Colorado Ongoing Basin Emissions (COBE) updated final report

Abstract

The Colorado Ongoing Basin Emissions (COBE) project was jointly developed between teams at Colorado Department of Public Health and Environment (CDPHE)'s Air Pollution Control Division (APCD) and Colorado State University (CSU)'s Methane Emissions Technology Evaluation Center (METEC) to help inform the 2026 Colorado greenhouse gas (GHG) Intensity Verification Rule. The project is also intended to help inform the implementation of the GHG Intensity Verification Rule for calendar year 2026 and beyond. COBE had three primary objectives: • Collect representative measurements of methane emissions from upstream oil and gas facilities throughout the state of Colorado via anonymous aerial campaigns. • Develop measurement informed inventory (MII)s using the aerial emissions data. • Compare the MIIs to operator-reported emissions in the Oil and Natural Gas Annual Emission Inventory Reporting (ONGAEIR) to provide recommended ratios of modeled total emissions to corresponding reported emissions. To collect aerial measurements, the project worked with Bridger Photonics, Inc. (Bridger), GHGSat, and Insight M. METEC formed a scientific modeling team with Colorado School of Mines (CSM). METEC's modeling approach used a discrete event simulation tool via the Mechanistic Air Emissions Simulator (MAES). MAES is intended to first match a reported inventory, here ONGAEIR [1], and then add in any measurements of emissions that are determined to not be included in the reported emissions. If there is missing key information in ONGAEIR the facility cannot be modeled in MAES, which was the case for 19% of facilities for this study. While 81% of ONGAEIR upstream facilities that were operating, or partially operating, were modeled in MAES. MAES allows understanding of emissions at the emitter level (most often, equipment level). CSM concurrently developed a statistical model that relied only on the emissions detections by the measurement technologies, using various data sets to inform emissions below the detection limits of the aerial companies, including one of emission estimates derived from continuous monitoring systems at facilities included in the study and two from the recent literature. Both models developed emissions totals and estimated ratios of total modeled emissions to reported emissions. These ratios were further split out by major basins and major facility classification. The CSM statistical model predicted higher state-wide emissions totals and ratios than the MAES model. It estimated emissions between 87,210 and 134,352 mt/y and ratios of 3.30 to 5.09 (depending on the below-threshold dataset used) when using the same subset of ONGAEIR facilities as the MAES model, and emissions of between 109,364 and 167,848 mt/y with ratios of 3.81 to 5.85 when using all ONGAEIR facilities. In comparison, MAES estimated emissions of 38,936 mt/y and a ratio of 1.47. These results are based on the 2024 ONGAEIR dataset and provide an update to a previous version of this report based on the 2022 ONGAEIR dataset. In addition to updating MII results to the 2024 ONGAEIR, this updated report includes: • The contribution of various emission rates to the MAES model total, showing the importance of small emissions (<5 kg/h) • Additional methods for estimating emissions below aerial threshold in the CSM model More work will be done by the science team in COBE-2 to provide a comprehensive method reconciliation between the two models developed in COBE. COBE-2, funded via the Mark Martinez and Joey Irwin Memorial fund, will additionally develop recommended default factors for 2027. Similar to COBE, a public report will be disseminated near the end of 2026.