Seismic-attribute Analysis for Gas-hydrate and Free-gas Prospects on the North Slope of Alaska
M. W. Lee, T. S. Collett, T. L. Inks, 2009. "Seismic-attribute Analysis for Gas-hydrate and Free-gas Prospects on the North Slope of Alaska", Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards, T. Collett, A. Johnson, C. Knapp, R. Boswell
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Identification and quantification of gas-hydrate and free-gas reservoirs in unconsolidated sediments using seismic data are important, because seismic methods are the most promising remote sensing technique for the delineation of such prospects. For many years, the seismic method has been used to detect free-gas reservoirs because of their association with high-amplitude events and a characteristic amplitude relative to offset behavior. However, seismic-data-driven analysis for detecting and quantifying gas-hydrate accumulations is uncommon. Gas hydrate in the pore space increases elastic velocities and reduces the bulk density. Because of these properties, coupled with the fact that gas hydrate tends to be more highly concentrated in high-porosity clean sands and sandstones, the combined effect of varying gas-hydrate saturation and reservoir thickness on seismic amplitude is complex. Depending on saturation, the seismic expression of a gas-hydrate accumulation can be that of a low-amplitude event (amplitude blanking) or a high-amplitude event (bright spot). This complex amplitude relationship with respect to gas-hydrate and gas saturations is described in this article and is used to estimate saturations and thicknesses of reservoirs on the basis of a thin-bed analysis of three-dimensional seismic data. Seismic interpretation of gas-hydrate and free-gas occurrences and saturations of the reservoirs agree well with geologic considerations as described by Inks et al. (2009). Because the quantitative interpretation is based on a reservoir model appropriate for the North Slope of Alaska, it is emphasized that a caution should be exercised to extend this method to other areas.
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Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards
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.