Carbon Intensity of Deep Geothermal Heat in Scotland. Scottish University Policy Briefing: May 2020

No abstract available

Carbon Intensity of Deep Geothermal Heat in Scotland. Scottish University Policy Briefing: May 2020

No abstract available

Life cycle assessment of the carbon intensity of deep geothermal heat systems : a case study from Scotland

Deep geothermal energy is widely recognised as a source of low carbon heat. However, to date there have been no specific assessment of the carbon intensity of low-enthalpy deep geothermal; previous studies focussed on geothermal power or higher enthalpy heat. As such, there is no established method for assessing the CO2 emissions from implementing a deep geothermal heating scheme. Here we address these gaps. We perform a life cycle assessment of greenhouse gas emissions relating to a deep geothermal heat system to (i) calculate the carbon intensity of geothermal heat; (ii) identify key factors affecting these values; (iii) consider the carbon abated if geothermal heat substitutes conventional heating; and (iv) present information that future projects can apply to assess the carbon emissions reduction offered by geothermal heat development. Our work is informed by parameters from a feasibility study for a proposed geothermal heat system in Banchory, Scotland. The project planned a 2.5 MWth geothermal plant extracting heat from the Hill of Fare granite via two boreholes, one injection and one production. We find that the majority of the emissions are associated with site construction, and sensitive to site and materials specific factors, for example the depth of the drilled boreholes and type and quantities of steel and cement used to seal them, or soils disturbed for laying pipelines and constructing access roads. During operation the carbon intensity of the electricity grid used to power hydraulic pumps largely determines the carbon intensity of the produced heat. We calculate that the carbon intensity of the heat produced is 9.7–14.0 kg(CO2e) MWhth which is 4.9–7.3% of the emissions from heat from natural gas. These values are compatible with Scotland's plans for long term decarbonisation of heat in line with national emission reduction obligations and would likely be compatible with any country's decarbonisation goals

Renewing the Exploration Approach for Mid-Enthalpy Systems: Examples from Northern England and Scotland

After a promising start in the 1970s and 80s, the UK rather fell behind other countries in the search for viable mid-enthalpy geothermal resources. This situation began to turn around in 2004, when the first of three deep geothermal exploration boreholes were drilled in northern England. What distinguished these from earlier drilling in Cornwall was the deliberate search for naturallyhigh permeability associated with major faults, especially those that have undergone strike-slip reactivation during the Cenozoic. Boreholes at Eastgate in the North Pennines targeted buried radiothermal granite, whereas the 1,821m-deep Science Central Borehole in Newcastle upon Tyne targeted a postulated deep sedimentary aquifer (the Fell Sandstones), which were inferred to be connected laterally to the granitic heat source by a major fault (the reactivation of the Iapetus geo-suture). The drilling was in both cases rewarded with impressive heat flows, and in the case of Eastgate with what is believed to be the highest permeability yet found in a deep granite batholith anywhere in the world. In parallel with these developments, a re-assessment was made of the preexisting geothermal heat flow database for the UK, applying newly-standardised correction protocols for palaeoclimatic and topographic distortions, which were found to be particularly marked in Scotland (where only shallow boreholes had been used to establish geothermal gradients in the original 1980s analysis), Similar prospects in northern England (similar to that drilled at Science Central) are now the focus of commercial exploration efforts. Appraisal of fault dispositions relative to the present-day maximum compressive stress azimuth are being used to identify the most promising areas for intersecting fault-related permeability at depth. New geophysical tools – most notably atomic dielectric resonance scanning – are also being appraised for their ability to directly detect features (such as hot brines) which are indicative of localised convection in target fault zones and aquifers

Shiremoor geothermal heat project: reducing uncertainty around fault geometry and permeability using Move™ for structural model building and stress analysis

Structural model building software, Midland Valley’s MoveTM, was used to reduce uncertainty around fault geometry and analyse the likelihood of encountering fault-driven enhanced permeability for a proposed geothermal heat production borehole in Shiremoor, UK.<p></p> Stress analysis was used to predict dilatant or compressional damage zones, and to assess likely permeability, under the present day stress regime. Before assessing whether a particular fault will have increased or decreased permeability, it was first necessary to build a structurally valid, constrained fault framework. Two seismic lines from the project area show evidence of faulting and deformation of horizons. After a simple depth conversion was applied, assuming average velocities for known lithologies, interpretation of the two lines, with additional information from the geological reports, maps and borehole data nearby allowed the construction of a first pass 3D valid structural model of the site using MoveTM software.<p></p> All geological models constructed by Midland Valley use structural geology principles (such as bed length or area balance) and known geometric relationships between faults and folds to build structurally valid models. This valid geological model was analysed to give insights as to the type of material that might be entrained in the fault cores, the amount of displacement on individual faults and hence potential damage zone sizes and critically the geometry and relationship to key horizons of the fault framework. Stress analysis of the linkage of faults was used to highlight potential areas of either compressional or dilatant damage zones and hence the predicted impact on fault permeability.<p></p&gt