Casanare had been explored for hydrocarbons well before BP. In fact, commercial discoveries were made in 1974 and 1975 when French operator Elf Aquitaine struck oil in the vast, grassy plains.
However, geologists had their sites trained on the foothills, where surface topography, rock samples and even outcrops pointed to the possibility of major hydrocarbon accumulations.
These proved elusive nevertheless as exploration wells drilled by Ecopetrol (Colombia's national oil company), and Exxon too, were abandoned due to mechanical failures or after being declared non-commercial discoveries.
The nature of these wells and the fact that hydrocarbon traces did effectively show up kept the Casanare foothills high on the prospectivity map. US firm Triton was a strong believer in the quality of the available subsurface data, and so they approached BP in 1983 with a proposal for exploring east of the Colombian Andes.
BP was initially reluctant as the geological information available at the time was viewed as high-risk. However, a re-evaluation of the foothill area conducted in the UK improved prospectivity and Triton's offer was accepted. In 1986 the company farmed into the Santiago de Las Atalayas association contract, move that prompted the opening of a small office in Bogotá that same year.
Located in the municipality of Aguazul, Casanare, Cusiana-1 well was started in October 1987, and after 14 months of eventful drilling activity, the well was declared a discovery in December 1988. Initial production rate was 2,000 barrels of oil and 13 million standard cubic feet of gas per day, all of which came from the prolific Mirador formation.
Despite initial expectations, three additional years were needed to confirm the find's magnitude: Cusiana-2 well was abandoned after mechanical trouble prevented its continuity, and so an entirely new well had to be drilled. Employing a refined drilling approach based on the experience gathered to date, Cusiana-2A well was started and in 1991 it confirmed significant reserves as well as reaching two other key reservoirs, Barco and Guadalupe.
The confirmation of a major discovery required the construction of long term test facilities at Cusiana 2A well site in 1992, which was also fundamental in obtaining commerciality from State partner, Ecopetrol. The small installations also allowed Cusiana field to produce an initial 10,000 barrels per day via the existing Oleoducto de Colombia pipeline infrastructure.
Success also prompted a new look at the Cupiagua structure a bit further north. Much like its hard-to-pin southern cousin, this same area had been drilled in the 70's with similar mixed results: technical prowess, hydrocarbon traces, yet non-commercial quantities. In 1993 BP discovered Cupiagua field, after drilling from almost the same exact spot as its predecessors. Commerciality was granted a year later in 1994.
The Cusiana and Cupiagua oil fields -Colombia's biggest oil find to date- booked combined reserves of 1.6 billion barrels of light, sweet crude (42 API on average).
With Cusiana as a driver, BP bid for additional acreage and subscribed the Recetor and Piedemonte contracts in 1989 and 1992 respectively, both following the northern trend. Drilling proved to be even more difficult given the highly faulted underground formations. Yet between 1993 and 1995, BP confirmed the Volcanera, Dele, Pauto and Floreña discoveries.
These fields advanced BP's comprehension of the complex geology underlying Casanare's foothills, and came on stream progressively between 2001 and 2006 after successful testing and commerciality agreements with Colombian regulators and partners.
In course of twenty years, BP's discoveries in Casanare were turned into a world-class oil project.
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