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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
Geology and Stratigraphy
of Fluvio-Deltaic Deposits in the Ivishak Formation: Applications for Development
of Prudhoe Bay Field, Alaska 1
David
D. Puls,5
and Richard A. Levinson
1Manuscript received March 17, 1998;
revised manuscript received February 5, 1999; final acceptance March 3,
1999.
2ARCO 2300 West Plano Parkway, Plano,
Texas 75075-8499; e-mail: rtye@is.arco.com
3ARCO El-Djazair, 2300 West Plano
Parkway, Plano, Texas 75075-8499.
4ARCO Alaska, Inc. 700 G Street, Anchorage,
Alaska 99510-0360.
5Exxon Azerbaijan Operating Company,
Landmark, Suite 300, 96 Nizami Street, Baku, 370000, Azerbaijan Republic.
ABSTRACT
Significant remaining reserves in Prudhoe Bay
field are confined within deltaic rocks at the base of the Triassic Ivishak
sandstone. The initial stratigraphic characterization of the Prudhoe Bay
reservoir was lithostratigraphically based, and it depicted this basal
reservoir interval as tabular zones between marine shale and overlying
coarse-grained, fluvial sandstones. A reassessment of this interval based
on cores and genetic-stratigraphic correlations depicts en echelon, offlapping,
fluvially dominated deltaic wedges.
Reservoir-quality rocks occur in distributary mouth bar, distributary channel, and fluvial facies associations. A paleogeographic reconstruction of one delta lobe includes an alluvial plain crossed by channels of possibly braided or low-sinuosity rivers. This alluvial plain graded into a delta plain cut by distributary channels that fed distributary mouth bars on a broad delta front. River dominance is inferred from the abundance of unidirectional current structures, normally graded beds, soft-sediment deformation, and general absence of wave-formed, tidal, and biogenic structures. Slumping and growth faulting locally replaced coarsening-upward deltaic successions with sharp-based, overthickened mouth bar and distributary channel deposits.
Mudstones deposited following delta-lobe abandonment form laterally extensive flow barriers between lobes. Compartmentalization is most pronounced distally, where deltaic sandstones are overlain by and pass laterally into marine shale. Proximally, fluvial and deltaic sandstones are juxtaposed across erosional contacts, improving reservoir continuity.
This stratigraphic interpretation is corroborated by production and surveillance data plus an interference test. Locally, stratigraphy and poor waterflood performance reflect completions in diachronous sandstones that originated in separate deltaic lobes. Previously, poor well performances were attributed to sandstone pinch-outs. In some cases, production can be enhanced with recompletions rather than infill drilling. Nonconventional wells planned and completed with the benefit of detailed facies-association correlations currently are recovering millions of barrels of previously bypassed oil.
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