Lower Cretaceous Rodby and Palaeocene Lista Shales: Characterisation and Comparison of Top-Seal Mudstones at Two Planned CCS Sites, Offshore UK

Richard H. Worden* (Corresponding Author), Michael Allen, Daniel R. Faulkner, James Utley, Clare E. Bond, Juan Alcalde, Niklas Heinemann, Stuart Haszeldine, Eric J. Mackay, S. Ghanbari

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)
8 Downloads (Pure)


Petroleum-rich basins at a mature stage of exploration and production offer many opportunities for large-scale Carbon Capture and Storage (CCS) since oil and gas were demonstrably contained by low-permeability top-sealing rocks, such as shales. For CCS to work, there must be effectively no leakage from the injection site, so the nature of the top-seal is an important aspect for consideration when appraising prospective CCS opportunities. The Lower Cretaceous Rodby Shale and the Palaeocene Lista Shale have acted as seals to oil and gas accumulations (e.g., the Atlantic and Balmoral fields) and may now play a critical role in sealing the Acorn and East Mey subsurface carbon storage sites. The characteristics of these important shales have been little addressed in the hydrocarbon extraction phase, with an understandable focus on reservoir properties and their influence on resource recovery rates. Here, we assess the characteristics of the Rodby and Lista Shales using wireline logs, geomechanical tests, special core analysis (mercury intrusion) and mineralogical and petrographic techniques, with the aim of highlighting key properties that identify them as suitable top-seals. The two shales, defined using the relative gamma log values (or Vshale), have similar mean pore throat radius (approximately 18 nm), splitting tensile strength (approximately 2.5 MPa) and anisotropic values of splitting tensile strength, but they display significant differences in terms of wireline log character, porosity and mineralogy. The Lower Cretaceous Rodby Shale has a mean porosity of approximately 14 %, a mean permeability of 263 nD (2.58 × 10−19 m2), and is calcite rich and has clay minerals that are relatively rich in non-radioactive phases such as kaolinite. The Palaeocene Lista Shale has a mean porosity of approximately 16% a mean permeability of 225 nD (2.21 × 10−19 m2), and is calcite free, but contains abundant quartz silt and is dominated by smectite. The 2% difference in porosity does not seem to equate to a significant difference in permeability. Elastic properties derived from wireline log data show that Young’s modulus, material stiffness, is very low (5 GPa) for the most shale (clay mineral)-rich Rodby intervals, with Young’s modulus increasing as shale content decreases and as cementation (e.g., calcite) increases. Our work has shown that Young’s modulus, which can be used to inform the likeliness of tensile failure, may be predictable based on routine gamma, density and compressive sonic logs in the majority of wells where the less common shear logs were not collected. The predictability of Young’s modulus from routine well log data could form a valuable element of CCS-site top-seal appraisals. This study has shown that the Rodby and Lista Shales represent good top-seals to the Acorn and East Mey CCS sites and they can hold CO2 column heights of approximately 380 m. The calcite-rich Rodby Shale may be susceptible to localised carbonate dissolution and increasing porosity and permeability but decreasing tendency to develop fracture permeability in the presence of injected CO2, as brittle calcite dissolves. In contrast, the calcite-free, locally quartz-rich, Lista Shale will be geochemically inert to injected CO2 but retain its innate tendency to develop fracture permeability (where quartz rich) in the presence of injected CO2.
Original languageEnglish
Article number691
Number of pages38
Issue number8
Publication statusPublished - 3 Aug 2020

Bibliographical note

Funding: The work reported here was part of the Accelerating Carbon Technologies (ACT) Acorn Carbon Capture and Storage (CCS) Project, under the ERA–NET Horizon 2020 programme, project 271500, and was jointly funded by the Department for Business, Energy and Industrial Strategy, United Kingdom; the Research Council of Norway; the Netherlands Enterprise Agency. Juan Alcalde is funded by the Spanish MICINN (Juan de la Cierva fellowship-IJC2018-036074-I). Alan James, CEO of Pale Blue Dot Ltd. (Banchory, UK), is warmly thanked for skilfully leading the Acorn Project and offering advice throughout the project, including during the preparation of this manuscript. We express our warm appreciation to guest editor Jim Buckman (Heriot Watt University, UK) for encouraging us to write and submit this paper. We would like to thank four diligent anonymous reviewers for their thoughtful and constructive comments on the initial version of the manuscript, and academic lead for this thematic issue.


  • Rodby shale
  • Lista shale
  • carbon capture and storage
  • North Sea
  • wireline logs
  • splitting tensile stress
  • mercury intrusion porosimetry
  • quantitative mineralogy
  • geomechanical properties
  • Young's modulus
  • CO2 column height
  • Young’s modulus
  • CO column height
  • Mercury intrusion porosimetry
  • Splitting tensile stress
  • Quantitative mineralogy
  • Lista Shale
  • Rodby Shale
  • Geomechanical properties
  • Wireline logs
  • Carbon capture and storage
  • CO2
  • CO(2)column height
  • CLAY


Dive into the research topics of 'Lower Cretaceous Rodby and Palaeocene Lista Shales: Characterisation and Comparison of Top-Seal Mudstones at Two Planned CCS Sites, Offshore UK'. Together they form a unique fingerprint.

Cite this