Unmanned aerial vehicle observations of cold venting from exploratory hydraulic fracturing in the United Kingdom

Abstract

Unmanned aerial vehicle (UAV) surveys allow for rapid-response near-field sampling, downwind of emission sources, such as gas extraction sites, without the need for site access. UAVs can be used in emission source identification alongside instantaneous flux estimation. A UAV was used to sample downwind of the UK’s first and only gas extraction site to use exploratory onshore horizontal hydraulic fracturing (fracking) of shale formations, in Little Plumpton, Lancashire. In-situ calibrated UAV methane mole fraction measurements were made from a neighbouring field on five sampling days between October 2018 and February 2019, during fracking, flow-back and flow testing. Methane emissions were identified on one of the five sampling days (14 January 2019), associated with known cold venting, following fluid unloading using a nitrogen lift. A near-field Gaussian plume inversion approach was used to calculate four instantaneous fluxes on this day (from four separate intermittent UAV flight surveys) with lower and upper uncertainty bounds of between 9–80 g s−1,23–106 g s−1, 16–82 g s−1 and 34–156 g s−1, respectively. The cold venting emissions observed on this single day were at least an order of magnitude higher than UAV methane fluxes calculated for nearby dairy farm buildings, also presented here. Identifying and quantifying these methane emission sources are important to improve the national emissions inventory and to regulate this developing UK industry.