ABSTRACT: High Resolution Sequence Stratigraphic Analysis of the Early Cretaceous Syn-Rift Succession, North Slope, Alaska

DAVIES, ROGER B., BP Alaska Exploration, Anchorage, AK, KERRY F. INMAN* and MICHAEL L. SWEET, BP Exploration, Houston, TX, and ROBERT L. RAVN, BP Alaska Exploration, Anchorage, AK

The Early Cretaceous syn-rift succession of the North Slope of Alaska contains five major discovered hydrocarbon accumulations, including the Kuparuk and Point McIntyre oil fields. Total recoverable fluids exceed 3 billion barrels.

A multidisciplinary regional review was initiated to constrain reservoir presence and quality. Initial exploration work had defined a coarse regional chronostratigraphic framework based on mapping of three seismically resolvable unconformities. Re-evaluation of biostratigraphic data delineated 7+ distinct sediment packages within the 26 +/- 5 m.y. interval. This framework was subdivided further using log and core-based correlation of potentially significant stratigraphic surfaces, including candidate sequence boundaries, maximum flooding surfaces, and transgressive surfaces. Candidate sequence boundaries were identified at the bases of sharp-based sands, at sharp erosive contacts with associated mudchip conglomerates within sandy packages, and at the bases of sands with unique detrita mineralogy. On logs, they were picked at the bases of blocky, low gamma-response, and at changes from cleaning to increasing-upward gamma ray character. Candidate flood surfaces were picked in core within intensely bioturbated, often highly glauconitic and sideritic zones interpreted as condensed intervals. On logs, high gamma-ray and often high density are characteristic features.

The high resolution framework has facilitated production of paleogeographic maps for well-constrained time slices, thereby establishing spatial and temporal relationships among the known accumulations. Lithofacies distributions and diagenetic histories are analyzed within this stratigraphic framework, providing an improved understanding of controls on reservoir quality. This integrated, iterative study provides an enhanced understanding of potential within the Early Cretaceous interval.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)