Potential for deep geothermal energy in Scotland: study volume 2

1 Introduction

This report contains the British Geological Survey ( BGS) contribution to a collaborative project between AECOM and BGS to produce a qualitative assessment of deep geothermal energy potential in Scotland for the Scottish Government (Scottish Government Contract Ref. AEC/001/11) Study into the Potential for Deep Geothermal Energy in Scotland). BGS was asked to provide the Stage One deliverable "Identifying and assessing geothermal energy potential", comprising an assessment of areas in onshore Scotland most likely to hold deep geothermal resources based on existing geological and geothermal data sets. AECOM undertook the Stage 2 deliverable "Development of Key Policy Options" in which policy options and key actions are identified that the Scottish Government can potentially implement to encourage commercial exploitation of the available geothermal resource.

The geological assessment (Stage One) presented here is limited to onshore parts of Scotland and to depths exceeding 100 metres below ground surface (defined as 'deep' in the project brief). No new measured data have been obtained for the project; the assessment is based on secondary sources of information (published data and data held by BGS). Data from offshore wells have been used to inform the assessment of the onshore geothermal resource, but offshore geothermal energy potential has not been assessed. The objective of Stage One, and this report, is to provide the Scottish Government with a qualitative assessment of the deep geothermal resource in Scotland, with supporting maps and models. The meaning of geological and technical terms is explained where appropriate in the text, and a glossary is provided.

The specific objectives of Stage One were framed as three tasks in the project brief:

• Task 1 - Identify and map areas most suitable for further investigation of deep geothermal energy potential.
• Task 2 - Collate all available data on the surface and subsurface rocks into a three dimensional model of structure and thermal patterns through the top few kilometres of Scotland's continental crust.
• Task 3 - Predict areas most likely to hold deep geothermal resource, to target for more detailed investigation.

For Task 2, a 3D model of abandoned mine working in the Midland Valley of Scotland has been built. However, it has been concluded that building a complete 3D model of thermal patterns in Scotland's continental crust would not benefit this study (see introduction to Part 2).

The report is divided into two parts: Part 1 contains background information relating to geothermal energy (section 2) and the geology of Scotland (section 3), and a review of existing geothermal data for Scotland (section 4); Part 2 contains an assessment of geothermal energy potential in three categories of potential resource that were specified t in the project brief: mine water, Hot Sedimentary Aquifer ( HSA), and Hot Dry Rock ( HDR).

The geothermal energy potential in Scotland was first investigated in detail in the late 1970s and early 1980s as part of the project "Investigation of the geothermal potential of the UK", funded by the then Department of Energy, and the European Union. In Scotland, the project focused mainly on the HDR potential of granite intrusions in the East Grampians region. The approach and outcomes of the project are reviewed in more detail in section 8.2 of this report. The conclusions were generally discouraging from a Scottish perspective, and several decades passed subsequently with little interest in the subject and virtually no new research.

In recent years, the potential for exploiting 'deep' geothermal energy in Scotland has been the subject of renewed interest, perhaps most notably in the form of several online articles by Professor Ed Stephens of St Andrews University (A growing number of publications includes two recent reports by engineering consultants Sinclair Knight Merz; these reports contain reviews of the geothermal resource in Scotland (Sinclair Knight Merz, 2012a,b).