The Bunter Sandstone Storage Complex in the Southern North Sea; geological perspectives from a three-year multi-disciplinary research programme

The Bunter Sandstone Storage Complex is a primary candidate for large scale CO₂ sequestration within the Southern North Sea (SNS) and the primary store for the UK Track 1 East Coast Cluster. This presentation will provide a high-level overview of CASP’s three-year multi-disciplinary Bunter Sandstone Storage Complex and Mudrock Seals research programmes, completed earlier this year, which aimed to provide a regional characterisation of the storage complex via a mix of well and outcrop studies. CASP is a not-for-profit geological research organisation based in Cambridge, funded by a mix of industrial sponsors, government bodies and the charity’s investment income. Multiple datasets were investigated by our team, including a unique, unreleased onshore well that provides continuous core coverage through the whole of the Triassic to Early Jurassic Bunter Sandstone Storage Complex. This well is accompanied by an industry-standard wireline log suite and multiple petrophysical and mechanical strength measurements. Information from the reference well was augmented by publically available wireline log data, and the analysis of core and cutting materials, from the UK and Dutch sectors of the SNS as well as extensive fieldwork along the North Yorkshire coast. The last of these elements enabled us to provide a detailed characterisation of the Redcar Mudstone Formation, the uppermost sealing element of the storage complex. These strata are also laterally equivalent to, and direct analogues for, the primary sealing elements of younger paired reservoir intervals such as the Gassum Formation in the Danish–Norwegian Basin.

Research delivery was modular and comprised the following nine projects: BSSC.1 focussed on refining age constraints to enhance regional correlations for the storage complex by constructing an improved palynological zonation of the Triassic, following detailed sampling of the onshore reference well. This scheme was then extended into the offshore, and enhanced in BSSC.2. Complementary to these efforts, BSSC.3 examined climatically driven sedimentary cycles to develop a biostratigraphically calibrated cyclostratigraphy, providing deeper insights into reservoir connectivity and stratal architecture correlating multiple wells in the SNS along a transect running from the Dutch to UK onshore. BSSC.4 and BSSC.5 investigated regional sedimentological, compositional and diagenetic controls on reservoir quality and sediment provenance, to aid prediction of reservoir capacity and performance prior to and during CO₂ injection. Meanwhile, BSSC.6 and BSSC.7 focussed on the sealing effectiveness of overlying Triassic units, via the analysis of a continuous suite of core samples from the onshore reference well and more stratigraphically limited material from offshore wells, respectively, to assess their capacity for long-term CO₂ containment. Lastly, MSP.1 and MSP.2 examined the potential links between a truly comprehensive catalogue of primary (compositional/sedimentological) and secondary (deformational/diagenetic) heterogeneities with variations in seal potential within the lower Lias Group at outcrop, primarily at Robin Hood’s Bay, to constrain sub-seismic seal failure risk. Ultimately, this comprehensive resource provides a consistent, fundamental approach to real-rock characterisation for a swathe of stratigraphy integral to geological carbon storage in the SNS and forms a basis upon which other studies can be built.