Despite the country having a proud coal heritage that goes back more than 160 years, the United Kingdom — unlike Australia and the United States that have well-developed coalbed methane (CBM) industries — has seen very little CBM activity. From 1900 to 1939 during the UK coal industry’s peak, it supplied all of the UK’s domestic energy needs and was the world’s largest source of exported coal.

Even into the early 1970s, the UK’s huge coal reserves supplied two-thirds of the country’s energy needs.

However, when North Sea oil started to flow in the 1970s and with the privatization of the UK coal industry in the mid ’90s, the importance of coal in the United Kingdom declined dramatically. Today in the United Kingdom there are a handful of deep and opencast mines operating in England and Wales, and only a few opencast mines operating in Scotland.

Because of the mining heritage and the needs of the Second World War, much is known

A rig sets up to evaluate methane content in Scotland’s unmineable coal beds. (Photo courtesy of Composite Energy)
about UK coals, and they are well-mapped, with logs existing from the early 1890s. UK coals are traditionally bituminous coal and anthracite, found in varying depths and ranging from a few centimeters to — in some cases — 16 ft (5 m) in thickness. UK coals generally have low permeability and a high sulfur content. Methane content has been a considerable problem over the life of coal mining, with companies have dealt with the dangers of methane in underground UK coal mines by employing various techniques for degasification and methane venting.

The United Kingdom’s remaining deep coal reserves are significant despite declining coal mining activity, and the most easily accessible coal reserves having been largely depleted. For CBM in particular, a 2002 UK government Department of Trade and Industry (DTI) funded study of all onshore coal deposits identified over 15,444 sq miles (40,000 sq km) of coal deposits of potential CBM-bearing quality. Mapping criteria was specific for underground coal 6.6-ft (2-m) thickness or greater, 1,969 to 3,937 ft (600 to 1,200 m) from the surface, with 328-ft (100-m) vertical separation from aquifers. These coals are contained in central and eastern England, South Wales and the Midland Valley of Scotland.

Interest in CBM is growing in the United Kingdom, not only because of the country’s coal heritage and CBM’s success in other parts of the world, but also because of the United Kingdom’s dwindling North Sea oil and gas reserves. The consensus is that North Sea oil and gas production reached its peak around 2001 and will move the United Kingdom to a net oil and gas importer this year. The aforementioned DTI study suggests that UK CBM has the potential to contribute around 29 years of natural gas consumption for the country, a significant contribution to the United Kingdom’s pressing need for a safe, secure and diverse energy mix.

Leading the CBM charge in the United Kingdom is Composite Energy, a privately-funded company working in partnership with BG Group and ScottishPower. The private firm is currently in the middle of a 12-well appraisal and development program. It owns a 500-sq-mile (1,295-sq-km) license in Scotland and is optimistic that it will be producing methane in early 2008. That methane will be fed directly into the gas distribution network of the United Kingdom.

Composite was founded on the belief that CBM trapped in deep coal seams can provide an untapped long-term source of indigenous United Kingdom gas. With many users in the area, this means that the methane will have a ready-made market in Scotland.

The coals being targeted — Namurian coals in the Kincardine Basin — are similar to those targeted in the United States by CBM producers. Found at depths of around 3,000 ft (915 m) and typically around 40 vertical ft (12 vertical m) in thickness, the coals have a high gas content, typically in the top-end range of 400 scf/ton. The production profile of Scottish CBM is expected to be similar to coals in New Mexico and Colorado that have a high water content and require significant de-watering to release the methane. The water in Composite’s coals is saline, essentially seawater with a high iron content. The result is expected to be a typical CBM bell curve production profile.

Thick, shallow coals that are easy wins for CBM companies are absent from the United Kingdom. Relatively deep wells are required to reach the coals, and a de-watering process is part of the production planning that also includes removing the iron. Close proximity to the sea means that re-injection of the water is not required. That can be an issue in an area with a significant fresh water table present.

In order to balance the high cost of deep wells and produce an economic return, Composite purchased its own drilling rigs, two Italian-made drilling units that are mounted on trucks. The rigs are ideally suited for initial quick vertical drilling and subsequent horizontal drilling. Since coals in the area have a low permeability and thin coal seams, horizontal drilling is ideally suited to access the coal seams — some of which can be as little as 2 ft (0.6 m) thick. The company has its own experienced drilling team that is able to steer the bore hole to optimize methane recovery from horizontal completion.

A horizontal drilling approach means that fewer wells are needed and the company can be flexible in its choice of surface location. Since it is drilling in a relatively populated area, a priority is minimal disturbance to the residents and agriculture. That encourages the company to choose drilling locations where it can exploit the natural features of the landscape to minimize the visibility of drilling and production facilities.

Composite has two pilot development programs currently under way, each consisting of six wells drilled in clusters. One of the programs is drilling on the location of a major power generation plant in the area. The company expects to produce methane from the other area in late 2007. In March 2007, it announced a project to evaluate the potential for enhancing methane recovery through the injection and subsequent storage of CO2 in coal. Co-funded by BG Group, ScottishPower and Royal Bank of Scotland, the project will involve assessing the gas adsorption and desorption properties and the mechanical properties of the coal. The 2-year program will focus on evaluating the direct injection of flue-gas into unmineable coal seams in the central belt of Scotland.

Where other CO2 storage projects store the gas in an underground void or rock-matrix, this project will evaluate the ability of CO2 to chemically bond to coal. In other coal-related CO2 projects, pure CO2 injection tended to swell the coal and reduce overall injectivity. Composite hopes to get around that drawback by focusing on flue-gas injection typically made up mostly of nitrogen. We are testing the idea that the nitrogen will maintain the injectivity of the coal, allowing the CO2 to bond to the coal much deeper into the seam.

Coal can typically adsorb five times more CO2 than the methane it releases, and Composite is hopeful that its CO2 project will be a local solution for reducing greenhouse gases as well as incorporating a new economic model to its methane recovery business. Since the company’s lease in Scotland is one of the most attractive deep coal-bearing areas in the country, the company is optimistic that this project will present a significant CO2 storage opportunity.

With massive remaining deep coal reserves and growing interest in the CBM opportunities, the UK coal industry is on the verge of a rebirth as a new source of clean energy and as a storage location for harmful emissions. Coal, the once valuable energy source which became known as a dirty source of energy, is now poised to supply clean energy and pollution solutions.