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 Results of a Large-Scale Refracture Stimulation Program, Kuparuk River Unit, Alaska
Gordon Pospisil, SPE, ARCO Alaska Inc.; K.W. Lynch, SPE, * ARCO Long Beach Inc.; and C.M. Pearson, SPE, and J.A. Rugen, SPE, ARCO Alaska, Inc.
This paper documents the evolution of fracture design at North America’s second largest oil field. Over 880 fracture stimulations have been performed in this single field, including over 200 refracture treatments. The authors had the benefit of an outstanding database with results of datafracs, pressure buildup tests, and extensive production data available for most wells.
Recent advances in fracturing design have resulted in an incremental two-fold increase in productivity. The primary recent change was the switch to larger ceramic proppants (10/14 and 12/18 CARBOLITE®) which allowed economic increases in job size. Prior attempts to increase job size using 20/40 natural sand were unsuccessful, as the fractures were conductivity-limited, and additional fracture length was ineffective.
Tip screen-out (TSO) designs are now routinely planned for all stimulations, as treatments exhibiting this behavior were shown to dramatically increase the stimulation effectiveness. As fracture conductivity has been proven to be the key to well productivity, a systematic elimination of silica flour, 100-mesh sand and other damaging fluid loss additives has been pursued.
The paper discusses strategies to identify refracture candidates. Candidates are not limited to highly damaged producers; in fact, some of the best economic refracs were found to be prolific wells showing little damage after the initial stimulation. Refracture treatments were shown to improve both the skin and the permeability-thickness product (kh), suggesting that refracturing provides benefit both in rate and recovery.
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