Do Dry Holes Lie? Cusiana and Cupiagua Fields, Colombia, South America

Woodruff G. Leel
Consulting Geologist, Plano, TX

The Cusiana and Cupiagua fields are located in the Llanos Basin foothills of the Andes Mountains' Eastern Cordillera. Geoscientists misinterpreted the geology of these giant oil fields, which remained hidden until 1988. Complex geographical, geological and engineering phenomena stymied early explorers. Although the surface expression of the frontal thrust faults containing the Cusiana and Cupiagua fields was mapped in the 1940's, no significant drilling took place until the 1970's when both fields were drilled and tested. However, the wells were not commercially successful and were abandoned. A remote area, expensive deep drilling and lack of state-of-the-art technology and equipment led to the failure of these early wells. In the late 1980s, the Cusiana Field finally was discovered, followed by the Cupiagua Field in the early 1990's. Extensive logging and testing led to the Cusiana find. Subsequent conventional coring and petrographic analysis in the confirmation well unlocked the mysteries of the Mirador formation. Geologists also found deeper productive reservoirs, which added to the significance of the discovery. Why did these giant oil fields remain a mystery for so long? A quartz arenite reservoir with low porosity, high permeability, high resistivity, fresh water, high GOR, high-gravity oil, overbalanced drilling and reverse drilling breaks challenged some of the industry's most experienced oil finders.