神狐水合物藏降压开采分解前缘数值模拟研究
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摘要
天然气水合物资源量大,广泛存在于深海和冻土带中,降压法是一种有效的开采方式.天然气水合物藏降压开采过程中,已经分解的水合物区域和尚未分解的水合物区域之间存在一个分解前缘,研究分解前缘的移动规律,有助于认识水合物藏的地层稳定性及进行产气量预测,因此对水合物藏分解前缘的研究具有重要意义.本文采用数值模拟的方法,针对神狐海域水合物藏地质条件,研究降压开采过程中分解前缘的形状及移动规律,并对影响分解前缘移动的敏感因素进行了分析.结果表明:降压分解时,分解前缘的形状为非活塞式,分解前缘1(水合物开始分解的位置)的移动速率近似为线性,分解前缘2(水合物完全分解的位置)的移动速率近似为指数增长.生产井压力越低,地层渗透率越大,初始水合物饱和度越小,初始温度越高,分解前缘移动速率越大.与一步降压相比,分段降压使得分解前缘1和前缘2的移动均滞后.水合物分解吸热导致地层温度降低,当到达冰点时,冰的生成将有助于水合物藏降压分解速率的增大.因此,水合物藏降压分解时,可考虑将压力降低至冰点所对应的相平衡压力附近.
Natural gas hydrates(NGH), widely distributed in the deep ocean and the permafrost, are considered as a potential energy resource. Depressurization is a promising method to exploit NGH reservoirs. There is a dissociation front between dissociated zone and dissociating hydrate zone during the production of NGH reservoirs by depressurization. The study of the movement of the dissociation front is very essential to understand the formation stability and predict the gas production performance of hydrate reservoirs. Based on the geological conditions of hydrate reservoirs in the Shenhu area, numerical simulation methods are used to investigate the shape and movement of the dissociation front during the depressurization production, and then the sensitive factors affecting the movement of dissociation front are analyzed. The results show that the dissociation front is not a definitely interface between the dissociated and dissociating zone but a transition zone, and the shape of the dissociation front is deemed to a non-piston model when depressurization is conducted. The movement rate of dissociation front 1(the position where the hydrate starts to dissociate) is almost approximately linear, but the movement rate of dissociation front 2(the hydrate saturation is reduced to 0) increases as approximately an exponential pattern. The greater movement rate of dissociation front could be observed clearly under the condition of the lower production pressure, the greater intrinsic permeability, the smaller initial hydrate saturation and the higher initial temperature condition, respectively. Compared to the one-step depressurization, the dissociation front 1 and dissociation front 2 are both delayed when the multi-steps depressurization is conducted. The formation temperature will decrease because of the endothermic effect of hydrate dissociation. If the ice point is reached, the extra latent heat generated from ice will contribute to the increase of the hydrate dissociation rate. Therefore, when the depressurization method is used to exploit NGH reservoirs, the pressure can be reduced to the vicinity of the phase equilibrium pressure corresponding to the freezing point.
Natural gas hydrates(NGH), widely distributed in the deep ocean and the permafrost, are considered as a potential energy resource. Depressurization is a promising method to exploit NGH reservoirs. There is a dissociation front between dissociated zone and dissociating hydrate zone during the production of NGH reservoirs by depressurization. The study of the movement of the dissociation front is very essential to understand the formation stability and predict the gas production performance of hydrate reservoirs. Based on the geological conditions of hydrate reservoirs in the Shenhu area, numerical simulation methods are used to investigate the shape and movement of the dissociation front during the depressurization production, and then the sensitive factors affecting the movement of dissociation front are analyzed. The results show that the dissociation front is not a definitely interface between the dissociated and dissociating zone but a transition zone, and the shape of the dissociation front is deemed to a non-piston model when depressurization is conducted. The movement rate of dissociation front 1(the position where the hydrate starts to dissociate) is almost approximately linear, but the movement rate of dissociation front 2(the hydrate saturation is reduced to 0) increases as approximately an exponential pattern. The greater movement rate of dissociation front could be observed clearly under the condition of the lower production pressure, the greater intrinsic permeability, the smaller initial hydrate saturation and the higher initial temperature condition, respectively. Compared to the one-step depressurization, the dissociation front 1 and dissociation front 2 are both delayed when the multi-steps depressurization is conducted. The formation temperature will decrease because of the endothermic effect of hydrate dissociation. If the ice point is reached, the extra latent heat generated from ice will contribute to the increase of the hydrate dissociation rate. Therefore, when the depressurization method is used to exploit NGH reservoirs, the pressure can be reduced to the vicinity of the phase equilibrium pressure corresponding to the freezing point.
引文
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2 Makogon Y E,Holditch S A,Makogon T Y.Russian field illustrates gas-hydrate production.Oil Gas J,2005,103:43-47
3 Grover T,Moridis G J,Holditch S A.Analysis of reservoir performance of the Messoyakha gas hydrate reservoir.In:Proceedings of the SPEAnnual Technical Conference and Exhibition.Society of Petroleum Engineers,2008.114375
4 Kurihara M,Sato A,Funatsu K,et al.Analysis of production data for 2007/2008 Mallik gas hydrate production tests in Canada.In:Proceedings of the International Oil and Gas Conference and Exhibition in China.Society of Petroleum Engineers,2010.132155
5 Fujii T,Takayama T.Wire-line logging analysis of the GMEC/NRCan/Aurora Mallik gas hydrate production test.In:Proceedings of the 6th International Conference on Gas Hydrates.Vancouver,2008
6 Yamamoto K.2013 methane hydrate offshore production test in the eastern Nankai Trough:A milestone on the path to real energy resource.In:Proceedings of the 8th International Conference on Gas Hydrate.Beijing,2014
7 Schoderbek D,Martin K L,Howard J,et al.North slope hydrate field trial:CO2/CH4exchange.In:Proceedings of the OTC Arctic Technology Conference.Offshore Technology Conference,2012.OPT-23725
8 Zhu Y H,Zhang Y Q.Overview on permafrost gas hydrate exploration in China.In:Proceedings of the 8th International Conference on Gas Hydrate,Beijing,2014
9 Fujii T,Suzuki K,Takayama T,et al.Geological setting and characterization of a methane hydrate reservoir distributed at the first offshore production test site on the Daini-Atsumi Knoll in the eastern Nankai Trough,Japan.Mar PetGeol,2015,66:310-322
10 Yousif M H,Li P M,Selim M S,et al.Depressurization of natural gas hydrates in berea sandstone cores.J Incl Phenom Macrocycl Chem,1990,8:71-88
11 Selim M S,Sloan E D.Hydrate dissociation in sediment.SPE Reservoir Eng,1990,5:245-251
12 Yousif M H,Abass H H,Selim M S,et al.Experimental and theoretical investigation of methane-gas-hydrate dissociation in porous media.SPEReservoir Eng,1991,6:69-76
13 Durgut I,Parlaktuna M.A numerical method for the gas production process in gas hydrate reservoirs.Gas Well,1996,48:549-556
14 Tsypkin G G.Regimes of dissociation of gas hydrates coexisting with a gas in natural strata.J Eng Phys Thermophys,2001,74:1083-1089
15 Hong H,Pooladi-Darvish M.A numerical study on gas production from formations containing gas hydrates.In:Proceedings of the Canadian International Petroleum Conference.Calgary,2003
16 Tabatabaie S H,Pooladi-Darvish M.Analytical solution for gas production from hydrate reservoirs underlain with free gas.J Nat Gas Sci Eng,2009,1:46-57
17 Zhang X H,Liu Y H,Li Q P.The dissociation scope of gas hydrate in deposit around heat conductor.Mech Eng,2010,32:39-41[张旭辉,刘艳华,李清平,等.沉积物中导热体周围水合物分解范围研究.力学与实践,2010,32:39-41]
18 Yang X,Sun C Y,Su K H,et al.A three-dimensional study on the formation and dissociation of methane hydrate in porous sediment by depressurization.Energy Convers Manage,2012,56:1-7
19 Du Q J,Chen Y M,Li S X,et al.Mathematical model for natural gas hydrate production by heat injection(in Chinese).Petrol Explor Develop,2007,34:470-473[杜庆军,陈月明,李淑霞,等.天然气水合物注热开采数学模型.石油勘探与开发,2007,34:470-473]
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22 Kumar A,Maini B,Bishnoi P R,et al.Experimental determination of permeability in the presence of hydrates and its effect on the dissociation characteristics of gas hydrates in porous media.J Pet Sci Eng,2010,70:114-122
23 Sun X,Nanchary N,Mohanty K K.1-D modeling of hydrate depressurization in porous media.Transp Porous Media,2005,58:315-338
24 Vasil’Ev V I,Popov V V,Tsypkin G G.Numerical investigation of the decomposition of gas hydrates coexisting with gas in natural reservoirs.Fluid Dyn,2006,41:599-605
25 Gamwo I K,Liu Y.Mathematical modeling and numerical simulation of methane production in a hydrate reservoir.Ind Eng Chem Res,2010,49:5231-5245
26 Liu Y,Gamwo I K.Comparison between equilibrium and kinetic models for methane hydrate dissociation.Chem Eng Sci,2012,69:193-200
27 Bai Y H,Li Q P.Simulation of gas production from hydrate reservoir by the combination of warm water flooding and depressurization.Sci China Tech Sci,2010,53:2469-2476[白玉湖,李清平.注温水-降压法联合开采天然气水合物藏模拟.中国科学:技术科学,2011,41:262-268]
28 Ji C,Ahmadi G,Smith D H.Natural gas production from hydrate decomposition by depressurization.Chem Eng Sci,2001,56:5801-5814
29 Ahamadi G,Ji C,Smith D H.Production of natural gas from methane hydrate by a constant downhole pressure well.Energy Conver Manag,2007,48:2053-2068
30 Yu X C,Wu Y X,An W J,et al.Mathematical model to recover gas hydrate from formations(in Chinese).Nat Gas Indust,2004,24:63-67[喻西崇,吴应湘,安维杰,等.开采地层中的天然气水合物的数学模型.天然气工业,2004,24:63-67]
31 Tang L G,Li G,Feng Z P,et al.Mathematic modeling on thermal recovery of natural gas hydrate(in Chinese).Nat Gas Indust,2006,26:105-107[唐良广,李刚,冯自平,等.热力法开采天然气水合物的数学模拟.天然气工业,2006,26:105-107]
32 Li G,Tang L G,Huang C,et al.Thermodynamic Evolution of hot brine stimulation for natural gas hydrate dissociation(in Chinese).J Chem Indust Eng,2006,57:2033-2038[李刚,唐良广,黄冲,等.热盐水开采天然气水合物的热力学评价.化工学报,2006,57:2033-2038]
33 Zhao Z W.Thermodynamic analysis for the gas production from gas hydrate be heating(in Chinese).China Mining Magazine,2013,8:125-128[赵振伟.天然气水合物加热开采的热力学分析.中国矿业,2013,8:125-128]
34 Li M,Fan S,Su Y,et al.Mathematical models of the heat-water dissociation of natural gas hydrates considering a moving Stefan boundary.Energy,2015,90:202-207
35 Selim M S,Sloan E D.Modeling of the dissociation of an in-situ hydrate.In:Proceedings of the SPE California Regional Meeting.Society of Petroleum Engineers,1985.13597
36 Jamaluddin A K M,Kalogerakis N,Bishnoi P R.Modelling of decomposition of a synthetic core of methane gas hydrate by coupling intrinsic kinetics with heat transfer rates.Can J Chem Eng,1989,67:948-954
37 Li M C,Fan S S.Thermal infection analysis on hot water flooding dissociation frontal brim of natural gas hydrate(in Chinese).Acta Oceanolog Sin,2012,34:116-119[李明川,樊栓狮.天然气水合物注热水分解前缘热作用因素分析.海洋学报,2012,34:116-119]
38 Briaud J L,Chaouch A.Hydrate melting in soil around hot conductor.J Geotech Geoenviron Eng,1997,123:645-653
39 Liu L L,Lu X B,Zhang X H.An experimental study of seepage front due to methane hydrate dissociation by depressurization in sandy sediments(in Chinese).Nat Gas Indust,2013,33:130-136[刘乐乐,鲁晓兵,张旭辉.砂土沉积物中甲烷水合物降压分解渗流阵面实验.天然气工业,2013,33:130-136]
40 Sung W M,Huh D G,Ryu B J,et al.Development and application of gas hydrate reservoir simulator based on depressurizing mechanism.Korean J Chem Eng,2000,17:344-350
41 Gaddipati M.Code Comparison of Methane Hydrate Reservoir Simulators Using CMG STARS.Dissertation for Dcotoral Degree.West Virginia:West Virginia University,2008
42 Adisasmito S,Frank R J,Sloan E D.Hydrates of carbon dioxide and methane mixtures.J Chem Eng Data,1991,36:68-71
43 Uddin M,Coombe D,Law D,et al.Numerical studies of gas hydrate formation and decomposition in a geological reservoir.J Energy Resour Technol,2008,130:032501
44 Tsypkin G G.Effect of decomposition of a gas hydrate on the gas recovery from a reservoir containing hydrate and gas in the free state.Fluid Dyn,2005,40:117-125
2 Makogon Y E,Holditch S A,Makogon T Y.Russian field illustrates gas-hydrate production.Oil Gas J,2005,103:43-47
3 Grover T,Moridis G J,Holditch S A.Analysis of reservoir performance of the Messoyakha gas hydrate reservoir.In:Proceedings of the SPEAnnual Technical Conference and Exhibition.Society of Petroleum Engineers,2008.114375
4 Kurihara M,Sato A,Funatsu K,et al.Analysis of production data for 2007/2008 Mallik gas hydrate production tests in Canada.In:Proceedings of the International Oil and Gas Conference and Exhibition in China.Society of Petroleum Engineers,2010.132155
5 Fujii T,Takayama T.Wire-line logging analysis of the GMEC/NRCan/Aurora Mallik gas hydrate production test.In:Proceedings of the 6th International Conference on Gas Hydrates.Vancouver,2008
6 Yamamoto K.2013 methane hydrate offshore production test in the eastern Nankai Trough:A milestone on the path to real energy resource.In:Proceedings of the 8th International Conference on Gas Hydrate.Beijing,2014
7 Schoderbek D,Martin K L,Howard J,et al.North slope hydrate field trial:CO2/CH4exchange.In:Proceedings of the OTC Arctic Technology Conference.Offshore Technology Conference,2012.OPT-23725
8 Zhu Y H,Zhang Y Q.Overview on permafrost gas hydrate exploration in China.In:Proceedings of the 8th International Conference on Gas Hydrate,Beijing,2014
9 Fujii T,Suzuki K,Takayama T,et al.Geological setting and characterization of a methane hydrate reservoir distributed at the first offshore production test site on the Daini-Atsumi Knoll in the eastern Nankai Trough,Japan.Mar PetGeol,2015,66:310-322
10 Yousif M H,Li P M,Selim M S,et al.Depressurization of natural gas hydrates in berea sandstone cores.J Incl Phenom Macrocycl Chem,1990,8:71-88
11 Selim M S,Sloan E D.Hydrate dissociation in sediment.SPE Reservoir Eng,1990,5:245-251
12 Yousif M H,Abass H H,Selim M S,et al.Experimental and theoretical investigation of methane-gas-hydrate dissociation in porous media.SPEReservoir Eng,1991,6:69-76
13 Durgut I,Parlaktuna M.A numerical method for the gas production process in gas hydrate reservoirs.Gas Well,1996,48:549-556
14 Tsypkin G G.Regimes of dissociation of gas hydrates coexisting with a gas in natural strata.J Eng Phys Thermophys,2001,74:1083-1089
15 Hong H,Pooladi-Darvish M.A numerical study on gas production from formations containing gas hydrates.In:Proceedings of the Canadian International Petroleum Conference.Calgary,2003
16 Tabatabaie S H,Pooladi-Darvish M.Analytical solution for gas production from hydrate reservoirs underlain with free gas.J Nat Gas Sci Eng,2009,1:46-57
17 Zhang X H,Liu Y H,Li Q P.The dissociation scope of gas hydrate in deposit around heat conductor.Mech Eng,2010,32:39-41[张旭辉,刘艳华,李清平,等.沉积物中导热体周围水合物分解范围研究.力学与实践,2010,32:39-41]
18 Yang X,Sun C Y,Su K H,et al.A three-dimensional study on the formation and dissociation of methane hydrate in porous sediment by depressurization.Energy Convers Manage,2012,56:1-7
19 Du Q J,Chen Y M,Li S X,et al.Mathematical model for natural gas hydrate production by heat injection(in Chinese).Petrol Explor Develop,2007,34:470-473[杜庆军,陈月明,李淑霞,等.天然气水合物注热开采数学模型.石油勘探与开发,2007,34:470-473]
20 Tsypkin G G.Mathematical models of gas hydrates dissociation in porous media.Annal New York Acad Sci,1999,912:428-436
21 Konno Y,Oyama H,Nagao J,et al.Numerical analysis of the dissociation experiment of naturally occurring gas hydrate in sediment cores obtained at the Eastern Nankai Trough,Japan.Energy Fuels,2010,24:6353-6358
22 Kumar A,Maini B,Bishnoi P R,et al.Experimental determination of permeability in the presence of hydrates and its effect on the dissociation characteristics of gas hydrates in porous media.J Pet Sci Eng,2010,70:114-122
23 Sun X,Nanchary N,Mohanty K K.1-D modeling of hydrate depressurization in porous media.Transp Porous Media,2005,58:315-338
24 Vasil’Ev V I,Popov V V,Tsypkin G G.Numerical investigation of the decomposition of gas hydrates coexisting with gas in natural reservoirs.Fluid Dyn,2006,41:599-605
25 Gamwo I K,Liu Y.Mathematical modeling and numerical simulation of methane production in a hydrate reservoir.Ind Eng Chem Res,2010,49:5231-5245
26 Liu Y,Gamwo I K.Comparison between equilibrium and kinetic models for methane hydrate dissociation.Chem Eng Sci,2012,69:193-200
27 Bai Y H,Li Q P.Simulation of gas production from hydrate reservoir by the combination of warm water flooding and depressurization.Sci China Tech Sci,2010,53:2469-2476[白玉湖,李清平.注温水-降压法联合开采天然气水合物藏模拟.中国科学:技术科学,2011,41:262-268]
28 Ji C,Ahmadi G,Smith D H.Natural gas production from hydrate decomposition by depressurization.Chem Eng Sci,2001,56:5801-5814
29 Ahamadi G,Ji C,Smith D H.Production of natural gas from methane hydrate by a constant downhole pressure well.Energy Conver Manag,2007,48:2053-2068
30 Yu X C,Wu Y X,An W J,et al.Mathematical model to recover gas hydrate from formations(in Chinese).Nat Gas Indust,2004,24:63-67[喻西崇,吴应湘,安维杰,等.开采地层中的天然气水合物的数学模型.天然气工业,2004,24:63-67]
31 Tang L G,Li G,Feng Z P,et al.Mathematic modeling on thermal recovery of natural gas hydrate(in Chinese).Nat Gas Indust,2006,26:105-107[唐良广,李刚,冯自平,等.热力法开采天然气水合物的数学模拟.天然气工业,2006,26:105-107]
32 Li G,Tang L G,Huang C,et al.Thermodynamic Evolution of hot brine stimulation for natural gas hydrate dissociation(in Chinese).J Chem Indust Eng,2006,57:2033-2038[李刚,唐良广,黄冲,等.热盐水开采天然气水合物的热力学评价.化工学报,2006,57:2033-2038]
33 Zhao Z W.Thermodynamic analysis for the gas production from gas hydrate be heating(in Chinese).China Mining Magazine,2013,8:125-128[赵振伟.天然气水合物加热开采的热力学分析.中国矿业,2013,8:125-128]
34 Li M,Fan S,Su Y,et al.Mathematical models of the heat-water dissociation of natural gas hydrates considering a moving Stefan boundary.Energy,2015,90:202-207
35 Selim M S,Sloan E D.Modeling of the dissociation of an in-situ hydrate.In:Proceedings of the SPE California Regional Meeting.Society of Petroleum Engineers,1985.13597
36 Jamaluddin A K M,Kalogerakis N,Bishnoi P R.Modelling of decomposition of a synthetic core of methane gas hydrate by coupling intrinsic kinetics with heat transfer rates.Can J Chem Eng,1989,67:948-954
37 Li M C,Fan S S.Thermal infection analysis on hot water flooding dissociation frontal brim of natural gas hydrate(in Chinese).Acta Oceanolog Sin,2012,34:116-119[李明川,樊栓狮.天然气水合物注热水分解前缘热作用因素分析.海洋学报,2012,34:116-119]
38 Briaud J L,Chaouch A.Hydrate melting in soil around hot conductor.J Geotech Geoenviron Eng,1997,123:645-653
39 Liu L L,Lu X B,Zhang X H.An experimental study of seepage front due to methane hydrate dissociation by depressurization in sandy sediments(in Chinese).Nat Gas Indust,2013,33:130-136[刘乐乐,鲁晓兵,张旭辉.砂土沉积物中甲烷水合物降压分解渗流阵面实验.天然气工业,2013,33:130-136]
40 Sung W M,Huh D G,Ryu B J,et al.Development and application of gas hydrate reservoir simulator based on depressurizing mechanism.Korean J Chem Eng,2000,17:344-350
41 Gaddipati M.Code Comparison of Methane Hydrate Reservoir Simulators Using CMG STARS.Dissertation for Dcotoral Degree.West Virginia:West Virginia University,2008
42 Adisasmito S,Frank R J,Sloan E D.Hydrates of carbon dioxide and methane mixtures.J Chem Eng Data,1991,36:68-71
43 Uddin M,Coombe D,Law D,et al.Numerical studies of gas hydrate formation and decomposition in a geological reservoir.J Energy Resour Technol,2008,130:032501
44 Tsypkin G G.Effect of decomposition of a gas hydrate on the gas recovery from a reservoir containing hydrate and gas in the free state.Fluid Dyn,2005,40:117-125