Key Learnings and Exploration Challenges in a Long-lived and Complex Deep Water Thrust Belt, Trinidad
Principal Geophysicist, Central and South Atlantic Group, BHP Billiton
In "conventional" thrust belts, like the South American Andes or the North American Rocky Mountains, deposition of reservoir rocks usually pre-dates a relatively time-constrained tectonic deformation event. Here, where solid evidence exists of detachment surfaces and sedimentary bed thickness, the primary goal in prospect delineation is to combine known stratigraphy and an unknown number of faults to construct antiforms on sparsely sampled and often poorly imaged on 2D seismic data.
The setting of the thrust belt in Trinidad & Tobago is quite different, and without a direct analog. The period of tectonic deformation is not related to one major time-constrained pulse, like the Laramide Orogeny of the U.S. Rocky Mountains, but is a continuum of events caused by the obduction of the Caribbean plate over the paleo-Caribbean region that started in the Cretaceous and continues today. Many areas have been subjected to multiple, discrete compressional events, and some have been overprinted by transtensional/transpressional deformation related to the oblique translation of previously thrusted terrains. Within this complex structural framework, marine depositional and erosional processes of varied spatial and temporal extent deposited sediment in some areas while removing and relocating it in others. So, although the elements of reservoir, seal, source rock and charge are clearly present at the play scale in deep water Trinidad & Tobago, their interaction in terms of prospect-specific risk is currently hard to evaluate using only 2D seismic data.
The lack of uniqueness in seismic interpretation combined with variability in stratigraphy and structural timing calls for an iterative model-driven approach to interpretation of these variable quality seismic data. BHP Billiton has built a best-fit regional geologic model that integrates our own learnings from the Angostura field area, published findings, observations taken from surface geology and well control, remote sensing, 2D and 3D seismic data. From this model, individual elements are tested and refined as necessary based on new data and revised interpretation.
Looking to the future, since 2D seismic data are rarely adequate to assess detailed structural and stratigraphic geometries and their interrelation, high quality 3D depth-migrated seismic data are a necessity for final regional play synthesis, prospect definition and safe well planning. To that end, starting as early as mid-March, 2014 BHP Billiton will acquire a state-of-the-art regional 17,719 km² 3D seismic survey across Trinidad’s deepwater foldbelt, from Blocks 23(b), 28 and 29 in the northwest to Blocks 5 and 6 in the southeast.
Finally, in preparation for exploratory drilling, a prudent Operator must build flexibility into drilling plans to allow for learning from each well result. Having the best possible pre-drill 3-D seismic framework pre-drill will allow BHP Billiton and partners to build progressively on past and future learnings to maximize the chance of safely and efficiently finding the sleeping giants within this unexplored segment of the prolific East Venezuela Basin petroleum province.
AAPG Search and Discovery Article #90203 © AAPG Geoscience Technology Workshop, Trinidad and Tobago Deep Horizon and Deep Water Frontier Exploration in Latin America and the Caribbean, March 9-11, 2014, Port of Spain, Trinidad