天然气水合物作为一种新型替代能源, 如何有效开发成为当前研究的热点, 热激发被认为是除降压法外天然气水合物开采的另一重要途径。目前对于天然气水合物注热开采效率和经济可行性仍没有清楚的认识。构建了通过垂直单井对天然气水合物进行注热开采的物理模型, 通过对物理模型的理想简化, 在水合物藏中划分出一个理想薄层, 对研究的储层体系进行了密集的网格划分, 并以南海北部陆坡神狐海域天然气水合物成藏特征为依据, 利用TOUGH+HYDRATE程序, 数值模拟研究了对天然气水合物藏进行热激发开采的潜力, 并与相同幅度的降压开发进行了效率对比分析。研究显示, 井孔高温热源的辐射半径很小, 水合物受热分解速率缓慢, 而且在注热和降压联合开采中, 注热作业对水合物分解的贡献很低, 水合物分解主要由降压操作引起。
Natural gas hydrate is a new potential energy, so how the gas can be effectively produced from hydrate deposits becomes a hot research topic. Heat stimulation is regarded as another important way for producing hydrate besides depressurization. However, production efficiency and economic feasibility of gas production by heat stimulation are not well understood. In this paper, a physical model for predicting gas production from hydrate deposits by heat stimulation through a vertical well is constructed. The model defines a laminar hydrate system of unit thickness. The reservoir system is discretized densely. We numerically simulate the production potential of hydrate deposit through thermal stimulation by employing the TOUGH+HYDRATE simulator with the characteristic parameters of Shenhu hydrate on the northern continental slope of the South China Sea. Then, we compare and analyze the efficiency of heat stimulations with a pure depressurization operation. Our research shows that the radioactive radius of the high-temperature heat source at the well is very small and that the hydrate dissociation rate is slow. The contribution of thermal injection operation is very small in the inter-productions of heat stimulation and depressurization, and the hydrate dissociation in the processes are mainly aroused by the operation of depressurization.
[1] SLOAN E D, KOH C A. Clathrate Hydrates of Natural Gases[M]. 3rd ed. Boca Raton: CRC Press, 2008: 537?550.
[2] MORIDIS G J, COLLETT T, DALLIMORE S, et al. Numerical studies of gas production from several methane hydrate zones at the Mallik Site, Mackenzie Delta, Canada[J]. Journal of Petroleum Science and Engineering, 2004, 43: 219?239.
[3] 郝永卯, 薄启炜, 陈月明, 等. 天然气水合物降压开采实验研究[J]. 石油勘探与开发, 2006, 33(2): 217?220.
[4] 杜庆军, 陈月明, 李淑霞, 等. 天然气水合物注热开采数学模型[J]. 石油勘探与开发, 2007, 34(4): 470?473.
[5] MORIDIS G J, REAGAN M T, KIM S J, et al. Evaluation of the gas production potential of marine hydrate deposits in the Ulleung Basin of the Korean East Sea [J]. SPE Journal, 2009, 14(4): 759?781.
[6] MORIDIS G J, REAGAN M T. Strategies for gas production from oceanic class 3 hydrate accumulations[C]. Houston: Offshore Technology Conference, 2007: OTC 18865.
[7] MORIDIS G J, REAGAN M T. Gas production from oceanic class 2 hydrate accumulations[C]. Houston: Offshore Technology Conference, 2007: OTC 18866.
[8] MORIDIS G J, KOWALSKY M B, PRUESS K. Depressurization-induced gas production from class 1 hydrate deposits [J]. SPE Reservoir Evaluation and Engineering, 2007, 10(5): 458?481.
[9] MORIDIS G J, COLLETT T S, BOSWELL R, et al. Toward production from gas hydrates: current status, assessment of resources, and simulation-based evaluation of technology and potential[J]. SPE Reservoir Evaluation & Engineering, 2009, 12(5): 745?771.
[10] MCDONNELL S L, MAX M D, CHERKIS N Z, et al. Tectono-sedimentary controls on the likelihood of gas hydrate occurrence near Taiwan[J]. Marine Petroleum and Geology, 2000: 9-936.
[11] WANG P, PRELL W, BLUM P. Ocean Drilling Program Leg 184 scientific prospectus South China Sea, site 1144, 184[C] // WANG P, PRELL W, BLUM P. Proceedings of the ocean drilling program, initial reports. College Station, USA: Ocean Drilling Program, Publications Distribution Center, 2000: 1-97.
[12] WU NENGYOU, YANG SHENGXIONG, ZHANG HAIQI, et al. Preliminary discussion on gas hydrate reservoir system of Shenhu Area, North Slope of South China Sea: Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008), 5700, Vancouver, British Columbia, CANADA, 6?10 July 2008[C/OL]. [2011-07-29]. https: //circle.ubc.ca/bitstream/handle/2429/1177/5700.pdf?sequence=1
[13] WU NENGYOU, YANG SHENGXIONG, ZHANG HAIQI, et al. Gas hydrate system of Shenhu Area, Northern South China Sea: wire-line logging, geochemical results and preliminary resources estimates[C]. Houston: Offshore Technology Conference, 2010: OTC 20485.
[14] MORIDIS G J, KOWALSKY M. Gas production from unconfined Class 2 hydrate accumulations in the oceanic subsurface[M]// MAX M, JOHNSON A H, DILLON W P, et al. Economic Geology of Natural Gas Hydrates. Kluwer Academic/Plenum Publishers, 2006: 249?266.
[15] SU Z, MORIDIS G J, ZHANG K, et al. Numerical investigation of gas production strategy for the hydrate deposits in the Shenhu area[C]. Houston: Offshore Technology Conference, 2010: OTC 20551.
[16] LI G, MORIDIS G J, ZHANG K, LI X. Evaluation of gas production potential from marine gas hydrate deposits in Shenhu area of South China Sea[J]. Energy Fuels 2010, 24: 6018-6033.
[17] CATHLES L M. Changes in sub-water table fluid flow at the end of the Proterozoic and its implications for gas pulsars and MVT lead-zinc deposits [J]. Geofluids, 2007, 7: 209-226.
[18] MORIDIS G J, KOWALSKY M B, PRUESS K. TOUGHFx/ HYDRATE v1. 0 user’s manual: A code for the simulation of system behavior in hydrate-bearing geologic media[M]. Berkeley: Lawrence Berkeley National Laboratory, 2005: 165?187.
[19] VAN GENUCHTEN M T. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils [J]. Soil Sci Soc Am J, 1980, 44: 892?898.
[20] 苏正, 曹运诚, 杨睿, 等. 南海北部神狐海域天然气水合物热开发效率的数值分析研究. 现代地质[J]. 2011, 25(3)?: 1?9.
