Hydrates of natural gas; a review of their geologic occurrence

CECIL D. ANDRUS, Secretary

TABLES

m Hydrates of Natural Gas:

INTRODUCfiON

Figure 1--Phase boundary diagram showin~: free methane gas and methane hydrate (pattern) for a fresh water-pure methane system. Addition of NaCl to water lowers temperature of hydrate formation, in effect shifting gas-hy~rate , H H , or curve to left. Addition of co S, c 2 2 2 6 c3n8 raises temperature of hydrate formation, in effect shifting curve to right. Therefore, impurities in natural gas will increase area of hydrate stability field. Depth scale is an approximation assuming that lithostatic and hydrostatic pressure gradients are b0th 0.1 atmosphere per meter (10.1 kPa/m), but the true lithostatic gradient is slightly greater. Redrawn after Katz and others (1959).

Figure 2.--Known and inferred accumulations of gas hydrate. Dots on land depict susp~cted or confirmed occurrences of gas hydrates beneath permafrost. Dots in oceans show areas where seismic or drilling evidence suggests presence of gas hydrates. See tables 1 and 2 for a listing of each site, along with geologic, geophysical, and geochemical evidence for hydrate presence, research organization involved, and pertinent references. significantly during penetration of these sands. references cited by Milton, 1976). Methane was Although these sands were very porous, their perreleased from the gas hydrate by injecting methmeability was extremely low. Low permeability anol into test wells that perforated the hydrate and pronounced gas release are characteristic of zone. The injections of methanol, which serves hydrate-filled reservoirs. '!he loP permeability as a hydrate inhibitor, resulted in a large inis thought to result from the plugring of sedicrease in gas productivity from the test wells. ment interstices by gas hydrate, and the gas libThe parts of the Messoyakha field containing gas erated is attributed to hydrate decomposition. hydrates are calculated to have 54 percent more Other characteristics of the ras hydrate reserves than would be expected in an equal volzone are visible on well logs (Bily and Dick, ume of reservoir rocks filled with free gas. 1974). The hydrate-bearing sands bive a relaTwo exploratory wells drilled in permafrost tively high resistivity. Spontanecus potential of the Mackenzie Delta penetrated shallow sand (SP) curves show very little deflection in hyreservoirs containing gas hydrate at depths of drate zones in comparison with deflections in 820 to 1,100 m (Bily and Dick, 1974). The amount free-gas and free-water zones. Sor.ic logs show of formation gas in the drilling mud increased

Figure 2.--Known and inferred accumulations of gas hydrate. Dots on land depict firmed occurrences of gas hydrates beneath permafrost. Dots in oceans show areas where seismic or drilling evidence suggests presence of gas hydrates. See tables 1 and 2 for a listing of each site, along with geologic, geophysical, and geochemical evidence for hydrate presence, research organization involved, and pertinent references. references cited by Milton, 1976). Methane was released from the gas hydrate by injecting methanol into test wells that perforated the hydrate zone. The injections of methanol, which serves as a hydrate inhibitor, resulted in a large increase in gas productivity from the test wells. The parts of the Messoyakha field containing gas hydrates are calculated to have 54 percent more reserves than would be expected in an equal volume of reservoir rocks filled with free gas.

Two exploratory wells drilled in permafrost of the Mackenzie Delta penetrated shallow sand reservoirs containing gas hydrate at depths of 820 to 1,100 m (Bily and Dick, 1974). The amount of formation gas in the drilling mud increased

--------------------No data in print------ Dome Petrole...,, Hitchson, 1974.

significantly during penetration of these sands. Although these sands were very porous, their permeability was extremely low. Low permeability and pronounced gas release are characteristic of hydrate-filled reservoirs. '!he loP permeability is thought to result from the plugring of sediment interstices by gas hydrate, and the gas liberated is attributed to hydrate decomposition.

Other characteristics of the ras hydrate zone are visible on well logs (Bily and Dick, 1974). The hydrate-bearing sands bive a relatively high resistivity. Spontanecus potential (SP) curves show very little deflection in hydrate zones in comparison with deflections in free-gas and free-water zones. Sor.ic logs show

l t 'l -

GAS HYDRATES IN OCEANIC SEDIMENTS

of ethane. Recent results from DSDP Legs 66 and 67 provide more evidence for the presence of gas hydrates in sediments on the slope of the Mid-America Trench off Central America (Geotimes,

leasing cores were observed. Frozen sediment was recovered from the zone of hydrate stability at Sites 490, 491, 492, 497, and 498. Gas expansion volumes as high as 50 to 1 (R. von Huene, oral commun., 1979) suggest that gas hydrates had indeed been sampled.

Methane in ocean sediment may be of either biochemical or thermal origin. It is uncertain, however, that enough gas to support the formation of gas hydrate can be generated by methane-producing bacteria alone. Claypool and Kaplan (1974) estimated that biological generation of methane in sediment containing 0.5 percent organic carbon near sediment depths of around 1,000 m (corresponding to 30°C) is 20 mmol per kilogram of interstitial water. They also estimated the threshold methane concentration for hydrate stability as 58 mmol/kg. Thermocatalytic methane is produced by alteration of organic matter at temperatures greater than 50°C, but gas hydrates are stable only at relatively low temperatures. For gas hydrates to form from thermocatalytic natural gas (methane), such gas must migrate upward from burial depths greater than 1,500 m into cooler regions where it could be incorporated into a gas hydrate zone.

BOTIOM-SIMULATING REFLECTORS

A bottom-simulating reflector is an anomalous seismic reflector that parallels the topography of the seafloor but lies anywhere from 100 to 1,100 m below the bottom. Bottom-simulating reflectors are most easily recognized on seismic records when they cut across other reflectors and occur in water depths greater than 400 m. They

Figure 4.--Idealized section of gas hydrate zone in sediments of outer continental mar.?ins, computed for pure methane. Stippled zone is potential area of hydrate formation, where pressure and temperature conditions are correct for hydrate stability assuming an adequate supply of methane. Presence of other gases in methane would increase methane hydrate envelope downward. Increasing pressure from height of water column causes increase in subbottom depth of gas hydrate zone. Decreasing sediment temperature (down to 1°C in coldest, deepest bottom waters) also decreases hydrate subbottom depth. Redrawn fron R.D. Mciver, written commun., 1979.

Figure 4.--Idealized section of gas hydrate zone in sediments of outer continental mar.?ins, computed for pure methane. Stippled zone is potential area of hydrate formation, where pressure and temperature conditions are correct for hydrate stability assuming an adequate supply of methane. Presence of other gases in methane would increase methane hydrate envelope downward. Increasing pressure from height of water column causes increase in subbottom depth of gas hydrate zone. Decreasing sediment temperature (down to 1°C in coldest, deepest bottom waters) also decreases hydrate subbottom depth. Redrawn fron R.D. Mciver, written commun., 1979. are generally characterized by reflection polarity reversals and large reflection coefficients (Shipley and others, 1979). Gas hydrate zones and diagenetic boundaries in sediment have been proposed as possible causes of these anomalous seismic reflectors.

Before DSDP Leg 11 in the Blake-Bahama region of the Atlantic Ocean, geophysicists of the Lamont-Doherty Geological Observatory were intrigued by bottom-simulating reflectors on their seismic records over the Blake-Bahama Outer Ridge (Markland others, 1970; Stoll and others, 1971). The observation that some of the seismic reflectors on their records intersected other reflectors and paralleled the seafloor (fig. 5) was unexplained. One of the major objectives of Leg 11 was to investigate the nature of the bottom-simulating reflectors and determine their relation, if any, to accumulations of gas hydrate beneath the seafloor. The strongest reflector on the ridge mimicked the ridge profile at a depth of more than 500 m below the seafloor. Samples from Sites 102, 103, and 104 of Leg 11 yielded mainly methane and traces of ethane (for quantitative gas composition data see Claypool and others, 1973). The strong bottom-simulating reflector was at that time correlated with a distinct break in the drilling rate and with a zone of nodules of siderite and ankerite (Lancelot and Ewing, 1972). Another explanation, suggested by Stoll, Ewing, and Bryan (1971), Ewing and Hollister (1972), and Dillon, Grow, and Paull (1980), is that the bottom-simulating reflector corresponds to the isotherm that separates a gas environment from a gas hydrate environment. The average thermal gradient for the ridge (about 35- 400C/km) permits a gas hydrate to exist at the 500-m sediment depth of the strong reflector, but below that level the temperature would be high

Figure 5.--Diagrammatic seismic profile of BlakeBahama Outer Ridge, showing thin, regularly spaced reflectors from strata. Bottom-simulating reflector (stippled) transects bedding and parallels seafloor and may represent hydrate-to-free-gas transition at bottom of gas hydrate zone. Redrawn from Tucholke and others (1977).

Figure 5.--Diagrammatic seismic profile of Blake-Bahama Outer Ridge, showing thin, regularly spaced reflectors from strata. Bottom-simulating reflector (stippled) transects bedding and parallels seafloor and may represent hydrate-to-free-gas transition at bottom of gas hydrate zone. Redrawn from Tucholke and others (1977).

enough that methane could exist only as a gas.

Laboratory experimental studies provide further evidence linking gas hydrates with the sediments of the Blake-Bahama Ridge. Stoll, Ewing, and Bryan (1971) demonstrated that when methane mixed with water-saturated sand w~s brought to the estimated temperatures and pressures of the Blake-Bahama Ridge sediment, the velocity of compressional seismic waves in the sand increased from 1.7 to 2.5 km/s. This experimental increase in seismic velocity helps explain the unusually high velocities observed in hemip~lagic sediment of the ridge.

Since they were first found in the Blake-Bahama Ridge (Markl and others, 1970; Ewing and Hollister, 1972), other bottom-simulating reflectors have been reported (fig. 3) from the western North Atlantic Ocean (Tucholke and others, 1977), the Beaufort ~a of the Arctic Ocean (Grantz and others, 1976), and the Bering Sec and elsewhere in the North Pacific Ocean (Scholl and Creager, 1973). Shipley and others (1979) described bottom-simulating reflectors in sediments off the east coast of the United States, in the western Gulf of Mexico, off the northern coasts of Colombia and Panama, and along the Pacific coast of Central America from Panama to k.apulco, Mexico.

From studies of the western North Atlantic, Tucholke, Bryan, and Ewing (1977) identified two high-amplitude reflecting horizons that ·are conformable with the seafloor and atout 500 to 600 m beneath it. These horizons show the following characteristics: they cut acros~ bedding-plane reflectors in the same manner as the reflector horizon observed on the Blake-Bab:tma Ridge; they appear to be restricted to areas where sedimentary strata dip landward; and th~ir subbottom depth increases with the seafloor depth, a relation consistent with theoretical predictions of the configuration of a hydrate zone (fig. 4). A zone of gas hydrates may overlie the anomalous horizons, and thus the seismic horizons could be reflectors representing an impedance contrast caused by the downward change from gas hydrate to gas in the sediment. Grantz and others (1976) identified a strong seismic reflector that mimics the bathymetry of the seafloor, 100-300 m beneath it, on the continental slope of the Beaufort Sea north of Alaska. The bottom-sim1uating reflector was identified in about 60 percent of seismic profiles obtained in water deeper than 400-600 m.

Not all bottom-simulating reflectors can be directly related to the presence of gas hydrates. Although gas hydrates provide one reasonable explanation for bottom-simulatin.~ reflectors, these acoustic features may also result from temperature controlled diagenetic effects. During DSDP Leg 19, Scholl and Creager (1973) noted seismic reflectors that tend to parallel the seafloor in some Bering Sea sediments draped on the Umnak Plateau, and they coined the acronym BSR for the bottom-simulating reflector. At two sites, 184 and 185, the reflector was penetrated. Although methane was observed in sediment from Site 185, no other evidence for gas hydrates was noted. Scholl and Creager (1973) attribute this reflector to a lithologic transition from hemipelagic diatom ooze to indurated claystone. Because of the time-transgressive nature of this horizon, this BSR appears to represent some sort of migratory diagenetic boundary related to the dissolution of diatoms and the formation of claystone. Hein and others (1978) confirmed that opal-A is transformed to opal-CT in the temperature range corresponding to a subbottom depth of 600 m, the depth of the BSR in Bering Sea sediment. Further, because the subbottom depth of the BSR on the flanks of Umnak Plateau decreases with increasing water depth, this BSR is probably not directly caused by gas hydrates (Shipley and others, 1979). Nevertheless, gas hydrates may still play an important role in the formation of this BSR. Claypool and Kaplan (1974) note that, in all cases of BSR's described from the Bering Sea, the lithologic change is consistent with the inferred depth of the isotherm where gas hydrate would decompose under the prevailing pressure conditions. Claypool and Kaplan (1974) suggest at least an indirect link between lithification and gas hydrate. Free carbon dioxide and methane concentrations determine the pH of interstitial water. The pH conditions determine the solubility of lithologic components such as carbonate and silica. Gas hydrate formation may influence carbon dioxide and methane activities and may therefore influence the dissolution and reprecipitation of carbonate and silica cements.

Thus, some bottom-simulating reflectors are not directly related to the presence of gas hydrates, as illustrated above, but bottom-simulating reflectors may not be observed even though gas hydrates are present. For example, in areas where sedimentary stratification parallels the seafloor, the bottom-simulating reflector may not be detectable. During drilling on DSDP Leg 67 in the Mid-America Trench off Guatemala, gas hydrates apparently were encountered at Sites 497 and 498, but the seismic records for these areas showed no obvious bottom-simulating reflectors (R. von Huene, oral commun., 1979).

Gas hydrate zones in the seafloor may form regionally extensive impermeable seals and may trap economically important accumulations of natural gas, provided sufficient sources for methane are present. If gas were to migrate upward and be impeded by hydrate, it would accumulate at the lower boundary of the hydrate zone as free gas and would cause a significant decrease in seismic velocity at that boundary (Bryan, 1974). Bottom-simulating reflectors are strongest in the vicinity of ridge crests and tend to fade out on the flanks (Mark! and others, 1970), a configuration that suggests gas accumulation at the crest as in an anticlinal trap.

OTHER SEISMIC EVIDENCE FOR GAS HYD~ATES IN OCEANIC SEDIMENTS

Seismic features other than bottom-simulating reflectors may be produced by gas hydrates. These features include bottom-parallel bright spots, pagoda structures, and deep-water velocity amplitude features (VAMP's). White (1977) suggested that seismic bright spots (amplitude anomalies) in the Gulf of Oman are caused by natural gas accumulations. These subbottom reflectors are curved, mimic the topography of the seafloor, and transgress local bedding (making these bright spots similar to bottom-simulating reflectors, but of lesser lateral extent). White (1979) inferred that the gas is held in place not by a stratigraphic trap but by an impe~eable gas hydrate layer that follows the seafloor topography.

Emery (1974) has suggested that pagoda structures may be related to gas hydrates, although these are very shallow subbottom seismic features, and there is little consensus regarding their significance. Geophysical traverses ~~ross nearly flat mud bottom at depths between 2,000 and 5,000 m off western Africa provided ext€nsive seismic shallow-penetration recordings at 3.5 kHz. The recordings reveal the presence of common alternating light and dark triangular S€ismic features, or pagoda structures, whose internal structure and acoustic properties may, according to Emery (1974), be due to local centers of gas hydrate induration.

Velocity-amplitude features (VAMP's) are acoustic anomalies showing narrow (1 to 2 km) subsurface columns of concave reflection horizons called pulldowns, associated with gently arched, high-amplitude horizons higher in the sectio~ (Scholl and Cooper, 1978). These kinds of acoustic anomalies, common on seismic profiles collected in the Bering Sea, are typically seen in flat-lying beds at subbottom depths greater than 500 m and in deep water around 4,000 m. VAMP's are essentially deep-seated "bright spots" u'"~der lain by reflection horizon pulldowns. Gas hydrates may be responsible for VAMP's by cont~ib uting to the restriction of upward-migrating gas and fluids.

It is difficult to detect gas hydrates by purely chemical and seismic means. Support for the indentification of gas hydrate in seafloor sediments will result when cores containing l.ydrates recovered at their subsea temperatures and pressures can be analyzed. A pressure core t .'lrrel capable of this task has been designed br DSDP but has never been successfully deploye~ in a gas hydrate horizon. From the geologic, g~o physical, and geochemical evidence obtained thus far, there is little doubt that gas hydrates are an important part of the marine sedimentary record. The following is a selected bibliography containing the references cited in this paper along with other papers dealing with the physical chemistry, geology, and geophysics of gas hydrates. This bibliography does not represent an exhaustive search of the literature, but rather includes those pertinent papers readily available to us.

Baker, P.E., 1974, Experiments on hydrocarbon gas hydrates in unconsolidated sand, in Kaplan, I.R., ed., Natural gases in marine sediments: New York, Plenum, p. 227-234.

Barnes, R.O., and Goldberg, E.D., 1976, Methane production and consumption in anoxic marine sediments: Geology, v. 4, p. 297-300.

Barnes, W.C., 1975, Some structural implications of gas hydrates in deep-ocean sediments: Geological Society of America Abstracts with Programs, v. 7, p. 989-999.

Barrer, R.M., and Stuart, W.I., 1957, Non-stoichiometric clathrate compounds of water: Proceedings of the Royal Society of London, Ser. A, v. 243, no. 1233, p. 172-189.

Bily, C., and Dick, J.W.L., 1974, Naturally occurring gas hydrates in the Mackenzie Delta, N.W.T.: Bulletin of Canadian Petroleum Geology, v. 22, p. 320-352.

Brown, J.F., Jr., 1962, Inclusion compounds:

Scientific American, v. 207, no. 1, p. 82-92.

Bryan, G.M., 1974, In situ indications of gas hydrates, in Kaplan, I.R., ed., Natural gases in marine sediments: New York, Plenum, p. 299-308.

Buffler, R.T., Shaub, F.J., Watkins, J.s., and Worzel, J.L., 1979, Anatomy of the Mexican ridges, southwestern Gulf of Mexico, in Watkins, J.S., Montadert, L., and Dickerson, P.- w., eds., Geological and geophysical investigations of the continental margins: American Association of Petroleum Geologists Memoir No. 29, P• 319-327.

Carson, D.B., and Katz, D.L., 1942, Natural gas hydrates: Petroleum Transactions of the American Institute of Mining Engineers, v. 146, p. 150-158.

Chan, J.P., and Giauque, W.F., 1964, The entropy of NH Journal of Physical Chemistry, v. 68, p. 3053- 3057.

Claussen, W.F., 1951a, Suggested structures of water in inert gas hydrates: Journal of Chemical Physics, v.19, p. 259-260.

SELECTED BIBLIOGRAPHY

o: Heat capacity from 15 to 300°K:

• 2H

Dillon, W.P., Grow, J.A., and Paull, C.K., 1980, ____1951b, Erratum: Suggested structures of water in inert gas hydrate: Journal of Chemical Physics, v. 19, p. 662.

gas hydrates: Journal of Chemical Physics, v. 19, P• 1425-1426.

Claypool, G.E., and Kaplan, I.R., 1974, The origin and distribution of methane in marine sediments, in Kaplan, I. R., ed., Natural gases in marine sediments: New York, Plenum, p. 99- 139.

Claypool, G.E., Presley, B.J., and Kaplan, I.R., 1973, Gas analysis in sediment sanples from Legs 10, 11, 13, 14, 15, 18, and 19, in Creager, J.S., Scholl, D.W., and others, Initial reports of the Deep Sea Drilling P-:-oject, v. 19: u.s. Government Printing Office, p. 879- 884.

Cooper, A.K., Scholl, D.W., Marlow, M.S., Childs, J.R., Redden, G.D., Kvenvolden, K.A., and Stevenson, A.J., 1979, Hydrocarbon p~tential of the Aleutian Basin, Bering Sea: .American Association of Petroleum Geologists Bulletin, v. 63, p. 2070-2087.

Creager, J.S., Scholl, D.W., and Supko, P.R., 1973, Introduction, in Creager, J.S., Scholl, D.W., and others, Initial reports of the Deep Sea Drilling Project, v. 19: U.S. Government Printing Office, p. 3-16.

Culbertson, O.L., and MCKetta, J.J., Jr., 1951, Phase equilibria in hydrocarbon-water systems III--the solubility of methane in water at pressures to 10,000 psia: Petroleum Transactions of the American Institute of Mining Engineers, v. 192, p. 23-226.

Davidson, D.W., 1971, The motion of guest molecules in clathrate hydrates: Canadian Journal of Chemistry, v. 42, p. 12~4-1242.

---=="'""',..-:-1973, Clathrate hydrates, in Franks, Felix, ed., Water: A comprehen;ive treatise, v. 2: New York, Plenum, p. 115-274.

Davidson, D.W., El-Defrawy, M.K., Fuglem, M.O., and Judge, A.S., 1978, Natural g~s hydrates in northern Canada: International Conference on Permafrost, 3d, Proceedings, v. 1, p. 937- 943.

Deaton, W.M., and Frost, E.M., Jr., 1948, Gas hydrates and their relation to the operation of natural-gas pipe lines: u.s. Bureau of Mines Monograph No. 8, 101 p.

Unconventional gas hydrate seals m~y trap gas off southeast U.S.: Oil and Gas Journal, v. 78, no. 1, p. 124-130.

Emery, K.O., 1974, Pagoda structures in marine sediments, in Kaplan, I.R., ed., Natural gases in marine sediments: New York, Plenum, P• 309-317.

Emery, K.O., and Hoggan, D., 1958, Gases in marine sediments: American Association of Petroleum Geologists Bulletin, v. 42, p. 2174-2188.

Enns, T., Scholander, P.F., and Bradstreet, E.D., 1965, Effect of hydrostatic pressure on gases dissolved in water: Journal of Physical Chemistry, v. 69, p. 389-391.

Evrenos, A.I., Heathman, J., and Ralstin, J., 1971, Impermeation of porous media by forming hydrates in situ: Journal of Petroleum Technology, v. 23, p. 1059-1066.

Ewing, J.I., Ewing, Maurice, and Leyden, R., 1966, Seismic-profiler survey of the Blake Plateau: American Association of Petroleum Geologists Bulletin, v. 50, p. 1948-1971.

Ewing, J.I., and Hollister, C.H., 1972, Regional aspects of deep sea drilling in the western North Atlantic, in Hollister, C.H., Ewing, J.I., and others~Initial reports of the Deep Sea Drilling Project, v. 11: U.S. Government Printing Office, p. 951-973.

Frost, E.M., Jr., and Deaton, W.M., 1946, Gas hydrate composition and equilibrium data: Oil and Gas Journal, v. 45, no. 12, p. 170-178.

Garg, S.K., and Davidson, D.W., 1973, N.M.R. properties of clathrate ice, in Whalley, E., Jones, S.J., and Gold, L.W., eds., Physics and chemistry of ice: Ottawa, Royal Society of Canada, p. 56-60.

Gas Supply Committee, 1979, Gas from natural gas hydrates: Gas energy review, American Gas Association, v. 7, no. 10, p. 1-5.

Geotimes, 1979a, Middle American Trench: v. 24, no. 9, p. 20-22.

Geotimes, 1979b, The Caribbean connection, v. 24, no. 12, P• 18-19.

Glew, D.N., 1962, Aqueous solubility and the gas-hydrates; The methane-water system: Journal of Physical Chemistry, v. 66, p. 605- 609.

Gold, L.W., and Lachenbruch, A.H., 1973, Thermal conditions in permafrost--A review of North American literature, in Permafrost--The North American contribution~2nd International Conference: Washington, National Academy nf Sciences, p. 3-23.

Goldberg, Paul, 1963, Free radicals and reactive molecules in clathrate cavities: Science, v. 142, p. 378-379.

Grantz, Arthur, Boucher, G. W., and Whitney, 0. T., 1976, Possible solid gas hydrate and natural gas deposits beneath the continental slope of the Beaufort Sea: U.S. Geological Survey

Hagan, M.M., 1962, Clathrate inclusion compounds: New York, Van Nostrand-Reinhold, 189 p.

Hampton, Loyd, ed., 1974, Physics of sound in marine sediments: New York, Plenum, 567 p.

Hand, J.H., Katz, D.L., and Verma, V.K., 1974, Review of gas hydrates with implication for ocean sediments, in Kaplan, I.R., ed., Natural gases in marine sediments: New York, Plenum, p. 179-194.

Hedberg, H.D., 1974, Relation of methane generation to undercompacted shales, shale diapirs, and mud volcanoes: American Association of Petroleum Geologists Bulletin, v. 58, p. 661- 673.

Hein, J.R., Scholl, D.W., Barron, J.A., Jones, M.G., and Miller, J., 1978, Diagenesis of late Cenozoic diatomaceous deposits and for~ation of the bottom simulating reflector in the southern Bering Sea: Sedimentology, v. 25, p. 155-181.

Hitchon, B., 1974, Occurrence of natural gas hydrates in sedimentary basins, in Kaplan, I.R., ed., Natural gases in marine sediments: New York, Plenum, p. 195-225.

Hodgson, Bryan, 1978, Natural gas: The search goes on: National Geographic Magazine, v. 154, p. 632-651.

Holder, G.G., Katz, D.L., and Hand, J.H., 1976, Hydrate formation in subsurface envirorments: American Association of Petroleum Geologists Bulletin, v. 60, p. 981-984.

Hollister, C.D., Ewing, J.I., and others, 1972, Sites 102-103-104--Blake-Bahama Outer fidge (northern end), in Hollister, C.D., Ewjng, J.I., and others:-Initial reports of tre Deep Sea Drilling Project, v. 11: U.S. Gove~nment Printing Office, p. 135-143.

Howitt, Frank, 1971, Permafrost geology at Prudhoe Bay: World Petroleum. v. 42~ no.~' P• 28-32 and 37-38.

Hunt, J.M., 1979, Methane hydrates, in Hunt, J~M., Petroleum geochemistry and geology: San Francisco, W.H. Freeman, p. 156-162.

Jeffrey, G.A., 1969, Water structure in organic hydrates: Accounts of Chemical Research, v. 2, P• 344-352. Jeffrey, G.A., 1972, Pentagonal dodecahedral water structure in crystalline hydrates: Material Research Bulletin, v. 7, p. 1259-1269.

Jeffrey, G.A., and McMullin, R.K., 1967, The clathrate hydrates: Progress in Inorganic Chemistry, v. 8, p. 43-108.

Jhaveri, Jaysukh, and Robinson, D. B., 1,965, Hydrates in the methane-nitrogen system: Canadian Journal of Chemical Engineering, v. 43, P• 75-78.

Judge, Alan, 1973, The prediction of permafrost thicknesses: Canadian Geotechnical Journal, v. 10, p. 1-11.

Kaplan, I.R., ed., 1974, Natural gases in marine sediments: New York, Plenum, 324 p.

Katz, D.L., 1945, Prediction of conditions for hydrate formation in natural gases: Petroleum Transactions of the American Institute of Mining Engineers, v. 160, p. 140-149.

--~---1971, Depths to which frozen gas fields (gas hydrates) may be expected: Journal of Petroleum Technology, v. 23, p. 419-423.

------~1972, Depths to which frozen gas fields may be expected--Footnotes: Journal of Petroleum Technology, v. 24, p. 557-558.

Katz, D.L., Cornell, D., Kobayashi, Riki, Poettmann, F.H., Vary, J.A., Elenblass, J.R., and Weinaug, C.F., 1959, Handbook of natural gas engineering: New York, McGraw-Hill, 802 p.

Kobayashi, Riki, and Katz, D.L., 1949, Methane hydrate at high pressure: Petroleum Transactions of the American Institute of Mining Engineers, v. 186, p. 66-70.

Lancelot, Y., and Ewing, J.I., 1972, Correlation of natural gas zonation and carbonate diagenesis in Tertiary sediments from the north-west Atlantic, in Hollister, C.D., Ewing, J.I., and others, Initial reports of the Deep Sea Drilling Project, v. 11: U.S. Government Printing Office, p. 791-799.

Langseth, M.G., Jr., and von Herzen, R.P., 1970, Heat flow through the floors of the oceans, in Maxwell, A. E., ed., The sea, v. 4: New York-;- Wiley-Interscience, p. 299-352.

Makogon, Yu. F., Trebin, F.A., Trofimuk, A.A., Tsarev, V.P., and Cherskiy, N.V., 1971, Obnarvzheniye zalezhi prirodnogo gaza v trerdom (gazogldratnom) sostoyanii ["Detection of a pool of natural gas in a solid (hydrated gas) state"]: Doklady Akademii Nauk SSSR, v. 196, p. 203-206 (in Russian); Doklady-Earth Science Section 196 (1972), p. 197-200 (in English).

Makogon, Yu. F., Trofimuk, A.A., Tsarev, V.P., and Cherskiy, N.V., 1973, Vozmozh~osti obrazovaniya gazogidratnykh zalezhey prirodnykh gazov v pridonnoy zone morey i okeanov [ "Possible origin of natural gas hydrates at floors of seas and oceans"] : Ak.ademiya N~uk SSSR Sibirskoye Otdeleniye Geologiya i Geofizika, no. 4, p. 3-6 (in Russian); International Geology Review, v. 16 (1974), p. 553-556 (in English).

Makogon, Yu. F., Tsarev, V.I., and Chersky, N.V., 1972, K voprosu formirovaniya krupnykh mestorozhdeniy gaza v zonakh pasprostraneniya ponizhennykh temperatur ["Formation of large natural gas fields in zones of permanently low temperatures"]: Doklady Ak.ademii t-'"uk SSSR, v. 205, p. 700-703 (in Russian); Doklady-Earth Science Section 205 (1973), p. 215-218 (in English).

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Markl, R.G., Bryan, G.M., and Ewing, J.I., 1970, Structure of the Blake-Bahama Outer Ridge: Journal of Geophysical Research, y. 75, p. 4539-4555.

Marshall, D.R., Saito, S., and Kobayashi, Riki, 1964, Hydrates at high pressure: I. Methane-water, argon-water, and nitrogen-water systems: American Institute of ctemical Engineers Journal, v. 10, p. 202-205.

Mciver, R.D., 1973, Hydrocarbons in canned muds from sites 185, 186, 189, and 191--Leg 19, in Creager, J.S., Scholl, D.W., and ethers, ~ tial reports of the Deep Sea Drilling Project, v. 19: u.s. Government Printing Office, p. 875-877.

--~---1974, Hydrocarbon gas (methane) in canned Deep Sea Drilling Project core samples, in Kaplan, I.R., ed., Natural gases in marine sediments: New York, Plenum, P• 63-69.

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