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 hydrogen storage and recovery within different facies of the Sherwood Sandstone Group (SSG).

Three 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 properties?
2. What are the influential 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?

The SSG is important to the UK as a hydrocarbon reservoir and as a significant source of groundwater. It also has potential to help with some of the imminent climate challenges by potentially acting as a storage reservoir for CO2 or reservoir for the temporary storage of hydrogen, thereby supporting the energy transition and Net Zero 2050 goals by the UK government [6]. However, discontinuities, such as deformation bands, have the potential to restrict the advantages of the SSG. For instance, clusters of cataclastic bands may limit lateral flow and porosity may be reduced [1], [3]. Further understanding of the effect of discontinuities on storage and recovery capabilities of different facies at field scale is needed to better model reservoir capacity and its response to cyclic perturbations so that we can manage our resources effectively, avoiding potential hazards and costly and disruptive interventions, such as those created by anomalous pressure increases at Snøhvit [2]. A better comprehension of SSG properties will further our understanding of other sandstone formations and improve our ability to use geological resources globally.

Potential impacts of this research are:
– Improved UK subsurface strategy. It will provide a scientific foundation for the UK Government regarding the extent of our resources and their geographical locations, impacting upon hydrogen transportation costs and the proximity of large industrial processes to storage sites, enabling them to create clear policy about the hydrogen network and focus resources toward building an integrated infrastructure with other technologies such as carbon capture and storage [4].
– Removal of some barriers to a hydrogen economy, one of the UK Government’s three pathways towards achieving its emissions goals [5] with recent substantial investment [7]. Storage and effective retrieval is an essential part of this relatively immature technology.
– Newly identified geological domains for hydrogen storage. Currently hydrogen is stored in solution-mined caverns in halite; understanding the potential for pore space storage could allow additional geological units to be identified as hosts, increasing the geographical extent of potential sites in areas of projected hydrogen demand remote from suitable accumulations of bedded halite.
– Reduction in hydrogen storage costs. Identification of storage sites and their fluid properties will cut research and exploration costs of industry, allowing resources to be targeted at areas with maximum chance of success, and provide companies and clusters with a more realistic understanding of the costs involved.

The overall effect will be to accelerate the UK industrial, domestic and transport sectors towards the Net Zero targets [6] by reducing information and cost barriers to their implementation. This research will also be relevant to energy storage for other technologies with potential in the SSG, including aquifer thermal and compressed air storage.

Methodology

Fieldwork: Obtain new SSG samples containing discontinuities from outcrops, subcrops and borehole material held in the National Geological Repository, representative of different facies within the geological unit. The samples will be collected from different SSG facies such as, 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. They will also be supplemented by borehole samples from the UKGEOS Cheshire observatory, when these become available.

Laboratory-based analysis: The collection of samples and existing samples will be analysed, using techniques such as 3D X-ray CT scanning, multi-sensor core logging and Scanning Electron Microscopy, available at BGS, to understand the pore-scale characteristics, including grain size, texture, sorting, roundness and sphericity, matrix and cement type. In addition, porosity, permeability and mineralogical information will be obtained on a representative amount of samples. This information will feed into dynamic reservoir modelling.

Modelling: Develop a 3D probabilistic fluid flow model showing the effects of discontinuities on a potential H2 storage site within the SSG, synthesising the results from the laboratory analyses and other sources, such as 3D seismic and borehole data. Devise a semi-automated sensitivity analysis to understand the importance and role of different reservoir properties.

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

Project Timeline

Year 1

Learn how to work safely in the field to collect samples and in analytical laboratories to conduct sample preparation, testing and analysis;
Review the literature on:
– characteristics and properties of SSG facies and the effect of discontinuities upon these;
– translating pore-scale properties to field-scale properties;
– 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;
– strategies for managing uncertainty in predictive modelling.
Refine the geographical context of the project based upon the literature review;
Compile a directory of the BGS’ SSG samples;
Complete practical experiments to optimise the efficiency of:
– identification of SSG sample characteristics;
– rock property testing, particularly fluid dynamics;
Produce the experimental design;
Collect, prepare and initially characterise rock samples for testing;
Complete relevant training courses;
Attend industry seminars and conferences.

Year 2

Complete rock sample collection;
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.

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] 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[2] 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.[3] 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.[4] UKGov (2018a) Clean Growth. The UK Carbon Capture Usage and Storage deployment pathway: An Action Plan [online]. Available at https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/759637/beis-ccus-action-plan.pdf.[5] UKGov (2018b) Clean Growth Strategy: Leading the way to a low carbon future [online]. Available at https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/700496/clean-growth-strategy-correction-april-2018.pdf.[6] 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[7] UKGov (2020) £90 million UK drive to reduce carbon emissions [online]. Available at https://www.gov.uk/government/news/90-million-uk-drive-to-reduce-carbon-emissions.

Further Information

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

Student – Doug Smith
Email: dosmi@bgs.ac.uk
Tel: 0782 1274437

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