Three-dimensional relationships between synchronous normal faulting, folding and sedimentation in the Columbus Basin, offshore Trinidad, W.I.

Tricia Alvarez, Lesli Wood, Paul Mann

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.  Previous tectonic models have emphasized either convergent structures related to the active Columbus foreland basin or the extensional structures produced by gravitational sliding or strike-slip faulting and pull-apart basin formation.  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.  9000 km² of 3D seismic data combined with well penetrations in the Columbus Basin were used to examine the three-dimensional relationships between synchronous listric normal faults, folds and the late Quaternary (last 500,000 yrs) sedimentary fill; including the influence of structuring on the depositional morphology and architecture.   

Northwest-to-southeast-striking normal faults and the northeast-to-southwest striking anticlines created structural traps which contain the 3 billion barrels of proven oil and 22 trillion feet of gas stored in vertically-stacked reservoirs.  Within this complex tectonic framework, 12-15 km of Plio-Pleistocene sediments were deposited on the shelf and slope at extremely high sedimentation rates of ~ 5 mm/yr.  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.  Quantitative data on the listric fault activity and on systems tract architectural elements, including spatial orientation and distribution should significantly improve 3D modeling of potential reservoir facies and improve understanding of sand distribution and the processes of sediment transfer from proximal sources to shelf staging areas, in a tectonically active setting.

TRICIA G. ALVAREZ

Tricia Alvarez is currently a PhD student at the Jackson School of Geosciences at The University of Texas at Austin.  She completed a B.Sc. in Geology at The University of the West Indies in 2001, and this was followed by five years of industry experience, working as an Exploration Geologist with BG Trinidad & Tobago.  Her return to graduate school in 2006 was fuelled by a passion for Geosciences, and a yearning to investigate the dynamics of sedimentary basin evolution.  She completed an MS in Geosciences in 2008 and commenced the PhD programme in 2009.  Her research interest at the Jackson School of Geosciences is focused on the study of the interaction of clastic sedimentation and tectonics, and their role in the source to sink evolution of sedimentary basins; through the application of an integrated geologic, geophysical and remotely sensed dataset.  She has presented aspects of her research at the annual meeting of American Association of Petroleum Geologists in 2008 and 2009.  Her academic awards include; EOG Resources Fulbright 2000 Fellowship; Chevron Fellowship, and an American Association of Petroleum Geologists Foundation Grants-in-Aid award.