of the reservoir. This work is devoted to the analysis of models for porosity evolution during the steam-assisted gravity drainage process. The authors have developed an original model to describe steam-assisted gravity drainage which includes the mass balance equation for a three-phase flow, the energy balance equation involving latent heat due to vaporization/condensation of water/steam and Darcy’s law for fluid filtration. Numerical implementation of the proposed equations was based on the pressure-saturation algorithm. The results have shown a substantial qualitative and quantitative disagreement between the considered models. Coupling of porosity with volumetric strain leads to the rise of its magnitude. Models relating porosity to pore pressure show simultaneous existence of high-porous (near the injection well) and low-porous (near the production well) areas. In case when porosity is dependent on effective stress a circular area of a compacted soil is formed. Therefore, to obtain a correct estimation of the oil production rate in an arbitrary reservoir it is necessary to define the prevailing mechanism of porosity evolution (volumetric strain, pore pressure or effective stress).