Extrapolation Approaches for Creating Comprehensive Measurement-Based Methane Emissions Inventories

Methane emissions inventories are essential for U.S. oil and natural gas operators to track their progress toward emissions targets, demonstrate the impact of improved operational and monitoring practices, and enable the scientific community to monitor methane budgets at various scales. There has been growing interest in relying less on accounting-style methods and more on direct emissions measurements. However, translating raw emission measurement data, whether from continuous monitoring systems, aerial flyovers, or operational cause analyses, into emissions inventories is nontrivial, and inventory numbers published by operators often lack any information about the methodology used to produce them. In this paper, we introduce the concept of a comprehensive measurement-based emissions inventory, which represents all emissions across the entire time frame, across all assets, and of all emission sizes for the target scope. We introduce practical extrapolation methods to account for incomplete measurement data across time, space, and emission sizes and focus on the impact that different extrapolation methods can have on the resulting emissions estimate. Understanding these methods is essential to create defensible and comparable emissions inventory reports that adhere to reporting frameworks such as Veritas and the Oil and Gas Methane Partnership 2.0.