Methane flux from flowback operations at a shale gas site

ABSTRACT

We report measurements of methane (CH₄) mixing ratios and emission fluxes derived from sampling at a monitoring station at an exploratory shale gas extraction facility in Lancashire, England. Elevated ambient CH₄ mixing ratios were recorded in January 2019 during a period of cold-venting associated with a nitrogen lift process at the facility. These processes are used to clear the well to stimulate flow of natural gas from the target shale. Estimates of CH₄ flux during the emission event were made using three independent modeling approaches: Gaussian plume dispersion (following both a simple Gaussian plume inversion and the US EPA OTM 33-A method), and a Lagrangian stochastic transport model (WindTrax). The three methods yielded an estimated peak CH₄ flux during January 2019 of approximately 70 g s⁻¹. The total mass of CH₄ emitted during the six-day venting period was calculated to be 2.9, 4.2 ± 1.4(1σ) and 7.1 ± 2.1(1σ) tonnes CH₄ using the simple Gaussian plume model, WindTrax, and OTM-33A methods, respectively. Whilst the flux approaches all agreed within 1σ uncertainty, an estimate of 4.2 (± 1.4) tonnes CH₄ represents the most confident assessment due to the explicit modeling of advection and meteorological stability permitted using the WindTrax model. This mass is consistent with fluxes calculated by the Environment Agency (in the range 2.7 to 6.8 tonnes CH₄), using emission data provided by the shale site operator to the regulator. This study provides the first CH₄ emission estimate for a nitrogen lift process and the first-reported flux monitoring of a UK shale gas site, and contributes to the evaluation of the environmental impacts of shale gas operations worldwide. This study also provides forward guidance on future monitoring applications and flux calculation in transient emission events.

Implications: This manuscript discusses atmospheric measurements near to the UK’s first hydraulic fracturing facility, which has very high UK public, media, and policy interest. The focus of this manuscript is on a single week of data in which a large venting event at the shale gas site saw emissions of ~4 tonnes of methane to atmosphere, in breach of environmental permits. These results are likely to beresults are likely to be reported by the media and may influence future policy decisions concerning the UK hydraulic fracturing industry.

Acknowledgment

The information reported here has been collected as part of two complementary projects both led by the British Geological Survey (BGS): an environmental monitoring project (www.bgs.ac.uk/lancashire) jointly funded by the BGS National Capability Programme and a grant awarded by the Department for Business, Energy and Industrial Strategy (BEIS; Grant code: GA/18F/017/NEE6617R), and the Equipt4Risk project (NE/R01809X/1) which is part of the NERC/ESRC Unconventional Hydrocarbon Research Programme (www.ukuh.org). BGS authors publish with the permission of the Executive Director, BGS UKRI-UKRI.

Data availability

Calibrated data from the Environmental Baseline Project can be found on the CEDA Archive (http://www.ceda.ac.uk/) at http://catalogue.ceda.ac.uk/uuid/17381cd841ba46aca622307cdcf95da7 (Purvis, 2016).

Disclosure statement

The authors declare that they have no conflict of interest.

Supplemental material

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

This work was supported by the Department for Business, Energy and Industrial Strategy [GA/18F/017/NEE6617R]; Natural Environment Research Council [NE/R01809X/1].

Notes on contributors

Jacob T. Shaw

Jacob T. Shaw is a post-doctoral research assistant at The University of Manchester working on quantifying greenhouse gas emissions from anthropogenic and natural sources.

Grant Allen

Grant Allen is a professor of atmospheric physics at The University of Manchester specialising in measurement and quantification of greenhouse gases and air quality. He can be contacted at http://[email protected].

Joseph Pitt

Joseph Pitt is a post-doctoral research associate at Stony Brook University, with a focus on quantifying greenhouse gas emissions. He was previously employed at The University of Manchester.

Adil Shah

Adil Shah was a Ph.D. student at The University of Manchester, supervised by Grant Allen, developing UAV-based methane measurement approaches and flux methods.

Shona Wilde

Shona Wilde is a Ph.D. research student at the University of York interested in the impact of emissions from the oil and gas industry on air quality.

Laurence Stamford

Laurence Stamford is a senior lecturer in sustainable chemical engineering at The University of Manchester, focusing on the sustainability assessment of energy systems and the production of foods, chemicals and materials.

Zhaoyang Fan

Zhaoyang Fan was a third year BSc Environmental Sciences student at The University of Manchester engaged in a project to study and analyse methane emissions from UK hydraulic fracturing.

Hugo Ricketts

Hugo Ricketts is a National Centre for Atmospheric Science instrument scientist at The University of Manchester with research interests including air pollution monitoring, atmospheric LIDAR and UAVs.

Paul I. Williams

Paul I. Williams is a National Centre for Atmospheric Science research scientist at The University of Manchester, who assisted with UAV-based field campaigns in this work.

Prudence Bateson

Prudence Bateson was a Ph.D. student at the Centre for Atmospheric Science at The University of Manchester researching greenhouse gas emissions from the UK offshore oil and gas industry.

Patrick Barker

Patrick Barker is a Ph.D. student at The University of Manchester, supervised by Grant Allen, researching global greenhouse gas emissions.

Ruth Purvis

Ruth Purvis is a research fellow for the National Centre for Atmospheric Science working in air quality and oil and gas emissions.

David Lowry

David Lowry is a reader in stable isotopes and greenhouse gases at Royal Holloway University London.

Rebecca Fisher

Rebecca Fisher is a lecturer in stable isotopes and greenhouse gases at Royal Holloway University London.

James France

James France is a greenhouse gas research scientist at Royal Holloway University of London and the British Antarctic Survey.

Max Coleman

Max Coleman was an MSc student in Earth Sciences at Royal Holloway, University of London. He is now pursuing a PhD in meteorology at the University of Reading.

Alastair C. Lewis

Alastair C. Lewis is professor of atmospheric chemistry at the University of York and a science director of the National Centre for Atmospheric Science. He can be contacted at http://[email protected].

David A. Risk

Dave A. Risk is a professor at St. Francis Xavier University specialising in the development and application of greenhouse gas measurement technologies for detecting and mapping fugitive emissions in Canada and the US.

Robert S. Ward

Rob S. Ward is Director of Science and Policy at the British Geological Survey. He directs the integrated programme of environmental monitoring and research that this paper is part of.