Oil exploration in the Trinidad and Tobago eastern offshore area historically has been concentrated on the shallow and deepwater plays of the Trinidad Basin, with the Columbus sub-basin providing the majority of the nation’s offshore production. The Columbus Basin is a prolific hydrocarbon basin that has produced more than 1 Bbbl of oil and holds an estimated 25 Tcf of natural gas.

However, the deep/ultra-deep Eastern Trinidad Basin to the east of the Columbus Basin remains, as yet, underexplored. Water depth, difficulty in obtaining quality seismic imaging at depth, and issues related to the complex offshore geology are some of the reasons why there has been a lack of recent exploration activity.

2-D Survey

The 2-D survey is situated off the eastern coasts of the two islands, where 39 blocks are delineated between 3,281 and 11,483 ft (1,000 and 3,500 m) water depth. (Map courtesy of Spectrum USA)

Spectrum currently is reprocessing 7,606 line miles (12,240 line km) of seismic data from the Trinidad and Tobago Deep Atlantic Area under an agreement with the nation’s Ministry of Energy and Energy Affairs to support the competitive bid round launched by Energy Minister Carolyn Seepersad-Bachan on Sept. 11, 2010.

The 2-D survey will gather data off the eastern coasts of the two islands, where 39 blocks are delineated between 3,281 and 11,483 ft (1,000 and 3,500 m) water depth. Eleven blocks on the northeast and east coasts are being offered in the deepwater bid round, which closes in January 2011.

Reprocessing seismic data
The primary aim of Spectrum’s reprocessing will be to derisk the deep/ultra-deep play targets that can be considered high-risk by prospective exploration companies. Improvements in imaging will enable data ties into the shallow play area and allow extrapolation of successful shallow play types as well as new plays in the deep/ultra deep area.

Reprocessing the seismic grid will make it possible to use modern concepts of shelf to deepwater sequence stratigraphy and compressional structural style analysis to better understand the hydrocarbon potential of this region.

The quality of a regional 2-D seismic dataset, which was shot in 2002 over the deep/ultra-deep offshore area, will be further improved by the application of Spectrum’s modern depth-imaging techniques. The main advances in the reprocessing sequence are in the application of surface-related multiple elimination and enhanced high-resolution Radon demultiple techniques.

Improvements in imaging also have been gained by velocity modeling, taking into account the significant geological changes from shallow to deepwater areas and allowing the identification of a slower deep-velocity trend that had been removed by an aggressive demultiple operator in the original dataset. Two passes of Kirchhoff prestack time migration also have provided better resolution of deeper structures.

Initial processing has shown potential within both shallow- and deep-target sequences and has highlighted a series of amplitude anomalies that could be indicative of direct hydrocarbon indicators associated with prospective structural configurations. Spectrum will apply an integrated approach spanning pre-processing, prestack depth imaging, and attribute analysis.

Improved imaging of the seismic lines also will better constrain the basinward extrapolation of successful shallow-water plays and derisk new play concepts in the deeper water trend. Together with improved government economic fiscal terms, low political risk, and stable crude oil prices, this should encourage exploration of the ultra-deepwater Trinidad and Tobago. www.spectrumasa.com