Underground Coal Gasification in the UK

1. Summary

The United Kingdom is well placed within Europe in having large reserves of indigenous coal both onshore and offshore in the southern North Sea. These reserves have the potential to provide security of future energy supplies long after oil and natural gas are exhausted.

Traditional mining methods however are not suited to working offshore reserves, and development and infrastructure costs of new mines can render the exploitation of landward reserves uneconomical. Underground coal gasification (UCG) has the potential to provide a clean and convenient source of energy from coal seams where traditional mining methods are either impossible or uneconomical.

Underground Coal Gasification is a method of converting unworked coal, deep underground, into a combustible gas, which can be used for industrial heating, power generation or the manufacture of hydrogen, synthetic natural gas or other chemicals. The gas can be processed to remove the CO₂ before it is passed on to end users, thereby providing a source of clean energy with minimal green house gas emissions.

Government policy is to encourage the development of cleaner coal technologies for application both at home and in overseas markets. The potential for UCG in the UK relates not only to reducing environmental emissions but also to ensuring security of energy supply and maintaining an acceptable level of diversity of energy supply.

A recent EU trial sponsored in part by DTI has demonstrated the feasibility of UCG at depths typical of European coal. The DTI has concluded that the UCG process has potential for UK coal reserves, particularly when considered against the massive offshore coal resource, which may be amenable to UCG.

Technology targets for UCG have been set in DTI Energy Paper 67 and a programme of studies, culminating in a UK trial, are currently underway with industry to critically assess the commercial feasibility of UCG. The technology, if successful, has export potential to countries such as China and India where coal reserves considerably exceed oil and gas reserves.

2. Introduction

The concept of gasifying coal underground and bringing the energy to the surface as a gas for subsequent use in heating or power generation has considerable attraction.

UCG is the partial in-situ combustion of a coal seam to produce a gas for use as an energy source. It is achieved by drilling two boreholes from the surface, one to supply oxygen and water/steam, the other to bring the product gas to the surface. The gas can be used for industrial heating, combustion in gas turbines for power generation, or for the manufacture of hydrogen, synthetic natural gas or other chemicals.

The benefits of UCG are the absence of waste tips and ash at the surface, the elimination of surface plant for gasification and coal preparation, and the availability of the energy as a clean fuel gas. Furthermore it provides access to the large-scale UK coal deposits, which would otherwise not be exploited. This could include the substantial coal resources under the North Sea.

The basic feasibility of UCG has been proven in previous trials. Further detailed studies are required to prove the technology of precision drilling process control over sustained periods of operation and to fully evaluate any possible environmental impact on underground aquifers and adjacent strata. One of the practical problems of UCG is that meaningful experiments cannot be carried out in the laboratory, and trials must be undertaken at pilot scale, which is both costly and time consuming.

The current DTI programme is aimed at addressing the uncertainties by field trial and attracting industry investment in a potentially promising new technology. The extraction of energy from the vast UK coal resources could reduce the UK’s future dependence on imported fuels and may also help the UK to retain its current position as a net exporter of energy.

3. Development of UCG to date

UCG is conceptually very simple but the development of a working system has proved more difficult in practice. The main problems are drilling the boreholes, controlling the reaction within the seam and producing a gas of a consistent and high quality.

The gasification of coal seams in situ was first developed in the former Soviet Union during the 1930’s and commercial-scale schemes have been operating since the Second World War; one project in Uzbekistan is still operating today. The same technology and technicians from Uzbekistan are currently operating a small trial scheme in Australia.

In the 1950’s, Britain embarked on its own long-term trial in shallow coal seams at Newman Spinney, Derbyshire, and although gasification was successful, the National Coal Board later abandoned the project for economic reasons.

US trials in the 1970’s proved the value of new technology from the oil and gas industry to control the process. These were followed up in Europe by studies¹, which concluded that the process was technically feasible in the thinner and deeper coal seams of Western Europe. This study led to the European trial of UCG in deep seams, which took place in Spain between 1992 and 1999. The DTI was a part sponsor, alongside the EC and Spanish and Belgium organisations.

The European trial was the first to use in-seam directional drilling at depth to construct the production well and the trial demonstrated² that UCG wells in deep seams could be successfully constructed. The encouraging results of the European trial led the DTI to re-evaluate UCG as a longer-term option for clean coal exploitation in the UK, as described below.

UCG is of growing interest in the largest coal producing countries, such as China and Australia, where new trials and supporting studies are underway. The prospect of international collaboration is growing, and a successful demonstration of the technologies in the UK could offer interesting export opportunities.

4. UCG and the DTI Clean Coal R&D Programme

The DTI review of cleaner coal technology, published as Energy Paper 67 in June 1999 examined the potential of UCG and other technologies like coal bed methane in the UK. While these technologies are far from being considered commercial alternatives to conventional mining, and substantial R&D effort is required, it is accepted that further work on cleaner coal power generation technologies is a priority task.

During the consultation exercise a number of consultees suggested that UCG could offer an alternative way to obtain the energy from coal without mining and would also provide access to the large-scale UK coal resources inaccessible by conventional mining - including the substantial resources under the southern North Sea.

For this reason, and with regard to the total project cost of the order of £15-20 million, it was judged that the UK alone could undertake the next stage of a sub-commercial programme. This would be more expeditious than seeking European partners. If however the tests were successful, partners would be sought for a full-scale semi-commercial UCG trial.

Energy Paper 67 identifies a series of technology targets for UCG that would need to be addressed over the next six years. These are:

• Improve the accuracy of in-seam drilling
• Examine the implications of burning UCG gas in gas turbines
• Estimate landward coal reserves for UCG
• Identify a semi-commercial site
• Establish cost parameters for the process to be competitive
• Carry out a pre-feasibility study of offshore exploitation of UCG

The aim is to achieve these goals, in association with industry, over the next six years.

A further objective of the development programme would be to consider how the licensing of future UCG operations would be facilitated within the existing licensing regime and to recommend and implement any changes that may be required.

5. Current UCG programme

The overall objective of the current programme is to demonstrate the technical feasibility of UCG in typical UK coal seams and to establish the economic and commercial conditions under which it will be competitively viable.

A key part of the study is to evaluate directional drilling, which offers the possibility of cost effective and reliable in-seam well construction. This data on directional drilling may also have application to enhanced coal bed methane (ECBM) and CO₂ sequestration.

The programme of work is on the broad principles of four phases:

• Phase 1 Identify possible UK trial sites, outline a demonstration programme and review the environmental, utilisation and drilling technologies.
• Phase 2 Design the drilling programme in detail, address the regulatory and planning issues and undertake paper studies into the environmental, process and economic issues of the UCG as an exploitation technology.
• Phase 3 Undertake the drilling test programme to explore the geology of the chosen site, test directional drilling equipment and strategies, and construct the trial wells.
• Phase 4 Perform the UCG trials and provide a critical assessment of the commercial feasibility.

As part of the programme to develop cleaner coal technology, the Coal Authority became involved in research into UCG and it was the Authority who initiated Phase 1 of the UCG programme. However, the Authority was unable to progress beyond Phase 1 because of restrictions of its powers under the 1994 Coal Industry Act. As an interim measure the work was transferred to ETSU to allow the programme to continue, but it is desirable that the Authority should be the body which undertakes the work because of the long term nature of the work and the standing of the Authority to undertake such innovative work. Accordingly, action is being taken to give powers to the Authority to allow it to resume responsibility for the UCG programme which, with relatively modest revisions to the Act, could be introduced by a Private Members Handout Bill.

The Authority determined that it was not within its remit to continue with the project.

6. Selection of a UK site

The site should be able to accommodate three different trials, namely:

• A directional drilling trial to prove the accuracy and control of in-seam drilling.
• A sustained single channel gasification trial to monitor cavity development in long in-seam channels.
• A semi-commercial project to produce power in association with operators and industry.

The target is bituminous or sub-bituminous coal in seams of at least 2m thickness and at depths between 600 and 1200 m. Active mining license areas are being avoided and the site should be some distance from any abandoned mineral workings.

The initial search is aimed at identifying at least two sites that are large enough to incorporate all the trials as the project develops. Such a site will require an overall coal reserve of about 4 million tonnes contained within a surface area of 100 hectares. However, sites that can accommodate only the drilling and gasification trials are not being discounted in the initial search.

Contracts have been placed with major UK consultants to undertake a UK wide search for a suitable UCG trial site. They will examine the geological setting, coal requirements, the presence of water aquifers and surface land requirements. Planning issues will be investigated in detail.

The Consultants have been provided with an initial list of possible sites and are required to make their own proposals for alternative sites. Ten coalfield areas have been identified and the aim is to identify a short list of suitable sites by summer 2001. These will then be subject to more detailed investigation, including possible borehole and site investigation.

7. Overall Project Plan

The key stages of the overall plan are:

• To complete the site search and on-site investigation, and identify one preferred site and at least one back-up site.
• To make planning applications, and environmental assessments for the selected sites.
• To undertake key studies to:
  • Investigate the environmental issues of UCG.
  • Establish the likely UK resources that are available for UCG, both onshore and in the UK territorial waters.
  • Identify worldwide capabilities in directional drilling.

• To invite suitably qualified Consultants (through EOI’s in the European Journal) to manage the drilling and gasification programme.
• To examine how CO₂ can be economically removed from the product gas.
• To undertake the economic/cost studies and technical appraisals identified in Energy Paper 67.
• To search for possible industrial participants and overseas collaborators for the semi-commercial gasification project.

The aim is to complete the UK trial within the six-year target and to progressively engage the support and involvement of industry as the trial develops. The trial and associated paper studies will place Government and UK Industry in a position to critically assess the commercial feasibility of UCG as a method of clean coal exploitation.

There are signs that current issues relating to green house emissions and global price increases in gas are generating higher levels of interest in UCG. Continued progress in the UK programme will leave the UK well placed to meet the potential demand for this technology in the coming years.

1  The Future Development of UCG, Comprehensive Report to CEC by the European Working Group Report on UCG, April 1989

2  Underground Coal Gasification – A Joint European Field Trial in Spain DTI Project Summary 017, March 1999

Comments relating to this briefing paper should be sent to markarmitage@coal.gov.uk