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Dzou, Leon1, S. Cheree Stover2, Andy Pepper2
(1) BP America GoM Deepwater Exploration, Houston, TX
(2) BP Exploration and Production Technology Group, Houston, TX

ABSTRACT: Controls on Fluid Distribution in the Alaskan North Slope Petroleum Systems

The prolific North Slope petroleum province contains accumulations ranging from undersaturated oil to dry gas, distributed among many trap types and reservoir layers. Historically, the commercially viable product for export has been oil, which has focused attention on understanding the distribution and quality of the major, chiefly oil-prone source rocks: Upper Triassic Shublik, Lower Jurassic Kingak and mid-Cretaceous HRZ and Shale Wall (Hue); a number of additional, volumetrically unimportant source rocks are present. However, presumably reflecting the bias toward oil exploitation, most models to-date seem to have ignored the role of the Mississippian Kekiktuk coals.
We constructed a system model which defines the location and extent of expulsion kitchens through time for both the oil and gas-prone source systems, using an improvised “two-and-a-half-D” approach (combining 60 calibrated 1-D models with map-based interpolation/extrapolation); additionally, a few 2-D sections were modeled using Temispack. Since much of the North Slope is not at maximal thermal stress at the present day, one particularly important aspect of this work was to restore eroded overburden carefully.
After calibration of the model against the “forensic” evidence from oil and gas geochemistry and fluid properties, our main conclusions are: (1) it is impossible to explain the petroleum distribution without including the Kekiktuk as a major gas source which “competes” with Shublik, and to a lesser extent HRZ oil to determine the composition and phase of each trap; (2) major capillary-dominated vertical migration and leakage occurred locally; and (3) vertical up-fault migration is inconsistent with geochemical data.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.