Study On Development Law Of Water Diversion Fracture Zone Of Underground Coal Gasification

Coal underground gasification is known as the second generation coal mining method.It is a new technology of building well,coal mining and gasification.It can effectively extract the combustible component in the underground coal and transform the traditional physical coal mining into chemical mining.The technology has the safety,efficiency and cleanliness of the traditional mining technology.By means of theoretical analysis,numerical simulation and similar material simulation,the distribution law of the temperature field of the surrounding rock of coal underground gasification,the law of the breaking ring of the overlying rock in the flammable zone and the law of the development of the water guide fracture zone are systematically studied in this paper.1)The roof rock strata in the burned area will cause micro thermal failure.Scanning electron microscope(SEM)is used to scan the roof rock samples of combustible area.When coal resources are exploited by underground coal gasification,the rupture of the roof is not only damaged by stress,but also caused by heat rupture caused by high temperature.The failure mode is the expansion of rock after high temperature,and a clear visible crack along rock joints is formed.2)The transmission range of underground coal gasification in different strata is different.Through the simulation of the temperature conduction in the gasification process in Wulanchabu mining area,the study shows that the temperature has a different influence on the roof,the coal wall and the floor,and the diffusion law in the respective rock layers also presents different trends.Through experimental comparison,the conduction range of the temperature in the roof is not more than 16.6 meters.The conduction range of the coal wall on both sides of the gasifier is not more than 11.8 meters,and the conduction range in the bottom is not more than 13 meters,and the gradient arrangement of the temperature decreases in each rock.3)An improved numerical modeling method for underground coal gasification is proposed.Because the underground coal gasification process produces great heat,the temperature can reach more than 1000 degrees Celsius.Considering the influence of temperature on the surrounding rock,the mechanical parameters of the surrounding rock should be stratified according to the temperature distribution in the surrounding rock,so that the numerical simulation results are more accurate.The accuracy of the numerical simulation and the feasibility of the modeling method are verified by comparing the numerical simulation with the measured data.4)The development form and height of the water flowing fractured zone of coal underground gasification have their unique development rule.Through the establishment of numerical model considering temperature factor mining and non consideration of temperature factors,the development of water conducting fissure zone in traditional well mining and underground coal gasification is compared and studied.The test shows that the ultimate development height of the water conducting fissure zone is 15 meters,the maximum subsidence value of the roof is 42 cm,and the development form of the water conducting fissure zone is similar to the "arch".The numerical model simulation results of coal underground gasification are set up,the height of the development of the water fissure zone is 47 meters,the maximum subsidence of the roof is 37 cm,and the shape of the fissure zone of the water guide is "butterfly wing" extending to the two sides.5)The development height of the water flowing fractured zone is related to the design width of the gasifier.When the width of mining width is small,the increase of the mining width will lead to the increase of the height of the fracture zone of the water guide.The existing formula for calculating the height of water diversion fracture zone only considers the factor of mining thickness,but when mining the coal underground gasification,it is generally not too large to take into account the width of the integrity design of the combustible zone.Therefore,two factors should be taken into consideration at the same time when the height of the water fissure zone of the overlying strata in the underground coal gasification is calculated.The calculation of the gap height is more accurate.