Geothermal energy from deep carbonate rock aquifers

Overview

The UK is committed to transition to a low-carbon economy requiring significant reduction of greenhouse gas emissions to net zero by 2050. In nearly all scenarios emission reductions are characterized not only by energy demand reductions, but also the decarbonization of electricity and new energy systems. Geothermal energy has considerable potential to decarbonise heating, deep geothermal systems (>100m depth) can provide up to 300 Exajoules of heat – sufficient to deliver a minimum 100 years of heating to the entire UK [1].

The development of geothermal energy systems has not been widespread and has in part been hindered by the high capital costs associated with drilling deep wells. Reducing the exploration risk is vital to lowering the entry barrier for investment in geothermal energy. One very promising geothermal play is the Lower Carboniferous (Dinantian) Limestone (LCL), which has potential for supporting large-scale geothermal (heating) developments in several UK regions [2].

Pore space connectivity within the subsurface is a key control on achievable water flow rates (yields) from geothermal reservoirs and hence on geothermal prospectivity [3]. In carbonate rocks, residual primary porosity and intergranular hydraulic conductivity are generally very low, and permeability is created by secondary processes (karstification, dolomitisation, faulting/ fracturing). These processes are controlled by the depositional, diagenetic (burial and uplift), structural history of, and the evolution of pore-fluid chemistry within, these carbonate rocks,

By combing outcrop studies, data from onshore exploration wells and experimental work, this project aims to come to a process-based understanding of interactions between fluid flow and water-rock interaction to assess rates and distributions of dissolution under geothermal reservoir conditions. This project has the prospect to reduce geological uncertainties of geothermal carbonate reservoirs through enhanced understanding of how different permeability elements (e.g. karstification, dolomitisation, fault/fracture networks) control fluid flow within the buried limestone over relevant length scales. Outcomes have direct application to reducing risks in geothermal prospects and can be applied to CO2 storage in carbonate reservoirs and cap-rock integrity of carbonate rocks.

Methodology

Data evaluation of existing geothermal schemes that utilise carbonate aquifers. Focussing on the Carboniferous Limestone which has been successfully developed as a source for low carbon district heating in the Netherlands and Belgium [4].

Characterisation of enhanced permeability intervals at pore, core and well-scales, contrast with comparable intervals at outcrop to assess the potential for lateral connectivity.

Controlled fluid-rock reactive flow experiments at geothermal reservoirs conditions to generate novel data and models on water-rock reaction rates that control the permeability evolution (e.g. mineral dissolution and precipitation) and validation of results using advanced microanalysis of representative LCL core and field samples.

Measure petrophysical and mechanical rock properties (strength, density, sound wave velocity, porosity, permeability, thermal stability) of various carbonate facies to develop new empirical relationships relating these properties to brittle-to-ductile rheology and permeability at geothermal conditions and potentially upscale the empirical relationships to well data and field sites using wireline logs.

Project Timeline

Year 1

Review of existing data and case studies, development of detailed research proposal. Design of experimental studies, design of field/site study. Review of core and well database.

Year 2

Core and outcrop characterisation study. Selection of samples for experimental work. Reactive flow experiments at geothermal reservoir conditions. Research visits to Durham University and BGS Keyworth. Present initial findings at relevant conference.

Year 3

Continued experimental work, generate petrophysical data, link with novel geochemical models. Integration of different types of datasets. Potential upscaling to well and field size. Research visits to Durham University and BGS Keyworth. Presentation of research at relevant conference.

Year 3.5

Continued integration of datasets. Thesis completion and manuscript submissions to international journals.

Training
& Skills

Training will be provided in carbonate rocktyping, diagenesis and geochemistry along with support in designing the relevant experiments. The successful candidate will be part of a strong research team in both carbonate geoscience and geothermal energy at Newcastle University and Durham University. The research builds on existing projects at both institutes, such as the 1.6km deep scientific borehole in Newcastle city centre [5]. You will gain specialist experience in organic and inorganic geochemistry, pore-scale processes and developing subsurface models, providing a unique and broad skill set targeted at careers in sustainable energy, both in the commercial sector and in academia.

References & further reading

[1] Gluyas, J.G., Adams, C.A., Busby, J.P., Craig, J., Hirst, C., Manning, D.A.C., McCay, A., Narayan, N.S., Robinson, H., Watson, S.M., Westaway, R. & Younger, P.L. (2018). Keeping warm; a review of deep geothermal potential of the UK. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 232: 115-126[2] Busby, J. (2014). Geothermal energy in sedimentary basins in the UK. Hydrogeology Journal 22: 129-141.[3] Goldscheider, N., Mádl-SzÃ…’nyi, J., ErÃ…’ss, A. and Schill, E. (2010). Review: Thermal water resources in carbonate rock aquifers. Hydrogeology Journal 18: 1303–1318.[4] Mijnlieff (2020). Introduction to the geothermal play and reservoir geology of the Netherlands. Geologie en Mijnbouw 99.[5] Net Zero Geothermal Research for District Infrastructure Engineering (NetZero GeoRDIE) https://gow.epsrc.ukri.org/NGBOViewGrant.aspx?GrantRef=EP/T022825/1

Further Information

Dr Cees van der Land
Earth, Ocean and Planetary Science research group
School of Natural and Environmental Sciences
Newcastle University
Cees.van.der.land@newcastle.ac.uk
07-435214029

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