| Gas disasters happen frequently in coal mining, consequently, coalbed methane(CBM) recovery is of great significance for comprehensive utilization, optimizedenergy structure and safe and efficient production of coal. However, in china, CBMindustry is faced with a series of technical development bottlenecks just like "three highand one low" etc. furthermore the migration characteristics of CBM is a little equivocalespecially the mechanism of high-permeability aggregation and low-permeabilitytransport. For a further exploration on migration law of CBM under complicatedgeological conditions, this paper took K3seam of Chongqing coal mine as the researchobject to research systematically on the physical and mechanical properties of coal,dynamic parameters of coal reservoir in CBM recovery process and dynamicalphenomena of the blowout process in CBM recovery engineering by the combinedmeans of the laboratory test, the theoretical analysis, the numerical simulation and theengineering application. And the migration law of CBM in multi-field couplingreservoir system was effectively discussed based on the basic theory such as RockMechanics, Advanced Mechanics of Fluids in Porous Media, Heat Transfer Theory, etc.The main conclusions of the research are as follows:1) The “Multi-field Coupling test System for CBM Exploitation” wasindependently developed based on the similarity theory, which is the first test device ofphysical simulation for coalbed methane exploitation. And then, a new test method ofphysical simulation for CBM exploitation was proposed, which provide a new researchmethod for the dynamic evolution of coal reservoir parameters in CBM exploitation.2) A series of physical simulations of CBM exploitation were conducted underdifferent reservoir pressures and variously spatial locations of the drill hole to discussspatial-temporal evolution of reservoir parameters in the process of CBM recover. Andthe mechanism of influence of reservoir pressures and spatial locations of the drill holeon reservoir parameters and CBM exploitation efficiency was preliminarily ascertained.Then the Weibull distribution was proposed to predict and evaluate CBM productivity.3) A series of physical simulations of drilling blowout were conducted underdifferent gas pressures, different drilling diameters and different moisture content tostudy the instability and failure evolution process of the drill hole and its dynamic effect, analysis of which revealed the variation laws of gas pressure, temperature, blowouttendentiousness, blowout intensity and fragmentation degrees of coal particle. And themechanism of influence of gas pressure, drilling diameter and moisture content on theabove-mentioned parameters.4) Based on the assumption of linear and thermal elastic, the total strain expressionof coal containing gas was derived including thermal strain, compressive strain causedby gas pressure, strain due to gas adsorption/desorption, strain induced by effectivestress. Then, the dynamic evolution models of porosity and fracture as well as thedynamic evolution models of porosity permeability and fracture permeabilityconsidering gas slippage effect were established, and then THM coupling model wasdeveloped with boundary conditions. Finally, the established model was provedcorrectness under multi-scale system and multi-field coupling conditions by means ofphysical simulation experiment in cooperation with numerical simulation analysis.5) Taking the K3seam of Shihao Mine in Chongqing as engineering background,we calculated and discussed the spatio-temporal evolution and linkage characteristics ofreservoir pressure, effective stress, permeability, slippage effect, recover production, etc.during CBM drainage process under the Multi-field coupling condition. And theinfluence and its mechanism of slippage effect, negative pressures and the drillingdiameter on CBM recovery productivity were also preliminarily ascertained... |
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