Maintaining inlet's infrastructure critical to industry, say officials

Posted: Thursday, May 08, 2003

ANCHORAGE Industry and state efforts are under way to extend the operating life of Cook Inlet's aging oil production platforms.

Unocal Corp., which operates 10 platforms in the inlet, is engaged in a multi-year effort to upgrade artificial lift equipment in some wells, and is pursuing new approaches to do "workovers," or major maintenance, on wells.

In Juneau, legislation that would reduce state royalties on 30-year-old oil fields in the inlet is moving through committees in the state House and Senate.

"It's critical that we maintain the Cook Inlet infrastructure we have," said Gary Carlson, Forest Oil Corp.'s senior vice president for Alaska.

"These platforms are irreplaceable assets, and any extension of their useful life, any delay in abandonment, keeps them available to explore and develop smaller new deposits," Carlson told a state legislative committee in Juneau late last month.

Forest is a partner with Unocal in several offshore inlet fields.

Meanwhile, one effort by Unocal to boost production from aging platform wells is having good results.

The company has had a program to replace gas-lift artificial lift equipment with down-hole electric pumps under way since 1999, according to Chet Starkel, a Unocal optimization engineer.

In most cases, the wells, which generally produce from 200 to over 600 barrels per day, have experienced a significant increase in their daily production rate once converted to electric pumps, Starkel said.

The electric pumps are placed near the bottom of the producing wells and pump fluids, a mixture of oil and water, about 10,000 feet from the reservoir up to the surface. The conversion costs Unocal about $1 million per well.

So far, wells on four platforms have been converted. The work was done on five wells on the Steelhead platform in 1999. One well was converted on the Grayling platform in 2000. Four additional wells on the Steelhead platform were converted in 2001.

In 2002 five wells were converted on the King Salmon platform and this year the electric pumps were placed in three wells on the Dolly Varden platform.

The gas-lift wells being replaced lift the fluids by injecting gas into the production tubing of the well to help lift fluids to the surface. The electric pumps replacing them are generally more automated and less costly to operate than the gas-lift completions.

However, the main problem with the gas-lift, Starkel explained, was that as the amount of water produced from the wells increases, gas-lift is less efficient because the fluid column being lifted is heavier, since water is heavier than oil.

It is common to see increasing amounts of water produced with oil in mature oil fields, particularly where water also is injected to increase oil recovery. Handling the large volumes of water is a major cost for operators of these fields.

In Cook Inlet, where fields have been producing since the 1960s and 1970s, some wells are producing 10,000 barrels per day of fluids but 95 percent of it, or more, could be water.

On most wells being converted the electric pumps are being placed lower in the well and are able to lift fluid from deeper in the producing reservoir than the gas-lift is able to.

This has helped to increase the production rate from the wells, Starkel said.

One other benefit of the program is that while the initial conversion well work was being done Unocal was able to add perforations, or openings, in some wells and further increase the oil flow rates.

Many of the wells were originally completed to produce from the Hemlock formation, Starkel said, but some of the converted wells are now able to produce from a second section of reservoir, which Unocal calls the "G-Zone."

Another initiative Unocal has under way is to find a less expensive way to do major well maintenance, or workovers, on the platforms.

Because of the 10,000-foot depth of most of the producing wells and the size of the steel production tubing, which ranges in diameter from 3 1/2 to 4 1/2 inches, workovers to repair a failed pump have had to be performed with workover rigs on the platforms.

These rigs are expensive to operate, and Unocal now is considering other options.

On the North Slope and other oil producing areas, field operators have been able to devise less costly ways of doing workovers. For example, use of coil-tubing units that lower tools with flexible metal tubing has been very successful on the slope.

However, inlet operators have had to continue using rigs for these artificial lift conversions because of the age, weight and size of the tubing, more than a mile and half in length, that must be pulled out of the well.

Starkel said Unocal is looking at the feasibility of other techniques that might be used to perform future pump repair workovers. In March, the company hosted a technology-review session with experts from other areas Unocal operates, such as the North Sea, where there are similar challenges.

In the North Sea, the company has used equipment such as heavy jacks and cranes as an alternative to drill rigs in doing major well workovers.

There are some differences between the operating areas, because the North Sea wells are shallower and the equipment that is pulled from the holes is usually smaller and lighter.

Still, some of this experience might be valuable in the Cook Inlet, Starkel said.

The majority of the fields in Cook Inlet are more than 30 years old, Roxanne Sinz, Unocal's spokes-person in Anchorage, said.

"We can extend the life of these fields by using technologies like the electric pumps, which are a more efficient way of doing business," she said.

Tim Bradner reports for the Alaska Journal of Commerce and Alaska Oil & Gas reporter.

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