Background

Coal mines are a legacy of Wales’ mining past, however where suitable they may now offer a potential source of heat to support the development of new mine water heat networks. Welsh Government commissioned the Coal Authority to produce a ‘mine water heat opportunity map’ for Wales which is designed to provide information to local authorities or developers as to where mine water heat schemes could be considered.

Methodology

All the recorded coal workings in Wales have been assessed for potential borehole-based mine water heat schemes. These areas have been designated to indicate where possible mine water heat schemes, using purpose drilled boreholes to access the workings, could be investigated further.

The opportunity maps consider many different factors which are assessed by technical experts. Factors considered include:

• Underground working depths
• Known mine water levels
• Mine water level recovery status
• Evidence of opencast mine workings

There are three levels of opportunities for mine water heat developments: “Good”, “Possible” and “Challenging”. In addition there is a ‘point source’ map illustrating locations where known mine water discharges could offer potential for heating schemes.

Mine Water Heat Opportunity Categories

Good Opportunities

These areas represent where there appear to be ideal conditions for a mine water heat scheme to take place, with fewer challenges. All the following criteria will be met, in order to classify an area as “Good”. However, these areas still require a site-specific assessment to determine local water levels, condition of the workings, and feasibility of developing a scheme.

• Multiple recorded underground coal mine workings overlap each other, and;
• Workings are flooded, and;
• Workings between 30 m and 300 m below ground level, and;
• Water level estimated to be less than 75 m below ground level, and;
• Water levels have recovered or are recovering.

Possible Opportunities

These areas represent where there appear to be challenges for developing mine water heat. If any of the conditions below are met, the area is to have “Possible” opportunities for mine water heat. These areas will need a thorough investigation, and may represent a good or poor opportunity in the future.

• Workings are overlapping, and;
• Workings are flooded, and;
• Workings are near to or shallower than 500 m below ground level, or;
• Water levels are between 75 and 100 m below ground level, either recovering or recovered, or;
• Water levels are deeper than 100 m below ground level, but recovering, or;
• There is evidence of open cast coal mine workings, with the possibility of underground workings beneath intact.

Challenging Opportunities

These areas represent where conditions do not appear favourable for developing a mine water heat scheme, and may not improve in the future. If any one of these criteria are met, the area is classified as “challenging”. It is not that a scheme could not be successful here, but that there would be a number of challenging barriers to overcome versus other opportunity areas for mine water heat.

• Workings may not be flooded, or;
• Workings are less than 30 m below ground level only, or;
• Workings are more than 500 m below ground level with no shallower targets, or;
• Water levels deeper than 100 m below ground level, and are recovered, or;
• There are known issues with mine gas, or;
• There is evidence of opencast workings where underground workings may have been completely removed, or;
• There is a single seam, which is fully flooded, and not impacted by opencast workings.

Single seam opportunities have been included as “challenging”, and would require a thorough appraisal to determine whether the nature of the workings would support a scheme. Having a borehole based scheme into a single seam can result in rapid “short circuiting” of a heat scheme, as colder spent water can rapidly move to the abstraction well after reinjection.