Abstract: Well-Log Sequence Stratigraphy of the Upper Miocene-Pliocene Deltaic Formations in the Onshore Southern Basin of Trinidad

Derek Hudson, John Keens-Dumas, Christopher Lakhan

The upper Miocene-Pliocene deltaic sediments (Cruse, Forest and Morne L'Enfer Formations) in the onshore Southern basin of Trinidad have produced in excess of 1 billion barrels of oil. Well-log sequence stratigraphic techniques have been applied to these third-order depositional cycles, with the following results: The Cruse Formation is a Type 1 depositional sequence, which is comprised of lowstand, transgressive and highstand systems tracts (HST), and was deposited in upper bathyal to marginal marine environments. Sediments of the Forest Formation overlie the Cruse depositional sequence, and are composed of transgressive and highstand systems tracts deposited in middle neritic to marginal marine palaeobathymetries. The Morne L'Enfer Formation, which is also characterized by transgres ive and highstand systems tracts, was deposited on the Forest deposition sequence under inner neritic to non-marine conditions. The sequence boundaries that culminated the Cruse and Forest formations have not been defined as Type 1 or Type 2, as a result of the non-recognition at present, of lowstand systems tract or shelf margin wedge deposits in the overlying sequences.

This sequence analysis has provided the framework for reducing the risk in development drilling and secondary oil recovery projects in the basin. A pilot study of the Cruse Formation in a localized area, utilizing the defined sychronous correlation surfaces and chronostratigraphic intervals, has indicated that a high-frequency progradational event within the HST is the most prolific oil producer. Reservoir accumulations in laterally continuous distributary-mouth bar and channel-fill sands provide favorable targets for enhanced oil recovery.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994