Stimulation Program in High Permeability Oil Sands - Case Study

Abstract

Argosy International operates several oil fields in southern Colombia, South America that were experiencing a significant decline in productivity. A study of numerous wells in these fields revealed the decrease in productivity was due to increasing skin damage near the wellbore. Lab tests and field observations indicated that fines migration and asphaltine deposition were the most likely causes. Several types of treatments were performed during a pilot program to overcome the near wellbore damage, including acid treatments, xylene treatments, clay stabilizer treatments, high pressure gas fracturing and hydraulic fracturing. The hydraulic fracture treatments provided the best results and justified the economics of implementing a major stimulation program. A total of 17 fracture treatments have been performed on 10 different wells. As a result, the productivity of the wells has increased by 2-3 fold, the total field production has increased substantially. As of February 1997 an additional 2,700,000 bbls of oil has been produced as a result of the fracturing program. The implementation of quality control and real-time analysis using a 3-Dimensional fracture model has allowed for on-site revisions of the fracture treatments. The amounts of pad and proppant volumes were optimized to achieve a proppant pack off in the fracture at the end of the flush. Introduction Argosy operates several fields in the Putumayo Basin in southern Colombia. These fields include the Toroyaco, Linda, Mary, and Miraflor fields. The main producing intervals in these fields are the Villeta U and T Sands. The formations vary in reservoir properties from well to well as indicated in Table 1. There is a strong water drive present in all of the fields for each formation. Therefore, the location of the oil-water contact is of great concern and is mapped very carefully. Most of the wells have very severe near wellbore formation damage. There is initial damage from drilling operations due to the high mud weight of 11 to 11.5 lbs/gal that is required to prevent the shales from sloughing into the wellbore. The excessive mud weight damages the formations which range in permeability from 120 to 1664 md. The amount of skin damage also increases over time, reducing the productivity. Several types of treatments have been performed to minimize the amount of damage and to lower the skin values. These treatments include pumping acids, solvents, and performing hydraulic fracture treatments. Based on an evaluation of the results of the treatments, hydraulic fracturing was determined to be the best method for overcoming the damage. To date, there have been 17 fracture treatments performed on 10 different wells. The fracture treatments have been performed in three phases. First was the Toroyaco No. 3 pilot well in January 1995. The second phase involved a 7 well, 12 treatment program between October 1995 and February 1996. The third phase included the stimulation of the Toroyaco No. 4 and Linda No. 4 upon initial completion in December 1996. The total proppant volume pumped during the 7 well program was 247,000 lbs. As a result, when the program was completed, it was one of the largest stimulation program performed in Colombia. This paper summarizes the results of the fracturing program.

Treatment of Oil Production Data under Fines Migration and Productivity Decline

“…This data is from a well in the Toroyaco field located in the Putumayo Basin in Southern Colombia. The main producing intervals are the Villeta U and T Sandsas reported by Davidson, Franco, Gonzalez and Robinson [47]. During the 6 years of recorded production, the well productivity index decreased 4.27 times.…”