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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Confined-flow Turbidite Reservoirs: Plio-Pleistocene,
Ship Shoal - Ewing Banks - Green Canyon areas, Offshore Louisiana
By
Mobil Oil Corporation, Dallas, Texas, USA
Seismic facies and high-resolution biostratigraphic
analysis
provide a
sequence
stratigraphic framework for interpreting
lateral distribution of sand-prone facies
and possible reservoir connectivity in the
Ship Shoal 351-358 to Ewing Bank 988
minibasin, offshore Louisiana. The interval
of interest is an isochron thick interpreted
as a lowstand systems tract
deposited in bathyal water depths within
an intraslope-minibasin. This basin
is approximately 50 km from the
age-equivalent shelf/slope break. The
isochron thick was deposited between the
late Pliocene Discoaster pentaradiatus
and early Pleistocene Discoaster brouweri
Condensed Sections, as calibrated by data
from five wells penetrating this interval
within the intraslope basin.
The D. pentaradiatus - D. brouweri sequence
consists of the synclinal fill of a
salt withdrawal basin forming an isochron
thick that thins onto adjacent salt-cored
structural highs. This isochron interval
was subdivided into four seismic facies
and each was calibrated with local
well
data. Mapped patterns of these seismic
facies suggest a network of channel-form
systems supplying sediment to depositional
lobe-forms within a slope valley.
Sandy sediments were transported by
gravity-driven processes from the shelf,
down slope through a valley and into this
local intraslope-minibasin. Upon filling
this minibasin, the gravity-driven sediments
spilled farther south into the area of
the Green Canyon 18 field, where these
sandstones are the main reservoir. The
mapping of channel-and levee-form patterns
suggests that the transport process
included turbid flow with consequent
overbanking of the channel and levee
formation.
Following the above analysis
, three wells
and two sidetracks were drilled to further
test the prospectivity of the area. Rock
type and hydrocarbon predictions based
on calibrated seismic
facies
analysis
were confirmed by
the new wells.
Sandstones occur within the axes of isochron thicks and shales
dominate the isochron
thins over paleo-highs
with gradational facies
between. Hydrocarbon accumulation occurs in two
settings: 1) channel-fed lobes with blocky log
character yield hydrocarbons within areas of structural closure; and 2) overbank facies that contain hydrocarbons in low-resistivity pay both within and outside of structural closure
Local abundance peaks of planktonic microfossils provide correlation control between the four depositional lobes of this lowstand deposit. The biostratigraphic data and paleogeographic interpretation suggest that each depositional lobe is separated from the others by mudstone
drapes, resulting in discrete partitioning of reservoir sands.
Unnumbered Figure. Gulf of Mexico Gravity Flow Event; from Shanmugam (1993, AAPG Bulletin) artwork Mark Lindsey, Mobil Technology Company.
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