WOOD, 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