ИСТИНА

In Koyna-Warna area of the reservoir triggered seismicity core samples of igneous rocks were collected from boreholes KBH-5, KBH-8 and KBH-9 to study physical properties during multistage stress. Cylindrical samples 60×30 mm from each core were tested in 5 stages of axial loading-unloading stress up intact rock sample. The confining pressure, axial stress, axial and radial strain, velocity of longitudinal and shear waves was measured during experiment under stress. The porosity and permeability by gas helium, and density were measured independently of multistage stress before the tests. All granitoid rocks show linear dependence of yield stress on external pressure. The dynamic Young modulus is close to static one but larger in 1-5 GPa. For most of granitoids under investigation it was found that the dynamic Poisson’s ratio is mostly in the range 0.23-0.25 and seldom shows values from 0.20 to 0.22. Low porosity (0.05 -0.20%) and very low permeability of rock matrix gives no possibility to clearly distinguish between the dynamic elastic moduli of water-saturated and dry samples. The increase of yield stress with confining pressure allows us to assume an increase in strength of the studied rocks with depth.