ИСТИНА

The study is devoted to the problem rock brittleness definition and determination based on the variety of geophysical studies. Although brittleness is an intuitively clear property, its numerical estimation is related to a number of considerable problems. There are roughly dozens of different ways to define brittleness with each way being preferable for its own rock. At the same time, it can still remain unclear, which particular way of defining brittleness is proper for a certain rock. The study is devoted to the analysis of different factors standing for the ‘proper’ way to define brittleness of particular rock. The inner structure of the rock is shown to have considerable effect on the brittleness indices calculated via different methods. This effect varies for different brittleness index definitions, yet it appears to be thermodynamically consistent for a limited number of definitions. It is shown that energy-based approaches of brittleness definition make it possible to establish a bridge between two distinguish sets of data. At the one hand, brittleness index can be estimated from laboratory studies on core samples: triaxial tests reveal the rheological stress-strain curve characterizing material inelastic –brittle or ductile –behavior. On the other hand, elastic wave velocities are generally used to evaluate brittleness of rock formations in field conditions. While these sets of data regarding brittleness seem to be separated by nature and scale, the results obtained in the study reveal the same tendencies in particular brittleness definitions of these two groups. As a result, the uncertainty in choosing the proper brittleness index decreases as well as the validity of brittleness estimation increases. The obtained results may be valuable for a number of problems of rock mechanics.