Modelling the multi-scale spatial variations in the geomechanical properties within the discontinuities of the Sherwood Sandstone Group and their influence on its capacity to provide large-scale H2 storage for sustainable decarbonisation of the UK economy

Overview

The aim of the research is to develop a 3D fluid flow model predicting the effect of discontinuities on the hydrogen storage and recovery within different facies of the Sherwood Sandstone Group (SSG).

Three key research questions will be addressed:
1. What are the key pore scale characteristics within the discontinuities of the SSG, that affect the reservoir scale H2 storage potential?
2. What are the principal fluid flow properties of the SSG that are needed to parameterise, develop, test and validate a 3D probabilistic geological model for H2 storage and recovery?
3. How can the sensitivities of the variables and uncertainties of the model be quantified and characterised so that they can be communicated to policymakers and industry?

It is anticipated that hydrogen will play a crucial role in the endeavour to meet the Net Zero targets and the UK Government has set an initial target 5GW of low-carbon hydrogen production capacity by 2030 and between 20% and 35% of total UK energy consumption by 2050 in their Net Zero scenario [1] [2]. This is to be supported by a £240 million Net Zero Hydrogen Fund in the first instance with the UK Government pledging over £1 billion of investment to develop “technologies of the future” such as hydrogen [3] [1].

The Sherwood Sandstone Group (SSG) is important to the UK as a hydrocarbon reservoir and as a significant source of groundwater, just under one third of the water supply for Severn Trent is extracted from the formation [4]. On the UK Continental Shelf (UKCS) the SSG stretches from the Irish Sea Basin to the North Sea and there are onshore outcrops on the Isle of Arran in the north and in Devon in the south [5].

The SSG is a potential subsurface storage unit for hydrogen, CO2 and heat but the impact of certain diagenetic features on hydrogen storage is not well understood. Deformation bands, which can be abundant in the aeolian deposits of the SSG, have the potential to affect fluid flow, altering the permeability of the rock, restricting storage capacity, affecting the quantities of cushion gas needed and the ability to recover hydrogen from the SSG [6] [7]. Further understanding of the effect of deformation bands on the storage and recovery capabilities of different facies at field scale is needed to better model reservoir capacity and how it reacts to cyclic perturbations so that we can manage and optimise the subsurface resource effectively, avoid potential hazards and costly and disruptive additional interventions, such as those created by the anomalous pressure increases and reduced storage capacity at Snøhvit [8]. Also, a better comprehension of the properties of the SSG will further our understanding of other sandstone formations and improve our ability to use geological resources on a global scale.

Methodology

Fieldwork: Obtain new SSG samples containing deformation bands from outcrops, subcrops and borehole material held by the BGS at the National Geological Repository, representative of different facies within the geological unit. The samples will be collected from different SSG facies including the Helsby, Wilmslow and Chester Pebble Beds Formations in Cheshire, the Chester Formation in the Needwood basin, Stoke-on-Trent, and the Otter Sandstone Formation on the south coast, near Sidmouth. They will hopefully also be supplemented by borehole samples from the UKGEOS Cheshire observatory.

Laboratory-based analysis: The collection of samples and existing samples will be analysed, using techniques such as the 3D X-ray CT scanner, multi-sensor core logger and SEM, to understand the pore-scale characteristics, including grain size, texture, sorting, roundness and sphericity, matrix and cement type as well as porosity and permeability. Conduct experiments to test the fluid flow and storage properties of the samples, particularly at temperatures and pressures experienced in H2 storage processes and under cyclical compression and decompression.

Modelling: Develop a 3D probabilistic fluid flow model showing the effects of deformation bands on a potential hydrogen storage site within the SSG synthesising the results from the laboratory analyses and other sources, such as 3D seismics and borehole data. Devise a semi-automated sensitivity analysis to understand the importance and role of different variables.

Statistical analysis: Quantify the uncertainty within the model to allow confidence in decision-making and enable model validation.

Communication: Construct a framework to facilitate the communication of storage properties and the uncertainty involved with the predictions.

Project Timeline

Year 1

Learn how to work safely in the field to collect samples and in BGS’ analytical laboratories to conduct sample preparation, testing and analysis;
Review the literature on:
– the provenance, characteristics and properties of different SSG facies and the effect of deformation bands upon these;
– translating pore-scale properties to field-scale properties;
– the technical aspects of processes involved in H2 storage;
– essential reservoir properties for fluid injection, storage and recovery;
– fluid flow modelling, particularly in sandstone and with regard to significant variables and uncertainties; and
– strategies for managing uncertainty in predictive modelling.
Refine the geographical context of the project based upon the literature review;
Compile a directory of the SSG samples that BGS already stores;
Complete practical experiments to optimise the efficiency of:
– the identification of SSG sample characteristics; and
– the rock property testing, particularly fluid dynamics;
Produce the experimental design for the following years;
Collect, prepare and initial characterisation of rock samples for testing; and
Complete relevant training courses and attend industry seminars and conferences.

Year 2

Complete the collection, preparation and initial characterisation of the rock samples;
Identify the potential H2 storage site to model;
Characterise the SSG rock samples using SEM, 3D X-ray CT scanner and multi-sensor core logger;
Analyse the geomechanical properties of the samples, including permeability, porosity, strength and elastic modulus. Rock to be tested at appropriate temperatures and pressures and with cyclical perturbations;
Complete data workup and start building 3D H2 storage model;
Complete relevant training courses;
Attend industry seminars and conferences.

Year 3

Complete data analysis and numerical modelling to understand the analytical results in the context of SSG facies characterisations and their correlation with rock properties;
Complete 3D storage model;
Validate model;
Complete sensitivity analysis on model and quantification of uncertainty;
Start thesis write up.

Year 3.5

Draft at least one paper suitable for peer-review publication;
Complete thesis write up.

Training
& Skills

Fieldwork and laboratory work – appropriate protocols and safety procedures for collecting samples and working with various laboratory instruments;
Fieldwork – rock identification and sampling;
Laboratory work – Training on various instruments to identify pore-scale characteristics;
Laboratory work and modelling – Fluid flow dynamics;
Modelling:
• Training on an appropriate modelling tool ie PETREL;
• Model validation, sensitivity analysis and model uncertainties;
• Methods of managing uncertainty in models.
Communication – communicating science and uncertainty to policymakers and industry.

References & further reading

[1] UKGov (2020) Energy White Paper: Powering our Net Zero Future [online]. Available at https://www.gov.uk/government/publications/energy-white-paper-powering-our-net-zero-future.[2] UKGov (2021) UK Hydrogen Strategy [online]. Available at https://www.gov.uk/government/publications/uk-hydrogen-strategy[3] UKGov (2020) The Ten Point Plan for a Green Industrial Revolution https://www.gov.uk/government/publications/the-ten-point-plan-for-a-green-industrial-revolution..[4] Severn Trent (2018) Draft Water Resources Management Plan Statement of Response – Appendix C [online]. Available at https://www.severntrent.com/content/dam/stw-plc/about-us-02/ST%20dWRMP%20SoR%20Appendix%20C%20Public.pdf.[5] Ambrose, K., Hough, E., Smith, N. J. P., and Warrington, G. (2014) Lithostratigraphy of the Sherwood Sandstone Group of England, Wales and south-west Scotland, British Geological Survey Research report RR/14/01.[6] Griffiths, J., Faulkner, D.R., Edwards, A.P., and Worden, R.H. (2018) Deformation band development as a function of intrinsic host-rock properties in Triassic Sherwood Sandstone, Geological Society, London, Special Publications, 435, 161-176, 19 January 2016, https://doi.org/10.1144/SP435.11.[7] Medici, G., Jared West, L., Mountney, N.P. and Welch, M. (2019) Permeability of rock discontinuities and faults in the Triassic Sherwood Sandstone Group (UK): insights for management of fluvio-aeolian aquifers worldwide, Hydrogeology Journal (2019) 27:2835–2855.[8] Jenkins, C., Chadwick, A and Hovorka, S.D. (2015) The state of the art in monitoring and verification—Ten years on, International Journal of Greenhouse Gas Control 40 (2015) 312–349.[9] UKGov (2019) UK becomes first major economy to pass net zero emissions law [online]. Available at https://www.gov.uk/government/news/uk-becomes-first-major-economy-to-pass-net-zero-emissions-law.

Further Information

Lead supervisor – Ed Hough
Email – eh@bgs.ac.uk

Student – Doug Smith
Email – dosmi@bgs.ac.uk

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