Characterization of major overburden leakage pathways above sub-seafloor CO2 storage reservoirs in the North Sea (CHIMNEY)

Lead Research Organisation: National Oceanography Centre
Department Name: Science and Technology


Industrial emissions of carbon dioxide (CO2), including fossil fuel power generation, are recognised as a likely agent of global climate change and acidification of the oceans, but most economies will remain dependent on these technologies for the next few decades. Carbon dioxide Capture and Storage (CCS) has been identified as an important way of reducing the amount of CO2 added to the atmosphere. CCS is seen as making a key contribution to reducing mankind's greenhouse gas emissions by 80-95% by 2050 and keeping climate change derived temperature increases below 2 degrees C, as outlined in European Commission policy. In addition, CCS is considered an important way of reducing the cost of mitigation measures around the continued use of fossil fuels. Offshore storage of CO2 in depleted oil and gas reservoirs and saline aquifers is the option of choice for most European nations, and there is currently one operational storage complex (Sleipner, Norway), and several other commercial scale demonstration projects are in late stages of development (e.g. ROAD-Netherlands, Peterhead and White Rose-UK), and expected to be in full operation by 2020.
A key element of CCS offshore is that there is confidence that the risks of any leakage are understood. The location and potential intensity of any possible CO2 leakage at the seafloor are critically dependent on the distribution of fluid (dissolved and gaseous CO2) pathways in the rocks overlying the reservoirs in which the CO2 is stored, and on the ability of these pathways to transmit fluid (termed permeability). Recent studies of the structure of marine sedimentary rocks in the North and Norwegian Seas have revealed that near-vertical structures, which resemble chimneys or pipes, cross-cut the sedimentary sequence. These structures may be pathways for fluid flow. Natural fluids from deeper rock layers have migrated through these structures at some point in geological time. If CO2 leaking from sub-seafloor storage reservoirs reaches the base of these structures, and if their permeability is sufficiently high, they could act as CO2 leakage pathways towards the seafloor and overlying water column. To provide a reliable prediction of potential seafloor seep sites, the degree to which these pathways are continuous and especially their permeability needs to be better understood.
In this project (CHIMNEY) we will collect new data over a chimney structure within the North Sea by using a ship to make new and unusual measurements with sound waves. We will use several different marine sound sources to make images of the chimney, using receivers at the sea surface, and also record the sound arrivals on sea bed instruments known as ocean bottom seismometers. By looking at the sound travel paths through the sub-surface from a range of directions and frequencies we will obtain information about fractures/fluid pathways in the chimney as well as the surrounding rocks. We will calibrate and understand our marine seismic results using laboratory studies of materials (synthetic rocks) that mimic the sub-surface rocks. By understanding the propagation of sound through synthetic rocks with known fluid pathways we can understand the results of the marine experiment. We will also drill into the chimney and collect core samples which we will analyse for core geology and fluid chemistry. A computer model of the sub-surface chimney will be constructed combining the results of the seismic experiment, rock physics, and chemistry. We will work with companies involved in CCS to build realistic computer models of fluid flow that tell us about the risk of leakage from chimney structures generally within the North Sea that are relevant to Carbon Dioxide Capture and Storage.

Planned Impact

Impact Summary

a. Who could potentially benefit from the proposed research over different timescales?

Identified user groups for the new knowledge that we will create:

(1) Policymakers and regulators, including Department of Energy & Climate Change and the European Commission
(2) CCS Operators
(3) General public, NGOs and fisheries organisations.

b. How might the potential beneficiaries benefit?

Policymakers and regulators
We will produce 3D models of the overburden and produce realistic leakage scenarios for structures relevant to Carbon Capture and Storage sites in the North Sea. This information is required for compliance with the EU CCS Directive and other international CCS agreements (e.g. London Protocol).

CCS Operators
Operators of CCS systems will benefit from the generation of new methodologies to constrain reservoir overburden CO2 permeability and potential near-surface fluid flow paths for relevant example structures in the North Sea. We will generate new tools to constrain leak risks for future CCS projects, developed through collaboration with stakeholders

General Public, NGOs and fisheries organisations
Acceptance of CCS, especially by local communities, depends on many factors, and confidence in the physical security of stored CO2 is a major issue. In this respect, clear and accessible communications designed for specific audiences are critical in ensuring that accurate information about sub-seabed CO2 storage is available to those who need it.

Specific activities for engagement with these target groups are covered in our Pathways to Impact document.


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Böttner C (2019) Pockmarks in the Witch Ground Basin, Central North Sea in Geochemistry, Geophysics, Geosystems

Related Projects

Project Reference Relationship Related To Start End Award Value
NE/N016041/1 01/05/2016 31/10/2019 £439,511
NE/N016041/2 Transfer NE/N016041/1 01/11/2019 31/10/2021 £45,391
Description Through laboratory experiments on sandstone samples, typical of proposed CO2 storage reservoir rocks in the North Sea and elsewhere, we have quantified the geophysical expressions of CO2 saturation in reservoir rocks, including supercritical CO2 for reservoir depths below about 800 m beneath the seafloor. With complementary theoretical modelling, we have identified possible seismic signatures indicative of the different amounts (saturations) of CO2 stored in rocks. his new knowledge will allow better seismic mapping and monitoring of the subsurface CO2 plume after CO2 injection below the seafloor.
Exploitation Route New rock physics datasets and knowledge can be used by CO2 storage site operators to provide public and regulatory assurance of safe CO2 storage below ground.
Sectors Energy,Environment,Security and Diplomacy

Title Experimental data from brine-CO2 flow-through test on a 45% porosity synthetic sandstone under shallow storage reservoirs conditions 
Description The spreadsheet gathers the data collected during a brine:CO2 flow-through experiment conducted on a weakly-cemented synthetic sandstone core sample using the multiflow experimental rig for CO2 experiments, designed and assembled at the National Oceanography Centre, Southampton. The test was configured to assess geophysical monitoring and deformation of reservoirs subjected to CO2 injection in shallow weakly-cemented (North Sea-like, e.g., Sleipner) CO2 storage sandstone reservoirs. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Impact The dataset was partially published in 
Title Experimental data from brine-CO2 flow-through test on an Utsira Sand core sample at Sleipner reservoirs conditions 
Description The spreadsheet gathers the data collected during an experiment conducted on a Utsira Sand formation core sample to complements and constrains existing geophysical monitoring surveys at Sleipner and, more generally, improves the understanding of shallow weakly-cemented sand reservoirs. The tests were conducted in the rock physics laboratory at the National Oceanography Centre, Southampton, during 2016. The experiment was a steady state brine-CO2 flow-through test to simultaneously evaluate ultrasonic waves, electrical resistivity (converted into pore fluid distribution) and mechanical indicators during CO2 geosequestration in shallow weakly-cemented reservoirs. The confining and pore pressure conditions were similar to those estimated for Sleipner (North Sea - like storage reservoirs), but simulating inflation/depletion cyclic scenarios for increasing brine:CO2 fractional flow rates. The data include primary ultrasonic wave velocities and attenuation factors, axial and radial strains, and electrical resistivity. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact Also, we have provided a velocity-saturation relationship of practical importance to CO2 plume monitoring, obtained from the inversion of ultrasonic velocity and attenuation data and extrapolation of results to field-scale seismic-frequencies using a new rock physics theory ( 
Title Geophysical, hydraulic and mechanical properties of synthetic versus natural sandstones under variable stress conditions 
Description This dataset gather ultrasonic P- and S-wave velocities and attenuations, electrical resistivity, axial and radial strains, permeability and mineralogical composition, of two synthetic and two natural sandstones, measured at variable realistic reservoir conditions of stress. The data were collected during an original study which aimed to assess the extent to which the measured properties between synthetic and natural sandstones are comparable. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Impact The work was accepted for publication in Geophysical Prospecting on the 01/10/2018*, which can be accessed following the link: *Falcon-Suarez, I.H., Amalokwu, K., Robert, K., North, L., Best, A.I., Delgado-Martin, J., Callow, B., Sahoo, S.K. (accepted). Comparison of stress dependent geophysical, hydraulic and mechanical properties of synthetic and natural sandstones for reservoir characterisation and monitoring studies. Geophysical Prospecting 
Description Carbon Capture and Storage Rock Physics Research at the NOC 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Youtube presentation of the experimental research related to Carbon Capture and Storage conducted at the National Oceanography Centre (NOC), Southampton, by the rock physics research team (Marine Geoscience group).
Year(s) Of Engagement Activity 2018
Description High Pressure Multi-flow Experimental Rig at the NOC 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Youtube video describing the features of the High Pressure Multi-flow Experimental Rig at the National Oceanography Centre (NOC), Southampton. The video also explains the procedure used in the NOC to run CO2-brine multi-flow tests using rock samples (reservoirs analogues) at realistic temperature and pressure conditions found in deep geological reservoirs.
Year(s) Of Engagement Activity 2018