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AOGCC approves produced water injection into Prudhoe Bay gas cap
Kristen Nelson Petroleum News
The Prudhoe Bay unit owners continue to work on maintaining production from the giant oil field, with a current project, just approved by the Alaska Oil and Gas Conservation Commission, focused on pressure maintenance.
Hilcorp North Slope, the Prudhoe Bay unit operator, requested approval from AOGCC to inject produced water into the Prudhoe oil pool gas cap. The injection is part of the pressure and vaporization enhancement, PAVE, project.
The commission said in a Feb. 1 decision that PAVE “would divert water that is currently going to disposal wells and waterflood patterns where water injection is no longer providing a significant benefit.” PAVE would build on the success of the gas cap water injection, GCWI, project which injects seawater into the Prudhoe gas cap to increase reservoir pressure and the seawater optimization project, SWOP, which diverted seawater from waterflood patterns to GCWI.
“Both of these projects have been shown to increase ultimate recovery from the field,” AOGCC said. GCWI increased ultimate recovery by slowing the rate of pressure decline in the Prudhoe oil pool and stabilizing average reservoir pressure. SWOP increased recovery by making additional seawater “available for the GCWI and by allowing waterflood patterns to transition to gravity drainage with lean gas vaporization recovery methods which result in a lower residual oil saturation.”
The commission said full field models of PAVE indicate it would increase ultimate recovery from the Prudhoe oil pool by some 85 million barrels of oil and natural gas liquids.
Earlier AOGCC approvals In late 2021 the commission removed the 20-year limitation on the Prudhoe gas cap water injection project and removed the limitation of the amount of water that could be injected. Hilcorp told the commission at that time that GCWI had performed as anticipated.
AOGCC approved the GCWI in 2001.
It was one of the measures taken at Prudhoe as the field matured to increase production and maintain reservoir pressure.
The initial application was for 20 years and a total injection volume of 4 billion barrels. The original total daily injection was estimated at up to 650,000 barrels of water per day. In 2021 Hilcorp told the commission the operational limit was currently estimated at 815,000 to 840,000 bpd of water as seawater availability for GCWI increased as demand for seawater in other areas decreased.
Hilcorp noted that in 2020 implementation of the seawater optimization plan shut in some 45,000 bpd of seawater injection and enabled an increase in GCWI injection.
The 2021 extension of the life of the GCWI and the removal of the limit of the water that could be injected was estimated to increase hydrocarbon recovery by 27.3 million barrels by 2055 - this from an increase in water injection from 650,000 bpd to 800,000 bpd.
Original project In an October 2001 hearing, representatives of the Prudhoe Bay working interest owners - then BP Exploration (Alaska), ExxonMobil Production and Phillips Alaska - told the commission that water injection projects were ongoing at the Prudhoe Bay oil rim but said those projects had limited pressure-support potential compared to the gas cap water injection project.
The Prudhoe Bay working interest owners formed a multi-company pressure studies initiative team in 1991, the companies told the commission, and that team looked at several options, most of which were rejected because of high capital costs and/or limited recovery benefits.
But the team found there would be significant recovery benefits and reasonable capital costs for a gas cap water injection project, and that process was recommended for more detailed study.
In June 2001, the owners approved the Prudhoe gas cap water injection project.
The companies told the commission in 2001 that average reservoir pressure at Prudhoe had been declining at a rate of 25-35 psi per year, reducing efficiency of every recovery mechanism at the field. The proposed gas cap water injection project was projected to maintain level reservoir pressure until the end of the proposed project in 2022, with the increased pressure expected to increase liquid recovery by 150-200 million barrels.
- KRISTEN NELSON
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