Assurance of CO₂ storage complex integrity is essential for both operators and regulators. This project will use outcrop-derived data to characterise the heterogeneity of a well-exposed mudstone analogue at nano- to meso-scales. This will enable the parameterisation of representative elemental volume (REV) geomodels to capture subseismic-scale heterogeneities in mudrock seals that will underpin long timescale models for fluid flow and reactivity, and secondary storage volume assessment.

The well exposed >180 m thick Early Jurassic Redcar Mudstone Formation study interval (Fig. 1) comprises a suite of shallow to open marine lithologies with a range of mudstone compositions (calcareous, argillaceous, siliceous etc., reflected in the individual member/unit names). It will form a useful generic mudrock seal analogue, whilst also forming a direct stratigraphic analogue for several planned CO₂ storage systems in the North Sea region (Fig. 1).

Research programme

This project will document vertical compositional variability observed at outcrop and calibrate the resultant facies/microfacies scheme with detailed compositional analysis, primary sedimentological observations and seal capacity measurements. The improved constraint on mudrock heterogeneity will help inform the assessment of compositional control on seal potential. The project will also establish the framework of understanding necessary to undertake the broader aims of the Mudrock Seals in CO₂ Storage Sytems research theme, underpinning analysis of seal development, stratal architecture and lateral variability first at outcrop and then widening scales of investigation using subsurface data inboard of, and paralleling the coastal sections.

Field investigation will occur at two scales: 1) A coarser resolution sampling (~2 m spacing) of the entire study interval with handheld XRF/gamma scanning, both calibrated to the existing bio- and lithostratigraphic framework, and; 2) targeted high-resolution logs accompanied by handheld scans and sampling providing detailed representative constraint on individual members as well as mudrock to sandy unit boundaries.

Deliverables

Results will be delivered via interim data releases, associated presentations for client companies, and a final technical report. The report will focus on two elements:

Composition

This will be achieved via an outcrop based assessment of vertical compositional heterogeneity over the study interval at Robin Hoods Bay, Yorkshire. The report will integrate the collected multi-proxy compositional dataset with high resolution sedimentary logs to produce a facies/microfacies schema for use in all subsequent projects.

Seal Capacity

We will relate composition based facies/microfacies subdivisions to outcrop observations and seal capacity data to parameterise REVs, conditioned to small to intermediate volumes constrained by the high-resolution logs.

Specific deliverables will include:

• A summary graphic log integrated with handheld gamma measurements and legacy biostratigraphic data.
• High-resolution logs of representative stratal elements with handheld XFR measurements.
• SEM mineral maps with compositional and porosity data.
• XRD analyses of compositional elements and mineralogy to augment the SEM data.
• Petrographic analyses of key samples highlighting texture, mineralogy, porosity and diagenesis.
• MICP and He porosity and permeability analyses.
• Up to 40 TOC measurements.

The project will conclude with a client workshop during which all data and interpretations will be presented and discussed.

Project duration

The project was launched at the beginning of July 2022 and has a planned duration of 24 months.

Contact: Stephen Vincent for further information about this research and licensing options