--> Abstract: Seismic Stratigraphy Near the Tunalik Well, North Slope, Alaska, by J. A. Grow, J. J. Miller, C. G. (Gil) Mull, and K. J. Bird; #90958 (1995).

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Abstract: Seismic Stratigraphy Near the Tunalik Well, North Slope, Alaska

J. A. Grow, J. J. Miller, C. G. (Gil) Mull, K. J. Bird

The Tunalik #1 well was drilled to 20,335 ft in 1978 on the North Slope of Alaska (northwest corner of the National Petroleum Reserve), terminating in Pennsylvanian limestones. A strong gas kick occurred at 12,500 ft in the Jurassic-Early Cretaceous Kingak Shale unit (11,400-14,400 ft), and drilling was shut down for a month before control was regained.

Seismic profiles in the vicinity of Tunalik indicate that the gas kick occurred in the to reset beds of a 1500-ft-thick deltaic system that was prograding to the south and west during deposition. The uppermost (topset) part of the deltaic system consists of an upward-coarsening 300-ft sandstone interval--an apparent equivalent of sandstones of the Kuparuk Formation. The gas kick occurred within a lower 100-ft-thick sandy unit, which has high velocities (12,000 ft/sec), high densities (2.6-3.0 g/cc), and high resistivities that decrease upward, indicating an overall fining-upward sequence. The densities in the lower part of the sandy unit are 2.8-3.0 g/cc and appear to reflect some combination of naturally occurring pyrite in the sediments and barite that was injected while regaining control of the well. A synthetic seismogram agrees well with the seismic profiles that show a moderate amplitude anomaly from the gas-bearing zone. The anomaly is caused by the high-velocity and high-density sands, and no wide spread gas zone is obvious.

Vitrinite reflectance values (RO) within the Kingak in the Tunalik well are 2.0-3.5, compatible with the occurrence of gas. The total organic carbon measurements average below 1% with only a few samples in the 1-2 % range. The Alaskan Division of Geological and Geophysical Surveys and the U.S. Geological Survey are initiating (1) a seismic stratigraphic study in an attempt to identify sequences in the northwestern part of the National Petroleum Reserve which might have more favorable hydrocarbon potential and (2) a study of the relationship of the turbiditic sandstones of the Kingak to the quartzose Tingmerkpuk sandstone that crops out in the western Brooks Range.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California