Onshore Oil and Gas: Quantification of whole–site methane emissions and associated uncertainties.

Methane emissions from onshore oil and gas (OOG) sites and facilities contribute towards the UK inventory of methane emissions, and these could be significant if not well controlled. Understanding and quantifying whole-site emissions is important in terms of prioritising action to reduce methane emissions.
This report reviews methods for quantifying whole-site emissions from OOG sites
regulated by the Environment Agency. It considers the wide range of approaches available to determine the combined plume of emissions from all sources within an OOG site, determines the methods best suited for different types of OOG sites, and presents information on the uncertainties associated with quantifying emissions for these selected methods. A taxonomy of methods for detecting and quantifying whole-site methane emissions for OOG facilities has been determined. After assessing the available methods against important criteria, the following 5 methods were selected for more detailed consideration:
• plume-based flux recovery (US EPA Other Test Method 33a (OTM33a) - Geospatial
Measurement of Air Pollution (GMAP))
• component-level measurements
• mass balance
• fenceline monitoring
• tracer method
The report introduces several concepts in uncertainties as part of the detailed assessment.
Method uncertainties are outlined for the 5 selected methods, with evidence drawn from studies in the literature.