Deployment of an In-Situ Tunable Diode Laser Absorption Spectrometer (TDLAS) on Unmanned Aerial Systems (UAS) to Quantify Offshore Emissions from Facility Level Down to Equipment Group Level
Authors: Corbett Abigail , Smith Brendan James , Melton Bobby 
Published: September 2023

Abstract
As political, environmental, and social pressures build, oil and gas operators are searching for ways to effectively reduce methane emissions. The first step to emission reduction is to understand the current state of facility emissions, which is typically estimated using bottom-up estimations or measured using a variety of technologies. Increasingly, these bottom-up estimations are under scrutiny due to their lack of agreement with independent, contemporaneous measurements from mass-balance methods or remote-sensing observations. In an offshore environment methane emissions measurement is particularly challenging, especially considering the absorption/reflectivity characteristics of water which inhibits sensors that measure backscatter, such as LiDAR and satellites. Deploying a high-resolution methane sensor onboard a UAS maximizes safety while allowing for accurate emission quantifications, in a way that most other approaches cannot. In this work, methane emissions are detected and quantified in an offshore environment using the SeekIR sensor, an in-situ tunable diode laser absorption spectrometer (TDLAS), mounted on a vertical takeoff and landing (VTOL) Uncrewed Aerial System (UAS). In Fall 2021, methane leak detection and quantification surveys were conducted at offshore facilities in the North Sea and northwest Europe. The TDLAS system was deployed on a DJI M300 multi-rotor drone from a contracted supply vessel to detect and quantify methane emissions at the facilities. Methane concentration, wind data, and other ancillary data were used to perform a mass-balance calculation that resulted in facility-level emissions, independent from background methane concentrations. Operational challenges were encountered and overcome, such as vessel contracting, weather, survey design, and strategizing on valuable data products. Using algorithms that have been validated in third party field trials and metered controlled release experiments, methane emissions were calculated using the measured methane mixing ratios and wind data collected during the survey. Methane emissions were detected and quantified from the 5 offshore facilities, with the results from the surveys used to compare with the bottom-up calculation performed during the same operational period. In one of the first applications of its kind for industry, high-spatiotemporal, high-spatiotemporal methane emission measurement surveys were conducted in an offshore environment, showcasing the application of small unmanned systems proximal to offshore assets as a viable operational approach to meet internal, voluntary, and/or regulatory emissions reporting. Using UAS systems with a TDLAS sensor allows for effective, safe, and accurate methane emissions quantification offshore, saving time and limiting any potential scheduling issues involved with sending manned crews onto the platform. The closed system sensor can be used offshore over water and other high reflective surfaces, allowing for estimates of methane emissions of individual equipment groups.