Simulation and application of borehole plastic zone range based on gas drainage effect

Abstract

Gas drainage by drilling is the main method of gas drainage. Based on this, gas drainage drilling with different diameters has been carried out. The study on the evolution characteristics of the surrounding plastic zone during the process shows that under the influence of drilling disturbance, expansion and deformation occurs around the hole, resulting in plastic zone, elastic zone and original stress zone; at the same time, the distribution of tangential stress around the five boreholes successively experienced a process of sharp increase, slow decrease until stress equilibrium. The larger the hole diameter, the farther the maximum point of stress around the hole is from the center of the hole; and it is found that the larger the hole diameter, the wider the width of the plastic zone. That is to say, the wider the pressure relief range around the borehole, the more adsorbed gas will be resolved into the free state, resulting in the expansion of the gas drainage radius; at the same time, according to the field test, it is found that when the width of the borehole plastic zone increases, the effect of gas extraction is significantly improved with the increase of pressure relief range around the hole.

Keywords

• gas drainage
• drilling
• plastic zone
• swelling deformation
• tangential stress