The Research Of Drilling Damage Zone Radius In Coal

Drilling technology of gas extraction is the most fundamental measures not only to control coal mine gas accident, but also to solve the most direct and effective way of safety accidents in coal mine. However, the coal seam drillinghole collapsing problem has restricted the efficiency of gas drainage, seriously affecting the safe production in coal mines. So the researching of drilling coal damage regional problems, finding out the different influence factors of coal drilling damage zone radius, providing the theoretical basis for solving the problem of coal seam drillinghole collapsing is of great theoretical value and practical significance for coal mine safe production.This paper mainly analysis the converse relation between two attributes of coal according to the experiment to study the relation between the mechanics properties of coal and Protodyakonov’s coefficient of the coal. and then analysis the different factors on the damage zone radius in the different conditions of coal drilling damage zone respectively according to the simulation by FLAC software. finally reduct the coal drilling damage zone radius theoretical solution combined with the numerical simulation results of the comparative analysis, to provide the theoretical basis for the prediction of drilling coal damage zone radius.The results of the study show that there is a relationship not only among the physical properties of coal, but also exists among the Protodyakonov’s coefficient of coal. Coal parameters can be expressed by functions, and conversed between different parameters of coal. In different conditions, the numerical solution of drilling damage zone radius decreases with the increase of Protodyakonov’s coefficient of the coal, increases with the increase of initial crustal stress, changes in different directions with the increase of lateral pressure coefficient. In the same condition, with the increase of Protodyakonov’s coefficient of the coal and the initial stress, numerical solution and the analytical solution of drilling damage zone radius show a linear correlation approximately, which illustrates that the theoretical prediction of drilling coal damage zone radius is feasible, with the increase of lateral pressure coefficient, solutions and analytical and numerical solution of drilling damage zone radius is close to each other in three directions. This study will provide the theoretical basis for the prevention of drilling damage zone radius and the measures taken for protecting drilling hole from collapse during gas extraction.