olombia's Orito field has operated for more than 35 years. By this decade, it had seen production decline to less than 3,500 bopd from a one-time peak of 66,000 bopd. Recently, Petrominerales achieved a significant increase in production and recoverable reserves by using a dual stimulation service that combines acid and propped fracturing technologies.

The treatment was successfully used in a reservoir that has frequently failed to respond to hydraulic fracturing, and where a 2002 third-party reservoir study concluded that the wells "indicate higher skin factors following the fracture treatment and lower production ratios, regardless of the fluid used." The service is designed to remove fracture face skin and optimize fracture conductivity.

ORITO FIELD AND CABALLOS FORMATION

Orito field, almost 17 [mi.sup.2] (43 [km.sup.2]) in area, is in Colombia's Putumayo basin, Fig. 1. As the basin's largest field, it originally contained more than 1 billion bbl of oil-in-place, in three primary reservoirs. The most significant is the Cretaceous Caballos formation, a complex series of fluvial/deltaic and marginal marine sands that originally contained more than 700 million bbl of oil-in-place, Fig. 2. The Caballos zone, alone, has produced 186.7 million bbl since the field was discovered in 1963. By 2005, the reservoirs had cumulatively produced 226 million bbl, or about 22% of original