Temporal Variability of Emissions Revealed by Continuous, Long-Term Monitoring of an Underground Natural Gas Storage Facility

Abstract

Temporal variability contributes to uncertainty in inventories of methane emissions from the natural gas supply chain. Extrapolation of instantaneous, "snapshot-in-time" measurements, for example, can miss temporal intermittency and confound bottom-up/top-down comparisons. Importantly, no continuous long-term datasets record emission variability from underground natural gas storage facilities despite substantial contributions to sector-wide emissions. We present 11 months of continuous observations on a section of a storage site using dual-frequency comb spectroscopy (DCS observing system) and aircraft measurements. We find high emission variability and a skewed distribution in which the 10% highest 3 h emission periods observed by the continuous DCS observing system comprise 41% of the total observed 3-hourly emissions. Monthly emission rates differ by >12×, and 3-hourly rates vary by 17× in 24 h. We find links to the operating phase of the facilityemission rates, including as a percentage of the total gas flow rate, are significantly higher during periods of injection compared to those of withdrawal. We find that if a high frequency of aircraft flights can occur, then the ground-and aircraft-based approaches show excellent agreement in emission distributions. A better understanding of emission variability at underground natural gas storage sites will improve inventories and models of methane emissions and clarify pathways toward mitigation.

Methane Emissions from the Fossil Fuel Industries of the Russian Federation

“…The problem is further compounded by the intermittency of gas leaks [Alden, 2020;Cusworth, 2021]. A single site visit will not find all sources of emission, but under favorable conditions average site emission rates will decrease with repeated inspections [Ravikumar, 2020].…”

On the Long-Term Temporal Variations in Methane Emissions from an Unconventional Natural Gas Well Site

“…Alden et al identified that methane emissions from natural gas storage facilities varied temporally after conducting continuous long-term monitoring. 10 From a total of 11 months of data, they showed that the highest 10% of 3 h time periods represented 41% of the total observed emissions. Maximum emissions were 2.4 times the 95% fractile of the distribution, and overall, the data were lognormally distributed.…”

“…Many of these studies have highlighted extreme distributions of measurement values 5−8 and others have identified significant temporal variations in methane emissions. 3,4,9,10 Various studies have focused specifically on methane emissions from natural gas production sites (well sites) using both direct component-level measurements and indirect downwind methods. 11−16 Well sites are the first step of the supply chain and include the wells and some associated equipment necessary to introduce the produced gas to a local gathering pipeline.…”

“…Any methane lost in the production and distribution of natural gas represents a loss of energy and offsets the lower carbon intensity of natural gas. , With the successful development of the shale gas, numerous studies have focused on improving the understanding of methane emissions from across the entire natural gas supply chain. Many of these studies have highlighted extreme distributions of measurement values − and others have identified significant temporal variations in methane emissions. ,,, Various studies have focused specifically on methane emissions from natural gas production sites (well sites) using both direct component-level measurements and indirect downwind methods. − Well sites are the first step of the supply chain and include the wells and some associated equipment necessary to introduce the produced gas to a local gathering pipeline. Improving the understanding of methane emissions from various sites or components can enable faster detection and repair to reduce losses and their associated environmental impacts.…”

“…Here, we have expanded the time scale to 4 years, and this extended analysis showed additional variability and now includes some super-emitter-type observations. Alden et al identified that methane emissions from natural gas storage facilities varied temporally after conducting continuous long-term monitoring . From a total of 11 months of data, they showed that the highest 10% of 3 h time periods represented 41% of the total observed emissions.…”