GEOSCIENCE EXPLAINED
Deep Structure: Strength through
integration in the deepwater Gulf of Mexico
Exploration interest in the deepwater US Gulf of Mexico is at an all time high following the discovery,
in 2001, of thick Paleogene submarine turbidite sands in the Baha #2 well. This ‘Wilcox’ sand play has
now expanded across most of the deepwater and is the main reservoir target. These reservoir targets
are typically 3 and 4 way structural closures, obscured by a thick allochthonous salt canopy and cored by
deep allochthonous salt.
Other potential deepwater plays include salt where seismic imaging is more of a
the Late Jurassic Norphlet aeolian dune challenge.
play and the Upper Cretaceous submarine The new interpreted magnetic base-
fan play in the Western deepwater Gulf. ment was constructed using standard
These potential plays combined with the depth-to-basement techniques. This quan-
Wilcox play ensure that the deepwater sec- titative analysis of the magnetic data was
tor will be an important exploration target primarily carried out by means of Werner
for many years to come. This was further deconvolution, Euler deconvolution and
reinforced by the record-breaking MMS Peters half slope methods. Gravity data
lease sales for the Western and Central Gulf was used to help resolve areas of dis-
of Mexico in 2007. crepancy between the basement surfaces
Understanding these play-fairway prior to finalizing the integrated basement
opportunities requires a regional, structur- surface.
al and stratigraphic context for the Paleo-
gene Wilcox including sub-salt sediment Constraining basement
distribution and a better understanding of This integrated basement, together with
the tectonic framework of the basement. top and base allochthonous salt horizons
Moreover, mapping the structure of the from the Deep Focus work outlined above,
rifted basement will progress our under- were then used as the cornerstone for 2D
standing of its impact on sedimentation, and 3D gravity and magnetics inversion
the distribution of autochthonous salt, and and forward modeling work. Again this
the location of the Continental-Oceanic Image of a 2D gravity and magnetic model using integration has lead to a much better con-
2ModTM.
Boundary (COB). strained basement for assigning density
Despite the huge volume of seismic data and susceptibility values.
(2D and 3D) acquired in the region, one of Fugro has also developed a workflow
the most fundamental challenges facing understanding of the sub-salt section and to distinguish basement signal from auto-
the industry is the problem of sub-salt has produced a robust and comprehensive chthonous and deep allochthonous salt
imaging. Even with the latest processing interpretation. The new interpretation and signals during the 3D modeling process.
technologies, seismic imaging of the sub- modeling results provide a solid platform All of this work has lead to a new under-
salt stratigraphic section is problematic for future exploration and research in the standing of the morphology and structure
due to the allochthonous salt canopy. sub-salt arena. of the basement and sub-salt stratigraphy
The new integrated basement interpre- in the area of Phase 1 (see inset figure) that
“Deep Structure” tation relies heavily on the seismic data could not have been achieved from using
The purpose of “Deep Structure” is to outboard of salt where seismic imaging seismic data alone. The implication of all of
combat the sub-salt imaging problem by is best. This area has been called the cali- this is that as we move into planned Phas-
using an integrated approach. By integrat- bration area and is the best area to com- es 2 and 3, the lessons learned and the
ing long-offset (10km) Deep Focus seismic pare the magnetic basement and acoustic techniques developed will allow Fugro to
data, high resolution marine gravity data basement without the influence of a salt better cope with the inevitable complexi-
and high resolution airborne magnetics canopy. ties that will be encountered as we work
data, Fugro has significantly increased its In the calibration area we have looked through Garden Banks, Green Canyon and
understanding of the sub-salt geology of at the relationship between acoustic base- East Breaks.
the Deepwater Gulf of Mexico. Although ment and magnetic basement anomalies. We have developed an important exam-
each dataset can be interpreted in isolation This allowed us to better assess the rela- ple of the power of integration and its
and used as a stand-alone product, integra- tionship underneath salt and enabled us to importance in geophysical and geological
tion of these datasets has lead to a better trace some of these anomalies back under interpretation.
41 GEO ExPro December 2007