After 40 years of sporadic exploration that yielded negative or marginal results, the Llanos basin of eastern Colombia was thrust to the forefront of world attention by the discovery of the giant Cano Limon field in July 1983.

This discovery was the culmination of an intensive three-year exploration effort by Occidental International Exploration and Production Co. involving 4000 km of dynamite seismic, 20 stratigraphic tests from 1300 to 3500 ft (395 to 1065 m) deep, and 12 exploratory wells.

Before Occidental entered the area, 61 exploratory wells were drilled with meager results--namely, two fields with total reserves of about 20 million bbl of light oil and one field with reserves of 90 million bbl of 13.6° API oil, none of which was commercial.

The Llanos basin was known for its abundant excellent reservoir sands, and opinions varied as to whether there was adequate source rock. The major problem had been definition of traps. Except for the very young folding along the Andean front, the known structural traps were sparse and subtle.

Most of the exploration had been done in the western part of the basin near the basin deep or in the Andean foothills. Occidental took a very large acreage position east of the area of past exploration efforts and found an exception to the small fault closures known elsewhere in the basin.

This exception, the Cano Limon area, is dominated by major early Tertiary northeast-southwest strike slip faulting. Concurrent folding in combination with fault sealing formed the Cano Limon field and other much smaller fields in the area.

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The Cano Limon field, encompassing 8821 ac, contains an estimated 1.800 billion BOIP, which 1.066 billion bbl are expected to be recovered with the very strong natural water drive.

The bulk of the oil is in deltaic sands of Eocene Mirador, with additional reservoirs in the Upper Cretaceous. Average porosity of the Mirador is about 25%, permeability about 5 darcys, and water saturation 23%. Individual well flow rates have exceeded 20,000 BOPD. The average oil gravity is 29.5° API, with a gas-oil ratio of 8 ft³/bbl (0.2 m³/bbl) and a sulfur content of 0.41%. Current production is about 230,000 BOPD.