Methane Emissions from Marginal Conventional Well Sites in Colorado

Oil and natural gas wells decline in production as they age and eventually become marginal, producing ≤15 barrels of oil per day or ≤90,000 cubic feet of natural gas per day. Once uneconomical, these wells may be shut in, left idle, or eventually abandoned. Plugged abandoned wells typically emit less methane than unplugged ones. The Colorado Methane Emissions Reduction Program (MERP) offers financial support to operators to voluntarily plug marginal wells to reduce their methane emissions. In support of MERP, marginal well locations in Colorado were surveyed, measured, and characterized. An Optical Gas Imaging (OGI) camera and a trace gas analyzer in a mobile laboratory were used concurrently to survey sites. Any identified methane emissions were quantified directly with a high-flow sampler or indirectly through downwind measurements using the OTM-33A method. No distinction was made between normal (expected) and fugitive (unexpected) emissions. Nine operators participated in the study, covering 46 locations containing major equipment: 117 wells, 95 separators, 127 tanks, and 18 enclosed combustor devices (ECDs). A total of 106 emission sources were identified: 48 were measured with the high flow sampler (1076.56 g CH₄ h^-1, total), and 20 with OTM-33A (4016.9 g CH₄ h^-1, total). Separators accounted for the largest number of emission sources (51), followed by tanks (29), ECDs (14), and wellheads (1). The fact that 1 emission was noted on 117 wellheads observed indicates that in this study, most emissions were associated with supporting production equipment, and not the wellheads themselves. Additionally, emissions were observed less frequently on separators and tanks outfitted with emission controls, resulting in lower average emissions per equipment vs those without controls. Only weak correlations were observed between CH₄ emissions and well count, oil and/or gas production rates, well age, and equipment count; of these, correlations with equipment count and well count were the strongest.