Aggressive Tip Screen-Out Designs Give North Slope Satellite Field Production a Boost

Abstract

Over 400 wells have been very successfully hydraulically fractured on the Kuparuk Sand for the Kuparuk River Unit Field (KRU)1. Comparatively smaller petroleum deposits of the Kuparuk Sand have recently been developed in the adjacent Prudhoe Bay Field. These satellite pools, namely the Aurora and Borealis, similarly benefit from fracturing. Significant productivity increases from aggressive Tip Screen-out (TSO) fracture designs have delivered over 40, 000 bopd from 11 wells. This paper describes the rationale, events and lessons learned leading up to the final very aggressive TSO designs for these satellite wells. In many cases, fracturing fluid efficiencies measured during datafracs for the satellite wells were approximately two times higher than the Kuparuk Sand analog in the KRU area. Pad volumes during fracturing were as little as 3% of the total treatment volume with modeled proppant concentrations of 5 lbs/ft2 placed. The majority of wells were S-shaped to minimize fracture complexity. Directional drilling costs, NWPL's and production results are shown. Bottom hole pressure gauge data is presented allowing refinement of the designs via net pressure analysis and times to start TSO. Production and pressure transient analysis results are also presented. Introduction Both Aurora &Borealis Pools are located on Alaska's North Slope and produce from the Kuparuk River Formation. (See figure 1). Although the structures were penetrated and proven to bear hydrocarbons in 1969, development did not commence upon until 1999. Reservoir Description The Kuparuk River Formation is stratigraphically complex and is characterized by multiple unconformities, changes in thickness, sedimentary facies, and local digenetic cementation. The Kuparuk Formation is divided into three intervals, the A, B, and C intervals, (from oldest to youngest) with the A and C intervals divided into a number of sub-intervals. See, figure 2 V-200 type log in appendix. An overlying unit, called the Kuparuk D Shale, is locally present in some areas of the Borealis Pool. The uppermost unit, the Kuparuk C sand is the primary reservoir sand. Although both the Aurora and Borealis Pools produce from the same formation and are in close proximity, structurally they are quite different. Kuparuk Aurora. Top Kuparuk structure in the Aurora area is broken up by north-south striking faults with up to 200 feet of down-to-the-west displacement. The faults effectively bisect the Aurora Pool and at least 7 different compartments have been identified based on pressure and fluid data. The Kuparuk thickness at Aurora is highly variable and ranges from 0 feet at the eastern truncation, to 210 feet at the Beechey Point wells in the northwestern portion. Kuparuk Borealis. The Borealis structure is shaped by basement-involved northwest-southeast trending faults that are intersected by a younger set of north-south striking faults. The trending faults were active during deposition of the lower Kuparuk C (C-1), but do not appear to have been contemporaneous with Upper Kuparuk C (C-2 to C-4) deposition. The compartmentalization within the Borealis field, it is not as severe as Aurora due to a relatively higher net and a significantly higher gross reservoir thickness. Kuparuk Aurora. Top Kuparuk structure in the Aurora area is broken up by north-south striking faults with up to 200 feet of down-to-the-west displacement. The faults effectively bisect the Aurora Pool and at least 7 different compartments have been identified based on pressure and fluid data. The Kuparuk thickness at Aurora is highly variable and ranges from 0 feet at the eastern truncation, to 210 feet at the Beechey Point wells in the northwestern portion. Kuparuk Borealis. The Borealis structure is shaped by basement-involved northwest-southeast trending faults that are intersected by a younger set of north-south striking faults. The trending faults were active during deposition of the lower Kuparuk C (C-1), but do not appear to have been contemporaneous with Upper Kuparuk C (C-2 to C-4) deposition. The compartmentalization within the Borealis field, it is not as severe as Aurora due to a relatively higher net and a significantly higher gross reservoir thickness.