PRODUCTION WELL WATER SHUT-OFF TREATMENT IN A HIGHLY FRACTURED SANDSTONE RESERVOIR

Abstract

As domestic oil and gas fields approach maturity or even abandonment, new methods are being tested to add life to the fields. One area being addressed is the reduction of water production to extend the economic life of a field. In many fields a very common problem is permeability heterogeneity from matrix variations, fractures, or both. Conventional procedures to remediate high water rates in fractured networks, including cement squeezing, openhole packers, and liners are generally unsuccessful. The objective of this project was to test the viability of using sequential treatment of a production well with a cross-linked polymer to restrict water production from highly permeable and fractured zones. The field used for testing was the Ashley Valley field in northeastern Utah. The process proposed for testing in this field was the sequential application of small batches of a cross-linked polymer, chromium (III) polyacrylamide polymer (Marcit{trademark}). First, the highest permeability fractures were to be blocked, followed progressively by smaller fractures, and finally the higher permeability matrix channels. The initial application of this polymer in September 1997 in the Ashley Valley (AV) well No.2 did increase oil production while decreasing both water production and the relative permeability to water. The successive application of the polymer was considered as a method to increase both daily and ultimate oil production and reduce produced water. The second polymer treatment was conducted in October 1999 in AV No.2. The treatment consisted of 4,994 barrels of 1,500-mg/l to 9,000-mg/l polymer at surface injection pressures no higher than 380 psig. During injection, four offset wells showed polymer breakthrough and were shut in during the remaining treatment. Present oil and water production rates for AV No.2 are 14 BOPD and 2,700 BWPD, which is a 44% decrease in the oil rate and a 40% reduction in water from the rates after the first treatment. The decrease in water production did result in a minimal savings on both utilities and water-treatment chemicals. However, the savings did not offset the decrease in oil production. The second treatment appears to have targeted a different, high-permeability network than the first treatment, indicating that the first treatment was still effective after two years. Because of the negative results from the second treatment, the conduct of a third treatment has been shelved. The possibility of a larger treatment in another well with the shut in of adjacent wells as the polymer is detected is being considered if further treatment is conducted.