Environmental monitoring in the energy sector: exploring parallels between shale gas and nuclear
Meeting report by Leo Salter
ECG Committee Member
ECG Bulletin January 2014
ECG Committee Member
ECG Bulletin January 2014
This event was held at the RSC’s Chemistry Centre, Burlington House on September 26th 2013 under the auspices of the Environment, Sustainability and Energy Division. The meeting overviewed the current energy landscape with particular reference to shale gas extraction by fracking and then gave a perspective on the environmental challenges for shale gas extraction compared to those of the nuclear industry.
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The meeting, attended by fifty delegates, began with a welcome from Dr Mindy Dulai (Programme Manager Environmental Sciences, RSC). There were four speakers: Professor Richard Clegg (Chair) (MD Lloyd’s Register Foundation), Professor Richard Davies (Dean of Knowledge Exchange and Impact and Director of Durham Energy Institute, Durham University), Professor Fred Worrall (Professor of Environmental Chemistry, Department of Earth Sciences, Durham University) and Dr Matthew Randall (Business Leader, Environmental Services Team, National Nuclear Laboratory).
In his introductory talk, Professor Richard Clegg pointed out that shale gas extraction by fracking creates land-based environmental issues with similarities to those generated by the nuclear industry, and that this suggests there are opportunities for knowledge transfer in areas such as geological/hydrogeological fracture flow modelling, the monitoring of gas evolution, post-closure risk assessment, clean-up and remediation, public engagement and stakeholder management. He welcomed the opportunity provided by the meeting to explore possibilities for the sharing of expertise and experience between the two industries. |
Credit: Laurie Barr/Shutterstock
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Environmental risks associated with fracking were discussed in detail by Richard Davies, who spoke on “Fracked or fiction: so what are the risks?” He focused on the way in which several aspects of risk in the shale gas extraction industry can be assessed using existing evidence. He argued that this approach not only enabled public concern to be addressed effectively but also provided a sound basis for effective legislation. When compared to commonly exploited (or conventional) traps of oil and gas such as those in sandstone and limestone, shale is often referred to as an unconventional source, because the technological challenge of working with the low permeability of the fine-grained source rock has made extraction commercially unattractive in the past. The nature of the reservoir is considered therefore unconventional. However, since the 1990s, hydraulic fracturing (“fracking”) of the Barnett Shale in Texas has been performed on a large scale, using horizontal shafts drilled off from the main vertical shaft to introduce water under pressure to create fractures from the horizontal sections. This approach has a primary environmental problem: not only are large volumes of water used but, depending on the particular well and the operating processes being applied, 10% to 50% of the water comes back to the surface as “flow-back.” This water can be contaminated with dissolved material/brine that shows measurable but low (1% above background) levels of radioactivity associated with uranium, radon, radium and thorium (arsenic concentrations are also elevated). Sourcing and treating the volumes of water involved is not without issues for local water suppliers and their treatment plants.
As well as the environmental problems associated with the sourcing and disposal of water, fracking has created public concern in relation to earthquakes and the contamination of water supplies. Richard Davies used the evidence available from hundreds of thousands of well-head operations to show that fracking-induced seismic events were not only rare (a total of three have been recorded so far; Canada, USA and Blackpool) but also small (1.5 to 3.5 on the Richter Scale), below those from conventional oil and gas extraction (events up to magnitude 5) or dam filling (magnitude 7 to 8). He also showed that the contamination of water supplies by leakage through well walls was of low probability. In the Barnett Shale area, for instance, thousands of feet separate the fractures from the sub-surface water supplies above them. In general, fractures have only a 1% chance of being greater than 300 m, and aquifers lying above much deeper horizontal well shafts are therefore unlikely to be contaminated by well water.
However, without the appropriate legislation and controls, well integrity (sealing after use) could become a much more serious issue. Typically, a small well-head will operate for up to a decade before being abandoned. As in the nuclear industry, a form of decommissioning is required to protect the environment for generations. Cement seals can corrode and crack, as can the steel components of the well that remain in situ after abandonment. There will be a large increase in the number of shale gas wells drilled in the UK (from 1902 to 2103, the UK drilled nineteen wells a year, but shale gas extraction could results in up to 500 wells drilled per year). Studies of abandoned wells suggest that leaks are probable, and given the number of wells likely to be in operation in the UK in the future, knowing their precise location and monitoring them post-operation is vital if their integrity is to be assured.
Fred Worrall spoke next (“Environmental impacts of shale gas – things we do not know”). He suggested that shale gas extraction should be categorised as industrial development in a rural area – an approach that draws out the ways in which fracking in a relatively small and congested country like the UK has a different impact compared with wells in the USA. Impacts on habitats, air quality (e.g. methane), water resources (quality and quantity; each new well has a water and waste demand equivalent to an extra population of 350 people), well integrity, public safety, agriculture and quality of life are all aspects of fracking about which little or nothing is known in the UK context. For instance, each well pad has a direct footprint of 9 acres and an indirect footprint of 21 acres and it is not known how much land is needed to minimise the impact of spills and leaks, whether riparian buffer zones should be mandatory, what the environmental consequences of increased construction and transport might be, and whether effects on animals would be significant—in the USA, ‘zero discharge’ requirements mean that well pads are being bundled to achieve the last mentioned. Apart from the impacts of transport to and from the well, air quality is mostly impacted by methane emissions and it needs to be established how these emissions compare to those produced from coal mines, landfill and conventional onshore oil and gas extraction before a useful estimate of the operational air quality risk can be made for shale gas extraction.
The final presentation was from Matthew Randall (NNL), who talked on “Environmental monitoring in the nuclear industry: underpinning clean up and remediation”, chiefly using Sellafield as a case study. The approach to environmental monitoring and assessment on the site (e.g. leakage and legacy storage issues) involves the integration of modelling with monitoring, environmental assessment and experimental data. Hence, boreholes at different depths in and around the source with γ-loggers, ERT monitoring (Electrical Resistance Tomography measurements of ionic strength/salinity), and gas monitoring are used around the low-level-waste repository to inform the modelling of plumes of low-flow contamination from the source. Ion chemistry was investigated by analysis and areas of large charge imbalance were indicative of challenges to the integrity of the monitoring. The data were used in a GIS (Geographic Information System) environment to produce a 3D visualisation of groundwater contaminant plumes which was integrated with 3D geological modelling of the superficial and bedrock geology underlying the Sellafield site. Given that leakage from abandoned shale-gas wells will almost certainly produce legacy problems associated with excursions of waste water and other material into the surrounding geological environment, this approach to long-term monitoring and assessment by the nuclear industry has a real relevance and applicability to shale gas extraction.
As well as the environmental problems associated with the sourcing and disposal of water, fracking has created public concern in relation to earthquakes and the contamination of water supplies. Richard Davies used the evidence available from hundreds of thousands of well-head operations to show that fracking-induced seismic events were not only rare (a total of three have been recorded so far; Canada, USA and Blackpool) but also small (1.5 to 3.5 on the Richter Scale), below those from conventional oil and gas extraction (events up to magnitude 5) or dam filling (magnitude 7 to 8). He also showed that the contamination of water supplies by leakage through well walls was of low probability. In the Barnett Shale area, for instance, thousands of feet separate the fractures from the sub-surface water supplies above them. In general, fractures have only a 1% chance of being greater than 300 m, and aquifers lying above much deeper horizontal well shafts are therefore unlikely to be contaminated by well water.
However, without the appropriate legislation and controls, well integrity (sealing after use) could become a much more serious issue. Typically, a small well-head will operate for up to a decade before being abandoned. As in the nuclear industry, a form of decommissioning is required to protect the environment for generations. Cement seals can corrode and crack, as can the steel components of the well that remain in situ after abandonment. There will be a large increase in the number of shale gas wells drilled in the UK (from 1902 to 2103, the UK drilled nineteen wells a year, but shale gas extraction could results in up to 500 wells drilled per year). Studies of abandoned wells suggest that leaks are probable, and given the number of wells likely to be in operation in the UK in the future, knowing their precise location and monitoring them post-operation is vital if their integrity is to be assured.
Fred Worrall spoke next (“Environmental impacts of shale gas – things we do not know”). He suggested that shale gas extraction should be categorised as industrial development in a rural area – an approach that draws out the ways in which fracking in a relatively small and congested country like the UK has a different impact compared with wells in the USA. Impacts on habitats, air quality (e.g. methane), water resources (quality and quantity; each new well has a water and waste demand equivalent to an extra population of 350 people), well integrity, public safety, agriculture and quality of life are all aspects of fracking about which little or nothing is known in the UK context. For instance, each well pad has a direct footprint of 9 acres and an indirect footprint of 21 acres and it is not known how much land is needed to minimise the impact of spills and leaks, whether riparian buffer zones should be mandatory, what the environmental consequences of increased construction and transport might be, and whether effects on animals would be significant—in the USA, ‘zero discharge’ requirements mean that well pads are being bundled to achieve the last mentioned. Apart from the impacts of transport to and from the well, air quality is mostly impacted by methane emissions and it needs to be established how these emissions compare to those produced from coal mines, landfill and conventional onshore oil and gas extraction before a useful estimate of the operational air quality risk can be made for shale gas extraction.
The final presentation was from Matthew Randall (NNL), who talked on “Environmental monitoring in the nuclear industry: underpinning clean up and remediation”, chiefly using Sellafield as a case study. The approach to environmental monitoring and assessment on the site (e.g. leakage and legacy storage issues) involves the integration of modelling with monitoring, environmental assessment and experimental data. Hence, boreholes at different depths in and around the source with γ-loggers, ERT monitoring (Electrical Resistance Tomography measurements of ionic strength/salinity), and gas monitoring are used around the low-level-waste repository to inform the modelling of plumes of low-flow contamination from the source. Ion chemistry was investigated by analysis and areas of large charge imbalance were indicative of challenges to the integrity of the monitoring. The data were used in a GIS (Geographic Information System) environment to produce a 3D visualisation of groundwater contaminant plumes which was integrated with 3D geological modelling of the superficial and bedrock geology underlying the Sellafield site. Given that leakage from abandoned shale-gas wells will almost certainly produce legacy problems associated with excursions of waste water and other material into the surrounding geological environment, this approach to long-term monitoring and assessment by the nuclear industry has a real relevance and applicability to shale gas extraction.
Matthew pointed out that the different chemical species in plumes needed to be assessed in terms of their persistence – radioactive lifetimes, mobility, reactivity in different geological environments etc. (MNA – Monitored Natural Attenuation). At Sellafield, some species (e.g. actinides) stay close to the source but others (such as 14C, 99Tc, and 90Sr) are predicted to have a greater impact on groundwater. Speciation (e.g. 99Tc is mostly present mostly as TcO4-) is also important for the mobility of contaminants through the geology (e.g. illite clay particles have significant numbers of high affinity edge sites and therefore a high capacity for immobilising ions). In fracking, the release of oxidising fluids into a reducing environment will cause complex speciation issues in the flowback water; for instance, arsenic remobilisation can occur as a consequence of the redox chemistry.
The meeting led to a good and informed discussion, the openness and lack of confrontation in the exchanges being particularly notable. A particular point of relevance was the comment that Bowland Shale in the UK was considerably thicker than that at US sites and that because of the way that this changed the structural integrity of horizontal shafts, it held out the prospect that fewer well pads may be needed in the UK than in the USA (i.e. it was suggested than many more horizontal shafts could be run off a central vertical shaft in the UK than in the USA). It was also pointed out that in isolated rural areas, the subtle changes in point source emissions to air from abandoned well-heads (e.g. long term release of low concentrations of volatile organic compounds such as polycyclic aromatic hydrocarbons and other aromatic compounds) will need careful long-term monitoring during the lifetime of the well but most particularly after closure.
LEO SALTER
September 30th 2013
LEO SALTER
September 30th 2013
