An Introduction to MII, MAES, and O&G Emissions

MAES (Mechanistic Air Emissions Simulator) is a simulation tool developed at Colorado State University to estimate emissions from a range of oil and gas facilities, including production sites, compressor stations, dehydration stations, and gas processing plants. These sites can emit hydrocarbons that can be grouped into two primary categories:

a) Normal-Operating Emissions: Routine emissions from regular equipment (e.g., wells, tanks, separators, compressors, heaters, flares, and dehydrators). Many of these are reported to regulatory inventories, such as the federal Greenhouse Gas Reporting Program (GHGRP) or Colorado’s Oil and Natural Gas Emissions Inventory Rule (ONGAEIR). Even though regulatory inventories have improved significantly over the years, ongoing research and field data continue to reveal emission sources that may still be underreported or missing. For example, crankcase emissions from reciprocating engines were not initially required under older versions of Subpart W, despite being an expected and normal operating emission.

b) Abnormal Process Emissions: Less frequent but potentially large release events. These can originate from equipment malfunctions or process upsets and are typically underreported or absent in conventional inventories. Despite their rarity, they can dominate total emissions when summed across an entire basin or region.

Accurately quantifying both normal and abnormal emissions is essential for developing a comprehensive inventory that reflects real-world emissions and informs regulatory and industry decision-making. By integrating field measurements with existing inventories, we establish the foundation for what we define as a Measurement Informed Inventory (MII).