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January 2010

Vol. 15, No. 4 Week of January 24, 2010

Wainwright CBM needs additional testing

Program in 2009 confirmed extent of resource but ran into a glitch with the production testing; team plans to return this summer

Alan Bailey

Petroleum News

The Chukchi Sea coastal community of Wainwright doesn’t know yet whether the rich seams of coal sitting a couple of thousand feet or so under the village can produce natural gas as a replacement for expensive diesel oil and heating oil, for power generation and keeping buildings warm.

As part of a multiyear project to test the feasibility of producing coalbed methane in the village, a U.S. Geological Survey and U.S. Bureau of Land Management team, supported by the North Slope Borough, Arctic Slope Regional Corp. and Olgoonik Corp., found a promising coal seam in an exploratory well in the village in 2007, returning the following year to drill a pattern of wells for a production test from the seam. The team went back to Wainwright in the summer of 2009 to conduct the production test and drill some further delineation wells, to verify the extent of the potential coalbed methane resource.

But, while the 2009 delineation drilling confirmed the lateral extent of the target coal seam, the production test hit some snags that will require the team to return to Wainwright in May or June of this year, to hopefully demonstrate that gas can be produced at viable rates in the village, Art Clark, USGS drilling project supervisor and co-project leader, told Petroleum News Jan. 13.

Two delineation wells

In 2009, using a truck-mounted rig that the team had airlifted into Wainwright in 2008, the team drilled two delineation wells, one about two miles northeast and the second about half-a-mile south-southwest of the original 2007 well, Clark said. Those delineation wells, drilled as far out from the 2007 well as the Wainwright road system would allow, confirmed that the coal seam discovered below the local permafrost at a depth of 1,250 feet in 2007 maintains a thickness of seven to eight feet from one well to another. And, although the team is still desorbing gas from coal samples from the delineation wells, results to date suggest that the gas content of the coal is consistent with that found from the 2007 drilling.

“The reservoir seems to be laterally continuous and appears to hold approximately the same amount of gas that we got from our 2007 well,” Clark said.

Unfortunately, however, the 2009 production test did not proceed as smoothly as the delineation drilling.

Reduce pressure

The idea behind coalbed methane production is to pump water from a coal seam, to release gas from the seam by reducing the pressure. And in the case of Wainwright the team placed a submersible pump down a central production well, while placing sensors in four surrounding monitor wells to measure the impact of gas production on the reservoir.

“Everything started out pretty good for about two days and then we started getting a bunch of water and (methane) hydrate ice pumping from the well,” Clark said. “So we were just pumping out slush after a while.”

To melt the ice the team bought two custom-made, 1,200-foot lengths of heater cabling — the type of cabling that people living in cold climates use to melt ice from house roofs and guttering — and ran one length of cable down the outside of the well draw pipe and one length down the inside of the pipe. The cabling required a special 220-volt power supply and was of a length that pushed the limits of what the cable manufacturer could produce, Clark said.

But it worked.

“Once we got those up and running we pretty much eliminated our icing issues,” Clark said. “The water was still very cold, but we were getting water and gas.”

The test then made good progress for a few days until the fluid level in the well dropped to a certain point.

“As the fluid level came down, all of a sudden we started losing the gas production and the water production … and we lost hydraulic, or pressure, communication through the reservoir to our monitor wells,” Clark said.

Stop and start

The team found that it could restore pressure communication with the monitor wells by filling the production well with a mixture of antifreeze and water (water, by itself, would have frozen in the well). It then became possible to re-start production, although as the fluid level dropped the production clogged up again.

Eventually, the team tried dropping the well pressure for about 30 days, to see what would happen, but it failed to entice much more than a trickle of oil and gas from the well.

“We’re still not exactly sure what happened, but we worked through the end of August and never were able to conduct a good production test,” Clark said. “We just continuously had problems.”

Clark said that the team has developed a couple of theories about what happened but that he is certain that the problem is associated with some form of reservoir damage and associated clogging around the production well bore — production fully met expectations until the fluid level dropped.

“I absolutely do believe that we have a problem with the well,” Clark said. “I don’t think it’s a problem with the producability of the reservoir.”

The team plans to return to Wainwright in the coming summer to try to resolve the production problem by stimulating the well, using a reservoir fracturing technique.

“We haven’t decided exactly how we’re going to do it, but we’re going to clean out the well, stimulate it, try to open up the near-bore fraction of the coal through some type of fracturing,” Clark said.






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