Experimental Study On Pressure Sensitive Effect Of Permeability Of Coal With Containing Gas And Low Permeability

Coal occupies a pivotal position in China’s energy structure. Disasters caused bythe gas in the underground mining of coal seriously restricting the coal mine productionsafety and development. However, the gas is available, clean, high calorific value ofenergy, with China’s economic development and energy structure adjustment, gas willcertainly become one of the main energy of the21st century. Whether the gas as disasterfactors to control, or as clean energy to take advantage of, its foundation is tounderstand clearly the rule of the gas’s storage and flow in the unconventional reservoirlike coal and rock mass. In this paper, according to the characteristic of coal containinggas, the fluid-solid coupling and finite element analysis theory are applied, with thenumerical simulation method and experiment, we get some useful results here:(1) The changing law of the permeability in the process of loading and unloading isobtained through laboratory simulation of the weak and the permeability of the coalseams in situ stress field experiment. And defines the penetration of thepressure-sensitive effect index, its variation of permeability is similar to effectivestresses and they can well reflect the evolution of the permeability; While theexperimental results with the numerical simulation, field measurement results show thatthe two match better.(2) Starting from the physical characteristics of coal containing gas, based on thebasic definition of the porosity, taking into account the effect of the free gas pressure onthe changes of the coal particles volume deformation, derived a mathematicalexpression of the porosity. Application of effective stresses of porous media theory anda series of hypothesis, deduced the equation of deformation control of coal containinggas. Based on the coal and rock mass with gas permeability pressure-sensitive effect,and fully taking into account the Klinkenberg effect, matrix shrinkage effect, derivedthe mathematical expression of permeability. Departure from a series of basicassumptions of the migration of gas, using the Darcy law, the law of conservation ofmass, deduces the equation of gas migration control. The experimental results have beentested by COMSOL multi-physical coupling field analysis software.(3) Migration law on the single-hole gas drainage under different conditions areanalyzed. The initial phase, the gas pressure change is bigger, the gas pressure gradient is larger, and there are a large quantity of gas emission; with the drainage time, coalreservoir gas pressure is reduced gradually, the gas pressure gradient also decreasedwith the increasing of the gas drainage range. This indicates that in the initial stage ofdrilling drainage, gas pumping very heavy volume, after a sustained period of time, theamount of gas gradually decay and become stable.(4) Simulated the gas migration’s law under the conditions of the smooth layermultiple drilling drainage gas. With the growth of the drainage time, the drilling ofdrainage expanding the scope of the mutual influence between the drill holes. With theborehole spacing decreases, borehole effect between enhancement, coal seam gaspressure decreases faster. At the same time as the gas pressure drop faster, in thedrainage period, the Klinkenberg effect and the matrix shrinkage effect appears morelikely, so we should enhance the observation, and adjust drainage deployment in time.