| Citation: | XIE Chonghong, ZHONG Dongliang, LI Mingwei. Study on the decomposition characteristics of natural gas hydrate formed in porous media with different saturations[J]. Marine Geology Frontiers, 2022, 38(3): 19-26. doi: 10.16028/j.1009-2722.2021.057 | 
The exploitation of natural gas hydrate (NGH) is of great significance to alleviate the world energy crisis and solve the problem of natural gas resource shortage in China. Facts prove that depressurization method is a relatively simple, safe, and effective method for the exploitation of natural gas hydrates. However, there is a lack of in-depth understanding of the decomposition characteristics of hydrates with high hydrate saturation under depressurization. Therefore, the formation and decomposition experiments of NGH were carried out in the porous medium (quartz sand) system. The decomposed characteristics of NGH under three different saturation conditions (38.1%, 42.1%, 46.4%) were studied, and the decomposition pressures were 2 MPa and 3 MPa, respectively. The results show that the hydrate decomposition rate is quite high corresponding to 2 MPa, and the simulated reservoir temperature drops below the freezing point, that will cause ice blocking to stop further decomposition of hydrate in the actual production of NGH. When the decomposition pressure is 3 MPa, from 0 h to 2 h, the gas production rate decreases with the increase in hydrate saturation, and from 2 h to the end of the experiment, the gas production rate increases with the increase of hydrate saturation. In the depressuring stage, the reservoir temperature (T1, T2, T3) of NGH with different saturations drops rapidly to a similar minimum. In the constant pressure stage, the reservoir temperature of NGH with different saturations recovers to rise. The higher the saturation, the greater the reservoir temperature fluctuation and longer the time to return to the experimental temperature. In order to achieve high-efficiency exploitation, measures have to be taken to prevent ice blocking. The hydrate decomposition pressure should be set at 3 MPa, and the reservoir with a high hydrate saturation should be set for a longer decomposition time to increase CH4 recovery rate and ensure the efficiency of exploitation.
 
		                | [1] | YIN Z Y,LINGA P. Methane hydrates:a future clean energy resource[J]. Chinese Journal of Chemical Engineering,2019,27(9):2026-2036. doi: 10.1016/j.cjche.2019.01.005 | 
| [2] | MORIDIS G J,KOWALSKY M B,PREUSS K,et al. Depressurization-induced gas production from class 1 hydrate deposits[J]. SPE Reservoir Evaluation and Engineering,2007,10(5):458-481. doi: 10.2118/97266-PA | 
| [3] | FENG J C,WANG Y,LI X S,et al. Production behaviors and heat transfer characteristics of methane hydrate dissociation by depressurization in conjunction with warm water stimulation with dual horizontal wells[J]. Energy,2015,79:315-324. doi: 10.1016/j.energy.2014.11.018 | 
| [4] | 丁蟠峰,杨富祥,程遥遥. 可燃冰的研究现状与前景[J]. 当代化工,2019,48(4):815-818. doi: 10.3969/j.issn.1671-0460.2019.04.040 | 
| [5] | ALMENNINGEN S,FOTLAND P,FERNØ M A,et al. An experimental investigation of gas-production rates during depressurization of sedimentary methane hydrates[J]. SPE Journal,2019,24(2):522-530. doi: 10.2118/190811-PA | 
| [6] | 陈朝阳,游昌宇,吕涛,等. 南海北部天然气水合物藏垂直井网降压开采数值模拟[J]. 天然气工业,2020,40(8):177-185. doi: 10.3787/j.issn.1000-0976.2020.08.015 | 
| [7] | LI S X,LI S,ZHENG R Y,et al. Strategies for gas production from Class 2 hydrate accumulations by depressurization[J]. Fuel,2021,286:119380. doi: 10.1016/j.fuel.2020.119380 | 
| [8] | 彭盈钰,苏正,刘丽华,等. 天然气水合物降压开采分解前缘移动数值研究[J]. 海洋地质与第四纪地质,2020,40(6):198-207. | 
| [9] | ANDERSON B I,COLLETT T S,LEWIS R E,et al. Using open hole and cased-hole resistivity logs to monitor gas hydrate dissociation during a thermal test in the mallik 5L-38 research well,Mackenzie Delta,Canada[J]. Petrophysics,2008,49(3):285-294. | 
| [10] | CHONG Z R,YANG M J,KHOO B C,et al. Size effect of porous media on methane hydrate formation and dissociation in an excess gas environment[J]. Industrial and Engineering Chemistry Research,2016,55(29):7981-7991. doi: 10.1021/acs.iecr.5b03908 | 
| [11] | LI B,LIU S D,LIANG Y P,et al. The use of electrical heating for the enhancement of gas recovery from methane hydrate in porous media[J]. Applied Energy,2018,227:694-702. doi: 10.1016/j.apenergy.2017.08.066 | 
| [12] | AMINNAJI M,TOHIDI B,BURGASS R,et al. Effect of injected chemical density on hydrate blockage removal in vertical pipes:use of MEG/MeOH mixture to remove hydrate blockage[J]. Journal of Natural Gas Science and Engineering,2017,45:840-847. doi: 10.1016/j.jngse.2017.06.030 | 
| [13] | YUAN Q,SUN C Y,YANG X,et al. Gas Production from methane-hydrate-bearing sands by ethylene glycol injection using a three-dimensional reactor[J]. Energy and Fuels,2011,25(7):3108-3115. doi: 10.1021/ef200510e | 
| [14] | 樊栓狮,郭 凯,王燕鸿,等. 天然气水合物动力学抑制剂性能评价方法的现状与展望[J]. 天然气工业,2018,38(9):103-113. doi: 10.3787/j.issn.1000-0976.2018.09.014 | 
| [15] | LIANG M,GUSHCHIN P A,KHLEBNIKOV V N,et al. Methane recovery from natural gas hydrate via CO2 /CH4 injection in the presence of methanol aqueous solution[J]. Journal of Petrochemical Universities,2018,31(6):61-66. | 
| [16] | WANG X H,SUN Y F,WANG Y F,et al. Gas production from hydrates by CH4-CO2/H2 replacement[J]. Applied Energy,2017,188:305-314. doi: 10.1016/j.apenergy.2016.12.021 | 
| [17] | MEREY S,AL-RAOUSH R I,JUNG J,et al. Comprehensive literature review on CH4-CO2 replacement in microscale porous media[J]. Journal of Petroleum Science and Engineering,2018,171:48-62. doi: 10.1016/j.petrol.2018.07.032 | 
| [18] | FALSER S,UCHIDA S,PALMER A C,et al. Increased gas production from hydrates by combining depressurization with heating of the wellbore[J]. Energy and Fuels,2012,26(10):6259-6267. doi: 10.1021/ef3010652 | 
| [19] | WANG B,FAN Z,ZHAO J F,et al. Influence of intrinsic permeability of reservoir rocks on gas recovery from hydrate deposits via a combined depressurization and thermal stimulation approach[J]. Applied Energy,2018,229:858-871. doi: 10.1016/j.apenergy.2018.08.056 | 
| [20] | WAN Q C,SI H,LI B,et al. Heat transfer analysis of methane hydrate dissociation by depressurization and thermal stimulation[J]. International Journal of Heat And Mass Transfer,2018,127:206-217. doi: 10.1016/j.ijheatmasstransfer.2018.07.016 | 
| [21] | ZHAO J F,ZHU Z H,SONG Y C,et al. Analyzing the process of gas production for natural gas hydrate using depressurization[J]. Applied Energy,2015,142:125-134. doi: 10.1016/j.apenergy.2014.12.071 | 
| [22] | 陈强,胡高伟,李彦龙,等. 海域天然气水合物资源开采新技术展望[J]. 海洋地质前沿,2020,36(9):44-55. | 
| [23] | WANG B,FAN Z,WANG P F,et al. Analysis of depressurization mode on gas recovery from methane hydrate deposits and the concomitant ice generation[J]. Applied Energy,2018,227:624-633. doi: 10.1016/j.apenergy.2017.09.109 | 
| [24] | CHONG Z R,MOH J W R,YIN Z Y,et al. Effect of vertical wellbore incorporation on energy recovery from aqueous rich hydrate sediments[J]. Applied Energy,2018,229:637-647. doi: 10.1016/j.apenergy.2018.08.020 | 
| [25] | MORIDIS G J,COLLETT T S,POOLADI-DARVISH M,et al. Challenges,uncertainties,and issues facing gas production from gas-hydrate deposits[J]. SPE Reservoir Evaluation and Engineering,2011,14(1):76-112. doi: 10.2118/131792-PA | 
| [26] | ZHAO J F,LIU D,YANG M J,et al. Analysis of heat transfer effects on gas production from methane hydrate by depressurization[J]. International Journal of Heat And Mass Transfer,2014,77:529-541. doi: 10.1016/j.ijheatmasstransfer.2014.05.034 | 
| [27] | GE B B,ZHONG D L,LU Y Y. Influence of water saturation and particle size on methane hydrate formation and dissociation in a fixed bed of silica sand[J]. Energy Procedia,2019,158:5402-5407. doi: 10.1016/j.egypro.2019.01.623 | 
| [28] | LI X Y,LI X S,WANG Y,et al. The determining factor of hydrate dissociation rate in the sediments with different water saturations[J]. Energy,2020,202:117690. doi: 10.1016/j.energy.2020.117690 | 
| [29] | YANG M J,ZHENG J N,GAO Y,et al. Dissociation characteristics of methane hydrates in South China Sea sediments by depressurization[J]. Applied Energy,2019,243:266-273. doi: 10.1016/j.apenergy.2019.03.160 | 
| [30] | ZHANG Y,LI X S,CHEN Z Y,et al. Effect of hydrate saturation on the methane hydrate dissociation by depressurization in sediments in a cubic hydrate simulator[J]. Industrial and Engineering Chemistry Research,2015,54(10):2627-2637. doi: 10.1021/ie5042885 | 
| [31] | REN X W,GUO Z Y,NING F L,et al. Permeability of hydrate-bearing sediments[J]. Earth-Science Reviews,2020,202:103100. doi: 10.1016/j.earscirev.2020.103100 | 
| [32] | DU P B,ZHAO C T,PENG P,et al. Fractal characterization of permeability prediction model in hydrate-bearing porous media[J]. Chemical Engineering Science,2020,218:115576. doi: 10.1016/j.ces.2020.115576 | 
| [33] | MAHABADI N,DAI S,SEOL Y,et al. Impact of hydrate saturation on water permeability in hydrate-bearing sediments[J]. Journal of Petroleum Science and Engineering,2019,174:696-703. doi: 10.1016/j.petrol.2018.11.084 | 
| [34] | 刘乐乐,刘昌岭,孟庆国,等. 分形理论在天然气水合物研究领域的应用[J]. 海洋地质前沿,2020,36(9):11-2. | 
| [35] | 杨胜雄,梁金强,陆敬安,等. 南海北部神狐海域天然气水合物成藏特征及主控因素新认识[J]. 地学前缘,2017,24(4):1-14. | 
| [36] | LIANG Y P,TAN Y T,LUO Y J,et al. Progress and challenges on gas production from natural gas hydrate-bearing sediment[J]. Journal of Cleaner Production,2020,261:121061. doi: 10.1016/j.jclepro.2020.121061 | 
| [37] | SLOAN E D, KOH C A. Clathrate Hydrates of Natural Gases[M]. New York: CRC Press, 2007, 731. | 
| [38] | 蔡建超,夏宇轩,徐赛,等. 含水合物沉积物多相渗流特性研究进展[J]. 力学学报,2020,52(1):208-223. doi: 10.6052/0459-1879-19-362 | 
| [39] | ZHANG L X,SUN M R,SUN L J,et al. In-situ obervation for natural gas hydrate in porous medium water performance and formation characteristic[J]. Magnetic Resonance Imaging,2020,65:166-174. doi: 10.1016/j.mri.2019.09.002 | 
 
			            
			            
			            
			        Schematic diagram of the experimental apparatus for natural gas hydrate exploitation
Gas consumption and temperature change with time
Gas production and pressure change at the dissociation pressure of 3 MPa
Gas production rate and simulated reservoir temperature at the dissociation pressure of 3 MPa
Gas production and pressure change at different dissociation pressures
Gas production rate at different dissociation pressures
The hydrate reservoir temperature change at different dissociation pressures
Gas production at different hydrate saturations
Gas production rate at different hydrate saturations
The reservoir temperature change at different hydrate saturations
Methane recovery at different hydrate saturations