On 8 September 2015, members of the AAPG Student Chapter at the University of the West Indies – St. Augustine (UWI STA), along with individuals from the Ministry of Energy and Energy Affairs and state-owned oil company Petrotrin, attended a core workshop hosted by Centrica Energy at Weatherford Labs at LP #7 in Chaguanas, Trinidad. The workshop was led by the Subsurface Team of Centrica Energy including Subsurface Manager Vishal Nagassar, Sedimentologist Richard Coutou and Geologists Xavier Moonan and Roger Kimber. The workshop provided attendees insight into the following subjects:

• Geology of the North Coast Marine Area
• Seismic Interpretation
• Process of Mapping a Basal Sand Prospect
• Geology of NCMA-4 and Block-22 in the North Coast Marine Area
• Development of Gross Depositional Environment
• Process of Obtaining Cores
• Core Description
• Core Preservation
• Utilization of New Technology in Obtaining of Data from Cores
• Petrophysical Analysis of wells within NCMA
• Petrological analysis of Thin Sections

Upon arrival at the conference room at Weatherford labs, participants underwent an HSE orientation and received an overview of Centrica’s efforts to map the Basal Sand. The Basal Sand is considered the lowermost sand within the Pliocene-Miocene siliciclastic sequence which sits atop volcanic or metamorphic basement. The Basal Sands were found gas-bearing in the Orchid gas discovery drilled during the 1970s. Since that time, Centrica Energy acquired full 3D seismic over the basin identifying further prospects similar to the Orchid discovery.  Attendees viewed seismic sections from both reflectivity and inversion (LambdaRho) datasets. They also observed structure maps of the basement at NCMA-4 and Block-22, as well RMS and Minimum Amplitude extraction maps of the Basal Sand prospects

It was well established that due to the lack of core data from the Orchid discovery and vintage electric logs, there was a dire need to seek out a modern day analogue to better understand the reservoir variability of a Basal Sand. The Subsurface Team introduced the attendees to some innovative sediment coring techniques which were implemented to acquire the Marianne River cores on the north coast of Trinidad. Participants also learnt of the technique involved in acquiring Jumbo Piston cores, which Centrica implemented along their Pipeline Route, off the northern coast of Tobago, from Southwest Tobago to the Cassra gas discovery in Block-22. Analysis on sidewall cores and drill cuttings from the recently drilled Iris-1 and Cassra-2 wells were also discussed. 

After the presentation by the Subsurface Team, attendees were split into two groups and taken to two core rooms at Weatherford. The first group, led by Xavier Moonan and Richard Coutou, introduced participants to the Pipeline Route Jumbo Piston Cores taken north of Tobago as well as some segments of the Iris-1 Core. Participants were allowed to touch and examine the Jumbo Piston cores and two hand lenses were also provided for further scrutiny. Segments of the Iris cores were also observed along with the CT scans done on these segments. It was specified that these scans were done as a measure of preservation of the internal structures of these cores. Participants observed that the Jumbo Piston cores provided insight into the sedimentation along the current shelf, slope and basin floor setting. A marked change in grain size, texture, composition and sorting were noted as one observed the profile. A present day turbidite sand deposit with its sharp erosional base was observed in the deep water cores. The Iris-1 cores generally demonstrated a series of stacked deep water sandy turbidite deposits with relative variation in sand concentration from one turbidite sand to the other.

At the second core room, led by Vishal Nagassar and Roger Kimber, attendees viewed the beach/shoreface Marianne River cores and the Cassra-1 and Cassra-3X full hole cores. The differing grain sizes of the dynamic environment from which the cores were taken were evident. These cores demonstrated the variation in grain size, texture and composition within a shelfal environment.

After lunch, attendees saw how the sedimentological and petrological data collected from the present day cores, the side wall cores and drill cuttings from the Iris and Cassra wells were integrated with seismic interpretation to develop the gross depositional environment of the Basal Sands. It was further demonstrated that Basal Sand exploration prospects such as Chillibibi is analogous to the Orchid discovery and will have a similar depositional framework.

Overall, the workshop was very beneficial to UWI STA students, most of whom had never seen a core nor or had had the opportunity to view CT scans used in core description and interpretation. The experience also exposed many individuals to the geology of the North Coast Marine Area, and the Basal Sand Prospects within this dynamic basin. Most significantly, students now understand and appreciate the importance or core in geological evaluation and the use of modern depositional analogues in the absence of data.