WELL TEST CAMPAIGN HELPS BETTER MANAGE BOREALIS RESERVOIR, NORTH SLOPE, ALASKA

The Borealis reservoir is a satellite of the giant Prudhoe Bay Field. The pool contains an estimated OOIP of 250 million barrels and currently produces ~30,000 bopd from lower shoreface sands of the Cretaceous Kuparuk River Formation. Production started in 2001, as of December 2004, Borealis has produced 30 million barrels of oil.

The reservoir section in Borealis is highly heterogeneous. The pay is glauconitic and sideritic shallow marine sands. The field is also heavily faulted, with throws typically between ten and 250 ft. Other types of heterogeneities include complex stratigraphy, reservoir compartmentalization, variable fluid contacts, and significant variation in pay thickness and mineralogy.

Given the high level of reservoir heterogeneity, effective reservoir management in Borealis is a severe challenge. To circumvent this problem a campaign of well test was conducted. PBU and fall off tests were conducted simultaneously in more than 50% of the existing wells to provide uniform aerial coverage, with long build up and fall off periods for accurate estimation of reservoir properties.

This paper presents the decision process, analysis and interpretation of the well tests in Borealis and discusses some of the learning. Sensitivity analysis was performed on the fault location and effectiveness of the sealing faults. The results showed that the faults in the center of Borealis are sealing necessitating effective pressure maintenance in these fault blocks. The results also helped define new injection patterns and balance existing patterns with infill wells, ascertain the effectiveness of the hydraulic fractures in the producers, and calibrate the pressure in the simulation model.