Đang tải... (xem toàn văn)
Ứng dụng hữu ích của Gas hydrates trong ngành công nghiệp dầu khí. Cung cấp các thông tin cần thiết cho các kỹ sư dầu khí nhằm đáp ứng cho nhu cầu năng lượng không chỉ của riêng nước ta mà còn trên thế giới.
Sloan 11/11/03 10:06 am Page 37 insight review articles Fundamental principles and applications of natural gas hydrates E Dendy Sloan Jr Center for Hydrate Research, Colorado School of Mines, Golden, Colorado 80401, USA (e-mail: esloan@.mines.edu) Natural gas hydrates are solid, non-stoichiometric compounds of small gas molecules and water They form when the constituents come into contact at low temperature and high pressure The physical properties of these compounds, most notably that they are non-flowing crystalline solids that are denser than typical fluid hydrocarbons and that the gas molecules they contain are effectively compressed, give rise to numerous applications in the broad areas of energy and climate effects In particular, they have an important bearing on flow assurance and safety issues in oil and gas pipelines, they offer a largely unexploited means of energy recovery and transportation, and they could play a significant role in past and future climate change U ntil mankind learns how to economically generate hydrogen for fuel cells, natural gas will be the premium fuel for this century for two reasons First, gas burns cleanly, causes few pollution problems and, relative to oil or coal, produces less carbon dioxide And second, liquid fuels are better used as feedstocks (raw material) for generation of petrochemicals Two examples herald this coming change: many power plants are being converted from coal to natural gas, and fleets of cars have been converted from petrol to natural gas fuel As we deplete the readily accessible reserves, we will need to obtain natural gas from conditions that are both more severe and more remote We will need to explore deep ocean environments with higher pressures, and permafrost environments with lower temperatures than we presently And gases that were previously thought to be uneconomical, such as those containing non-combustible components of nitrogen, carbon dioxide and hydrogen sulphide, will also be explored Such unusual conditions also promote the formation of a solid compound of gas and water — namely clathrates of natural gas — commonly called gas hydrates Here, I indicate the motivation for hydrate science and engineering; that is, the applications where technical workers find a use for the physics, chemistry and biology that are associated with science This is not to indicate that hydrate engineering is simply an applied science As indicated recently in a defining book1 on differences in technical philosophy, engineering frequently cannot afford the luxury of a thorough scientific foundation, and must proceed at risk As only one example, the past decade’s development of the new ‘low-dosage’ pipeline hydrate inhibitors proceeded in an Edisonian research mode (a process of intelligent guesswork, intuitive reasoning and testing), and scientific progress is currently being made to refine trial and error research gaps in inhibitor developments Below, I describe five major applications of hydrate research: flow assurance, safety, energy recovery, gas storage/transportation and climate change Before the applications are addressed, an introduction to hydrate structures and their overall properties is presented I conclude this review with an outline of future challenges For readers who want a more detailed understanding, several hydrate reviews2–8 are available Hydrate structures Clathrate hydrates typically form when small (1,000 bar), in unusual fluids such as black oils, hydrate–sediment mixtures, and the methanol-partitioning challenge indicated earlier As an example of one such challenge, hydrate– sediment mixtures have an unexplained thermal diffusivity maximum when plotted against sediment concentration As we begin to examine hydrates in nature, such challenges for time-independent properties will require decades to resolve However, the largest challenge is to describe the kinetics of hydrates42 The fact that hydrates are solid compounds makes their slow, solid-phase kinetics particularly challenging to researchers An additional challenge arises from the fact that hydrate solids form interfacial barriers between the liquid and vapour phases that typically compose them Hydrate research is most accurate when studying a time-independent target Typically, time-dependent (kinetic) research is much more difficult and at least an order of magnitude of accuracy is lost, relative to time-independent (thermodynamic) research The use of kinetic-model results to predict data from other laboratories is problematic Molecular dynamic simulations of hydrate kinetics have been hindered by stochastic nucleation and the large number of molecules and time required for growth processes More hydrate phase measurements are required to provide a needed breakthrough — a unified hydrate kinetics model Conclusions and outlook Wherever small molecules contact water, the potential for a hydrate phase should be considered The size ratio (guest to cavity) determines hydrate structural stability to a first-order approximation Other simple hydrate properties such as solid behaviour, density and concentration of guest molecules affect the major applications of hydrate safety, flow assurance, energy production and storage and climate change During the next decade, gas production will begin from permafrost hydrates associated with conventional gas reservoirs However, efficient production of ocean hydrates is problematic and requires an engineering breakthrough to be economically feasible Yet, the potential to tap the Earth’s largest hydrocarbon energy resource cannot be ignored Although hydrate thermodynamics are understood to an acceptable degree for most engineering applications, the kinetics arena will represent the largest challenge for advancing the information on hydrates Although we know quite a lot about what hydrates are, the question of how hydrates form is still very much unanswered FindNATURE | VOL 426 | 20 NOVEMBER 2003 | www.nature.com/nature ing the answers to such questions provides the intrinsic motivation for future research ■ doi:10.1038/nature02135 Koen, B V Discussion of the Method: Conducting the Engineer’s Approach to Problem Solving (Oxford Univ Press, Oxford, 2003) Sloan, E D in Clathrate Hydrates of Natural Gases (Marcel Dekker, New York, 1998) Ripmeester, J A Hydrate research – from correlations to a knowledge-based discipline: the importance of structure Ann NY Acad Sci 912, 1–16 (2000) Sloan, E D in Hydrate Engineering (Soc Petrol Eng., Richardson, TX, 2000) Makogon, Y F Hydrates of Hydrocarbons (Pennwell Books, Tulsa, 1997) Sloan, E D Clathrate hydrate measurements: microscopic, mesoscopic, and macroscopic J Chem Thermo 35, 41–53 (2003) Davidson, D W in Water: A Comprehensive Treatise (ed Franks, F ) (Plenum, New York, 1973) Englezos, P Clathrate hydrates Ind Eng Chem Res 32, 1251–1274 (1993) Mao, W L et al Hydrogen clusters in clathrate dydrate Science 297, 2247–2249 (2002) 10 von Stackelberg, M Solid gas hydrates Naturwissenschaften 11-12, 1–22 (1949) 11 Huo, Z., Hester, K., Miller, K T & Sloan, E D Methane hydrate non-stoichiometry and phase diagram Am Ind Chem Eng J 49, 1300–1306 (2003) 12 Kobayashi, R & Katz, D L Methane hydrate at high pressure J Petrol Technol 2579, 66–70 (1949) 13 Holder, G D & Manganiello, D J Hydrate dissociation pressure minima in multicomponent systems Chem Eng Sci 37, 9–16 (1982) 14 Hendriks, E M., Edmonds, B., Moorwood, R A & Szczepanski, R Hydrate structure stability in simple and mixed dydrates Fluid Phase Equilibria 117, 293–298 (1996) 15 Subramanian, S., Kini, R A., Dec, S F & Sloan, E D Evidence of structure II hydrate formation from methane+ethane mixtures Chem Eng Sci 55, 1981–1985 (2000) 16 Staykova, D K., Hansen, T., Salamatin, A N & Kuhs, W F Kinetic diffraction experiments on the formation of porous gas hydrates Proc 4th Int.Conf Gas Hydrates (2002) 17 Hester, K & Sloan, E D Structure II hydrates from binary structure I simple guests Fluid Phase Equilibria (in the press) 18 Davidson, D W., Handa, Y P., Ratcliffe, C I., Tse, J S & Powell, B M The ability of small molecules to form clathrate hydrates of structure II Nature 311, 142–143 (1984) 19 Ripmeester, J A., Ratcliffe, C I & Powell, B M A new clathrate hydrate structure Nature 325, 135–136 (1987) 20 Ballard, A & Sloan, E D The next generation of hydrate prediction: An overview Proc 4th Int.Conf Gas Hydrates (2002) 21 van der Waals, J H & Platteeuw, J C Clathrate solutions Adv Chem Phys 2, 1–58 (1959) 22 Mehta, A P., Hebert, P B., Cadena, E R & Weatherman, J P Fulfilling the promise of low-dosage hydrate inhibitors: Journey from academic curiosity to successful field implementation SPE Prod Facil 73–79 (2003) 23 Kvenvolden, K A in Methane Hydrates: Resources in the near Future? (Proc Int Japan Natl Oil Comp, Chiba City, Japan, 1998) 24 Milkov, A V & Sassen, R Resource and economic potential of gas hydrates in the northwestern gulf of Mexico Proc 4th Int.Conf Gas Hydrates 111–114 (2002) 25 Soloviev, V., Ginsburg, G., Telepnevm, E & Mikhailyk, Y Cryogeothermy and Natural Gas Hydrates of the Arctic Ocean Sediments (Ministry of Geology USSR, Leningrad, 1987) 26 Dallimore, S R et al (eds) Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada Bull Geol Soc Can 585 (in the press) 27 Dallimore, S R., Collett, T S & Uchida, T Summary of Mallik 21–38 Well GSC Bull 544 1, 1–10 (1999) 28 Paull, C K & Matsumoto R Leg 164 overview Proc ODP Sci Res 164, 3–10 (2000) 29 Moridis, G et al Numerical simulation studies of gas production scenarios from hydrate accumulations at the Mallik Site, Mackenzie Delta, Canada Proc 4th Int.Conf Gas Hydrates 239-244 (2002) 30 Gudmundsson, J & Borrehaug, A Frozen hydrate for transport of natural gas in Proc 2nd Int Conf on Natural Gas Hydrates 415–422 (1996) 31 Nakajima, Y., Takaoki, T., Ohgaki, K & Ota, S Use of hydrate pellets for transportation of natural gas – II; Proposition of natural gas transportation in form of hydrate pellets in Proc 4th Int.Conf Gas Hydrates 987–990 (2002) 32 Shirota, H et al Measurement of methane hydrate dissociation for application to natural gas storage and transportation Proc 4th Int.Conf Gas Hydrates (2002) 33 Gudmundsson, J., Andersson, V., Levik, O I., Mork, M & Borrehaug, A Hydrate technology for capturing stranded gas Ann NY Acad Science 912, 403–410 34 Kennett, J P., Cannariato, G., Hendy, I L & Behl, R J Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis (Am Geophys Union, Washington DC, 2003) 35 Dickens, G R., Castillo, M M & Walker, J C G A blast of gas in the latest paleocene: simulating firstorder effects of massive dissociation of ocean methane hydrate Geology 25, 259–262 (1997) 36 Dickens, G., O’Neil, J., Rea, D & Owen, R Dissociation of oceanic methane hydrates as a cause of the carbon isotope excursion at the end of the Palaeocene Paleoceanography 10, 965–971 (1995) 37 Kaiho, K et al Latest palaeocene benthic foramiferal extinction and environmental changes at Tawanui, New Zealand Paleoceanography 11, 447–465 (1996) 38 Maslin, M & Thomas, E The clathrate gun is firing blanks: Evidence from balancing the deglacial global carbon budget Geophys Res Abstr 5, 12015 (2003) 39 Dickens, G R A methane trigger for rapid warming? Science 299, 1017 (2003) 40 Dillon, W P et al in Gas Hydrates: Relevance to World Margin Stability and Climate Change (eds Henriet, J.-P & Mienert, J.) 293–302 (Geol Soc., London, 1998) 41 Paull, C K & Dillon, W P (eds) Natural Gas Hydrates: Occurrence, Distribution and Detection (Am Geophys Union, Washington DC, 2001) 42 Bishoi, P R & Natarajan, V Formation and decomposition of gas hydrates Fluid Phase Equilibria 117, 168–177 (1996) 43 Sloan, E D Jr in Gas Hydrates: Relevance to World Margin Stability and Climate Change (eds Henriet, J.-P & Mienart, J.) 31–40 (Spec Publ 137, Geol Soc, London, 1998) 44 Dickens, G R Methane oxidation during the Late Palaeocene Thermal Maximum Bull Soc Geol Fr 171, 37–49 (2000) 359 ©2003 Nature Publishing Group © 2003 Nature Publishing Group