Vol. 26, No.48 Week of November 28, 2021
Providing coverage of Alaska and northern Canada's oil and gas industry

Hilcorp: commingling for more Prudhoe production, well restarts

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Kristen Nelson

Petroleum News

Prudhoe Bay is Alaska’s largest oil field and it is mature, long past its peak production. Making the most of the remaining resource is a continuing challenge, and one that Hilcorp North Slope took up in mid-2020 when it took over from BP Exploration (Alaska) as the field’s operator.

One approach Hilcorp is continuing is commingling injection between the various oil pools at Prudhoe.

In a recent application the company made to the Alaska Oil and Gas Conservation Commission it requested permission to commingle injection fluids on a pool wide basis for the Prudhoe oil pool, Polaris oil pool, Orion oil pool and Aurora oil pool.

Aurora, Orion and Polaris, along with Borealis, are satellite fields on the western side of Prudhoe.

In a notice of the filing the commission said Hilcorp requested amendment of existing area injection orders and a conservation order “to allow the commingling of injected water and miscible injectant between the Prudhoe and Polaris Oil Pools, Prudhoe and Orion Oil Pools, and the Polaris and Aurora Oil Pools.”

Wells into multiple pools

The commission said it isn’t uncommon for a well to encounter multiple pools and what typically happens is that the operator will produce from or inject into the deepest pool until the oil has been depleted or the injection has swept the available oil, then plug off that pool and move up in the well, repeating until all pools are depleted or swept.

But if one or more of the pools doesn’t warrant production or injection on its own or there are other reasons to allow commingling, the operator can apply to the commission for an order approving downhole commingling. The commission then reviews the application “to assure waste will not occur and all owners receive their share of the production.”

Commingling for injection isn’t a new approach at Prudhoe. The commission said injection commingling is already authorized between the Prudhoe oil pool and the Aurora and Borealis oil pools.

Potential wells for commingling

In its application Hilcorp said the commingling “will not promote waste, cause damage, or jeopardize correlative rights.”

The volumes injected can be properly allocated, the company said, and said the proposed changes are based on “sound engineering and geoscience principles, and will not result in fluid movement outside of the authorized injection zones.”

Hilcorp provided examples of proposed commingling.

For the Polaris and Aurora pools, Hilcorp said wells drilled for the Aurora oil pool frequently penetrate the Polaris pool in an ideal location for water alternating gas, WAG, injection. “To accelerate oil production and reduce waste, many AOP wells should be converted into commingled AOP and POP WAG injectors.”

The company said the Polaris oil pool is a very immature WAG flood, relying on water displacement and miscible injectant enhanced oil recovery to produce oil “due to low system compressibility.” Additional water injection in Polaris is “extremely valuable,” Hilcorp said.

The Aurora oil pool is also “an immature WAG flood and retains significant value for continued WAG injection.”

Hilcorp said the S-104 well exemplifies the value of commingled WAG injection. The well is an Aurora injector that penetrates the Polaris oil pool “in an ideal location to support S-202,” and is evenly spaced with offset Polaris pool injectors S-210 and S-201A.

“WAG injection in POP could sweep up to 1 million barrels of … additional oil to S-202,” the company said.

S-104 supports production of some 200 barrels per day from S-122 and 178 bpd from S-103, with WAG causing those Aurora pool wells “to have extremely low decline rates that support baseline production in Prudhoe.”

Commingling WAG injection between the Aurora and Polaris pools will increase the value of existing injectors and bring online long-term shut-in wells.

Long-term shut-in wells

S pad sits on top of the Aurora and Polaris pools and has many long-term shut-in wells that penetrate the pools, but workovers on these S pad long-term shut-in wells “are often uneconomic because oil in place in either AOP or POP WAG patterns is too small to justify capital expenditures,” while the two pools together have enough oil in place to justify the capital to bring long-term shut-in wells on as commingled injectors.

Hilcorp said while the Prudhoe oil pool is a more mature WAG flood than the Aurora or Polaris pools, continued injection into the Prudhoe oil pool “is extremely valuable due to the vast original oil in place and low oil decline rates.”

The company said the W-01 well is an example of the value of commingling Prudhoe and Polaris WAG injection. It is a long-term shut-in Prudhoe producer that penetrates the Polaris oil pool in “an ideal location to support W-205 and W-203” and in the Polaris pool W-01 is “evenly spaced out up dip of W-205 and W-203 outside the existing WAG pattern.”

Hilcorp said WAG injection into W-01 could sweep an additional 1.5 million barrels to W-205 and W-203. Injection from W-01 into the Prudhoe pool would also be “extremely valuable” as in the Prudhoe pool it supports W-8, producing 215 bpd and U-16, producing 195 bpd, and WAG from W-01 will cause those Prudhoe pool wells “to have extremely low decline rates that support baseline production in Prudhoe.” Because of W-01’s ideal injection location for both the Prudhoe and Polaris oil pools, it is “most valuable as a commingled (Prudhoe) and (Polaris) WAG injector.” Hilcorp said capital to bring the long-term shut-in W-01 online with a rig workover is justified by commingled injection into the two pools.


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