Abstract: The Newest Giant of the Americas: An Overview of the Petroleum Geology of the Cusiana Field, Eastern Cordillera, Colombia

A. B. Hayward, G. Espinosa, M. Coudeyre, W. G. Leel, Jr.

Cusiana Field is located in the Llanos Foothills, 150 miles northeast of Bogota. Light (>34° API) oil, gas and condensate in Cusiana occur at drilling depths which average 16,000 ft, in an asymmetric hanging-wall anticlinal trap 14 miles long and 3 miles wide, formed during the Miocene-to-Recent deformation of the Eastern Cordillera. Top and lateral seals are provided by marine mudstones of the Oligocene Carbonera Group and support a hydrocarbon column of over 1,600 ft. The hydrocarbon composition indicates a marine mudstone source, interpreted to be the Turonian/Coniacian Gacheta Formation.

Over 50% of the reserves occur in upper Eocene Mirador Formation sandstones, deposited in fluvial and shallow marine environments. Additional, deeper reservoirs include fluvial and shallow marine Paleocene Barco Formation sandstones, and the shallow marine Campanian upper Guadalupe Sandstone Formation.

Porosity in Cusiana is relatively low, and averages 9% in the Mirador Formation. Good permeability is retained, however, because the reservoirs are pure quartz-cemented quartz arenites, in which permeability-reducing authigenic clays and carbonate cements are absent. Core and well test analysis indicate matrix permeability, not fracture permeability, provides the high deliverability (>12,000 BOPD) of Cusiana wells.

Cusiana hydrocarbon phases exist in a near-miscible, critical-point state. Analysis indicates very high liquid recoveries will be achieved using reinjection of produced gas. The field will therefore be developed using reinjection of produced gas to maintain reservoir pressure and vaporise residual liquids. The field contains up to 1500 MMSTB of hydrocarbon liquids and large volumes of gas.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994