Abstract

The Cusiana reservoir in the Casanare region of Colombia is currently being appraised and developed. Cost effective development of the reservoir will be dependent on applying optimum drilling and completion practices. The purpose of this poster session is to provide a case study history for the approach and evolution of the project as it pertains to attaining an improved understanding of formation damage mechanisms.

Introduction
Background

Cusiana Field is located in the Llanos Foothills, 150 miles northeast of Bogota, Colombia. Light (>34° API) oil, gas and condensate in Cusiana occur at drilling depths which average 16000 ft. in an asymmetric hanging wallanticlinal 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 1600 ft. The region is tectonically stressed in the formations which overlay the Cusiana reservoir. Because of this, drilling conditions are difficult with well bore instability, mud losses, and stuck pipecommon.

Geology and Mineralogy

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

Porosity in Cusiana is relatively low, and averages 9% in the Mirador Fm. Good permeability is retained, however, because the reservoirs are purequartz-cemented quartz arenites, in which permeability-reducing authigenicclays 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.

Reservoir Fluids

Cusiana hydrocarbon phases exist in a near-miscible, critical point state. Analysis indicates very high liquids 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 vaporize residual liquids. The field contains significant volumes of hydrocarbon liquids and large volumes of gas.

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