Early optimism from results of a test coalbed methane well drilled in the summer of 2007 in the Chukchi coast village of Wainwright has proved justified.
The well encountered a total of 70 feet of coal dispersed across multiple seams. And the presence of a significant gas resource in the coal is triggering a more extensive drilling and testing program at Wainwright during the summer of 2008, Art Clark, U.S. Geological Survey drilling project supervisor and co-project leader of the Department of the Interior-led Wainwright project, told Petroleum News May 29.
“There’s enough gas contained within these coal seams (at Wainwright) to warrant the next phase of work. … These coals are fully saturated with gas,” Clark said.
The DOI team drilled the 2007 well as part of a program to investigate the possibility of using coalbed methane as an energy source for some remote Alaska villages.
Wainwright with a population of 500 to 600 depends on expensive diesel fuel for electricity generation — an ability to switch to natural gas as an energy source for the electricity power plant could represent a substantial economic benefit for the community. Tests in 2007 indicated the presence of about 1.24 billion cubic feet of gas in one square mile of just one subsurface coal seam. That might scale up across multiple seams and a wider area to supply enough gas to meet Wainwright’s electricity generation needs for several decades.
More powerful rigBecause the lightweight coring rig that the team used to drill the 2007 well at Wainwright is not capable of the open-hole drilling required for the 2008 drilling program, the DOI team has obtained a more powerful rig.
“We still have a small portable rig up there … but we have transported a truck-mounted rotary-core rig up to the slope,” Clark said. “… We’ll be doing some coring but primarily we’ll be doing open-hole rotary drilling, and that is why we wanted to have the larger rig.”
As of May 29 the truck-mounted rig and other equipment were staged at Prudhoe Bay for airlifting to Wainwright. The team had hoped to start drilling at Wainwright around June 2, but is currently in a holding pattern until all of the required permits have been obtained, Clark said.
The team will begin by drilling a delineation well about two miles from the 2007 drill site, he said.
“We’ll be drilling a delineation well to somewhere in the neighborhood of 2,500 to 3,000 feet,” Clark said. “The purpose of that will be to define the lateral extent of the individual coal beds.”
That well depth is substantially more than the 1,613-foot depth of the 2007 well. The purpose of drilling a deeper hole is to look for more coal beds and learn more about the subsurface geology, Clark said.
The team also wants to drill deep to look for sand beds that might prove suitable for the re-injection of produced water — tests of water from the well in 2007 showed that water to be highly brackish and unsuitable for drinking.
The team will also collect 50 to 100 feet of core below a depth of about 1,250 feet in the delineation well. That core will include the primary coal seam that the team is interested in for coalbed methane production. After the coring the team will open-hole drill to the full depth of the well before running a suite of geophysical logs. The team will then plug and abandon the well, Clark said.
Coal samples from the coring will provide material to verify the gas desorption data from 2007.
Multi-well test arrayClark expects the drilling of the delineation well to take about a week to 10 days, after which drilling of the test wells will commence.
“We’re going to come back over to the area that we drilled last year and we’re going to install a multi-well test array and conduct a short production test,” Clark said. “We’ll have one production well set and several monitor wells and we’ll be pumping water and presumably gas … from the central production well.”
Although the team has considered drilling as many as five monitor wells, Clark expects that four wells will suffice. The drilling of those wells and the production well, together with the installation of equipment in the wells, will likely take a month or so. The team will then spend about two weeks doing coalbed methane production testing — the length of the testing program will depend on available time and money, Clark explained.
The testing will enable an assessment of how easily gas and water can flow through the coal and will measure the amount of water produced for a given amount of gas. The testing will also involve monitoring pressure changes in the coal during gas production.
Publish in the winterAfter completion of the testing program the team will analyze and evaluate the test data for eventual publication of the test results at some time in the winter. And, depending on those results, the team hopes to do a more extensive production test in the summer of 2009 — the team plans to leave its equipment at Wainwright over the winter in preparation for a 2009 program.
However, no funding has been committed for 2009 work yet, Clark said.
USGS, the Bureau of Land Management, the North Slope Borough, Arctic Slope Regional Corp. and Olgoonik Corp, are all involved in the 2008 program, with the North Slope Borough being the primary funding agency. Olgoonik is the village corporation for Wainwright.