SUBSURFACE TEMPERATURES AND GEOTHERMAL GRADIENTS ON THE NORTH SLOPE OF ALASKA

On the North Slope of Alaska, geothermal gradient data are available f rom high-resolution, equilibrated well-bore surveys and from estimates based on well-log identification of the base of ice-bearing permafros t. A total of 46 North Slope wells, considered to be in or near therma l equilibrium, have been surveyed with high-resolution temperatures de vices and geothermal gradients can be interpreted directly from these recorded temperature profiles. To augment the limited North Slope temp erature data base, a new method of evaluating local geothermal gradien ts has been developed. In this method, a series of well-log picks for the base of the ice-bearing permafrost from 102 wells have been used, along with regional temperature constants derived from the high-resolu tion stabilized well-bore temperature surveys, to project geothermal g radients. Geothermal gradients calculated from the high-resolution tem perature surveys generally agree with those projected from known ice-b earing permafrost depths over most of the North Slope. Values in the i ce-bearing permafrost range from almost-equal-to 1.5-degrees-C/100 m i n the Prudhoe Bay area to almost-equal-to 4.5-degrees-C/100 m in the e ast-central portion of the National Petroleum Reserve in Alaska. Geoth ermal gradients below the ice-bearing permafrost sequence range from a lmost-equal-to 1.6-degrees-C/100 m to almost-equal-to 5.2-degrees-C/10 0 m.