Print this pageThe Costayaco Field — Reinterpretation of Old Data Leads to Largest Putumayo Basin Discovery Since the 1960s
The Costayaco Field, discovered in 2007 by Gran Tierra had gross proven and probable reserves of 31 mmbo at year-end 2008. This makes Costayaco the third largest discovery in the Putumayo Basin of Colombia after the Orito and Acae Fields discovered in the 1960’s.
The structure is a high relief anticline with an east verging reverse fault in the foothills of the Andes Mountains. It was first tested in 1964 by the Cafelina-1 well drilled on the flank. Weak oil and gas shows were encountered during drilling of the Cretaceous sandstones but low sand content in the cuttings suggested thin reservoirs. Excellent reservoir quality was proven with core in the Caballos Formation but drill stem testing recovered tar and fresh formation water.
In 2005, a single 2D seismic line was acquired to confirm structural closure. A four-way dip closure was mapped requiring fault seal to the north. A difficult well-tie to Cafelina-1 and poor imaging as a result of surface conditions and proximity to the Urcusique fault complex resulted in uncertainties in mapping. Costayaco-1 was drilled at the crest of the structure in 2007 and tested up to 5,906 BOPD. A 70 km2 3D seismic survey was acquired in 2007 followed by five delineation wells to the end of 2008. Production from the Villeta T Sandstone and the Caballos Formation reached a maximum of 15,422 bopd by Q1 2009, with additional development wells planned.
Operational challenges have included sloughing shales, poor cuttings recovery and freshwater reservoirs. Sparse 2D seismic coverage resulted in difficulty tying wells to seismic and predicting localized faulting. Variations in seismic velocities due to anisotropic affects of the overlying deformed strata have complicated depth conversion. These challenges have been overcome by changing drilling procedures, casing design and wireline logging programs. Acquisition of 3D seismic allowed for the proper spatial imaging of the bounding faults. Attention to velocities and application of prestack migration has aided in the identification of shallow velocity affects.
The Costayaco Field is a significant discovery made in an established petroleum province underexplored in recent decades. Further exploration success is anticipated with the application of modern techniques including 3D seismic that are considered standard practice in other well established basins.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil