A story was reported yesterday (30 November 2017) by various media outlets about carbon dioxide storage in the North Sea, based on research from Heriot-Watt University. SCCS welcomes the additional information provided by this research study on the Captain Sandstone, which relates to an area much further west than that currently being considered for CO2 storage. It adds to our understanding and confirms what we already know.
The occurrence of faults that cross-cut the seal rock of the Captain Sandstone formation and its subcrop at the seabed are well known, and their presence has been included in various CO2 storage studies. Additional interpretation of the Captain Sandstone over 70 km further to the west than the sites being considered for CO2 geological storage is welcomed. Extensive studies undertaken by industry and by research consortia have investigated CO2 storage within the Captain Sandstone away from cross-cutting faults and in its eastward extension, and at depths that exceed 1000m.
In fact, the connected reservoir and subcrop at the seabed have been identified as beneficial. They enable pressure to dissipate, reducing the risk of the injection site becoming over-pressured and improving CO2 storage capacity and security. Calculations show that without these features the Captain Sandstone formation could store around 360 million tonnes of CO2, but that with the subcrop the capacity for secure storage increases to over 1,550 million tonnes. That is the equivalent of increasing capacity from about seven years of all of Scotland’s CO2 emissions to over 30 years of emissions storage. These findings were reported in a March 2011 public report “Progressing Scotland’s CO2 storage opportunities”, page 28.
Industry has undertaken robust geological screening to ensure the integrity of any CO2 storage in the Captain Sandstone formation. An extensive research study undertaken with industry to investigate storage in two or more sites in the Captain Sandstone identifies that this formation contains six oil and gas fields, as shown in the September 2015 public report “Optimising CO2 storage in geological formations; a case study offshore Scotland”, page 4. This fact demonstrates containment of oil and gas over millions of years. In addition to the geological features that lead to oil and gas trapping (called stratigraphic trapping), CO2 is additionally retained in the deep subsurface by a combination of factors. These include the CO2 dissolving into the pore water, making the water denser and so liable to migrate downdip away from the outcrop, and by leaving a trail of microscopic micro-bubbles isolated in pores (called residual trapping).
It is very useful and timely to draw attention to the potential of CO2 storage in the Captain Sandstone, since the UK is lagging behind our counterparts in Norway, and will need to use CO2 storage to meet greenhouse gas emissions targets by 2050 in a cost-effective manner. The Sleipner site, which lies immediately adjacent to the UK/Norway North Sea maritime boundary, is an aquifer that has been used to store CO2 for over two decades now. Learning gained from the appraisal, monitoring and operation of this and other Norwegian storage sites has been applied to the assessment of the UK Captain Sandstone, and due to its location, existing infrastructure, and especially the suitability of the geology, it is currently the most promising prospect for CO2 storage in UK Continental Shelf.
Professor Stuart Haszeldine was interviewed on BBC Scotland's Good Morning Scotland on 1 December, 6.45am: http://www.bbc.co.uk/programmes/b0074hf7
The authors of this briefing, Prof Eric Mackay (Heriot-Watt University), Dr Maxine Akhurst (British Geological Survey) and Prof Stuart Haszeldine (University of Edinburgh) are members of the SCCS Directorate and are internationally recognised CO2 storage experts.
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