Simulation Study on the Characteristics of Gas Extraction from Coal Seams Based on the Superposition Effect and Hole Placement Method

Abstract

In order to obtain a reasonable extraction drilling method for coal seam working faces and to carry out targeted as well as cost-effective hole placement optimization, a gas–solid coupled model based on the coal rock deformation field and the matrix–fissure dual seepage–diffusion field was established and numerically solved via the use of COMSOL Multiphysics finite element software to optimize the gas transport parameters of the Dongpang coal mine based on the study of the coal seam gas transport law. This study shows the following: With an increase in the extraction time, the gas content of the coal seam was reduced to a minimum. It shows that, with an increase in the extraction time, the gas pressure and seepage velocity keep decreasing the stable value, the main stress around the borehole redistributes, and the coal permeability keeps decreasing with an increase in the decay coefficient. The extraction radius of the boreholes increases exponentially with the extraction time, and the reasonable extraction hole size is 94 mm; the use of multiple boreholes for pre-drawing gas via the use of the interval between the effective extraction radius and the influence radius results in a blind extraction zone caused by the superposition effect between the boreholes, and the residual gas value of the coal seam increases with an increase in the borehole spacing. The use of an equilateral triangular hole layout can avoid the extraction blind zone, and the pre-sumping effect is good after field application, which ensures the safe production of coal mines as well as the reasonable use of resources.

Optimization of Accurate Spacing for Gas Extraction from Damaged Coal Seams Based on a Dual-Penetration Model

“…where G is the shear modulus of the coal body, MPa; u j,ji is the displacement components in different directions, m; ν is Poisson's ratio of the coal body; β f , β m are the Biot coefficients of the fracture and matrix; p f,i and p m,i are gas pressures in different directions for the fissure and matrix, respectively; K is the bulk modulus of coal, MPa; p i is the gas pressure, MPa; ε L is the strain tensor of the coal body; P L is the Langmuir pressure, MPa; and F i is the bulk force of the coal body, MPa. The D-P criterion with the Molr-Coulomb criterion plasticity model was selected under plane strain conditions [19], and it was determined that the damage equation can be expressed in terms of the cohesion and angle of internal friction as…”