A ROCK BRITTLENESS EVALUATION METHOD BASED ON ENERGY DISSIPATION

Brittleness evaluation plays an important role in both shale drilling and fracturing design. However, the definition of brittleness is unclear and the method for brittleness evaluation has no reliable theory to support. Based on stress-strain relationship, this paper uses energy method to evaluate rock brittleness. According to nonlinear crack-tip field theory in fracture mechanics, considering frontal zones as special shielding configurations of crack tip to describe energy dissipation during the process of fracturing. The ratio between the intrinsic cohesion energy and the steady-state resistance of frontal zones can be used as rock brittleness index. The study indicates that the more the energy dissipates, the lower the value of rock brittleness, and the plastic property will become even more obvious. This rock brittleness evaluation based on energy dissipation is essential in analyzing rock mechanics and selecting fracturing section.