Experimental And Numerical Simulation Study On The Influence Of Heat Injection On Coalbed Methane Exploitation

Steam injection has both advantages and disadvantages for coalbed methane exploitation.The steam heat carried by it can promote the desorption of coalbed methane,but the steam and its condensed water itself will bring certain obstacles to coalbed methane seepage.In order to study the influence of heat injection on coalbed methane mining,first of all,low-temperature nitrogen adsorption tests are conducted on raw coal and coal samples treated by heat injection steam.It is found that the average pore diameter and total pore capacity of coal after heat injection steam increase,and in the process of heat injection steam,there is a certain erosion effect on the pore structure of coal,and then the pore expansion effect occurs.Hot steam obviously promotes the development,expansion and penetration of coal matrix pores.Secondly,based on the principles of heat transfer,mass transfer,stress conservation and steam phase transition,a three-phase twocomponent model of thermal-fluid-solid coupling considering the dual effects of steam on coalbed methane thermal injection mining was established.Secondly,based on the principle of porous elasticity,the model is divided into a coal deformation equation which takes into account the deformation of coal skeleton under in-situ stress and pore pressure,the shrinkage of coal matrix caused by desorption,and the thermal strain of coal skeleton caused by thermal convection and heat conduction.The heat flow equations composed of mass and energy conservation of water and gas components and the coal deformation equation are divided into two calculation modules.The two modular differential equations were discretized by the finite volume method,and the solid deformation equations and heat flow equations were solved by the combination of Newton-Rafson iteration and GMRES(generalized minimal residual algorithm),and the solution process was realized by the FORTAN language programming.Finally,by establishing a two-dimensional plane model composed of five Wells,three injection and production schemes of 250℃ steam injection,250℃ hot water injection and direct extraction were numerically simulated.The results show that,under the set injection pressure and time,the water injection amount of 250℃ steam injection is 83.1% of that of 250℃ hot water injection,and the water saturation,temperature and pressure near the bottom of coal seam change obviously after the injection of 250℃ steam injection.After 250℃ steam injection,the cumulative extraction of coalbed methane was significantly improved,but the range of improvement gradually decreased with the increase of extraction time.According to statistics,the cumulative extraction of coalbed methane after 250℃ steam injection increased by 17.5%compared with direct extraction for 100 days,while the cumulative extraction of coalbed methane after hot water injection decreased by 9.8% compared with direct extraction.The simulation results show that steam injection can effectively improve the extraction efficiency of coalbed methane within a certain extraction time.Figure 34 Table 8 Reference 100...