Variation in Petroleum Source Potential of the Kingak Shale, Central North Slope Alaska

Margaret A. Keller
USGS Menlo Park, Menlo Park, CA

USGS petroleum resource assessment of the central North Slope of Alaska included evaluation of source potential of the Jurassic and Lower Cretaceous Kingak Shale. One of the major marine mudstone formations of the North Slope, the Kingak Shale is a southward prograding unit with multiple depositional sequences that were deposited during rifting of Alaska's Arctic margin. The purpose of this study was to characterize the variation in source potential of this thick formation (as much as 4,000 ft) by analysis of geophysical log data integrated with data from Rock-Eval Pyrolysis and paleontologic study.

Profiles of total organic carbon (TOC) were determined for eight wells using the DeltaLogR technique (Passey and others, 1990). Kerogen Type was inferred from Rock-Eval pyrolysis and overall patterns of TOC occurrence. Results show that the Kingak succession in most wells contains predominantly < 2 wt.% TOC (cut-off used for effective source potential) and primarily Type III kerogen. However, organic-rich facies commonly occur in the basal and upper parts of the Kingak. Overall, the organic-rich facies of the Kingak successions in these wells averages 2.4-3.4 wt.% TOC (individual DeltaLogR values, 2.0-8.0 wt.%) over total cumulative thickness per well of 221-806 ft.

Rock-Eval pyrolysis, lithologic descriptions of "paper shale", and paleoenvironmental data suggest that this organic-rich facies contains oil prone Type II kerogen in depositional settings characterized by low influx of clastic sediment and low oxygen. This interpretation indicates that thermally mature Kingak Shale had significant oil and gas generation potential in this region.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005