Technical Guidance Document Number 6: Unstabilized Hydrocarbon Liquid Storage Tanks

This document provides technical guidance to Partners of the CCAC Oil and Gas Methane Partnership (OGMP). It is one in a series describing a core source of methane emissions from oil and natural gas production operations. The guidance documents introduce suggested methodologies for quantifying methane emissions from specific sources and describe established mitigation options that Partners should reference when determining if the source is “mitigated.”

Emissions from storage vessels are a function of flash, working, and standing losses. Flash losses (the most significant of the three) occur when a liquid with dissolved gases is transferred from a vessel at higher pressure relative to the receiving vessel. The instantaneous pressure drop causes gas to rapidly vaporize  (i.e., flash). Working losses refer to vapor released due to changing fluid levels and agitation of liquids in tanks associated with circulation of fresh liquid through them. Standing losses refer to vapor release 35 associated with daily and seasonal temperature and barometric pressure changes.