--> Caribbean Hydrocarbon Potential from Regional Seismic Data Analysis

Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins

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Caribbean Hydrocarbon Potential from Regional Seismic Data Analysis

Abstract

The Caribbean Plate is set within a unique tectonic framework, being bound to the north by a main transform zone responsible for the formation of the Cayman Trough pull-apart basin, the only area in the Caribbean and Gulf of Mexico where magnetic striping associated with oceanic crust formation is clearly identified. To the south, the South American Plate margin is characterised by a transpressional strike slip boundary. To the east and west, both the Pacific and Atlantic Oceans are subducting under the apparently lower density Caribbean Plate. The intraplate region comprises the Grenada, Venezuelan and Colombia Basins (Figure 1), which are bound by the Barbados, Aves, and Beata Ridges, all with a close to North-South alignment. The Hess Escarpment to the west separates the Caribbean Plate proper from the Chortis Block and Nicaragua Rise which have a very different bathymetric expression to the Caribbean Plate but still within the Caribbean. The Caribbean is rimmed by a series of hydrocarbon fields and wells that encountered oil and gas shows. However, in an area up to five times the size of the North Sea, exploration activity to date resembles that of the North Sea back in the 1960s, i.e. extremely under-explored. The lack of industry activity is partly a result of a very poor understanding of the basin, added to the perception that there are no significant working petroleum systems, as well as limited investment in new data which would help improve understanding. However, a series of multiclient and academic seismic surveys have been acquired. This evaluation is based on the analysis of 70,000 km of 2D seismic data. Caribbean Plate Origin Models There are 2 main models for the formation of the Caribbean. The most accepted is the Pacific model which assumes formation over the Galapagos hot spot (Pindell, 1991). In this model, the Caribbean Plate is oceanic and migrated from the Pacific, with its movement marked by a series of successive arc locations. It would have formed as Jurassic crust in the Pacific, thickened to km pile of basalt in the Cretaceous and subsequently collided with an intra-oceanic volcanic arc, driving it east to form the Greater and Lesser Antilles. The second, much less accepted and quoted, is the Intra-plate, in situ model between both Americas (James, 2005). In this model the Caribbean Plate is an independent lithospheric element consisting of an undeformed Cretaceous plateau of up to 20 km thick crust (Colombia/Venezuela basins). It is not known whether it is part of a continent or spreading ridge. It is interesting to note that there are no spreading ridges or magnetic anomalies in the whole of middle America, save for the central 300 km of the Cayman Trough (Miocene — Recent). Several oceanic plateaux (Ontong-Java, Iceland, Kerguelen, V.ring, Rockall) are known to have continental roots. Could this be true of the Caribbean Plateau? The Chortis Block is believed to be a Palaeozoic-Mesozoic continental block. The model of choice will have an impact on the expected petroleum systems and the perception of prospectivity. Key Seismic Observations from Jamaica Over 10,000 km of a regional 2D seismic dataset offshore Jamaica were analysed. The data were acquired by CGG in 2009 and reprocessed by Spectrum in 2016. The data over the Southern Nicaragua Rise were acquired with a 9 km long streamer, providing a long offset dataset with deep imaging. Finder Exploration carried out a detailed evaluation of the Walton Basin using a modern seismic dataset that changed their view of the stratigraphy offshore Jamaica. Up until the end of the 1990s it was believed that there was a shallow basement with no source rock or reservoir potential. But by 2009, significant pre-rift Cretaceous stratigraphy had been recognised as well as multiple mature source rock and reservoir pairs. The most striking observation from the Jamaican dataset is the thick, over 9 km, sedimentary section revealed in the Southern Nicaragua Rise. Jamaican Petroleum Systems and Prospectivity Evaluation Oil and gas shows have been recorded in 10 wells drilled onshore and offshore Jamaica and four main source rocks have been inferred. These include a Smackover Fm (Oxfordian) equivalent (Windsor-1 well); a regionally extensive Maastrichtian marine source rock with indications from oils from the Dominican Republic, Venezuela, Antigua, Lesser Antilles, Puerto Rico and DSDP 146 well; high TOC intervals of Cretaceous age in DSDP wells; and the Eocene Guy’s Hill Fm (Content -1 well) with TOC up to 22%. Presence and maturity of at least one source rock is supported by fluid pipes seen in several seismic sections and oil seep data, with live oil confirmed by Tullow and onshore seeps recently recovered onshore by CGG. Multiple reservoirs are expected including Cretaceous sandstone intervals and Guinea Corn Rudist Limestones, Eocene carbonate reefs on crests of rotated fault blocks and fluviatile to estuarine sandstones, as well as Oligo-Miocene limestones with reefal enhancement. Several trapping mechanisms are recognised from the seismic dataset including tilted fault blocks, inverted basins, anticlines, folds, thrusts and stratigraphic onlaps onto the Base Tertiary Unconformity and onto basement highs, reef build-ups and basin floor fans. Several leads were identified and evaluated. Significant potential supported by structures seen in the PSDM reprocessed data, as well as AVA anomalies conforming to depth. An example of a Tertiary basin floor fan draping a four-way dip closed structure with a clear amplitude and AVA anomaly is shown in Figure Other Caribbean Seismic Data Observations A recently reprocessed dataset in the Southern Caribbean reveals intriguing characteristics within the Caribbean Plate where clear tilted fault blocks are seen below what could be considered oceanic crust. Similar tilted fault blocks are seen associated with DSDP 146 where high TOC intervals were recovered. Also a line over the Beata Ridge shows clear extension and relatively deep grabens with significant sediment infill are observed. Conclusions Regional seismic data analysis and evaluation in the Caribbean have revealed strong evidence for significant prospectivity offshore Jamaica. This evaluation does not clearly favour either of the models for the origin of the Caribbean Plate but it does raise interesting questions which require further evaluation to understand and predict petroleum systems in and around the Caribbean Plate.