Evaluation of local geothermal gradients on North Slope of Alaska
The US Geological Survey is conducting a detailed assessment of worldwide natural-gas hydrate occurrences. Thermodynamic conditions controlling hydrate occurrences of northern Alaska have been examined. Pressure and temperature conditions on the North Slope indicate that hydrates would be potentially stable both above and below the permafrost base. Geothermal gradients needed to predict the thickness of the hydrate stability zone are not easily obtained. A survey of preliminary data suggested wide variations in averaged regional geothermal gradients across the North Slope. To evaluate regional variations of geothermal gradients, 2 techniques were employed to calculate local gradients. The first method used bottom-hole temperatures recorded during successive wireline logging runs and corrected by Horner crossplots to determine undisturbed formation temperatures. The Horner crossplot method requires a series of recorded bottom-hole temperatures. However, in most of the North Slope production wells, only 2-3 log runs are conducted per well, thus limiting the number of bottom-hole temperatures. To overcome this limiting factor, a second method has been developed to evaluate local geothermal gradients. This new technique uses permafrost depths delineated from well-log data to project geothermal gradients. Gradients within the permafrost zone have been projected from the base of permafrost, which is in equilibrium at -1/sup 0/C. A series of mean ground temperatures has been used to project the upper extent of each gradient. Geothermal gradients change abruptly at the base of the permafrost. In order to calculate the gradient below the permafrost base, a constant generated from subsurface temperature data was used to correct for this change in geothermal gradient. Data from 398 wells were examined by each method to develop a series of geothermal gradient maps.
- Research Organization:
- Geological Survey, Menlo Park, CA
- OSTI ID:
- 5857500
- Report Number(s):
- CONF-850322-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 69:2; Conference: American Association of Petroleum Geologists annual meeting, New Orleans, LA, USA, 25 Mar 1985
- Country of Publication:
- United States
- Language:
- English
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