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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: West Cameron 76 Field and Deep Lower Tertiary
Framework Revealed Using Sequence Stratigraphy
Integrated with SPICE
By
Silver Grass Enterprises
Sugar Land, Texas
The Miocene to Cretaceous geology of the northern Gulf of
Mexico is the subject of active investigation with the most
modern data and techniques available in the industry. The geology
is examined here with long-cable 3D seismic data and prestack
depth migration (PSDM) processing to better image from
below 13,000 ft to greater than 40,000 ft. The data is also input to
a new type of transform. The SPICE (Spectral Imaging of
Correlative Events) transform combines wavelet decomposition
with spectral characterization and the result looks similar to an
“outcrop.” This bed
form, layered framework is derived from all
the frequencies in the seismic data and provides precise sharpboundary
criteria for interpretation.
The West Cameron 76 Field area and several deep lower Tertiary
drilling sites are examined to illustrate the architecture of the bed
forms and faults. Emerging ideas include a mid-Tertiary section
composed of many cycles of upward-thickening
bed
forms that
represent prograding sediments filling and driving large expansion
faults, Paleogene features that resemble rafted blocks as in West
Africa, and a Lower Tertiary to Mesozoic extensional and
compressional structured platform that shows upper to
mid-slope criteria of thick wedges filling broad canyons cutting
fairways to deep water.
Mid-Tertiary sediments were deposited, during many cycles of
sea level rises and falls, into a complex series of large, expanding,
down-to-basin regional décollements that sole out onto lower
Tertiary to Mesozoic blocks. The West Cameron 76 Field area
sediments are the result of a combination of changing sea level
and rapidly expanding accommodation basins forming at each
expansion fault. A new attribute called SPICE is
applied to the data and the resulting bed
form,
layered framework shows distinct sequence and
parasequence packages, with sands distributed in
shelf to slope environments of deposition. Well
log gamma ray curves tie to sharp SPICE
bed
form boundaries defined by downlap and onlap
geometries, just like seismic data. The sequence
architecture shows a thick stack of repetitive,
bed
thickening-upward cycles that are interpreted as
prograding complexes filling the accommodation
space at each lowstand of sea level. These tie
to upward-coarsening log shapes. Slope fan
parasequence sets also fill the rapidly forming
accommodation space, and these tie to upwardfining
log shapes. Pay sands are distributed
among these prograding elements with distinct
fairways of deposition. This architecture can be
interpreted at great depths below existing well
data and facies reliably predicted at these depths.
End_Page 28---------------
The High Island (HI) state waters area has been the site of deep
drilling recently by the Shell Joseph well in HI State block 10. The
SPICE sections on PSDM data show a structured platform of
lower Tertiary to Mesozoic sediments in this area. These structures
are extensional but in places look like compressional reverse faults.
The top of this section shows features that are possible rafted
blocks and major slump scars that fill in with younger sediments,
similar to the offshore West Africa and Brazil shelf margins. The
lower Tertiary bed
forms are characterized by laterally continuous
conformable
bed
sets, but also by packages of disconformable
beds that resemble hummocky slope fans. Criteria indicative of
broad canyon cuts are seen on several sequence boundaries and
these canyons are filled with sediment onlap wedges. This is
characteristic of upper to mid-slope environments of deposition,
and these canyons could provide fairways to transport sands into
deeper water. This geologic time is at the end of the Late
Cretaceous Laramide orogeny. Uplift and restructuring of this
area would enhance canyon cutting, erosion and redeposition of
sediments to the basin in deeper water. Compressional features in
the deep shelf platform may be linked to structural overprints
from the end of the Laramide orogeny that could restructure the
original graben/transform architecture. The Cretaceous section is
interpreted as the most conformable
bed
-set package; possible salt
welds are seen at the deepest levels of the data.
End_of_Record - Last_Page 33---------------