Study On Mechanism Of Injection Heat Increasing Production In Coal-bed Gas Of Low Permeability Coal Seam

The reserve of coal-bed gas is rich in china and the exploration of coal-bed gas can relax the short state of energy and protect the environment and prevent the gas disaster at the same time. At present, the characteristic, high reserve and low permeability restrict the development of coal-bed gas industry. The difficulty of coal-bed gas exploration is how to improve the permeability of coal-bed, and the theory breach is not formed. The technology of heat injection to exploit coal-bed gas that the scholar identified commonly maybe becomes a practical way, but there is a big disputed to the mechanism of the technology. Based on the theory of heat transfer, thermodynamics, rock mechanics, elastic mechanics, seepage mechanics, through the method of experiment and numerical simulation, the change rule of deposit and flow of coal-bed gas under the conditions of different temperature, the theory of thermodynamic evaluation and the coupling mechanism and rule of heat-solid-fluid is studied by the numbers.The main result of this paper is list as follows:(1) Through modified tri-axial seepage instrument of our own property rights, the two coal samples of coal-bed gas desorption and seepage experiment were carried in laboratory considered at different temperatures, stress conditions. The experimental results showed that the coal-bed gas molecules absorbed heat after elevated temperatures, the activity and inner energy increased, and desorption capacity increased from the surface of coal unite, coal bed gas permeability increases with temperature exponentially increasing. coal-bed gas seepage increases than lower temperature; at low stress, due to the expansion of coal was less affected, this increment is more evident.(2) The experimental result show the increase production mechanism of heat injection to exploit coal-bed gas: After the coal-bed gas absorbed heat, the kinetic energy and nature of molecules enhanced and escaped from coal mass surface greatly, and the consistency of gas enhanced. More coal-bed gas diffuses to crane from bedrock and pore under the condition of consistency gradient. In crane, the density of coal-bed gas induced to the increase of pressure gradient, and it's a main reason that results in the increase of the seepage flux.(3) Based on heat transfer, after heat injection to coal-bed, desorption area of gas is divided to three according to different temperature: heated area, heated boundary and non-heated area. The one-dimensional mathematical model is set up to three area and resolve result is gained using similarity transform and integral equation approximated solution. On the basis of this solution, the exploitation thermal efficiency and energy efficiency is obtained and the theory to appraise the economy is supplied.(4) Utilize the heat transfer theory and elasticity theory, introduce heat elasticity Huke law, set up a hot - solid coupling mathematical model of coal seam and make use of FEPG. to set up examples of numerical simulation. The simulation results show that, in spite of smaller thermal conductivity of coal seam, because of the latent heat of water vapor phase change is released, the radius of thermal diffusivity is desirable, and the pressure difference is increased because of the pressure of heat injection, so desorption capacity of coal-bed gas is further increased.(5) The theory of heat transfer, thermodynamics, elasticity mechanics, seepage mechanics, rock mechanics is applied to set up the hot - solid - fluid coupling mathematical model of coal-bed methane with diffusivity seepage, and the finite element software is used to simulate a single well when exploited with heat rejection. The simulation results show that, the seepage pressure dropped more obvious and the production increase more than general exploitation under the condition of heat injection. The simulation results are accorded with experiment, therefore confirm the correctness of the mathematical model and the reasonability of heat injection is reasonable further.(6) On the basis of the exploitation of a single well, in order to improve the limitations of single well production, the impact on seepage rule of coal-bed gas of inter-well interference is further studied. By simplifying the mathematical model, the calculation procedures are writing and the seepage rule of coal-bed gas is stimulated under the conditions of multi-producing wells. The simulation results show that multi-production wells will increase desorption capacity and production of coal-bed gas. By the numerical simulation results can be drawn that on the base of single well exploitation with heat injection, the effect of heat injection exploitation is enhanced if the technology of multi-production well heat injection is adopted.Through the above research, the heat rejection exploitation of coal-bed gas is reasonable and feasible and a well-established channel is provided.