Analysis of Enhancing Coalbed Methane Recovery and Improving Coal Mining Safety by CO2 Injection: Model of the Critical CO2 Volume Fraction
Keywords:Coal mining, CO2 injection, CBM recovery, Explosion limit, Gas explosion prevention
Coalbed methane (CBM) is produced before coal mining at the Qinshui Basin in China to utilize CBM and reduce CH4 volume fraction for coal mining. However, the volume fraction of CH4 often reaches the range between lower and upper explosion limits after CBM production, which is a great threat to coal mining safety. In previous work, we analyzed the feasibility of injecting CO2 into coalbeds to control CH4 volume fraction for mining safety and simultaneously enhancing CBM recovery. In this paper, we extended our work to propose a model to calculate the critical CO2 volume fraction for CO2 injection. We simplified the gas mixture during coal mining as the CO2/CH4/air mixture. The model of the critical CO2 volume fraction was then built based on the explosion limit formula for the CO2/CH4/N2 mixture. The formula for the critical CO2 volume was derived using the critical CO2 volume fraction. The model of the critical CO2 volume fraction was applied in a CBM reservoir at the South Shizhuang Block in the Qinshui Basin. The CO2 injection rate for this block was optimized to obtain the highest CBM recovery using the reservoir simulation method. Results show that the critical CO2 volume fraction is 7.97%, which makes the CH4 volume fraction out of the explosion limits. The optimum CO2 injection rate for this block is 8000m3/d which improves the CBM recovery up to 86.24%.
Yang Y. Coal mine safety statistics and analysis. Chinese State Administration of Coal Mine Safety. 2015.
Liu S, Wu W, Zhang X, Chen H. The production curve and recovery rate of coalbed methane well in Panzhuang block. Journal of China Coal Society. 2013; 38(Supp.1): 164-167.
Huang H, Li M, Gu A, Shi Y. Theoretical analysis on the explosion limit of coalbed methane gas. Natural Gas Industry. 2010; 30(12):104-107.
Jia L, Gao S. Simulation of mineral dissolution after CO2 injection in coal seams in southern Qinshui Basin. Coal Engineering. 2019; 38(03): 89-91.
Mo F, Peng X, Du Z. Enhancing the Safety of Coal Mining by Injecting CO2 into Coalbeds. Applied Mechanics & Materials, 2014, 694:307-311. https://doi.org/10.4028/www.scientific.net/AMM.694.307
Wei C. Porous materials inhibition on gas explosion. PhD thesis, Harbin Institute of Technology. 2012.
Ma F, Wang L, Liu Q, Bao X, Wang H, Xie S. Study on enhancing oil recovery by CO2 injection in late production stage of coalbed methane well group. Journal of Guangdong University of Petrochemical Technology. 2016; 26(06): 9-11+27.
Li S, Bai Y, Lin H, Yan M, Long H, Guo D. Effect of N2/CO2 injection pressure on methane desorption in coal rock containing gas. Natural Gas Industry. 2021; 41(03): 80-89.
Zhang R, He X, Nie B, Li X, Dai L, Zhao C. Status quo and prospect of gas explosion suppressing and isolating techniques in coal mines. Journal of Safety Science and Technology. 2011; 7(7): 15-19.
Liu L. Research on liquid nitrogen accompanied injection and CO2 displacement technology for hydraulic fracturing of coalbed methane Wells. Coal Engineering. 2020; 52(04): 124-129.
Wang Z, Meng S, Zhang S, Jia J .Study on CO2 injection parameters of horizontal well in deep coal seam north of Shizhuang in Qinshui Basin. Coal Geology & Exploration. 2018: 46(05): 188-192.
Gant SE, Pershell MR, Lea CJ, Fletcher J, Rattigan W, Thyer AM, Connolly S. Flammability of hydrocarbon and carbon dioxide mixtures. Process Safety and Environmental Protection. 2011; (89): 472-481. https://doi.org/10.1016/j.psep.2011.06.017
He K. Experiment on performance of CO2 suppressing methane explosion. Fire Science and Technology. 2011; 30 (6): 476-495.
Li S, Sun L, Chen Z, Li J, Pan Y, Tang Y. Re-discussion on the development of CO2 flooding enhanced oil recovery reservoir engineering concept and development model. Reservoir Evaluation and Development. 2020; 10(3): 1-14.
Ma L, Xiao Y, Deng J, Wang Q. Effect of CO2 on explosion limits of flammable gases in goafs. Mining Science and Technology. 2010; 20 (2): 193-197. https://doi.org/10.1016/S1674-5264(09)60183-6
Benedetto AD, Sarli VD, Salzano E, Cammarota F, Russo G. Explosion behavior of CH4/O2/N2/CO2 and H2/O2/N2/CO2 mixtures. International Journal of Hydrogen Energy. 2009; 34(16): 6970-6978. https://doi.org/10.1016/j.ijhydene.2009.05.120
Wei G, Wen H, Deng J, Li Z, Fan S, Lei C, Liu M, Ren L.Enhanced coalbed permeability and methane recovery via hydraulic slotting combined with liquid CO2 injection. Process Safety and Environmental Protection. 2021: (147): 234-244. https://doi.org/ 10.1016/j.psep.2020.08.033
Luo Z, Wang T, Tian Z, Cheng F, Deng J, Zhang Y. Experimental study on the suppression of gas explosion using the gas-solid suppressant of CO2/ABC powder. Journal of Loss Prevention in the Process Industries. 2014; (30): 17-23. https://doi.org/10.1016/ j.jlp.2014.04.006
Ren S, Li H, Li L, Zhang L, Wang F. An experimental study of effects of inert and special flammable gases on methane's explosion characteristics. Natural Gas Industry. 2013; 33(10): 110-115.
Kondo S, Takizawa K, Takahashi A, Tokuhashi K. Extended Le Chatelier's formula for carbon dioxide dilution effect on flammability limits. Journal of Hazardous Materials. 2006; (A138): 1-8. https://doi.org/10.1016/j.jhazmat.2006.05.035
Wang ZR, Ni L, Liu, X, Jiang J, Wang R. Effects of N2/CO2 on explosion characteristics of methane and air mixture. Journal of Loss Prevention in the Process Industries. 2014; (13): 10-15. https://doi.org/10.1016/j.jlp.2014.06.004
Jia L, Liu P, Yuan D, Lei T, Ran J, Wang G. CO2 injection to improve the recovery rate of shale adsorbed gas: taking Chang 7 shale gas of Yanchang Formation in Ordos Basin as an example. Petroleum Geology & Oilfield Development in Daqing. 2021; 40(2):153-159.
Scheper K, Oudinot A. Enhanced gas recovery and CO2 storage in coalbed-methane reservoirs: optimized injected-gas composition for mature basins of various coal rank. SPE International Conference on CO2 Capture, Storage and Utilization, Louisiana, U.S.A. 2010; 10-12. https://doi.org/10.2118/139723-MS
Liang W, Zhang P, He W, Yao H. Experimental study on CH4 mining by supercritical CO2 flooding in different rank coal. Journal of China Coal Society. 2020; 5(01):197-203.
Lin H, Liu J, Yan M, Bai Y, Liu B. Molecular dynamics simulation of CO2/CH4 diffusion in coal reservoir. Journal of Safety Science and Technology. 2017; 13(01): 84-89.
Shi JQ, Durucan S. Modelling of mixed-gas adsorption and diffusion in coalbed reservoirs. SPE Unconventional Reservoirs Conference, Colorado, U.S.A. 2008; 10-12. https://doi.org/10.2118/114197-MS
Lang D, Lun Z, Lv C, Wang H, Zhao Q, Sheng H. Influencing factors of CO2 injection for shale oil to enhance oil recovery. Nuclear magnetic resonance experiment. Petroleum Exploration and Development. 2021; 48(3): 1-10. https://doi.org/10.1016/S1876-3804(21)60056-3
Zhang C, Shen J, Qin Y, Ye J, Zhang B. CO2 injection to improve CBM recovery and CO2 storage technology. Coal Science and Technology. 2016; 44(06): 205-210.
Zheng X, Huang Y, Wen H, Wang X, Wang B. Industry and Mine Automation. 2021; 47(4): 73-78.
Liu H, Wu H, Xu H, Lan, T. Characteristics and controlling factors of supercritical CO2 adsorption in deep coal seams in southern Qinshui Basin. Coal Geology & Exploration. 2018; 46(05): 37-42+48.
How to Cite
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.