U.K. pushes novel coalbed methane project

Vented coalbed methane extraction plant [80,502 bytes] Recovering vented coalbed methane [111,569 bytes] A small U.K. company has found a novel solution to developing coalbed methane projects economically at a time of low natural gas prices. Coalgas (U.K.) Ltd. of Mansfield, U.K., plans to pump gas from poorly sealed vents in abandoned mines, rather than drill into coal seams and dewater the coal, as is done in conventional coalbed methane projects.

June 29, 1998

5 min read

A small U.K. company has found a novel solution to developing coalbed methane projects economically at a time of low natural gas prices.

Coalgas (U.K.) Ltd. of Mansfield, U.K., plans to pump gas from poorly sealed vents in abandoned mines, rather than drill into coal seams and dewater the coal, as is done in conventional coalbed methane projects.

Cameron Davies, managing director of Coalgas, told OGJ it would not be worthwhile to drill wells that would typically produce 300-400 cfd of coalbed gas when natural gas costs less than $1.60/MMBTU.

"Instead," said Davies, "we decided to reperforate coal measures without having to drill. We discovered that lots of old mine shafts, which were capped with concrete and fitted with vent pipes, are pouring out gas."

These vent pipes emit gas or suck in air, depending on atmospheric pressure. Coalgas reckons they can flow more than 1 MMcfd of coalbed gas by installation of a relatively small pump.

Coalgas worked out which shut-in coal fields had vent pipes, as opposed to completely sealed shafts, and applied for licenses in those areas under U.K.'s eighth onshore licensing round (OGJ, Mar. 30, 1998, p. 37).

"To make sure we got the PEDL01 license covering the Mansfield area," said Davies, "I rushed down on the morning of the opening of the licensing round and was first in the queue."

Through the eighth round and purchase of other companies' licenses, Coalgas now has 12 licenses covering more than 2,800 sq km in total. They are in former coal fields in the East Midlands, Yorkshire, South Wales, Lancashire, Cheshire, the Liverpool area, and Kent.

During 1947-95, state firm British Coal Corp. held the monopoly on U.K. coal production. Coalbed methane projects only became possible when the U.K. decreed in 1995 that coalbed gas belonged to the government and not to British Coal. Since then, the government has offered coalbed gas exploration licenses separately.

New production method

British Coal normally sealed mine shafts completely, but Coalgas reckons that 1 in 10-20 has an open shaft into the coal measures, capped with concrete and a vent pipe.

"There are six or seven such vent pipes in the Mansfield license area," said Davies, "which covers roughly 290 sq km. We are doing an inventory of our acreage to discover how many vent shafts we have."

Davies said that mining in the area typically recovered 20-25% of the coal reserves. The remainder contains trapped gas, which seeps into the mine's roads and shafts from measures above and below the worked seams.

This seepage is aided by the great amount of fracturing of coal measures by early mining, and by overlapping of mined areas and subsidence in many coal fields, where only a few out of sometimes 25-30 seams were mined.

The gas-to-coal ratio varies greatly in coal fields, with the Mansfield area reckoned to have 5 cu m/metric ton. Davies said Coalgas expects to recover 10-12% of gas in place.

Estimating reserves is the key question, said Davies. Although Coalgas has not completed estimates for its licenses, Davies said a simple volumetric calculation on a typical block offered in the licensing round showed it had 500 bcf of gas in place, or reserves of roughly 50 bcf of gas.

Coalgas has approval to generate up to 15 MW of electric power from three sites in the Mansfield license area: 3 MW at the Steetley mine; 9 MW at the Shirebrook colliery; and 3 MW at Markham.

At each of these sites, initially a single vent will be fitted with a pump taking gas straight to a small generating plant, which will deliver electric power either to local customers or to the national grid.

Coalgas carried out a test at the Steetley colliery, in which 1 MMcfd of gas was pumped out over 36 days with two 17-kw pumps of a type used for landfill power projects. Produced gas was sent to a flare stack during testing.

"This technique will give much better economics than typical coalbed methane drilling," said Davies. "For a start, we won't have any delays for drilling and dewatering of the wells.

"The average production in the U.S. for coalbed methane wells is 300 cfd. Here we should be able to produce ten times this from one vent shaft, and 2-3 MMcfd of gas can be used to generate about 6 MW of electric power."

Coalgas is working to bring Steetley into operation in January 1999 and Markham in March or April that year. Site investigation work has been completed, and Coalgas is marketing the power to local industry and the regional electric utility.

Davies said the next phase of work will be a full inventory of potential vent shaft power generation sites across its U.K. licenses. The company believes at least 20 suitable vent sites will be available for development.

Further down the line, Coalgas will look to identify sites where a well could be drilled to produce gas right on a customer's doorstep. In the meantime, the first three projects will help the company standardize development techniques as a way of reducing costs further.