Research On Thermal Elastic-plastic Damage Model Of Low Permeability Coal Seam Under Supercritical Carbon Dioxide Action And Its Numerical Simulation

According to the low permeability characteristic of the coal seam in our country, to improvethe CBM recovery efficiency, takes use of the special property of supercritical CO₂that itcould damage the coal in some degree and increase the pore and fracture in the coal so that coalseams permeability could be improved, and researches on coal damage change rule in differenttemperature, pore pressure and action time conditions under the action of supercritical CO₂bycombining the methods of experimental, theoretical analysis and numerical simulation together.The results have been got as flollows:The damage change rule of coal elastic modulus after the action of supercritical CO₂indifferent temperature, pore pressure and action time conditions have been got by experiments.Introducing weight factors to make a definition of coal damage variable to describe the coaldamage functional relation with temperature and pore pressure in the same action time,established a new thermal elastic-plastic damage constitutive model based on the heat transfertheory, thermodynamics, damage theory, and elastic-plastic theory.As Abaqus provided the function of subroutine development, programed the damagefunction and introduced it into Abaqus constitive equation, then simulated the different workconditions of injecting supercritical CO₂into the coal seam through single and double holesbased on the new constitutive model. In single hole injection condition, the quantitative damagedegree and damage range change rule has been got around the hole; The coal damage caused bysupercritical CO₂presented an positive exponent increasing change rule with temperatureincreasing, however, the damage degree growth range became less and less with temperatureincreasing. The coal damage caused by supercritical CO₂presented a positive exponentincreasing change rule with pore pressure increasing; in double holes injection condition, a newhigh damage region occured because of the pore pressure interference between the two holes,and the damage reached the whole region very soon, which could provide a theoretical basis forthe best distance choice between two injection holes.