El Furrial Oil Field: A New Giant in an Old Basin
In 1978, Lagoven, S.A., an affiliate of Petróleos de Venezuela, S.A., started an exploration program aimed at deeper targets on the northern flank of the Eastern Venezuelan basin, where the shallow upper Tertiary section had been explored for more than eight decades. The quality of the seismic data collected was sufficient to give indications of thrust faults with associated structures. From 1978 to 1985, geologic surveying, structural modeling, and interpretation of seismic data were combined to define the first prospect: El Furrial. The discovery well, FUL-1, penetrated 276 m (905 ft) of net oil sand and produced up to 7331 bbl of 26° API oil per day. This is the largest single discovery of medium-gravity oil in the last 25 years in South America. Folding and thrusting of the northern flank of the Eastern Venezuelan basin occurred during the collision of the Caribbean and South American plates. The evolution began at least by the early Paleocene. Cylindrical folds associated with thrusts are aligned in series for a distance of up to 70 km. They constitute a typical foreland overthrusted basin. The reservoir rock is a shallow marine sandstone deposited during the late Oligocene. Gross thickness ranges from 457 to 518 m (1500 to 1700 ft), and porosities range from 11 to 16%. The El Furrial discovery represents an excellent example of the prospectivity of a foreland overthrusted area and also an example of continued successful exploration to pursue deeper objectives in an area already considered mature.