Equipment leak detection and quantification at 67 oil and gas sites in the Western United States

Abstract

Emissions from equipment leaks from process components, such as valves and flanges, were measured at 67 sites in the oil and natural gas production and gathering and boosting segments in four different onshore production basins in the western United States. Component counts were obtained from 65 of the 67 sites where nearly 84,000 monitored components resulted in a leak detection rate of 0.39% when detection results using both optical gas imaging (OGI) and a handheld flame ionization detector (FID) were combined. OGI techniques identified fewer leaks but greater total emissions than surveys using an FID operated in accordance with United States Environmental Protection Agency (EPA) Reference Method 21. Many of the leaks that were identified only with an FID were on the lower end of the emission rate distribution in this study. Conversely, OGI identified several components on the higher end of the study emission rate distribution that were not identified with FID-based methods. The most common EPA estimation method for greenhouse gas emission reporting for equipment leaks, which is based on major site equipment counts and population-average component emission factors, would have overestimated equipment leak emissions by 22% to 36% for the sites surveyed in this study as compared to direct measurements of leaking components because of a lower frequency of leaking components in this work than during the field surveys conducted more than 20 years ago to develop the current EPA factors. Results from this study further support emerging evidence that methane detection technologies for oil and gas applications should be evaluated on a different framework than a simple comparison of the counts of leaks detected.

Closing the methane gap in US oil and natural gas production emissions inventories

“…We applied emission factors as reported in the individual studies, with no modifications beyond unit conversion (noting that there are some differences between studies in High Flow Sampler bias correction for gas concentration and flow rate, which may introduce uncertainty to our results). Data for component counts and fraction of components emitting (the ratio of emitting components to all components counted) was scarce, with only 3 studies containing useful information for both ( [35][36][37] for component counts and 35,36,38 for fraction of components emitting).…”

“…In addition to component-level emissions measurements, we also require component counts and fraction of components emitting. A total of 3 studies contained information on component counts [35][36][37] , and we aligned the data into our standard categories. Data on fraction of components emitting was also scarce, with 3 studies containing useful information 35,36,38 .…”

Revised Estimation Method for Emissions from Automated Plunger Lift Liquid Unloadings

“…The revised method based on venting duration and gas production rate predicts that these events would be elevated compared to other measurements in the dataset, but the revised emission method continues to under-predict the emissions per event from these two wells. The ability of a predictive model to account for outlier wells within a sample is particularly important for estimating emissions from natural gas systems due to numerous findings of skewed distributions for component-level emission rates [24][25][26] and specifically for liquid unloadings [2,11,17]. The statistical performance of the revised method, excluding the two outlier wells, is better than Method 3 in terms of MB and MNB (Table 1), and the revised method (733 scf/event) more accurately predicts the mean emissions per event in the measured dataset (810 scf/event) compared to predictions made with Method 3 (1195 scf/event).…”

Closing the gap: Explaining persistent underestimation by US oil and natural gas production-segment methane inventories

“…We applied emission factors as reported in the individual studies, with no modifications beyond unit conversion (noting that there are some differences between studies in High Flow Sampler bias correction for gas concentration and flow rate, which may introduce uncertainty to our results). Data for component counts and fraction of components emitting (the ratio of emitting components to all components counted) was scarce, with only 3 studies containing useful information for both ([35]- [37] for component counts and [35], [36], [38] for fraction of components emitting).…”

“…A total of 3 studies contained information on component counts [35]- [37], and we aligned the data into our standard categories. Data on fraction of components emitting was also scarce, with 3 studies containing useful information [35], [36], [51]. The fraction emitting rate is an important parameter in deriving equipment-level emission factors, but varies greatly by study due to (i) differences in screening methods between studies (e.g., Method 21 vs. infrared camera) and (ii) use of different screening sensitivity to assign a component to the emitting state (10 ppmv vs. 10,000 ppmv).…”