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DETECT: Determining the risk of CO2 leakage along fractures of the primary caprock using an integrated monitoring and hydro-mechanical-chemical approach

Carbon Capture and Storage (CCS) involves using established technologies to capture carbon dioxide produced or released at source sites such as power stations or other industrial sites, transport it and then store it safely deep underground, as an alternative to emitting it into the atmosphere.The widespread use of CCS may significantly reduce the impact of emissions from those industrial sectors that will continue to rely on hydrocarbons for decades to come. The technology could be critical to achieving global climate-change goals set within the Paris Agreement and also domestically by the British and Scottish governments.

However, carbon capture and storage development has been hampered by high commercial costs and in order to verify and demonstrate successful long-term storage to the regulators and the public, it is critical to improve our understanding of leakage from CO2 storage reservoirs along natural pathways.

Currently, there are significant gaps in the general understanding of leakage along fault zones and fracture networks through the primary caprock. CO2 or CO2-bearing brine at pressures above hydrostatic below the caprock, may fracture the caprock or flow along existing fracture networks, potentially leading to CO2 escape from the reservoir. The flux rates depend on pressure differentials, effective stress, fracture apertures and the connectivity of fracture networks. In addition, CO2 or CO2-bearing fluids pose an increased complexity over other fluids such as water or hydrocarbon as they can chemically react with the rock, significantly dissolve in formation waters or can physically interact with certain minerals, e.g. smectite leading to expansion and the build-up of swelling stresses. Although some fundamental experimental or modelling studies are available in the literature, a large integrated study, involving a complete life cycle risk assessment of CO2 leakage along fractures in caprocks has been lacking, until now.

A study led at Heriot-Watt by Professor Andreas Busch and supported by the Department of Business Energy and Industrial Strategy will determine realistic fracture flow rates and geometries across fractured and faulted caprocks, and aims to identify monitoring tools.

Professor John Underhill, chief scientist at Heriot-Watt University and director of the Shell Centre for Exploration Geoscience, said: "The research to be undertaken by Dr Busch and the team will provide a critical test and validation of the seals for carbon storage sites. “The results will help evaluate the risk or any threat of carbon dioxide leakage into the overburden, something that is crucial to know before any gas injection takes place."

Parts of this article are abstracted from an article published in Scottish Energy News on January 4th 2018

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