|
Testing for shallow gas at Wainwright Well to be drilled in the early summer will test for gas in coal seams under the Chukchi coast village Alan Bailey Petroleum News
After a pause of a couple of years, the project to test the potential to use coalbed natural gas as an energy source in rural Alaska is under way again, this time in Wainwright on the Chukchi Sea coast. Drilling should start right after Memorial Day.
The multi-year project involving the U.S. Bureau of Land Management and the U.S. Geological Survey, and at various times Alaska’s Division of Geological and Geophysical Surveys and the U.S. Department of Energy, started out by drilling a coalbed methane test well in 2004 at Fort Yukon in Alaska’s Interior.
That well encountered coal seams but did not find viable quantities of gas. In 2005 a well at Franklin Bluffs, just off the Haul Road in the central North Slope, tested the potential to drill for coalbed gas in an area of deep permafrost, prior to drilling in the less accessible Wainwright area. Wainwright has permafrost to a depth of about 1,000 feet.
BLM, USGS and the Arctic Slope Regional Corp. are involved in the Wainwright phase of the project, Art Clark, the co-project chief from USGS told Petroleum News March 13. The team is also talking to other potential participants, to increase the available funding, Clark said.
“We have the funding for sure to start the drilling,” Clark said. “We are still in the process of finalizing all the funding.”
Lightweight rig The project team will use the lightweight CS 1000 rig that it used at Fort Yukon and Franklin Bluffs to drill into shallow coal-bearing strata of the Tertiary Nanushuk formation.
“We are thinking of a total (well) depth somewhere in the region of 2,000 feet, possibly as deep as 2,500 feet,” Clark said.
The coal-bearing strata probably extend down to somewhere between 1,500 and 2,000 feet, he said. However, conventional opinion, confirmed somewhat by the results from Franklin Bluffs, suggests that coal gas is unlikely within the 1,000-foot thick permafrost zone near the surface.
“If we do encounter coal gas in the permafrost, it will be interesting to determine whether it’s thermogenic gas, which would indicate migration from a deeper source, or biogenic gas, which would indicate in-situ microbial generation,” Clark said.
Depending on the funding available, the drillers may take core all the way down the well from the bottom of the surface casing. Or, if funds are short, they may open-hole drill to the bottom of the permafrost and then core below there.
Test for gas Whenever the well encounters a coal seam, the team will bring a coal sample to the surface to conduct a gas desorption test. If that test indicates the presence of significant gas in the coal, the drillers will ream out the well to a diameter just under 6 inches, down to the base of the coal seam. Then, using a pneumatic packer to seal the well bore at the top of the coal seam, the drillers will use the hollow drill rod, in effect, as a temporary well that is only open to the coal seam at the bottom of the well bore.
“Then we’ll go in and flush out all of the drill mud and everything … from the inside,” Clark said.
The team will then draw down the pressure by pumping water out of bore, while monitoring the pressure with a transducer. By then turning the pump off and monitoring the time taken for the well pressure to come back up it will be possible to determine parameters such as the permeability and storage capabilities of the coal.
“What that tells you is how quickly the fluids flow through that seam. That’s what we want to know — as goes the water, so goes the gas,” Clark said.
The team will also collect a water sample from the coal — the water chemistry becomes especially important for determining water disposal options, if the coal proves suitable for gas production.
The team will repeat the coal sampling and testing procedure for each coal seam that the well encounters, although it may curtail some of the testing if there are an especially large number of coal seams.
Upon completion of the drilling, if there appears to be a viable gas resource, the drillers would set a 2.5-inch PVC well targeting a specific coal seam. That well would then be used to monitor the pressure and temperature in the coal over the winter.
And the next step in evaluating a promising coal seam might be another drilling program in 2008. That program would likely create a pattern of four wells, including the 2007 well, to test the production characteristics of the coal. But the open-hole drilling needed for that would require a larger rig than the lightweight rig being used in 2007, Clark said.
Most equipment in Wainwright The CS 1000 rig being used for the 2007 drilling is already in Wainwright.
“We barged it from Deadhorse last August,” Clark said. “So, most of the equipment is already in Wainwright and we stored it there over the winter.”
The team will probably use a transport airplane to fly in materials such as cement and the drilling mud, so that drilling can start promptly at the end of May.
“We’re thinking that the whole project should take somewhere in the neighborhood of five to six weeks,” Clark said.
That should enable completion of the drilling by July 4, in time to make decisions about moving equipment in or out of Wainwright during the summer barging season.
“That way we could either bring more equipment in or take equipment out via the barges that run in July and August,” Clark said. “So we’re pushing (the drilling) a little bit earlier than what we might normally want to do.”
The biggest time constraint involves any equipment that the team might decide to have barged up to Wainwright in 2007, because the barge departs from Seattle for Alaska in mid to late-July.
“We want to at least have a rough preliminary idea of what our information is telling us by middle to end of July at the very latest,” Clark said.
Multiple benefits Although the purpose of the well is to test for a potential natural gas resource for use in the village of Wainwright, the team is anxious to obtain as much benefit from the drilling as possible.
“We talk to as many people as we can and try to maximize the scientific value of whatever it is we’re doing, because these opportunities don’t come along very often,” Clark said.
In particular, the well core will provide valuable information about the subsurface geology — the nearest previous well to Wainwright is about 25 miles away, Clark said.
“There’s a lot more interest in this than just the assessment of the coalbed potential there,” Clark said. “It’s also going to be a continuous-core data point.”
Another possibility is the future use of the Wainwright well for long-term temperature monitoring.
And the team will publish its findings from the drilling at Wainwright.
“We are hoping to present preliminary results in mid-October in Anchorage during the Arctic Energy Summit,” Clark said.
| 