Print this pageWOOD, LESLI
Bureau of
Economic Geology, The University of Texas at Austin, Austin, TX
Abstract: Technical Lessons Learned
from a World-Class Hydrocarbon 
Basin
: Columbus Basin, Trinidad and Tobago,
West Indies
The Columbus Basin forms the easternmost
extension of the East Venezuelan Basin and contains more than 3.27 billion
barrels of oil and 20+ Tcf of gas in place. It is estimated that an equal
amount of resources remains undiscovered in the basin. The basin is situated
along the transpressional margin of the Caribbean and South American plates.
It contains two primary structural elements: transpressional northeast-trending
anticlines and northwest-oriented, down-to-the-northeast, extensional normal
faults. The basin is filled with more than 40,000 ft of Plio-Pleistocene
fluvial, deltaic, and deep-marine clastics that form seven progradational
megasequences. Several observations have been made regarding the basin's
geology that bear on exploration risk and success: (1) Megasequences wedge
bidirectionally, and consideration of hydrocarbon system risk across any
area requires looking at these sequences as complete paleofeatures. (2)
Reservoir location is influenced by structural elements in the basin
. (3)
High sedimentation rates and unconsolidated and expanded section inhibit
the occurrence of nannofossils and planktonic foraminifera and complicate
the use of traditional biostratigraphic techniques. (4) The lower limit
of good-quality reservoir in any megasequence deepens closer to the proximal-bounding
normal fault. (5) Quality of deep-marine reservoir is strongly influenced
by the type of shelf system developed (bypass or aggradational) and by
the location of both subaerial and submarine highs. (6) Fault seal is a
function of the lithology mix that has been displaced past the reservoir
interval of interest and less a function of the present-day juxtaposition
of lithologies across faults. (7) Submarine surfaces of erosion partition
the megasequences and influence hydrostatic pressure, migration and trapping
of hydrocarbons, and the distribution of hydrocarbon type.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas