Study On The Evaluation Of Energy Migration And Thermal Economics Evaluation Of CBM Thermal Injection Mining In Low Permeability Reservoirs

Coal-bed methane(CBM)has geological characteristics,such as high reserve and low permeability,making it commercially difficult to have it excavated.Heat injection is one of the means to fundamentally change the geological characteristics of coal bed gas and increase the production.Evaluating the thermal efficiency of “high reserve,low permeability”CBM is the key in using heat injection for the excavation,thus determining the feasibility of the technology.To realize the thermal economic evaluation of the CBM injection heat production process in low-permeability reservoirs,it is necessary to obtain the distribution law of heat injected into the coal seam through numerical simulation.Therefore,the thesis firstly used a self-made temperature-controlled triaxial coal bed methane desorption and permeability experimental device and added a heat monitoring system to carry out experimental research on coal sample permeability,desorption output and desorption calorimeter measurement,and obtained the theory of coal permeability and effective stress and temperature.The model,the theoretical model of the desorption output changing with the heat injection time,and the theoretical characteristic model of the dynamic change of the desorption heat and the desorption amount.These relationship equations provide the necessary coupling conditions for the subsequent numerical simulation of the thermal fluid-solid coupling of CBM thermal injection.The mathematical model of heat-fluid-solid coupling and heat distribution of CBM in low-permeability reservoirs by heat injection mining is established.Combining the experimental relationship obtained from the experiment,the numerical simulation of the heat-fluid-solid coupling of CBM thermal injection using COMSOL Multiphysics software is carried out.A thermal economic evaluation system based on the thermal efficiency and energy efficiency of the low-permeability CBM thermal injection process was established.The thermal economic evaluation and well layout optimization of the CBM heat injection production were carried out.The experimental results show that the change trend of permeability is mainly determined by the thermal stress and effective stress.In the low stress area,as the temperature increases,the coal permeability increases;in the high stress area,as the temperature increases,the coal mass The permeability decreases,and there is a turning stress zone for coal sample permeability with temperature changes.The experiment obtained the theoretical model relationship of methane permeability with respect to temperature and effective stress;the temperature-controlled triaxial coal bed methane desorption and permeation experiment device was used to obtain the desorption heat required for the coal bed methane desorption process,and the desorption required for the coal bed methane desorption process was found.The heat increases exponentially with the increase of CBM desorption flow rate.At the same time,the reason for the change of CBM desorption heat is explained from the theory of adsorption potential well;the simulation results show that the hot working medium is injected into the coal seam during the injection of CBM in the low permeability reservoir.The distribution law of the temperature field,gas pressure field and seepage velocity field of the back coal seam,and the numerical calculation according to the temperature field distribution law to obtain the heat distribution of the coal body,the heat absorption of the coal bed methane absorption and the heat distribution of the CBM desorption.Under the conditions,the heat absorption of various parts in the coal seam is used as the thermal efficiency evaluation factor to evaluate the thermal economy of the CBM injection mining.Thermal economic evaluation results show that different well layout methods,well spacing,and heat injection temperature have a direct impact on the thermal economic evaluation of the CBM thermal injection production process.By comparing different well layout schemes,comprehensive economic and energy saving aspects It is considered that in the multi-well mining single-well heat injection layout mode,the center of the well is selected to arrange heat injection wells,and the four corners are production wells.The thermal efficiency and energy efficiency of coal bed methane injection heat production are best when the heat injection temperature is 120?.The thesis provides important theoretical support and reference value for the process of heat injection recovery of low permeability reservoir coalbed methane project.This paper has 37 pictures,9 tables,and 87 references.