The Geology of the Penal/Barrackpore Field, Onshore Trinidad

DYER, BRIAN LINDSAY, Trinidad and Tobago Marine Petroleum Company Limited, Pointe-a-Pierre, Trinidad

The Penal/Barrackpore field was discovered in 1938 and is located in the southern subbasin of onshore Trinidad. It is one of a series of northeast-southwest trending en echelon middle Miocene anticlinal structures that was later accentuated by late Pliocene transpressional folding.

The middle Miocene Herrera and Karamat turbiditic sandstones are the primary reservoir rock in the subsurface anticline of the Penal/Barrackpore field. These turbidites were sourced from the north and deposited within the marls and clays of the Cipero Formation.

The Karamat sandstones are followed in vertical stratigraphic succession by the shales and boulder beds of the Lengua formation, the turbidites and deltaics of the lower and middle Cruse, and the deltaics of the upper Cruse, the Forest, and the Morne L'Enfer formations.

Relative movement of the South American and Caribbean plates climaxed in the middle Miocene compressive tectonic event and produced an imbricate pattern of southward-facing basement-involved thrusts.

The Pliocene deltaics were sourced by erosion of Miocene highs to the north and the South American landmass to the south. These deltaics exhibit onlap onto the preexisting Miocene highs.

Further compressive interaction between the Caribbean and Southern American plates in the late Pliocene produced a transpressive tectonic episode that resulted in northwest-southeast oriented transcurrent faults, tear faults, basement thrust faults, lystric normal faults, and detached simple folds with infrequent diapiric cores.

The late Pliocene transpression also coincides with the onset of oil migration along faults, diapirs, and unconformities from the Cretaceous Naparima Hill source. The Lengua Formation and the upper Forest clays are considered effective seals.

Hydrocarbon trapping is structurally and stratigraphically controlled, with structure being the dominant trapping mechanism.

Ultimate recoverable reserves for the Penal/Barrackpore field are estimated at 127.9 MMBO and 628.8 bcf. The field is presently owned and operated by the Trinidad and Tobago Oil Company Limited (TRINTOC).

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)