Upscaling of carbon capture and storage (CCS) technology and rapid market growth is required for it to be an effective tool in meeting net-zero emissions targets, which includes identification and characterisation of further CO2 storage sites. Saline aquifers offer large storage capacities, but previous work is mostly limited to basin-scale screening. Here, the northern Utsira-Skade Aquifer, northern North Sea is assessed. This aquifer is a contender for future CO2 storage, due to its proximity to the Northern Lights CO2 storage licence (EL001) and its similarity to the Sleipner CO2 storage site in the southern Utsira Fm., a strong operational analogue. The main aims of this work are to assess whether the northern Utsira-Skade Aquifer is suitable for CO2 storage and to develop a broadly applicable, systematic workflow for CO2 storage site exploration. Regional 3D broadband seismic data, 141 wells and full waveform inverted velocity data are integrated to assess architectural variability in the reservoir, seal and overburden, and highlight a suite of potential storage sites. Static and dynamic capacity estimation approaches are compared and dynamic simulations using invasion percolation physics are used to understand plume migration and trapping. An exploration-style workflow is presented for regional assessment of containment (seal and overburden) and capacity (reservoir) of the aquifer. This is the first academic study to present a full workflow from regional aquifer characterisation to prospect maturation. Key elements that could facilitate seal bypass and migration through the overburden (seal interval geometry, sandstone presence, and sandstone connectivity) were mapped and scored using a newly developed Containment Confidence (CC) risk matrix, which was applied to the top Utsira Fm. and top Skade Fm. The area with the highest containment confidence is in the northeast of the Utsira Fm., where positive CC scores were assigned due to flat-lying mudstone dominated stratigraphy in the seal interval (first 50 m above the top reservoir). This area was also found to have good reservoir properties in the capacity study, with porosities of 30-37% and intraaquifer mudstones that would likely aid CO2 trapping. Seismically-resolvable mudstones were mapped, structural closures were identified and their static storage capacities were estimated. Any closure with a static storage capacity >5 MtCO2 and apex depth >700 m was considered a prospect. There were five prospects with positive CC scores, four in the Utsira Fm. and one in the Skade Fm. The combined static storage capacity for the Utsira Fm. closures was found to be 49 MtCO2. This is lower than previous capacity estimations of structural closures (300-1,100 MtCO2), due to the focus here on the northern part of the formation, delimitation of the suitable area through the CC assessment and detailed reservoir characterisation. Further areas of the aquifer could be suitable for storage if the seal thickness threshold (50 m) is reduced or if detailed prospect-scale assessments de-risk containment. A geomodel that captured geological heterogeneity was built for the best prospect in the Utsira Fm. (static storage capacity of 32 MtCO2) and adjacent closures. Dynamic simulations were performed, varying the threshold pressure of the intra-reservoir mudstones and injection strategy. Mudstone threshold pressure highly influenced CO2 plume behaviour and dynamic storage capacity, which ranged from 34-70 MtCO2. The disparity between static and dynamic storage capacity estimations is attributed to the uncertain storage efficiency parameter used in the static calculations. This should be considered for future exploration that typically relies on a static approach. This work demonstrates that it is fundamentally important to locally constrain geological heterogeneity in the reservoir, seal and overburden to identify and appraise suitable CO2 storage sites and provide reliable capacity estimations. T
Date of Award | 1 Aug 2022 |
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Original language | English |
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Awarding Institution | - The University of Manchester
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Supervisor | Jonathan Redfern (Supervisor) & Mads Huuse (Supervisor) |
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- Aquifer characterisation
- CO2 capacity
- CO2 containment
- seismic interpretation
- CO2 storage
- Utsira-Skade Aquifer
- CCS
Integrated subsurface characterisation of a basin-scale carbon reservoir target
Lloyd, C. (Author). 1 Aug 2022
Student thesis: Phd