Migration of CO2 through North Sea Geological Carbon Storage Sites: Impact of Faults, Geological Heterogeneities and Dissolution

Lead Research Organisation: NERC British Geological Survey
Department Name: Energy & Marine Geoscience

Abstract

The storage of CO2 in deep geological formations is one of the chief technological means of reducing anthropogenic emissions of CO2 to the atmosphere. The process requires capturing CO2 at source (e.g. coal-fired power plants), transporting CO2 to the injection site, and pumping liquefied CO2 into kilometre deep, porous reservoirs that are typically initially saturated in saline water or previously contained oil or gas. Initially, buoyant CO2 tends to rise through the porous reservoir until it is trapped by an impermeable horizon, in the same way that oil or gas has been trapped over millennia. Subsequently, buoyant CO2 may be more securely trapped by dissolving CO2 into water (carbonated water is more dense than non-carbonated water and will sink), or by capillary forces acting to hold the CO2 in the small confines of the pore space. Any risk of buoyant CO2 migrating through the overburden is therefore reduced by these trapping processes. Constraining the rates of dissolution and capillary trapping in realistic geological overburden is a key component of strategies to quantify and reduce the risks of leakage. The UK is geologically well placed to implement offshore CO2 storage, with many potential reservoirs in the North Sea.

This proposal will improve our understanding of the risks of leakage through the overburden by quantifying trapping rates in faults and heterogeneous strata typical of the overburden of North Sea reservoirs, and by quantifying our ability to seismically detect any CO2 in the overburden. CO2 is less viscous than water and will finger along more permeable layers. Sedimentary strata exhibit large variations in permeability on all scales that will substantially increase the rates at which CO2 dissolves in the formation waters.

The analysis, while general in scope and resultant techniques, is applied to the Goldeneye field, a target for CO2 storage and a candidate for the Government's CCS commercialisation competition. Our approach is to geologically characterise the relevant geological heterogeneity within the overburden, and to map the structure and propensity for fluid flow within faults in that locality. Drill core provides samples of rock (5x20 cm) that can then be interrogated in the laboratory. We will directly image, at conditions typical of the overburden, the rates of fluid flow, dissolution, and capillary trapping both at the scale of individual pores within the rock (microns) and over the length of the core (centimetres). Geochemical analysis of the fluids will allow us to measure in situ dissolution and precipitation rates in our core flooding experiments. In order to determine how rates of flow and trapping may be applied at the scale of the reservoir and overburden the results must be interpreted in light of flow through 1-100 centimetre scale geological heterogeneities and along faults. To assess the impact of heterogeneities on the rates of trapping we will construct simplified models of flow along predominantly layered strata, or along cross-cutting faults, along with laboratory analogue experiments in which we can optically assess trapping rates and thereby provide a firm benchmark for our predictions. Finally, at larger scales, we will image flow up chimney structures in existing CO2 experiments (eg Sleipner in the North Sea) and thus provide quantitative estimates of our ability to seismically resolve leakage pathways in the storage overburden.

Our proposal will develop tools needed to geologically characterise the North Sea overburden, provide quantitative estimates of trapping rates in geologically complex overburden and fault complexes, and demonstrate the ability to seismically resolve fluid flow pathways. To date geological CO2 storage has been demonstrated at relatively safe storage sites. This work would greatly expand the potential for geological CO2 storage by quantifying the potential risks associated with leakage in more geologically complex storage sites.

Planned Impact

The following groups will benefit from this research:

1. The UK economy (including UK households) will benefit from lowered barriers to the implementation of CCS arising from decreased risk and increased certainty in predictive modelling capabilities developed in this project.

2. The CO2 storage industry will benefit from understanding how to quantify permanent trapping in natural heterogeneous systems.

3. Government and regulators who require objective information about the security of stored CO2 from analysis that incorporates the uncertainty of pervasive geological heterogeneity.

4. The UK CCS Research Centre funded by the EPSRC who will use the data, tools and training for further input into the strategic directions for academic CCS research.

5. The public who require an understanding of the opportunity for CCS to provide a safe and secure means of mitigating CO2 emissions and climate change.

The UK Advanced Power Generation Technology Forum 2014 report on major R&D needs for CO2 capture and storage identified the "scale-up of small-scale measurement to large scale" systems, the development of "strategy to understand and characterize dynamic flows ... of major deep saline formations including dissolution rates and convective processes in real storage systems" and "modeling strategies for prediction of whole-system CO2 dynamic performance in subsurface from pore-scale to basin-scale for multi-scale processes" as priority areas all of which are directly addressed by this proposal. Similarly the 2012 CCS roadmap produced by the Department of Environment and Climate Change (DECC) identified "improved understanding of subsurface CO2 behaviour" as a top priority to forward the development of CCS in the UK.
 
Description Current research is showing an improved understanding of how the underground carbon dioxide plume stored at the Sleipner field in the North Sea is migrating in the storage reservoir. Research is currently very much 'in progress' but we have identified high permeability channels in the reservoir sandstones that control horizontal flow and have also improved understanding of short vertical 'chimneys' that allow CO2 to migrate vertically through thin sealing layers in the reservoir. Forensic analysis of seismic amplitude information on high resolution time-lapse seismic data has improved our understanding of seismic velocity variations and indirectly CO2 saturations in the CO2 plume at Sleipner.
Exploitation Route At the moment our results are being fed through to project partners. In the longer term results will enable CO2 storage site operators to better predict migration of CO2 in their storage reservoir and better assess and predict possible risks of unwanted migration into the overburden.
Sectors Creative Economy,Energy,Environment

 
Description Findings are limited at the moment because the Grant is in its early days. We have made a presentation at the GHGT-13 conference in Lausanne on some preliminary findings. The paper is now published in the conference proceedings (via Energy Procedia). We have included some results into a number of workshops and external presentations, notably to the UK Parliamentary Science Committee, at a research seminar at Edinburgh University, and to Bath Geological Society. We have explained our research aims to a number of industry Stakeholders, have received a very positive response leading to successful discussions with them regarding the provision of key datasets from the North Sea. We have started discussions with the NERC 'Chimney' project to exchange ideas and datsets as the two projects proceed in parallel. We are also looking to integrate some aspects of our research, notably the preferential fractionation and migration of methane in CO2-methane mixtures, into a D.Eng project that we are co-supervising at the EPSRC Centre for Doctoral Training in Carbon Capture and Storage and Cleaner Fossil Energy [http://www.ccscfe-cdt.ac.uk/index.aspx].
First Year Of Impact 2018
Sector Energy,Environment
Impact Types Societal

 
Title Overburden model for a key CCS aquifer in the Central North Sea 
Description A geological model of the key Palaeogene saline aquifers in the Central and Northern North Sea (specifically the Forties Sandstone). This model is focussed on the overburden sequence comprising a series of possibly inter-connected sands. Objectives: 1) Characterise the full stacked Palaeogene reservoir/seal system of the north-western part of the CNS. 2) Use detailed well correlations and seismic reflection data to map reservoirs and seals. 3) Characterise migration risk features in overburden, including diapirs, injectites, permeable lithologies, pipes/chimneys, glacial scours and faults. 4) Evaluate pressure responses due to production activities in vertically stacked sandstones. 5) Generate holistic risk maps for the various reservoir units. 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? No  
Impact The database is still in production, so no notable impacts to date. 
 
Description Migration of CO2 through North Sea Geological Carbon Storgae Sites 
Organisation Imperial College London
Department Imperial College Trust
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution Geological and geophysical interpretation and analysis of seismic time-lapse datasets. Numerical modelling of CO2 flow in reservoirs and overburden sequences.
Collaborator Contribution Cambridge University: Mathematical/analytical modelling of underground CO2 migration in CO2 storage sites. Shell UK: Seismic and other geological datasets of locations beneath the North Sea suitable for underground CO2 storage. Imperial College London: Relative permeability analysis of CO2 reservoir formations.
Impact The research is still in its very early stages so we have not generated any outputs/outcomes.
Start Year 2016
 
Description Migration of CO2 through North Sea Geological Carbon Storgae Sites 
Organisation Shell International Petroleum
Department Shell UK Ltd
Country United Kingdom 
Sector Private 
PI Contribution Geological and geophysical interpretation and analysis of seismic time-lapse datasets. Numerical modelling of CO2 flow in reservoirs and overburden sequences.
Collaborator Contribution Cambridge University: Mathematical/analytical modelling of underground CO2 migration in CO2 storage sites. Shell UK: Seismic and other geological datasets of locations beneath the North Sea suitable for underground CO2 storage. Imperial College London: Relative permeability analysis of CO2 reservoir formations.
Impact The research is still in its very early stages so we have not generated any outputs/outcomes.
Start Year 2016
 
Description Migration of CO2 through North Sea Geological Carbon Storgae Sites 
Organisation University of Cambridge
Department Department of Surgery
Country United Kingdom 
Sector Academic/University 
PI Contribution Geological and geophysical interpretation and analysis of seismic time-lapse datasets. Numerical modelling of CO2 flow in reservoirs and overburden sequences.
Collaborator Contribution Cambridge University: Mathematical/analytical modelling of underground CO2 migration in CO2 storage sites. Shell UK: Seismic and other geological datasets of locations beneath the North Sea suitable for underground CO2 storage. Imperial College London: Relative permeability analysis of CO2 reservoir formations.
Impact The research is still in its very early stages so we have not generated any outputs/outcomes.
Start Year 2016
 
Description Chadwick A. 2017. Carbon Capture and Storage (CCS). Holes - what use are they? Given to the Parliamentary Scientific Committee, Portcullis House, Westminster. 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact This was a talk given to given to the Parliamentary Scientific Committee at Portcullis House, Westminster. The morning workshop was devoted to a number of presentations aimed at explaining to parliamentarians how the subsurface could be exploited for sustainable energy purposes.
Year(s) Of Engagement Activity 2017
 
Description Chadwick A. 2017. Carbon capture and storage: demonstrating the safety and performance of underground CO2 storage by site monitoring. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Invited lecture to the Bath Geological Society. Included lay members of the public, professional practitioners in geology and the media.
Year(s) Of Engagement Activity 2017
 
Description Chadwick A. 2018. The Climate Change Crisis and Carbon Storage. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Undergraduate students
Results and Impact Invited lecture to the Earth and Planetary Science Research Group Seminar, Edinburgh University, 18 January 2018.
Year(s) Of Engagement Activity 2018
 
Description Chadwick, R.A. CO2 storage: setting a simple bound on potential leakage through the overburden in the North Sea Basin. Energy Procedia. IEA Greenhouse Gas Technologies conference (IEAGHGT-13) held in Lausanne Switzerland, 14-18 November 2106. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation at the GHGT-13 conference in Lausanne. This is the major biennial CCS conference, with around 1000 participants.
Year(s) Of Engagement Activity 2016
 
Description Conference presentation EAGE 5th CO2 Geological Storage Workshop: Forensic Mapping Of Spatial Velocity Heterogeneity In A CO2 Layer At Sleipner Using Time-Lapse 3D Seismic Monitoring 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Conference presentation at the 5th EAGE CO2 Geological Storage Workshop. The purpose of this activity was to present project research to Industry and the wider academic community.
Year(s) Of Engagement Activity 2018
 
Description Conference presentation at the 5th EAGE CO2 Geological Storage Workshop: Chimneys And Channels: History Matching The Growing CO2 Plume At The Sleipner Storage Site 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Conference presentation at the 5th EAGE CO2 Geological Storage Workshop. The purpose of this activity was to present project research to Industry and the wider academic community. This talk generated interest from EQUINOR and led to a further presentation to EQUINOR scientists.
Year(s) Of Engagement Activity 2018