Hydrocarbon Gas Composition and Origin of Gas Hydrate from the Alaska North Slope
Thomas D. Lorenson, Timothy S. Collett, Michael J. Whiticar, 2009. "Hydrocarbon Gas Composition and Origin of Gas Hydrate from the Alaska North Slope", Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards, T. Collett, A. Johnson, C. Knapp, R. Boswell
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Hydrocarbon gas composition and isotopic composition of methane were analyzed from cutting samples obtained from industry oil wells penetrating the Eileen and Tarn gas-hydrate deposits. These gas-hydrate deposits overlie the Prudhoe Bay and Kuparuk River oil fields and are restricted to the updip part of a series of nearshore deltaic sandstone reservoirs in the lower Tertiary (Eocene) Mikkelsen Tongue of the Canning Formation and the Tertiary Staines Tongue of the Sagavanirktok Formation, respectively. The Eileen and Tarn gas hydrates are thought to contain a mixture of deep-source thermogenic gas and shallow, microbial gas (methane carbon isotopic composition ranges from —54 to —46% in the gas-hydrate zone). Thermogenic gases likely come either from existing oil and gas accumulations or from source rocks within the oil- and gas-generating window that have migrated updip and or upfault and formed gas hydrate. The timing of gas source mixing is unknown. The microbial gases likely have a source contribution from biodegraded oil or gas in the underlying oil fields, as evidenced by the carbon isotopic composition of methane, ethane, propane, and carbon dioxide. The distribution of the Eileen and Tarn gas-hydrate accumulations appears to be controlled in part by the presence of large-scale regional faults that may have acted as vertical and lateral gas migration conduits.
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In September 2004, the American Association of Petroleum Geologists (AAPG) convened a Hedberg Research Conference in Vancouver, British Columbia, Canada titled "Natural Gas Hydrates: Energy Resource Potential and Associated Geologic Hazards." As a continuation of the Hedberg Research Conference in Vancouver, the conveners of the conference and the editors of this Memoir have worked with more than 150 authors and coauthors to prepare this Memoir on gas hydrates. This publication follows the goals of the Hedberg conference; however, the contents of this Memoir were expanded to include all aspects of gas hydrates in nature. This Memoir contains 39 individual contributions, ranging from long topical summaries to shorter focused research papers. This Memoir has been published in two parts, with digital versions of all the complete research papers included on the enclosed CD. The hardcopy portion of the Memoir includes abstracts and several key figures for each of the contributions along with a complete copy of a gas hydrate technical review. The digital portion of this Memoir has been organized into a series of topical sections consisting of review articles, marine gas hydrate papers, and gas hydrate laboratory and modeling studies. Because of the rapidly emerging worldwide interest in gas hydrates, this comprehensive treatise on the geology of gas hydrates will be valuable to both the gas hydrate research community and exploration/development geologists working in arctic and deep marine environments.