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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: [email protected]
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
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.
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.
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