Tectonic Geomorphology of the Eastern Trinidad Shelf, Implications for Influence of Structure from Reservoir Distribution and Nature in Older Basin Fill

Tricia Alvarez and Lesli Wood
Bureau of Economic Geology, Jackson School of Geosciences University of Texas at Austin, Austin, TX

Many deltaic systems have been described in passive shelf settings, but the narrow, eastern Trinidad shelf has been tectonically active throughout the late Tertiary and into the Quaternary, undergoing both extension and shortening. Paralic and shelf reservoir sand distribution and geometry have been significantly influenced by both structuring and strong offshore current activity, as well as large forced and unforced regressions. These deposits hold significant shallow gas across the region, but the complexity of their distribution and architecture is poorly understood. A large merged 3D seismic survey (~10,000 sq km) was integrated with well penetrations across the modern shelf to examine the near-modern basin fill and examine the influence of structuring on the morphology and architecture these systems.

Key horizons mapped across the area allow attribute imaging of the modern sediments which preserve a record of shelf evolution. Of particular interest are the reservoir elements such as channels and channel belts, tidally inundated interfluves, shelf delta topsets, interdistributary areas and ridge and swale topography. The channels, which are ubiquitous across the shelf during lowstand times, show vivid patterns of avulsion and lateral migration. They range from 1-4 km wide to smaller channels of less than 100 meters in width. Several active listric faults interact with landward and basinward migration of shoreline during base level changes to influence depositional systems. Quantiative data on systems tract architectural elements, including spatial orientation and distribution should significantly improve 3D modeling of these reservoirs and improve understanding of sand distribution and the processes of sediment transfer from proximal sources to shelf staging areas.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas