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

Lead Research Organisation: Imperial College London
Department Name: Earth Science and Engineering

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.

Publications

10 25 50
 
Description We have made key advancements in our understanding of how CO2 will flow and be trapped in naturally heterogeneous subsurface systems. The key findings include: (1) an understanding as to the best approach for characterising heterogeneous rocks in the lab, where no previous characterisation protocol had been develoed, and (2) the best approach for upscaling the results of the characterisation so that we may evaluate the impact of heterogeneity on large scale reservoir flows. We now aim to incorporate our recent findings in the analyses of specific field sites and large scale impacts on CCS.
Exploitation Route We anticipate that these findings will lead to significant changes in the approach taken to characterise flow properties of reservoir materials, and significantly enhance the predictive abilities of flow models in which this approach has been taken.
Sectors Digital/Communication/Information Technologies (including Software),Energy,Environment

URL https://eartharxiv.org/wcxny/
 
Description Our findings on the characterisation and impact on natural reservoir heterogeneity on subsurface fluid flow has been of great interest to industry and researchers involved in understanding subsurface flows, including CO2 injection underground and oil production. We have been invited several times to speak with industry practitioners on the techniques we have developed to help them understand how they may be adopted to their own practice. We are now engaged with industry to develop this activity into a joint industry project to further develop and apply these ideas to a range of subsurface flows types.
First Year Of Impact 2017
Sector Energy
Impact Types Economic

 
Description ACT ERA-NET
Amount £15,600,000 (GBP)
Funding ID EC Grant Agreement 691712 
Organisation Department for Business, Energy & Industrial Strategy 
Sector Public
Country United Kingdom
Start 08/2017 
End 08/2020
 
Description UK Carbon Capture and Storage Research Centre 2017
Amount £7,792,199 (GBP)
Funding ID EP/P026214/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2017 
End 03/2022
 
Title Combined laboratory and modelling approach to the characterisation of heterogeneous rocks for modelling subsurface fluid flow 
Description A new approach has been developed to characterise the flow in naturally heterogeneous subsurface rocks, using laboratory measurements combined with numerical modelling 
Type Of Material Improvements to research infrastructure 
Year Produced 2017 
Provided To Others? Yes  
Impact We have received numerous invitations from industry interested in the characterisation and modelling of fluid flow in the subsurface to work with them on the integration of this tool into their practice 
URL https://eartharxiv.org/wcxny/
 
Title Experimental and numerical data for Characterising Drainage Multiphase flow in Heterogeneous Sandstones 
Description The data presented here contains the experimental X-ray CT dataset used as the basis for developing a new method for characterising subsurface flows through heterogeneous rocks. The approach and use of the data is detailed in the manuscript "Characterising Drainage Multiphase flow in Heterogeneous Sandstones" by Jackson et al, available at https://eartharxiv.org/wcxny/. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact We have received numerous invitations from industry interested in the characterisation and modelling of fluid flow in the subsurface to work with them on the integration of this tool into their practice 
URL https://www.bgs.ac.uk/ukccs/
 
Description Attendance of the Mission Innovation workshop on CCUS 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I attended the Mission Innovation workshop on CCUS Sept 25-29, 2017. This was a large workshop hosted by the US Department of Energy focused on identifying key challenges that should be the focus of CCUS research for the Mission Innovation research initative
Year(s) Of Engagement Activity 2017
 
Description Presentation at the regional meeting of the Society of Petroleum Engineers London 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Industry/Business
Results and Impact We were invited to present the findings of our research to the London meeting of the Society of Petroleum Engineers on 30th January, 2018
Year(s) Of Engagement Activity 2018
 
Description Presented findings of the work to the BP Subsurface research team at BP Sunbury 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Interested in the findings of our research, the BP Research Centre at Sunbury invited us to present our findings and ongoing activity. A seminar was held in January, 2018 that included ~50 employees from various parts of upstream research at BP. Further detailed discussions were held as to how to further develop our findings and incorporate them into industry practice.
Year(s) Of Engagement Activity 2018