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.

Methane flux from flowback operations at a shale gas site

“…The peak flux values for each of the three methods were all in agreement with each other and with the operator reported peak gas flow, within 1σ uncertainty. These values were also in excellent agreement with fluxes calculated from four UAV surveys, which reported instantaneous emission fluxes within a range of 9 to 156 g s −1 on 14 January (Shah et al 2020a). The total CH 4 mass estimates were also in good agreement with each other, within their respective uncertainties (at 1σ).…”

“…Summary of peak and mean CH 4 fluxes, and total CH 4 mass emitted, as calculated by three different flux estimation methods. UAV measured fluxes derived from mobile surveys are also provided (seeShah et al 2020a for more information) alongside the operator/regulator reported flux and total CH 4 mass estimates.…”

Quantification and assessment of methane emissions from offshore oil and gas facilities on the Norwegian Continental Shelf

“…Other survey platforms, such as unmanned aerial vehicles (UAVs) also offer potential for CH4 flux quantification from numerous sources (e.g. Nathan et al, 2015;Yang et al, 2018;Allen et al, 2019;Shah et al, 2020;Shaw et al, 2021). For an interesting overview…”

Methods for quantifying methane emissions using unmanned aerial vehicles: a review

“…Air is sampled through a tube (often referred to as a tether) carried by the UAV and measured by an instrument on the ground (e.g. [ 34 , 38 , 65 ] and figure 2 ). This method allows for the beneficial use of high-performance ground-based instrumentation which would otherwise be impossible for a UAV to carry, and which can also be operated continuously.…”

“…Such a heavy payload will only be useful when using larger, sturdier UAVs with maximum take-off weights greater than 20 kg, however. A prototype of a miniaturized off-axis integrated cavity output spectrometer (3.4 kg, 32 W, 2 ppb at 1 Hz precision) built specifically for UAV use was tested on a rotary-wing UAV and successfully used to calculate methane fluxes [ 38 , 65 ]. Similarly, an open-path cavity ring-down spectroscopy instrument (4.1 kg) was successfully integrated onboard a rotary-wing UAV, demonstrating in-flight precisions of between 10 and 30 ppb [ 77 ].…”