Jennifer J. Roberts

Assessing the health risks of natural CO2 seeps in Italy

Industrialized societies which continue to use fossil fuel energy sources are considering adoption of Carbon Capture and Storage (CCS) technology to meet carbon emission reduction targets. Deep geological storage of CO2 onshore faces opposition regarding potential health effects of CO2 leakage from storage sites. There is no experience of commercial scale CCS with which to verify predicted risks of engineered storage failure. Studying risk from natural CO2 seeps can guide assessment of potential health risks from leaking onshore CO2 stores. Italy and Sicily are regions of intense natural CO2 degassing from surface seeps. These seeps exhibit a variety of expressions, characteristics (e.g., temperature/flux), and location environments. Here we quantify historical fatalities from CO2 poisoning using a database of 286 natural CO2 seeps in Italy and Sicily. We find that risk of human death is strongly influenced by seep surface expression, local conditions (e.g., topography and wind speed), CO2 flux, and human behavior. Risk of accidental human death from these CO2 seeps is calculated to be 10-8 year-1 to the exposed population. This value is significantly lower than that of many socially accepted risks. Seepage from future storage sites is modeled to be less that Italian natural flux rates. With appropriate hazard management, health risks from unplanned seepage at onshore storage sites can be adequately minimized.

Natural CO2 sites in Italy show importance of overburden geopressure, fractures and faults for CO2 storage performance and risk management

Abstract The study of natural analogues can inform the long-term performance security of engineered CO2 storage. There are natural CO2 reservoirs and CO2 seeps in Italy. Here, we study nine reservoirs and establish which are sealed or are leaking CO2 to surface. Their characteristics are compared to elucidate which conditions control CO2 leakage. All of the case studies would fail current CO2 storage site selection criteria, although only two leak CO2 to surface. The factors found to systematically affect seal performance are overburden geopressure and proximity to modern extensional faults. Amongst our case studies, the sealing reservoirs show elevated overburden geopressure whereas the leaking reservoirs do not. Since the leaking reservoirs are located within <10 km of modern extensional faults, pressure equilibration within the overburden may be facilitated by enhanced crustal permeability related to faulting. Modelling of the properties that could enable the observed CO2 leakage rates finds that high-permeability pathways (such as transmissive faults or fractures) become increasingly necessary to sustain leak rates as CO2 density decreases during ascent to surface, regardless of the leakage mechanism into the overburden. This work illustrates the value of characterizing the overburden geology during CO2 storage site selection to inform screening criterion, risk assessment and monitoring strategy.

Bursting bubbles: can experiments and analogues help stakeholders and the public visualise risks?

Laboratory experiments, natural analogues and pilot projects have been fundamental in developing scientific understanding of risk and uncertainty from georesource exploration. International research into CO2 and CH4 leakage provide scientific understanding of potential leakage styles, rates and environmental impacts. However, the value of these experiments as a communication tool for stakeholders and the wider public is often overlooked in the form of visual information and comparisons. Quantifiable laboratory experiments, measurement of gas at natural springs or controlled release of CO2 (e.g. Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage Project (QICS)) raise awareness and commitment to understanding environmental impacts and geological complexities. Visuals can greatly facilitate communication, and research into public understanding of the subsurface demonstrates that quality and scale of schematics can affect perceived risk. Here we consider how public perception of subsurface activities could be shaped by relevant and applicable research that shares accessible and visually engaging information. Could images showing bubbles of seeping gas, or showcasing monitoring methods and capabilities, help to contextualise risks and geoscientific concepts and shape opinions? Can these materials aid dialogue between the wider scientific community, publics and stakeholders? We propose that future projects could improve dialogue through use of context-appropriate visuals to enhance dialogue on risks, impacts and monitoring of subsurface engineering technologies.