research on chaos characteristic of crack evolution in coal-rock fracturing

Precisely describing the formation and evolution rules of coal-rock fracturing crack have great value on reservoir fracturing improvement and highly efficient mining of coal bed methane well. in this paper, a non-linear dynamic method is used to study crack damage evolution behavior of coal-rock fracturing. considering distribution characteristics of natural cracks in coal-rock, and based on damage mechanics, a mathematical model on stress around the tip of coal-rock fracturing crack and crack evolution is developed. micro-crack amounts, circumferential stress, and axial stress at the crack tip of coal-rock fracturing crack evolution process are used as characteristic indicators to describe crack evolutionary. c-c method is chosen to reconstruct the phase space of coal-rock fracturing crack evolution. correlation dimension, lyapunov index, and kolmogorov entropy are introduced as chaos characteristic quantities of crack evolution system, and the process of coal-rock fracturing crack damage evolution could be calculated and described. coal-rock mass of zhangchen mining area in heilongjiang, china was used as a research object, and the results show that as the radial stress increases, the kolmogorov entropy and the degree of chaos decrease; also, as the circumferential stress increases, the kolmogorov entropy increases, and a higher degree of chaos is obtained; increasing the number of micro-cracks evolution raises kolmogorov entropy up to a critical value, and then the kolmogorov entropy drops, which means the chaotic degree decreases. the results calculated show that crack formation is a damage evolution process which has chaos characteristics. finally, we provided a new way for further research on coal-rock fracturing crack evolution regularities