3D Seismic Acquisition
A major milestone of 2011 was the acquisition
and receipt of initial processing of nearly 3,075km of 3D seismic
in the Southern Licence area.
These data were collected by CGG Veritas using
their state-of-the-art 'BroadSeis' technology. Initial results
indicate the data are of high quality and it is now being used to
advance our understanding of the hydrocarbon systems.
The 3D confirms and better defines the prospective structures
mapped on the 2D. Significantly the data also provides additional
encouragement regarding source potential and fetch area. The 3D
indicates the basement to be deeper than previously mapped implying
a thicker, deeper Jurassic (source rock) interval. Further the
interpretation indicates a uniform south west dip under the
Cretaceous platform (Fold/Trend A) indicating access to a large
fetch area toward the Cuban mainland under the North Cuban basin.
We are currently engaged in seismic facies and seismic lithology
studies, including inversion and expect to have preliminary results
from this work during the second quarter.
Figure 1 Top Cretaceous Structure
Image from high frequency depth volume illustrating the
depth to the 'Top Cretaceous' horizon.
Hotter colours are highs, cooler colours lows. The 3 highs
shown are from left to right Trend 'A' the top Cretaceous platform
margin, Fold 'B' and Fold 'C' respectively. The crest of Fold
'B' at the Cretaceous level occurs at 700 metres. The contour
interval is 50 metres. Note the leftward (southwest) shift of
the platform edge about midway in the figure on Trend 'A'.
This appears to be the result of collapse of the platform margin
suggesting reworked platform sediments and breccia are likely to be
present in the forereef environment.
Figure 2 Top Cretaceous Structure
Same horizon as in Figure 1 but shown in map
Hot colours are highs and cooler colours lows. Note the
scale bar and north arrow in the bottom right corner. These
are very large structures: Fold B closure covers 423 square
kilometres, over 100,000 acres; Fold C 63 square kilometres, nearly
Figure 3 Top Albian Structure
The bottom half of the map view and left side of the 3D
image represents the Albian platform, the irregular topography
interpreted to be the result of karst development on this
The boundary between the hummocky appearing surface and the
smoother surface representing sediments deposited in deeper water
in front of the Albian platform covers more of Fold 'B' to the
north and steps behind toward the south. Fold 'C' can be seen
on the right.
Figure 4 Top Aptian Structure
Figure 4 illustrates the structures on the top Aptian
Fold 'B' is in the centre of the image and has a structural
crest at 2500 metres. The image shows the Aptian surface
dipping to the southwest (left) toward the Cuban foredeep.
Hydrocarbons generated in the North Cuban Basin appear to have an
uninterrupted migration pathway toward our structures,
significantly increasing the potential fetch area beyond what was
understood from the 2D. The length of Fold 'B' shown in the
3D view is approximately 50 kilometres; it extends an additional
Figure 5 Top Aptian
Folds B and C persist as large traps at the Aptian level
We expect regionally extensive anhydrite layers (seal) to become
more frequent below this horizon. Trend A is not a defined
structure at this level.
Figure 6 Top Aptian Amplitude
Figure 6 is zoomed in to show the nature of the seismic
events more clearly on the vertical seismic line.
Note the strong increase in amplitude on Fold 'C' just above the
rendered surface. This amplitude increase occurs only on
structure and is conformable to structure. Although we are
constrained by lack of carefully calibrated well control, our work
programme is geared toward understanding to what extent these
changes might be hydrocarbon indicators. Note additional 'on
structure' amplitude changes above the Aptian surface. This
view also illustrates the effect of the shallower Albian platform
on our imaging of deeper events on Fold 'B'. We are also
working on this issue as we continue to reprocess the data.
Figure 7 Seismic Facies
Seismic facies interpretation along a 3D line through
one of our possible locations on fold B.
This work is being done at the Reservoir Characterization
Research Lab (RCRL) at the Bureau of Economic Geology, University
of Texas. Understanding the likely facies will assist our
prospect evaluation, provide context for further seismic studies
and guide our well planning. Bahamas Petroleum Company believes the
thrust faults are detaching in the Upper Jurassic source rocks.
Note unit 4A in the Albian, starved basin mudstones, could provide
an effective seal over Fold B at that level. We are planning a well
to drill to 22,500' subsea which would correspond to the black line
just below the "8".
Figure 8 Seismic Lithology
In conjunction with the seismic facies work we are reprocessing
the data through seismic inversion to gain a better understanding
of lithology, fracturing and possible fluid content. Because there
are no direct well ties within our 3D data volume interpretation of
the inversion has much uncertainty.