The numerical simulation is used to research the influence of nitrogen injection on spontaneous combustion in goaf. The spontaneous combustion mathematical model on the coupling of air flow field, oxygen concentration...The numerical simulation is used to research the influence of nitrogen injection on spontaneous combustion in goaf. The spontaneous combustion mathematical model on the coupling of air flow field, oxygen concentration field, and residual coal temperature field was established with nitrogen injection in goat＇. Then the software of numerical computation was pro- grammed by Finite Volume Method. Combined with the example, the distributions of air flow field, oxygen concentration field and residual coal temperature field at different nitrogen injection volume were obtained by the software. The results show that the nitrogen injection could effectively prevent the spontaneous combustion fire in goaf and the highest temperature in goaf decreased with the nitrogen injection volume increasing. Finally, the accuracy of the numerical simulation was verified by the temperature observation in field. The achievement of this research is of theoretical and practical significance for the prevention of coal spontaneous combustion in goaf.展开更多
Based on heterogeneous and porous medium seepage of air leakage-diffusion equation, as well as, gas and porous medium synthesis heat transferring equation, a spontaneous combustion non-steady numerical model of nitrog...Based on heterogeneous and porous medium seepage of air leakage-diffusion equation, as well as, gas and porous medium synthesis heat transferring equation, a spontaneous combustion non-steady numerical model of nitrogen injection goaf was established, which can be solved by upwind finite element numerical simulation method si- multaneously. Taking the working face for example; air leakage seepage, nitrogen flow and gas distribution can be described in visual display in nitrogen injection goaf and the oxygen （O2）, carbon monoxide （CO） concentration and temperature distribution, as well as, their change were described in theory during the coal left behind combustion in goaf, which above reveals the complex mechanics course （mechanism） of seepage, diffusion and oxidation heat releasing during coal spontaneous combustion and its restraining. During the calculation, the effect factors of gas springing out and working face advancing were considered fully, and the spontaneous combustion course under different amount of nitrogen injection was simulated. The conclusions were obtained that under nitrogen injection condition, the high spontaneous combustion temperature area lean to the inlet air, but the shape becomes narrower, with the amount of nitrogen rising, the spontaneous combustion period becomes longer till to it does not happen. Meanwhile the nitrogen injection accelerates gas springing out in goaf. The result that turns out in theory simulation fits to practical nitrogen injection.展开更多
On the basis of heat transfer and chemical kinetics theory, both connections coal self ignite with oxygen concentration and range of oxidation zone with air leak intensity are analyzed, and calculating method is deduc...On the basis of heat transfer and chemical kinetics theory, both connections coal self ignite with oxygen concentration and range of oxidation zone with air leak intensity are analyzed, and calculating method is deduced to gain the lower limit of oxygen concentration and the range of oxidation zone. The change rule of correlative parameter is quantitatively researched between before nitrogen injection and after nitrogen injection in gob, such as oxygen concentration, oxidation zone width, etc. According to theoretical calculation, the relation position and flow of nitrogen injection with oxidation zone width is conformed, and computational formulas of the best flow and position of nitrogen injection are obtained. It offers a theoretic criterion for preventing and controlling float coal self ignite by nitrogen injection in gob.展开更多
Cyclic pressure pulsing with nitrogen is studied for hydraulically fractured wells in depleted reservoirs.A compositional simulation model is constructed to represent the hydraulic fractures through local-grid refinem...Cyclic pressure pulsing with nitrogen is studied for hydraulically fractured wells in depleted reservoirs.A compositional simulation model is constructed to represent the hydraulic fractures through local-grid refinement.The process is analyzed from both operational and reservoir/hydraulic-fracture perspectives.Key sensitivity parameters for the operational component are chosen as the injection rate,lengths of injection and soaking periods and the economic rate limit to shut-in the well.For the reservoir/hydraulic fracturing components,reservoir permeability,hydraulic fracture permeability,effective thickness and half-length are used.These parameters are varied at five levels.A full-factorial experimental design is utilized to run 1250 cases.The study shows that within the ranges studied,the gas-injection process is applied successfully for a 20-year project period with net present values based on the incremental recoveries greater than zero.It is observed that the cycle rate limit,injection and soaking periods must be optimized to maximize the efficiency.The simulation results are used to develop a neural network based proxy model that can be used as a screening tool for the process.The proxy model is validated with blind-cases with a correlation coefficient of 0.96.展开更多
The method of steam huff and puff is a common method for heavy oil production. This method requires the cooperation of nitrogen heat insulation technology. Membrane separation and PSA pressure swing adsorption are com...The method of steam huff and puff is a common method for heavy oil production. This method requires the cooperation of nitrogen heat insulation technology. Membrane separation and PSA pressure swing adsorption are commonly used in oilfields to extract nitrogen from the air. If the purity of the obtained nitrogen is not enough and the oxygen content is too high, it will cause equipment corrosion and scaling, and there are potential safety hazards. This article analyzes the reasons for the non-compliance of nitrogen purity and the problems in the detection of nitrogen injection purity in oilfields through the principle and process of nitrogen production, and gives countermeasures.展开更多
Since the West-to-East Pipeline I was put into production,operators have made many attempts and accumulated valuable experiences in gas pipeline commissioning.However,there are still some problems.For example,the inje...Since the West-to-East Pipeline I was put into production,operators have made many attempts and accumulated valuable experiences in gas pipeline commissioning.However,there are still some problems.For example,the injected nitrogen quantity was determined only by experience rather than by quantitative calculation formula;there are some unnecessary steps in the nitrogen displacement process.Therefore,the authors summarized experiences from various scenarios at home and abroad over the past decade,and introduced some innovative practices in the preparation of pipeline commissioning schemes.Particularly,the calculation formula was first developed for the required nitrogen quantity in the commissioning process;the in-turn nitrogen displacement was replaced by the simultaneous way in the paralleling pipes at the stations;nitrogen displacement was abolished in vent and drainage lines;and several other tips were concluded for the nitrogen displacement process.Supported by scientific evidences,previous commissioning experiences and data,the above innovative practices help not only simplify the on-site operation on the premise of safe production but also shorten the nitrogen displacement time greatly,and save a large quantity of nitrogen gas,as a result,the economic benefit is significantly enhanced.展开更多
As energy demand increases,the depth of mining is increasing,and methane disasters grow more serious,efficient extraction of methane is the ultimate method of preventing and controlling methane disasters.The objective...As energy demand increases,the depth of mining is increasing,and methane disasters grow more serious,efficient extraction of methane is the ultimate method of preventing and controlling methane disasters.The objectives for this research are to explore the efficiency of N_(2) injection to enhance gas extraction from coal seams(N_(2)-ECGE)and its impact on coal seam permeability.By developing a fluid-solid coupling model and using COMSOL Multiphysics to perform numerical simulations,the changes in gas pressure,methane content,gas production,output rate and permeability of coal seams were comparatively analyzed under the two methods of direct extraction and N_(2)-ECGE.The research results show that N_(2)-ECGE can significantly improve the coal seam gas pressure and reduce the coal seam CH_(4) content,and the larger the N_(2) injection pressure the more significant the reduction effect.Meanwhile,N_(2)-ECGE can significantly increase the CH_(4) extraction and output rate,and the increase of N_(2) pressure further improves the extraction efficiency.In addition,the pressure of nitrogen injection has a remarkable effect on coal seam permeability,high pressure of nitrogen injection can increase the permeability in the time of no disturbance,but the rate of permeability decreases more quickly after disturbed.The effect of strain due to adsorption desorption on coal seam permeability dominates.Despite model construction limitations,this research offers essential theoretical and practical direction for N_(2) injection to enhance the permeability evolution law of coal seam gas extraction process.展开更多
基金Supported by the National Natural Science Foundation of China （51174211）
文摘The numerical simulation is used to research the influence of nitrogen injection on spontaneous combustion in goaf. The spontaneous combustion mathematical model on the coupling of air flow field, oxygen concentration field, and residual coal temperature field was established with nitrogen injection in goat＇. Then the software of numerical computation was pro- grammed by Finite Volume Method. Combined with the example, the distributions of air flow field, oxygen concentration field and residual coal temperature field at different nitrogen injection volume were obtained by the software. The results show that the nitrogen injection could effectively prevent the spontaneous combustion fire in goaf and the highest temperature in goaf decreased with the nitrogen injection volume increasing. Finally, the accuracy of the numerical simulation was verified by the temperature observation in field. The achievement of this research is of theoretical and practical significance for the prevention of coal spontaneous combustion in goaf.
文摘Based on heterogeneous and porous medium seepage of air leakage-diffusion equation, as well as, gas and porous medium synthesis heat transferring equation, a spontaneous combustion non-steady numerical model of nitrogen injection goaf was established, which can be solved by upwind finite element numerical simulation method si- multaneously. Taking the working face for example; air leakage seepage, nitrogen flow and gas distribution can be described in visual display in nitrogen injection goaf and the oxygen （O2）, carbon monoxide （CO） concentration and temperature distribution, as well as, their change were described in theory during the coal left behind combustion in goaf, which above reveals the complex mechanics course （mechanism） of seepage, diffusion and oxidation heat releasing during coal spontaneous combustion and its restraining. During the calculation, the effect factors of gas springing out and working face advancing were considered fully, and the spontaneous combustion course under different amount of nitrogen injection was simulated. The conclusions were obtained that under nitrogen injection condition, the high spontaneous combustion temperature area lean to the inlet air, but the shape becomes narrower, with the amount of nitrogen rising, the spontaneous combustion period becomes longer till to it does not happen. Meanwhile the nitrogen injection accelerates gas springing out in goaf. The result that turns out in theory simulation fits to practical nitrogen injection.
基金NationalNaturalScienceFoundationofChina! (No .5 99740 2 0 )
文摘On the basis of heat transfer and chemical kinetics theory, both connections coal self ignite with oxygen concentration and range of oxidation zone with air leak intensity are analyzed, and calculating method is deduced to gain the lower limit of oxygen concentration and the range of oxidation zone. The change rule of correlative parameter is quantitatively researched between before nitrogen injection and after nitrogen injection in gob, such as oxygen concentration, oxidation zone width, etc. According to theoretical calculation, the relation position and flow of nitrogen injection with oxidation zone width is conformed, and computational formulas of the best flow and position of nitrogen injection are obtained. It offers a theoretic criterion for preventing and controlling float coal self ignite by nitrogen injection in gob.
文摘Cyclic pressure pulsing with nitrogen is studied for hydraulically fractured wells in depleted reservoirs.A compositional simulation model is constructed to represent the hydraulic fractures through local-grid refinement.The process is analyzed from both operational and reservoir/hydraulic-fracture perspectives.Key sensitivity parameters for the operational component are chosen as the injection rate,lengths of injection and soaking periods and the economic rate limit to shut-in the well.For the reservoir/hydraulic fracturing components,reservoir permeability,hydraulic fracture permeability,effective thickness and half-length are used.These parameters are varied at five levels.A full-factorial experimental design is utilized to run 1250 cases.The study shows that within the ranges studied,the gas-injection process is applied successfully for a 20-year project period with net present values based on the incremental recoveries greater than zero.It is observed that the cycle rate limit,injection and soaking periods must be optimized to maximize the efficiency.The simulation results are used to develop a neural network based proxy model that can be used as a screening tool for the process.The proxy model is validated with blind-cases with a correlation coefficient of 0.96.
文摘The method of steam huff and puff is a common method for heavy oil production. This method requires the cooperation of nitrogen heat insulation technology. Membrane separation and PSA pressure swing adsorption are commonly used in oilfields to extract nitrogen from the air. If the purity of the obtained nitrogen is not enough and the oxygen content is too high, it will cause equipment corrosion and scaling, and there are potential safety hazards. This article analyzes the reasons for the non-compliance of nitrogen purity and the problems in the detection of nitrogen injection purity in oilfields through the principle and process of nitrogen production, and gives countermeasures.
文摘Since the West-to-East Pipeline I was put into production,operators have made many attempts and accumulated valuable experiences in gas pipeline commissioning.However,there are still some problems.For example,the injected nitrogen quantity was determined only by experience rather than by quantitative calculation formula;there are some unnecessary steps in the nitrogen displacement process.Therefore,the authors summarized experiences from various scenarios at home and abroad over the past decade,and introduced some innovative practices in the preparation of pipeline commissioning schemes.Particularly,the calculation formula was first developed for the required nitrogen quantity in the commissioning process;the in-turn nitrogen displacement was replaced by the simultaneous way in the paralleling pipes at the stations;nitrogen displacement was abolished in vent and drainage lines;and several other tips were concluded for the nitrogen displacement process.Supported by scientific evidences,previous commissioning experiences and data,the above innovative practices help not only simplify the on-site operation on the premise of safe production but also shorten the nitrogen displacement time greatly,and save a large quantity of nitrogen gas,as a result,the economic benefit is significantly enhanced.
基金supported by the National Natural Science Foundation of China(52374249,52130409,52121003)the National Key R&D Program(2023YFC3009003)+1 种基金the Basic Research Business Fees for Central Universities(2024JCCXAQ01)Open Fund of State Key Laboratory of Coal Mine Disaster Dynamics and Control(2011DA105287-FW202303).
文摘As energy demand increases,the depth of mining is increasing,and methane disasters grow more serious,efficient extraction of methane is the ultimate method of preventing and controlling methane disasters.The objectives for this research are to explore the efficiency of N_(2) injection to enhance gas extraction from coal seams(N_(2)-ECGE)and its impact on coal seam permeability.By developing a fluid-solid coupling model and using COMSOL Multiphysics to perform numerical simulations,the changes in gas pressure,methane content,gas production,output rate and permeability of coal seams were comparatively analyzed under the two methods of direct extraction and N_(2)-ECGE.The research results show that N_(2)-ECGE can significantly improve the coal seam gas pressure and reduce the coal seam CH_(4) content,and the larger the N_(2) injection pressure the more significant the reduction effect.Meanwhile,N_(2)-ECGE can significantly increase the CH_(4) extraction and output rate,and the increase of N_(2) pressure further improves the extraction efficiency.In addition,the pressure of nitrogen injection has a remarkable effect on coal seam permeability,high pressure of nitrogen injection can increase the permeability in the time of no disturbance,but the rate of permeability decreases more quickly after disturbed.The effect of strain due to adsorption desorption on coal seam permeability dominates.Despite model construction limitations,this research offers essential theoretical and practical direction for N_(2) injection to enhance the permeability evolution law of coal seam gas extraction process.
