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Abstract

The Mayaro Formation, which is exposed in SE Trinidad, is the key outcrop analogue for prolific hydrocarbon reservoirs in the Columbus Basin, offshore east Trinidad, because it was deposited in the same basin setting by the same depositional system (the palaeo-Orinoco) as the offshore reservoirs. Sequence and parasequence stacking patterns affect the distribution of different types of reservoir sand bodies and heterogeneities, with the potential to influence fluid flow in subsurface hydrocarbon reservoirs. Spectacular outcrops of successions of storm-wave-influenced sand bodies, tens to hundreds of metres thick, deposited in axial and medial delta-lobe settings are characterized by high sand–shale ratios (0.7–>0.95), and are analogues for many producing reservoirs in the basin. Fluvial- and tide-influenced sand bodies deposited in distal distributary settings are also recognized in the outcrops, but may be difficult to distinguish from medial delta-lobe deposits in subsurface data. More complex, thinly bedded distal delta-lobe deposits, with subsurface reservoir potential, exhibit lower sand–shale ratios (0.3–0.6). Complex depositional architectures, with a high proportion of thinly bedded sandstones, also occur in association with delta-front deposits. The distal delta-lobe and delta-front deposits are analogous to some of the most challenging to develop reservoirs in the Columbus Basin.

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