Issue 49

A. Kostina et alii, Frattura ed Integrità Strutturale, 49 (2019) 302-313; DOI: 10.3221/IGF-ESIS.49.30 310 rate predicts the Eqn. (18) and the second set of operational parameters. The first set of the parameters for the same porosity model gives almost threefold smaller rate. The Eqn. (17) predicts moderate value of the oil production rate due to the pore compression. In this case, the second set of the parameters are also preferable to the first. The high values of injection pressure and temperature result in a faster development of the steam chamber, so the more oil becomes mobile. However, there is a possibility to change the structure of the reservoir in such a way that there will be little pore space available for the oil filtration and the reservoir can become almost impermeable. Thus, if the prevailing physical mechanism of the porosity evolution for the specific formation is the pore compaction, the increase in the values of the operational parameter can lead to the drop in the oil production rate instead of its rise. (a) (b) Figure 3 : Typical distribution of porosity according to: (a) model (17), (b) model (18). Figure 4 : Oil production rate obtained under the following conditions: (1)-porosity model (18), p b =3.5 MPa, T =220 K; (2)-porosity model (18), p b =2.5 MPa, T b =213 K; (3)-porosity model (17), p b =3.5 MPa, T =220 K; (4)-porosity model (17), p b =2.5 MPa, T =213 K. The main criteria for the optimal choice of the operational parameters is to ensure the safe conditions which will not lead to the caprock failure. Loss of a caprock integrity is the serious problem for a human safety and the environment. The overburden provides isolation of the injected material from penetration of it into the water. Fig. 5 shows assessment of the caprock integrity according to the Drucker-Prager fracture criterion for two sets of operational parameters. The strength parameters a and b are equal to 0.19 and 243623 Pa. The following cases have been considered. The first and the second cases correspond to the solution to the thermo-poroelastic problem (neglecting of the visco-plastic strains defined by Eqn. (11)) obtained for both sets of operational parameters (fig. 5, (a)-(b)). In all other cases, visco-plastic strains were taken into account. The second and the third case describe porosity evolution according to the Eqn. (17) (fig. 5, (c)-(d)). As regards to the fourth and the fifth, the Eqn. (18) was used (fig. 5 (e)-(f)). The obtained results show that neglecting of the plastic strains in the reservoir leads to the high values of mechanical stresses which induce caprock failure for both