Guardbridge geothermal technology demonstrator project: feasibility report
Report of the study exploring the potential of a geothermal district heating system accessing hot sedimentary aquifer resources underlying Guardbridge, Fife.
2. Methodology
2.1 Overview of methods
In the following sections of this report, each of the key components of our feasibility study are presented. The 3D geological model and rock characteristics are presented first and form the baseline data for the geothermal well design. Different well options are investigated based on the underlying geology, the rock characteristics, and estimated flow rates and water temperatures. The well performance scenarios are integrated into a district heating network design, and an economic model has been constructed that includes the heat demands for current and future scenarios and the capital, operation and maintenance costs of exploration, production and heat network development. Finally, the legislative and environmental issues arising from any HSA geothermal heat project are investigated with input from the relevant regulatory bodies, and recommendations for Phase 2 of the project to develop on-site heat and storage systems at the Guardbridge site are presented.
2.1.1 Geological models
A regional-scale 3D geological model was developed by the University of St Andrews and the British Geological Survey using the 1:100,000 - 1:250,000 British Geological Survey digital maps, geological data from all the surrounding boreholes, and previously constructed geological cross-sections. One aspect of the geological modelling involved choosing an orientation for the Dura Den Fault which is located to the south of the Guardbridge site, and modelling the amount of offset and horizontal extent of the fault zone. This involved incorporating previous published work, including a PhD thesis. All data was compiled in Midland Valley Move TM software and the depths to the relevant sedimentary units, their orientation and thickness, and the behaviour of the Dura Den Fault are presented as a number of cross-sections ( Section 3.1).
Simple 2D and 3D hydrogeological models have been constructed which incorporate rock characteristics described below and test flow rate scenarios for the sedimentary aquifers ( Section 3.4). The modelling is limited by the lack of necessary data, namely adequate detail on the geological units, aquifer recharge, source of water, and influence of the saline wedge from the Eden Estuary. The modelling is performed in FEFLOW ®, a finite element fluid flow model and was performed by the British Geological Survey and the University of St Andrews.
2.1.2 Geothermal well design and regional impacts
The geological model provides estimates of the thicknesses and depths of the sedimentary units for both sides of the Dura Den Fault. In order to characterise the sedimentary rock characteristics for the units, such as porosity and permeability, a combination of wireline datasets from onshore oil and gas wells, and published hydrogeological data, were used (compiled by Town Rock Energy Ltd and the University of St Andrews). The necessary and sufficient data do not as yet exist for the sedimentary aquifers below Guardbridge, and this is one of the limiting aspects of this (and any) geothermal study. However, the wireline data is representative of rocks with similar properties and provides estimates for the rock characteristics at depths relevant to this study (up to 2500 m depth).
Each sedimentary unit is given a porosity, permeability and thickness, with appropriate levels of uncertainty ( Section 3.3). The final aspect of the geological investigation is to define the change in temperature with depth, called the geothermal gradient. The study updates the geothermal gradient of Gillespie et al. (2013) to calculate temperatures at depth.
Well design was undertaken by Town Rock Energy Ltd and utilises the geological model, rock characteristics and geothermal gradient estimates. Four well scenarios were proposed (two on the Guardbridge site and one off-site) and different pumping technologies were investigated. Well performance is estimated based on a range of possible flow rates and water temperatures at the surface, and costs associated with drilling and production are calculated ( Section 3.3).
A regional approach to de-risking geothermal exploration has been developed by Town Rock Energy Ltd which utilises an approach standard in the oil and gas industry ( Section 3.5), and is generally applicable to the Central Belt of Scotland. The regional impact of the well design results are outlined in Section 3.6.
The well design and drilling strategies were fully costed to well production stage ( Section 4). Based on the initial productivity predictions, it was possible to eliminate three of the well scenarios and focus the final economic model on one well scenario.
2.1.3 District heating network design and economic model
The aim of this part of the study was to prepare preliminary district heating network layouts at different scales, based on the demand analysis and the Scottish Heat Map ( www.gov.scot/heatmap), and was conducted by Ramboll Energy ( Sections 5 - 6). The various options provide an indication of the potential annual and peak heating demands that can then be compared against the geothermal heat potential estimated for the geothermal well design. An economic modelling tool was developed to analyse the performance of the overall system, to incorporate all costs associated with the network construction, operational costs of the well on completion, and includes key performance indicators to evaluate the financial viability ( Sections 7 - 0).
2.1.4 Environmental impacts and regulatory requirements
The Guardbridge site is adjacent to the nationally important Eden Estuary, which is a Site of Scientific Interest and a Local Nature reserve. It is also part of the Firth of Tay and Eden Estuary Special Area of Conservation. Gavin Johnson (Operations Officer for Fife SNH) has been made aware of the project and provided an outline of the issues and regulatory requirements. An existing set of Environmental Statements, approved by Fife Council in 2014, document the identified impacts on air quality, noise levels, water resources, landscape, ecology and nature conservation arising from the ongoing construction and development at Guardbridge and these were reviewed for this report, along with the Regulatory Guidance:Geothermal Heat in Scotland publication by DECC (2016). Guidance was also sought from SEPA (Steve Archibald, Glenrothes office) on abstraction and disposal regulations and the Water Environment (Controlled Activities) Regulations (2011) was reviewed to outline the levels of authorisation that will be required.
2.1.5 Stakeholder Engagement
The University has been involved with community engagement over a protracted period of years due to the developments at the former Guardbridge Paper Mill. This communication has increased over the last 12 months due to acceleration of on-site demolition and construction, and the closure of sections of the road between the site and St Andrews as the pipes connecting the biomass plant to St Andrews are Leuchars and the A91 are put in place. The University has incuded discussions about the potential for a geothermal well into these discussions, involving Councillor Brett and members of the Community Council.
2.2 Role of consortia partners
The University of St Andrews was Lead Partner in this feasibility study. The British Geological Survey and the University of St Andrews developed all the geological and hydrogeological models. Town Rock Energy Ltd, with the University of St Andrews, developed all the well Statement of Requirements and Town Rock Energy developed the well options and drilling strategies, and the costings associated with well exploration, production, operation and maintenance. Ramboll Energy evaluated the heat demand, designed the district heat network and built an economic model for the project. Resource Efficient Solutions had responsibility for project management, and the University of St Andrews, with Iain Todd Consulting, coordinated the stakeholder engagement. The University of St Andrews investigated the legislative and environmental issues and had responsbility for the compilation of the final report.
2.3 Data sources and key documents
| Datasets |
Sources |
|---|---|
| Ordnance Survey Maps |
Digimap through Academic License with EDINA. 1:10,000 Scale Colour Raster [GeoTIFF geospatial data], Scale 1:10,000, Tile(s): no41ne; no41nw; no42se; no42sw; no51nw; no52nw. Updated: March 2013, Ordnance Survey, Using: EDINA Digimap Ordnance Survey Service, http://digimap.edina.ac.uk, Downloaded: March 2013. |
| Digital Terrain Models |
Digimap through Academic License with EDINA. OS Terrain 5 DTM [ASC geospatial data], Scale 1:10,000, Tile(s): no41ne; no41nw; no42se; no42sw; no51nw; no52nw. Updated: March 2015, Ordnance Survey, Using: EDINA Digimap Ordnance Survey Service, http://digimap.edina.ac.uk, Downloaded: June 2015 |
| British Geological Survey digital maps and cross-sections |
1:100,000 to 1:250,000 NO41 and NO49 tiles. Reproduced with the permission of the British Geological Survey © NERC. All rights Reserved. |
| Scottish Natural Heritage shapefiles for protected areas |
Public sector information licensed under the Open Government Licence v3.0. |
| Wireline data |
Inch of Ferryton #1; Firth of Forth #1; Milton of Balgonie #1, #2, #3; Thornton #1; Cousland #6; Carrington #1; Midlothian #1; Stewart #1; Data analysed by Town Rock Energy and underlying analyses are not presented here. |
| Heat map demand |
Scotland Heat Map Local Development Plan http://www.fifedirect.org.uk/fifeplan FIFEplan Fife Local Development Plan Proposed Plan Pre-examination Editing - June 2015) Guardbridge Energy Centre Master Plan (revised January 2016) and input from Guardbridge Director (Ian McGrath) |
Key Documents
Regulatory Guidance: Geothermal Heat in Scotland (2016)
Scottish Government (DECC) http://www.gov.scot/Topics/Business-Industry/Energy/Energy-sources/19185/GeothermalEnergy/RegulatoryGuidance
AECOM (2014) Study into the Potential for Deep Geothermal Energy in Scotland: Volume 1 & 2
Volume 1 http://www.gov.scot/Resource/0043/00437977.pdf
Volume 2 http://www.gov.scot/Resource/0043/00437996.pdf
Supporting Guidance (WAT-SG-62) Groundwater Abstractions - Geothermal Energy
https://www.sepa.org.uk/media/143949/watsg62_groundwater_abstractions_geothermal_energy.pdf
The Water Environment (Controlled Activities) Scotland) Regulations 2011 (as amended)
http://www.sepa.org.uk/regulations/water/
Conservation (Natural Habitats, &c.) Regulations 1994, as amended - guidance
Natura sites and the Habitats Regulations - How to consider proposals affecting Special Areas of Conservation and Special Protection Areas in Scotland
2.4 Assumptions and limitations
The conclusions and recommendations arising from this report are based on assumptions outlined below and are limited by the considerable uncertainty regarding the quality of the geothermal resource. All estimates assume that the HSA behaves in a similar way to rock intervals that are within the eastern Midland Valley and have been analysed using wireline data; those rocks have been drilled at depths similar to the position of the aquifers beneath Guardbridge. The behaviour of the fault adjacent to the site is critical and could either be a conduit or an inhibitor of flow. These aspects of rock characteristics and potential flow rates, which control the geothermal heat potential, are the largest unknowns in this study. Temperature at depth is also not tightly constrained, but since geothermal gradients for the onshore sub-surface are known from bottom hole temperatures, the uncertainty on this is smaller (± 3-4 oC /km). It is impossible to constrain these parameters better without drilling to reasonable depths (500 - 1000 m).
The Scotland Heat Map has been used to calculate heat demand, and most of the uncertainties in these estimates arise from the scale of future expansion of the network within the towns around Guardbridge and within the site itself. If new housing projects are of a larger scale than modelled in this report, our residential heat demand estimates are too low. The data used to finalise the heat demand estimates for the Guardbridge Energy Centre are based on an up-to-date version of the Guardbridge Energy Centre master plans (revised January 2016).
The economic viability is based on heat sale price and and biomass heat sale cost, and it is possible that these will change. All price estimates for CAPEX, OPEX and REPEX are subject to inflation and although inflation of costs has been accounted for in the network development costings, prices quoted from December 2015 to January 2016 may be subject to change as the project develops.
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