Natural Gas Hydrates Occurrence, Distribution, and Detection

About this book

Natural Gas Hydrates is published at a time when there is a growing interest in gas hydrates and major expansion in international research efforts. The first recognition of natural gas hydrate on land in Arctic conditions was in the mid-1960s (by I. Makogon) and in the seabed environment only in the early 1970s, after natural seafloor gas hydrate was drilled on the Blake Ridge during Deep Sea Drilling Project Leg 11. Initial scientific investigations were slow to develop because the study of natural gas hydrates is unusually challenging. Gas hydrate exists in nature in conditions of temperature and pressure where human beings cannot survive, and if gas hydrate is transported from its region of stability to normal Earth-surface conditions, it dissociates. Thus, in contrast to most minerals, we cannot depend on drilled samples to provide accurate estimates of the amount of gas hydrate present. Even the heat and changes in chemistry (methane saturation, salinity, etc.) introduced by the drilling process affect the gas hydrate, independent of the changes brought about by moving a sample to the surface. Gas hydrate has been identified in nature generally by inference from indirect evidence in drilling data or by using remotely sensed indications, mostly from seismic data. Obviously, the established techniques ofgeologic analysis, which require direct observation and sampling, do not apply to gas hydrate studies, and controversy has surrounded many interpretations. Pressure/temperature conditions appropriate for the existence of gas hydrate occur over the greater part of the shallow subsurface of the Earth beneath the ocean at water depths exceeding about 500 m (shallower beneath colder Arctic seas) and on land beneath high-latitude permafrost. Gas hydrate actually will be present in such conditions, however, only where methane is present at high concentrations. In the Arctic, these methane concentrations are often associated with petroleum deposits, whereas at continental margins in the oceans, where by far the greatest amount of gas hydrate occurs, the gas is almost all microbially derived methane. The margins of the oceans are where the flux of organic carbon to the sea floor is greatest because oceanic biological productivity is highest and organic detritus from the continents also collects to some extent. Furthermore, the continental margins are where sedimentation rates are fastest, so that the rapid accumulation of sediment serves to cover and seal the organic material before it is oxidized, allowing the microorganisms in the sediments to use it as food and form the methane that becomes incorporated into gas hydrate.

Contents

Preface
      Charles K. Paull and William P. Dillon vii

GENERAL ISSUES
The Global Occurrence of Natural Gas Hydrates
      Keith A. Kvenvolden and Thomas D. Lorenson 3
Modeling the Global Carbon Cycle With a Gas Hydrate Capacitor: Significance for the Latest Paleocene Thermal Maximum
      Gerald R. Dickens 19

GEOCHEMISTRY OF GAS HYDRATE
Overviews and Methods of Geochemistry
Ion Exclusion Associated With Marine Gas Hydrate Deposits
      William Ussier III and Charles K. Paull 41
History and Significance of Gas Sampling During the DSDP and ODP
      Charles K. Paull and William Ussier III 53
Gas Hydrates in Convergent Margins: Formation, Occurrence, Geochemistry and Global Significance
      Miriam Kastner 67

Geochemical Regional Studies
Cascadia
Sea Floor Methane Hydrates at Hydrate Ridge, Cascadia Margin
      E. Suess, M.E. Torres, G. Bohrmann, R.W. Collier, D. Rickert, C. Goldfinger, P. Linke, A. Heuser, H. Sahling, K. Heeschen, C. Jung, K. Nakamura, J. Greinert, O. Pfannkuche, A. Trehu, G.Klinkhammer, M.J. Whiticar, A. Eisenhauer, 8. Teichert, and M. Elvert 87
Gas Hydrate-Associated Carbonates and Methane-Venting at Hydrate Ridge: Classification, Distribution and Origin of Authigenic Lithologies
      Jens Greinert, Gerhard Bohrmann, and Erwin Suess 99
Carbon Isotopes of Biomarkers Derived from Methane-Oxidizing Microbes at Hydrate Ridge, Cascadia Convergent Margin
      Marcus Elvert, Jens Greinert, Erwin Suess, and Michael J. Whiticar 115

Gulf of Mexico
Stability of Thermogenic Gas Hydrate in the Gulf of Mexico: Constraints on Models of Climate Change
      Roger Sassen, Stephen T Sweet, Alexei V. Milkov, Debra A. DeFreitas, Mahlon C. Kennicutt, and Harry H. Roberts 131
Fluid and Gas Expulsion on the Northern Gulf of Mexico Continental Slope: Mud-Prone to Mineral-Prone Responses
      Harry H. Roberts 145

GEOPHYSICS
Geophysical Overviews and Methods
Deep-tow Seismic Investigations of Methane Hydrates
      Warren T Wood and Joseph F. Gettrust 165
Comparison of Elastic Velocity Models for Gas-Hydrate-Bearing Sediments
      Myung W. Lee and Timothy S. Gollett 179
Quantitative Well-Log Analysis of In-Situ Natural Gas Hydrates
      Timothy S. Gollett 189

Geophysical Regional Studies
Blake Ridge
Seafloor Collapse and Methane Venting Associated with Gas Hydrate on the Blake Ridge—Causes and Implications to Seafloor Stability and Methane Release
      William P. Dillon, Jeffrey W. Nealon, Michael H. Taylor, Myung W. Lee, Rebecca M. Drury, and Christopher H. Anton 211
Seismic Studies of the Blake Ridge: Implications for Hydrate Distribution,Methane Expulsion, and Free Gas Dynamics
      W. Steven Holbrook 235

Peru/Middle American Trenches
Gas Hydrates Along the Peru and Middle America Trench System
      Ingo A. Percher, Nina Kukowski, Cesar R. Ranero, and Roland von Huene 257

Cascadia
Geophysical Studies of Marine Gas Hydrates in Northern Cascadia
      R. D. Hyndman, G. D. Spence, R. Chapman, M. Reidel, and R. N. Edwards 273
High-resolution Multibeam Survey of Hydrate Ridge, Offshore Oregon
      David Clague, Norm Maher, and Charles K. Paul I 297

IMPLICATIONS
Potential Influence of Gas Hydrates on Seabed Installations
      Martin Hovland and Ove Tobias Gudmestad 307

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