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Abstract: Drilling for Oily Elephants in the Andean Foothills of Colombia

COOPER, MARK
PanCanadian Petroleum, Calgary, Alberta, Canada

The Llanos Basin lies east of the Eastern Cordillera in northeast Colombia. Basin development commenced in the Triassic and became increasingly dominated by marine sediments until the early Maastrichtian accretion of the Western Cordillera. This created the Pre-Andean Foreland Basin (late Maastrichtian to early Miocene), which covered the Magdalena Valley, Eastern Cordillera, and Llanos Basin. The overlying Andean Foreland Basin resulted from mid-Miocene to Recent deformation in the Eastern Cordillera which shed a classic "molasse" sequence into the basin. This deformation created the eastern foothills belt of the Eastern Cordillera, which hosts a number of giant fields, including the Cusiana field.

Light oil, gas, and condensate in Cusiana occur at depths of 4500 m in an asymmetric, hanging-wall anticlinal trap 25 km long and 5-6 km in width. The top and lateral seals are marine Oligocene mudstones trapping a hydrocarbon column of more than 460 m. Upper Eocene Mirador Formation sandstones, which contain more than 50% of the reserves, were deposited in estuarine environments. Other reservoirs include the Paleocene Barco Formation estuarine sandstones and the shallow-marine Santonian-Campanian Upper Guadalupe Sandstone. The porosity is relatively low, but good permeability in these pure quartz-cemented quartzarenites allows wells to produce at rates >10,000 bbl/day. Biomarker data suggest that the Turonian-Coniacian Gachetá Formation marine mudstones are the source rocks. The Cusiana field contains up to 1.5 billion bbl of liquids and 3.4 tcf of gas.

The other giant fields discovered in the trend to data are Cupiagua, Volcanera, Pauto Sur, and Floreña, which together contain an additional estimated 2 billion bbl of liquids and 7 tcf gas. The remaining potential in the trend is considerable with some large untested structures still to be drilled, for example, Samore, which lies to the north near the Venezuelan border; the elephant hunt continues. 

AAPG Search and Discovery Article #[email protected] AAPG Distinguished Lectures