Artificial ground freezing is an efficient technique which allows one to sink the mine shafts under complex hydrogeological conditions. The aim of artificial ground freezing is a creation of a temporary wall of frozen soil around the intended excavation. To estimate an optimal thickness of an ice-soil wall, the Vyalov's formula is widely used by engineers. The article is devoted to analysis of Vyalov's formula on the basis of the numerical simulation. The numerical simulation has been conducted by the finite element method. For the simulation of a stress-strain state of an ice-soil wall a new computational scheme has been proposed. The scheme is based on Vyalov's design layout for a vertical shaft sinking and takes into account a soil layer beyond the excavation bottom. A mechanical behavior of frozen soil is described by Vyalov's constitutive relations. As a result, it has been shown that values of the wall thickness given by Vyalov's formula do not agree with the ones obtained by the numerical simulation. In order to conform results given by Vyalov's formula and the numerical simulation, two modifications of the formula have been proposed.

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.

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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).

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