Issue 49

A. Kostina et alii, Frattura ed Integrità Strutturale, 49 (2019) 302-313; DOI: 10.3221/IGF-ESIS.49.30 311 sets of operational parameters (fig. 5, (a)-(b)). On the contrary, the more sophisticated model which takes into account plastic strains in the reservoir predicts integrity of the caprock for all considered cases (fig. 5, (c)-(f)). Therefore, neglecting of the inelastic strains leads to the overestimation of the caprock strength even for the small values of the operational parameters. The potentially dangerous zones are located over the steam chamber which produces a Gaussian-type loading acting on the base of the caprock. It is interesting to note that higher values of operational parameters predict safer condition than lower in case of the porosity model (17). This effect can be attributed to the Drucker-Prager model which is a pressure-dependent fracture criterion. According to this criterion, stress state with the lower value of the hydrostatic pressure is closer to the fracture surface than the state with the higher value under the same value of the equivalent (von Mises) stress. (a) (b) (с) (d) (e) (f) Figure 5 : Drucker-Prager yield (fracture) surface (contour lines denote effective plastic strains): (a)-solution to thermo-poroelastic problem, p b =2.5 MPa, T =213 K; (b)-solution to thermo-poroelastic problem, p b =3.5 MPa, T =220 K; (c)-solution to thermo- poroinelastic problem with porosity model (17), p b =2.5 MPa, T =213 K; (d)-solution to thermo-poroinelastic problem with porosity model (17), p b =3.5 MPa, T =220 K; (e)-solution to thermo-poroinelastic problem with porosity model (18), p b =2.5 MPa, T =213 K, (f) - solution to thermo-poroinelastic problem with porosity model (18), p b =3.5 MPa, T =220 K. C ONCLUSION n this study, an assessment of the caprock integrity during oil production by SAGD is carried out. The evaluation of the loadings acting on a base of the caprock was calculated with the use of the originally proposed thermo-hydro- mechanical model of steam injection into the porous media. The model describes convective heat transfer, phase change process, thermal expansion of solid grains and influence of the pore pressure on the stress-strain state of the reservoir. The process of steam injection is governed by mass conservation law, energy conservation law, Darcy’s law for oil, steam and water filtration. Water-vapor phase change is determined by the additional heat source. Inelastic deformations of the reservoir induced by propagation of the thermal front are described by the phenomenological viscoplastic model. Two qualitatively and quantitatively different scenarios of porosity evolution is considered. The first I