A regional CO₂ containment assessment of the northern Utsira Formation seal and overburden, northern North Sea

Abstract

Upscaling Carbon Capture and Storage requires identification of suitable storage sites, with robust reservoir seals. The Utsira Formation in the northern North Sea has been flagged as a target for further storage. However, there are no regional studies of seal variability addressing heterogeneities that could facilitate seal bypass. This study aims to: (a) identify, assess and map the elements that promote or restrict fluid migration, (b) develop a matrix to regionally map containment confidence (CC) and (c) rank the different areas for CO 2 containment across the Utsira Formation. The seal and overburden were mapped using a high-resolution, pre-stack depth-migrated Highlights• There is not a laterally-extensive and homogenous seal above the Utsira Formation.• Regional high-resolution data and modern interpretation approaches illuminate potential seal bypass systems.• A novel containment confidence matrix is used to rank the potential CO 2 storage areas.• The workflow for detailed seal and overburden assessment is highly applicable to other basins. | 1987 EAGE LLOYD et aL. F I G U R E 1 Study area with wells and data extent. (a) Context of the study area in the North Sea and the location of the Sleipner injection site. Satellite imagery from the World Imagery layer of ArcMap online. Bathymetry from EMODnet Bathymetry Consortium (2018). (b) A simplified map showing the main structural elements in the study area (modified from Faerseth et al., 1996). (c) Utsira Fm. thickness map (Eidvin et al., 2013) with seismic dataset extent (yellow box). Dots show wells used in this study, and data from those highlighted in white are presented in this study.Oil and gas fields in the region are also indicated. (d) Regional west-east profile of the Jurassic Rift and overlying stratigraphy split into groups to show main structural elements for reference. Inset shows the studied interval.

Regional Exploration and Characterisation of CO2 Storage Prospects in the Utsira-Skade Aquifer, North Viking Graben, North Sea

“…The Naust Fm. is intersected by a regional unconformity, the Upper Regional Unconformity (URU), which removed the topsets of many of the clinoforms (Ottesen et al, 2014;Lloyd et al, 2021). Above the URU, the Naust Fm.…”

“…Most of the wells are clustered around prolific hydrocarbon provinces (Tampen Spur region) or plays (e.g., tilted Jurassic fault blocks). 83 of the studied wells have a full lithological column interpreted from petrophysical logs and well completion reports, provided by TGS with their Facies Map Browser (FMB) tool, which is described in Lloyd et al (2021).…”

“…Detailed characterisation of saline aquifers is required to identify the most economicallyviable and geologically-secure potential CO 2 storage sites (Ringrose et al, 2021). Such analyses should assess three elements: 1) CO 2 containment, through assessment of seal integrity, seal bypass systems and overburden migration paths (e.g., Lloyd et al, 2021;Wu et al, 2021); 2) CO 2 capacity, including identification of structural traps and reservoir heterogeneities (this study); and 3) injectivity, assessing the well design/placement, potential flow and trapping style of the CO 2 plume within the reservoir through dynamic modelling.…”

“…The objectives are to: 1) define the vertical and lateral extent of the aquifer; 2) calculate the porosity distribution across the aquifer sandstones, through application of a well data-derived function to the velocity cube; 3) identify and assess the spatial extent, geomorphology, thickness variability, and containment confidence of mudstones within the Utsira-Skade Aquifer; 4) identify structural closures within the aquifer; and 5) calculate the storage capacity of the identified prospects. We consider containment of the identified prospects through application of the containment confidence map from Lloyd et al (2021) for the Utsira Fm. and apply the methodology to the Skade reservoirseal pair in this study.…”

“…Each column represents processes/data required for a single step, but the processes within each step can be performed in any order. *Containment confidence map summarises the results of the seal and overburden analysis; the separate workflow is provided in Lloyd et al (2021). (B) Storage capacity estimation parameters.…”