Hilcorp Energy said it halted a four-year decline in Prudhoe Bay, the largest producing field on the North Slope and has seen a small increase so far this year, a top company manager said at an Alaska business conference.

“Prudhoe Bay was declining at 4 percent annually between 2016 and 2020 regardless of capital investment or new drilling,” Jill Fisk, Hilcorp’s Prudhoie Bay West Asset Team Leader, told the Resource Development Council in Anchorage Nov. 18.

Like other slope field operators Hilcorp had to halt new drilling of production wells in Prudhoe but the company was still able to stem the decline through “hundreds of small projects across the field,” Fisk said.

The company’s unique culture of empowering decisions “downward” to staff in the field helped generate ideas for improving productivity. Hilcorp took over as operator in Prudhoe after buying BP’s Alaska assets in mid-2020 and began an aggressive remediation of aged wells and facilities in the field, which is now four decades old.

“We focused first on repairing and returning old wells to service and we now have a record number of wells producing in the field,” Fisk said.

Another focus was on “debottlenecking” production plants, essentially reworking the plumbing to increase effiency. A result of this has been to increase the performance of field production plants from 85 percent to 94 percent, meaning a reduced “downtime” for plants and more oil being processed.

Increasing the capability to handle and inject back underground the water and gas produced the oil has been another goal. As producing wells age more water and “solution” gas contained in the oil comes up the wells and field operator must dispose it.

On the North Slope the only practical option is to inject the water and gas (there is no gas pipeline from the slope) back underground, which is increasingly costly as the volumes rise.

“Prudhoe oil production is actually constrained by the ability of facilities to inject produced gas and water,” back underground, Fisk said.

“We have been able to increase our ability to inject produced water underground by 200,000 barrels per day, which allowed us to produce an additional 10,000 barrels of oil per day,” she said.

There was similar success in an increase of produced gas handling and injection: “We increased our ability to handle gas by 500 million cubic feet a day, which resulted in another 5,000 barrels of oil per day,” Fisk said.

Hilcorp also increased the volume of water being injected into the Prudhoe Bay “gas cap” to increase pressure in the reservoir and produce more oil.

The water-injection into the gas cap, the natural gas reservoir that overlies Prudhoe’s main oil-producing reservoir, was a step taken several years ago by BP, the previous field operator.

Injecting water into a gas formation to pump up reservoir pressure had never been done before and it was considered risky at the time but over the years it has worked well to increase oil production.

Fisk said Hilcorp increased the volume of water being injected from 400,000 barrels of oil per day to 700,000 barrels of oil per day over the last year, which resulted in about 1,000 b/d of addition oil because of the higher pressure in the reservoir.

The company is now studying the application of a polymer injection into deposits of viscous oil in the western part of the Prudhoe field. Hilcorp has been successful in an experimental, polymer injection in viscous oil in the nearby Milne Point field, where is also the field operator.

The project aided by U.S. Department of Energy and University of Alaska scientists, and is now expanded to other Milne Point wells, Fisk said.

At Prudhoe Bay Hilcorp carried out a short injection test with positive results and plans a larger pilot program this year to gather more data, she said.

Viscous oil deposits are shallower and overlie deeper conventional oil formations in several fields on the slope including Milne Point, Prudhoe Bay and the Kuparuk River field to the west.

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