Modelling the two-phase plume dynamics of CO2 leakage into open shallow waters

A numerical model of two-phase plume developments in a small scale turbulent ocean is proposed and designed as a fundamental study to predict the near field physicochemical impacts and biological risk to the marine ecosystem from CO2 leakage from potential carbon storage locations around the North Sea. New sub-models are developed for bubble formation and drag coefficients using in-situ measurements from videos of the Quantifying and monitoring potential ecosystem Impacts of geological Carbon Storage (QICS) experiment. Existing sub-models such as Sherwood numbers and plume interactions are also compared, verified and implemented into the new model. Observational data collected from the North Sea provides the ability to develop and verify a large eddy simulation turbulence model, limited to situations where the non-slip boundary wall may be neglected. The model is then tested to assimilate the QICS experiment, before being applied to potential leakage scenarios around the North Sea with key marine impacts from pCO2 and pH changes. The most serious leak is from a well blowout, with maximum pH changes of up to -2.7 and changes greater than -0.1 affecting areas up to 0.23 km2. Other scenarios through geological structures would be challenging to detect with pH changes below -0.27

Dynamics of rising CO\u3csub\u3e2\u3c/sub\u3e bubble plumes in the QICS field experiment: Part 1 - The experiment

© 2015 The Authors. Published by Elsevier Ltd. The dynamic characteristics of CO2 bubbles in Scottish seawater are investigated through observational data obtained from the QICS project. Images of the leaked CO2 bubble plume rising in the seawater were captured. This observation made it possible to discuss the dynamics of the CO2 bubbles in plumes leaked in seawater from the sediments. Utilising ImageJ, an image processing program, the underwater recorded videos were analysed to measure the size and velocity of the CO2 bubbles individually. It was found that most of the bubbles deform to non-spherical bubbles and the measured equivalent diameters of the CO2 bubbles observed near the sea bed are to be between 2 and 12 mm. The data processed from the videos showed that the velocities of 75% of the leaked CO2 bubbles in the plume are in the interval 25-40 cm/s with Reynolds numbers (Re) 500-3500, which are relatively higher than those of an individual bubble in quiescent water. The drag coefficient C d is compared with numerous laboratory investigations, where agreement was found between the laboratory and the QICS experimental results with variations mainly due to the plume induced vertical velocity component of the seawater current and the interactions between the CO2 bubbles (breakup and coalescence). The breakup of the CO2 bubbles has been characterised and defined by Eötvös number, Eo, and Re

Dynamics of rising CO2 bubble plumes in the QICS field experiment: Part 2 – Modelling

An oceanic two-phase plume model is developed to include bubble size distribution and bubble interactions, applied to the prediction of CO2 bubble plume and CO2 solution dynamics observed from the recent QICS field experiment in the Scottish sea at Ardmucknish Bay. Observations show bubbles form at between 2 and 12 mm in diameter, where the inclusion of the interactions within the simulations brings results of bubble plumes closer to that of the experiment. Under a given leakage flux, simulations show that the bubble size affects the maximum pCO2 dissolved in the water column, while the bubble interactions affect the vertical bubble distribution. The maximum modelled pCO2 increases from a background 360 μatm to 400, 427 and 443 μatm as CO2 injection rates increase from 80, 170 to 208 kg/day respectively at low tide. An increase of the leakage rate to 100% of the injection rate shows the maximum pCO2 could be 713 μatm, approaching the mean pCO2 observed of 740 μatm during the high leakage component of the experiment, suggesting that the flux may be greater than estimated due to the varied flux and activity across the pockmarks during the leakages

Dynamics of rising CO2 bubble plumes in the QICS field experiment: Part 1 – The experiment

The dynamic characteristics of CO2 bubbles in Scottish seawater are investigated through observational data obtained from the QICS project. Images of the leaked CO2 bubble plume rising in the seawater were captured. This observation made it possible to discuss the dynamics of the CO2 bubbles in plumes leaked in seawater from the sediments. Utilising ImageJ, an image processing program, the underwater recorded videos were analysed to measure the size and velocity of the CO2 bubbles individually. It was found that most of the bubbles deform to non-spherical bubbles and the measured equivalent diameters of the CO2 bubbles observed near the sea bed are to be between 2 and 12 mm. The data processed from the videos showed that the velocities of 75% of the leaked CO2 bubbles in the plume are in the interval 25–40 cm/s with Reynolds numbers (Re) 500–3500, which are relatively higher than those of an individual bubble in quiescent water. The drag coefficient Cd is compared with numerous laboratory investigations, where agreement was found between the laboratory and the QICS experimental results with variations mainly due to the plume induced vertical velocity component of the seawater current and the interactions between the CO2 bubbles (breakup and coalescence). The breakup of the CO2 bubbles has been characterised and defined by Eötvös number, Eo, and Re

Quantification of a subsea CO2 release with lab-on-chip sensors measuring benthic gradients

We present a novel approach to detecting and quantifying a subsea release of CO2 from within North Sea sediments, which mimicked a leak from a subsea CO2 reservoir. Autonomous lab-on-chip sensors performed in situ measurements of pH at two heights above the seafloor. During the 11 day experiment the rate of CO2 release was gradually increased. Whenever the currents carried the CO2-enriched water towards the sensors, the sensors measured a decrease in pH, with a strong vertical gradient within a metre of the seafloor. At the highest release rate, a decrease of over 0.6 pH units was observed 17 cm above the seafloor compared to background measurements. The sensor data was combined with hydrodynamic measurements to quantify the amount of CO2 escaping the sediments using an advective mass transport model. On average, we directly detected 43 ± 8% of the released CO2 in the water column. Accounting for the incomplete carbonate equilibration process increases this estimate to up to 61 ± 10%. This technique can provide long-term in situ monitoring of offshore CO2 reservoirs and hence provides a tool to support climate change mitigation activities. It could also be applied to characterising plumes and quantifying other natural or anthropogenic fluxes of dissolved solutes

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Effects of antiplatelet therapy after stroke due to intracerebral haemorrhage (RESTART): a randomised, open-label trial

Background: Antiplatelet therapy reduces the risk of major vascular events for people with occlusive vascular disease, although it might increase the risk of intracranial haemorrhage. Patients surviving the commonest subtype of intracranial haemorrhage, intracerebral haemorrhage, are at risk of both haemorrhagic and occlusive vascular events, but whether antiplatelet therapy can be used safely is unclear. We aimed to estimate the relative and absolute effects of antiplatelet therapy on recurrent intracerebral haemorrhage and whether this risk might exceed any reduction of occlusive vascular events. Methods: The REstart or STop Antithrombotics Randomised Trial (RESTART) was a prospective, randomised, open-label, blinded endpoint, parallel-group trial at 122 hospitals in the UK. We recruited adults (≥18 years) who were taking antithrombotic (antiplatelet or anticoagulant) therapy for the prevention of occlusive vascular disease when they developed intracerebral haemorrhage, discontinued antithrombotic therapy, and survived for 24 h. Computerised randomisation incorporating minimisation allocated participants (1:1) to start or avoid antiplatelet therapy. We followed participants for the primary outcome (recurrent symptomatic intracerebral haemorrhage) for up to 5 years. We analysed data from all randomised participants using Cox proportional hazards regression, adjusted for minimisation covariates. This trial is registered with ISRCTN (number ISRCTN71907627). Findings: Between May 22, 2013, and May 31, 2018, 537 participants were recruited a median of 76 days (IQR 29–146) after intracerebral haemorrhage onset: 268 were assigned to start and 269 (one withdrew) to avoid antiplatelet therapy. Participants were followed for a median of 2·0 years (IQR [1·0– 3·0]; completeness 99·3%). 12 (4%) of 268 participants allocated to antiplatelet therapy had recurrence of intracerebral haemorrhage compared with 23 (9%) of 268 participants allocated to avoid antiplatelet therapy (adjusted hazard ratio 0·51 [95% CI 0·25–1·03]; p=0·060). 18 (7%) participants allocated to antiplatelet therapy experienced major haemorrhagic events compared with 25 (9%) participants allocated to avoid antiplatelet therapy (0·71 [0·39–1·30]; p=0·27), and 39 [15%] participants allocated to antiplatelet therapy had major occlusive vascular events compared with 38 [14%] allocated to avoid antiplatelet therapy (1·02 [0·65–1·60]; p=0·92). Interpretation: These results exclude all but a very modest increase in the risk of recurrent intracerebral haemorrhage with antiplatelet therapy for patients on antithrombotic therapy for the prevention of occlusive vascular disease when they developed intracerebral haemorrhage. The risk of recurrent intracerebral haemorrhage is probably too small to exceed the established benefits of antiplatelet therapy for secondary prevention