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 view.
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 16,000 acres.
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 surface.
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 horizon.
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 25kms northward.
Figure 5 Top Aptian
Folds B and C persist as large traps at the Aptian level and below.
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”.