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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
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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.
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