Physical parameters controlling gas hydrate stability and distribution on the North Slope, Alaska

Conference · Fri May 01 04:00:00 EDT 1987 · AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)

OSTI ID:6310293

Collett, T S

The natural gas hydrate stability field and its controlling factors on the North Slope have been evaluated as part of the US Geological Survey-US Department of Energy worldwide gas hydrate assessment program. Gas hydrates exist under relatively limited conditions of pressure and temperature, the hydrate stability field, which must be evaluated along with other factors prior to volumetric assessment. Their North Slope studies suggest that the gas hydrate stability field is controlled primarily by subsurface temperatures and gas chemistry. Other factors, such as pore-pressure variations, pore-fluid salinity, and reservoir-rock grain size, appear to have little effect on the gas hydrate stability field. Data necessary to determine the distribution of the gas hydrate stability field are difficult to obtain. Subsurface-temperature data come from 46 high-resolution equilibrated well-bore surveys and from estimates based on identification of the base of ice-bearing permafrost in 98 other wells. Geothermal gradients in ice-bearing permafrost range from 1.55/sup 0/C/100 m in the East Bay State-1 well to 4.46/sup 0/C/100 m in Fish Creek-1. Methane is the dominant species of gas in the near-surface (0-1500 m) sediment, on the basis of mud log gas-chromatograph data. However, because nitrogen was detected in several analyses of recovered gas hydrate and drill cuttings, several different gas mixtures other than pure methane were assumed in the stability calculations. Formation water samples and well log calculations indicate low pore-fluid salinities, ranging from 0.5 to 18.1 ppt. The maximum recorded salinity would suppress methane hydrate stability temperatures by approximately 1.0/sup 0/C. Pressure data, obtained from drill-stem testing and well log calculations, indicate a hydrostatic pore-pressure gradient (9.795 kPa/m or 0.433 psi/ft) within the near-surface sediments, thus having no abnormal effect on gas hydrate stability.

• Research Organization: Geological Survey, Menlo Park, CA
• OSTI ID: 6310293
• Report Number(s): CONF-870606-
• Conference Information: Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Journal Volume: 71:5
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
ALASKA
ALASKAN NORTH SLOPE
EXPLORATION
FEDERAL REGION X
GEOLOGIC DEPOSITS
NATIONAL ORGANIZATIONS
NATURAL GAS HYDRATE DEPOSITS
NORTH AMERICA
RESEARCH PROGRAMS
RESERVOIR ROCK
US DOE
US DOI
US ORGANIZATIONS
USA