The basic objective of this study was to evaluate the relative oil recovery potential of the Sadlerochit Reservoir at Prudhoe Bay under a number of different operating conditions. The reservoir was modeled in cross section, using a six-layered, two-dimensional, three-phase mathematical fluid-flow simulator. This work was preceded by a published volumetric study and other preceded by a published volumetric study and other independent, confidential studies based on proprietary information which were designed to proprietary information which were designed to develop the best basic data with which to describe initial reservoir geometry, volume, fluid and energy conditions.


General boundary conditions were established such that the following basic cases could be evaluated and compared:

  1. Depletion drive with gas cap expansion and gas reinjection into the gas cap from the start of producing operations—no aquifer. producing operations—no aquifer.

  2. Depletion drive with gas cap expansion and gas reinjection, supplemented by a moderate-sized aquifer.

  3. Depletion drive with gas cap expansion, gas reinjection and a moderate-sized aquifer supplemented by water injection.

  4. All of the preceding cases were also considered with gas cap sales of 2 MMMSCF/D, and some cases with 3 MMMSCF/D, and 4 MMMSCF/D.

  5. Special cases, all with aquifer, water injection and gas cap sales, where certain operating limits were changed:

    • Five well groups were recompleted and GOR limits increased to 25,000 SCF/STB on allwells after 13 years (GOR limit otherwise was 15,000 SCF/STB and WOR limit was3 STB/STB for all cases).

    • Two more well groups were added near the gas-oil contact after 14.75 years to control the potential loss of oil into the gas cap.

  6. Five of the above special cases had gas sales delayed.

  7. A range of maximum sustained oil-producing rates of 1.2 MMSTB/D, 1.6 MMSTB/D and 1.8 MMSTB/D was set for most of the preceding cases. All runs were scheduled to produce at 0.6 MMSTB/D for the first 3 months, 1.4 MMSTB/D for the next 12 months, and then at one of the above maximum rates until the start of decline.

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