Geologic interrelations relative to gas hydrates within the North Slope of Alaska: Task No. 6, Final report

• Main Authors: Collett, T.S., Bird, K.J., Kvenvolden, K.A., Magoon, L.B.
• Language: unknown
• Published: 2015
• Subjects: 03 NATURAL GAS; ALASKA; NATURAL GAS HYDRATE DEPOSITS; GAS HYDRATES; STABILITY; DRILL CORES; GAS SATURATION; GEOLOGY; ORIGIN; PHASE DIAGRAMS; POROSITY; PROGRESS REPORT; SAMPLING; SANDSTONES; WELL LOGGING; DIAGRAMS; DOCUMENT TYPES; FEDERAL REGION X; GEOLOGIC DEPOSITS; HYDRATES; NORTH AMERICA; ROCKS; SATURATION; SEDIMENTARY ROCKS; USA; north slope; Alaska
• Online Access: http://www.osti.gov/servlets/purl/6177614; https://www.osti.gov/biblio/6177614; https://doi.org/10.2172/6177614

The five primary objectives of the US Geological Survey North Slope Gas Hydrate Project were to: (1) Determine possible geologic controls on the occurrence of gas hydrate; (2) locate and evaluate possible gas-hydrate-bearing reservoirs; (3) estimate the volume of gas within the hydrates; (4) develop a model for gas-hydrate formation; and (5) select a coring site for gas-hydrate sampling and analysis. Our studies of the North Slope of Alaska suggest that the zone in which gas hydrates are stable is controlled primarily by subsurface temperatures and gas chemistry. Other factors, such as pore-pressure variations, pore-fluid salinity, and reservior-rock grain size, appear to have little effect on gas hydrate stability on the North Slope. Data necessary to determine the limits of gas hydrate stability field are difficult to obtain. On the basis of mud-log gas chromatography, core data, and cuttings data, methane is the dominant species of gas in the near-surface (0--1500 m) sediment. Gas hydrates were identified in 34 wells utilizing well-log responses calibrated to the response of an interval in one well where gas hydrates were actually recovered in a core by an oil company. A possible scenario describing the origin of the interred gas hydrates on the North Slope involves the migration of thermogenic solution- and free-gas from deeper reservoirs upward along faults into the overlying sedimentary rocks. We have identified two (dedicated) core-hole sites, the Eileen and the South-End core-holes, at which there is a high probability of recovering a sample of gas hydrate. At the Eileen core-hole site, at least three stratigraphic units may contain gas hydrate. The South-End core-hole site provides an opportunity to study one specific rock unit that appears to contain both gas hydrate and oil. 100 refs., 72 figs., 24 tabs.