American Oil and Gas Reporter - October 2015 - 162

SpecialReport: Gulf of Mexico Activity
FIGURE 2
Appomattox & Vicksburg Discovery Locations
Depth Range is 40,000 (Red) to 60,000 (Blue) Feet

the Appomattox structure on the downthrown side of the fault is 54,000 feet.

Sequence Of Events
IGC delivered the first version of a
Gulfwide basement structure in 1983.
The structural configuration was based
on four- by eight-mile coverage of aeromagnetic surveys.
Since we had no basement control
within the Gulf, the data coverage provided
an opportunity to tie to onshore structures.
We interpreted that the Louisiana and
Texas troughs reached depths of 65,000
feet, while the average depth across the
Gulf was close to 40,000 feet below sea
level. At that time, the seismic community
had mapped the Gulf's basement as planar,
sloping down to the abyss. The significant
seismic assurance to the structural configuration did not develop until the arrival
of the 14-second seismic section.
It was then that serious interest developed in the structural framework of the
Gulf of Mexico. New, high-resolution
aeromagnetic data were acquired from
1992 to 2009, such that today, the northern
Gulf is covered with 0.5- to 0.25-mile by
1.0-mile surveys.
The correlation between magnetically-based basement structure and oil/gas
production has been demonstrated in
many basins around the world. A few
examples are Argentina, the Austrian Vi-

enna Basin, China (onshore/offshore),
Ecuador, the Hungarian Plains, India
(western/eastern offshore), Peru, Sumatra
(northwestern), former Soviet Union, and
Yugoslavia.
The statistics we started to gather in
2000 indicate the Gulf of Mexico can be
added to the list. The 2015 analysis indicates that approximately 70 percent of
the Gulf's oil- and gas-field discovery
reserves can be related to structure described as either steep/faulted flanks or
drape-over of basement highs. Early discoveries in the deepwater Gulf of Mexico-Tahoe (Viosca Knoll Block 783 in
1984), Bullwinkle (Green Canyon Block
65 in 1983), Auger in 1987, and Mars in
1989-led to an awareness of its prospectivity by a vast majority of pioneer companies (Figure 3).

These initial discoveries flanked our
interpretation of a ridge complex of structural highs with an average depth of
44,000 feet and an average water depth
of 5,200 feet paralleling the Louisiana
Coastline, which I called the "first buttress"
into the deepwater region. There are more
examples, such as ExxonMobil's Hadrian
discoveries in Keathley Canyon. The
Davy Jones discovery on the Louisiana
Shelf lies on what I interpret as a basement
embayment, as do the Lower Tertiary
discoveries in Alaminos Canyon.
This started our collection of discovery
statistics published in various industry
sources. The 15-year collection is evidence
that the Gulf of Mexico's structural framework is a critical and integral part of the
hydrocarbon evaluation process. We are
aware that the oil and gas play within the
sedimentary section differs with each
discovery, yet 70 percent correlate to
basement structure.
Basement structure is defined as the
topography and structural fabric (shear
zones and fault zones) within the crystalline basement. These deepwater and
Shelf structures in the Gulf of Mexico
are the result of uplifts, platforms, or
multiple deep-seated tensional and shear
faulting.
The process of delineating regional
uplifted blocks (horsts) and depocenters
associated with faults/fracture zones, enables companies to locate hydrocarbon
prospects (migration pathways). The
Wilcox and Norphlet plays appear to correlate to basement embayments (platforms).
Structural framework controls alternating extensional and compressional dynamics of the Louann Salt. The rate of
sedimentation and the rate of subsidence
are controlled by the structural configuration and tectonics of the basement; i.e.,
sedimentary regression and transgression
through channels and fan systems. Un-

FIGURE 3
"First Buttress" Northern Gulf Deepwater Discoveries
Depth Range is 35,000 (Red) to 60,000 (Blue) Feet

162 THE AMERICAN OIL & GAS REPORTER

American Oil and Gas Reporter - October 2015

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