GAS HYDRATES RESOURCES AND ASSOCIATED CATASTROPHIC PROCESSES IN THE CONTINENTAL MARGINS OF NORTHEASTERN SOUTH AMERICA

The deep marine depositional margin of Trinidad and eastern Venezuela is located along the tectonically active southeastern margin of the Barbados Accretionary Prism. This area receives sediment from the Orinoco and smaller rivers along the northeastern South American margin, and is at the mercy of significant currents sweeping northwest along the margin. The margin is incredibly dynamic with prolific massive debris flow deposits and leveed channel development having occurred over the past 1 million years. A 10,000 km2 3-D seismic data volume and over 130 dropcore, as well as conventional deepwater well results have led to the mapping of significant gas hydrate deposits throughout the margin. The largest is along the uplifted northern margin of the Deep Columbus Sub-basin. A bottom simulating reflector can be seen associated with these deposits. Calculations show that this deposit covers an area approximately 750 km2 in water depths of 900 to 1300 m. Total thickness of the hydrate zone is between 150 and 700 meters. At a velocity of 321 microsec/m, this deposit calculates a volume of 1,036 km3. A conservative porosity estimate of 20% in the shallow sediment, and recent cathrate saturations estimated in similar deposits at 11%, suggest this deposit could represent up to 23 km3 of frozen hydrate. Assuming a formation volume factor of approximately 10 under standard pressure and temperatures, this gas resource could conceivably be over 8 TCF. Deepwater wells drilling this hydrate zone have encountered significant technical problems. Drop core samples show that hydrates occur as large blocks and disseminated in seafloor muds. Debris flows capable of generating tsunamigenic waves occur along the margin, in some instances in close association with the base of the hydrate stability zone suggesting a possible link between hydrate dissolution and catastrophic slumping along the margin. Current research is underway in understanding historical records of slope failure, fault activity and hydrate dissolution events that will impact the future energy exploration and development and geohazard assessment for surrounding populations.