Effect of geothermal pore-pressure conditions and natural gas composition on in situ natural gas hydrate occurrences, North Slope, Alaska
The factors controlling the distribution of natural gas hydrates (solid compounds composed of natural gas and water) in the earth include mean annual ground temperatures, geothermal gradients, subsurface pressure conditions, gas composition, and pore-fluid salinity. A thorough analysis of the effect of these parameters on thickness and depth of hydrate stability zones has been conducted. A thermodynamic model has been used to compute depth and thickness of zones of stability of gas hydrates in 34 representative wells on the North Slope. Several well logs in these depth ranges have been analyzed to determine hydrate zone thickness, porosity, and hydrate saturation. In well log analysis, the hydrate presence has been indicated by the following evidence: increase in acoustic velocity, strong resistivity deflection, small spontaneous potential deflection, gas shown on mud log, oversized caliper increase in the neutron porosity, separation of long normal from short normal, and decrease in drilling rate. In several of these wells, multiple zones of hydrates have been detected. In the Prudhoe Bay and Kuparuk fields, hydrates are expected to occur primarily in six stratigraphic horizons, mostly in an unconsolidated unit characterized by a poorly sorted sandstone and conglomeratic lithology. Detailed examination of the neutron porosity and sonic velocity responses within one hydrate horizon in six wells in Kuparuk field indicates an average porosity of 44% and hydrate saturation of 93%. Such information is extremely relevant to quantification of gas hydrate deposits.
- Research Organization:
- Univ. of Alaska, Fairbanks
- OSTI ID:
- 5922564
- Report Number(s):
- CONF-8505215-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 69:4; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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