Methane Emissions from Process Equipment at Natural Gas Production Sites in the United States: Pneumatic Controllers

Abstract

Emissions from 377 gas actuated (pneumatic) controllers were measured at natural gas production sites and a small number of oil production sites, throughout the United States. A small subset of the devices (19%), with whole gas emission rates in excess of 6 standard cubic feet per hour (scf/h), accounted for 95% of emissions. More than half of the controllers recorded emissions of 0.001 scf/h or less during 15 min of measurement. Pneumatic controllers in level control applications on separators and in compressor applications had higher emission rates than controllers in other types of applications. Regional differences in emissions were observed, with the lowest emissions measured in the Rocky Mountains and the highest emissions in the Gulf Coast. Average methane emissions per controller reported in this work are 17% higher than the average emissions per controller in the 2012 EPA greenhouse gas national emission inventory (2012 GHG NEI, released in 2014); the average of 2.7 controllers per well observed in this work is higher than the 1.0 controllers per well reported in the 2012 GHG NEI.

Emissions from oil and gas operations in the United States and their air quality implications

“…Similarly, multiple studies (Prasino 2013; Allen et al, 2015a;Gibbs, 2015) have found that a small subpopulation of pneumatic controllers (the largest source of greenhouse gases in the petroleum and natural gas supply chains) dominates emissions. Allen et al (2015a), for example, estimated that 20% of pneumatic controllers in a national sampling of natural gas sites account for 95% of pneumatic controller emissions, and Gibbs (2015) found that 3.5% of controllers accounted for 73% of controller emissions at sites sampled in Oklahoma.…”

“…Recent field studies have sought to quantify these uncertainties. For example, Allen et al (2015a) assessed differences between observed and inventoried pneumatic controller activity factors and reported a factor of 2-3 difference between observed numbers of pneumatic controllers per well Aircraft-based measurements upwind and downwind of production regions; methane measured using high-precision, high-time-resolution instruments, absorption spectrometry at precise infrared wavelengths; light alkanes analyzed from discrete air samples Emissions (0.48 ± 0.13 Tg/yr) 6.2-11.7% of natural gas production Bottom-up inventories for cattle and gas seepage were subtracted from total emissions; difference assigned to oil and gas activity based on methane to light-alkane ratios Barnett Shale Karion et al, 2015 Aircraft-based measurements upwind and downwind of production regions; methane measured using high-precision, high-time-resolution instruments, absorption spectrometry at precise infrared wavelengths…”

Constraining sector-specific CO<sub>2</sub> and CH<sub>4</sub> emissions in the US

“…For example, a number of studies report on direct GHG measurements from individual facilities. These include direct stack measurements of power plant CO 2 emissions (e.g., Teichert et al, 2003) and numerous recent studies of CH 4 emissions from oil and gas operations: measurements of emissions from pneumatic controllers (Allen et al, 2015), compressor stations , transmission and storage systems , and abandoned wells (Kang et al, 2014). In addition, several site-level studies target agricultural emissions.…”

“…For example, facility-level observations provide the most insight into detailed emission processes from specific source sectors but can miss emission events or processes. Observations of oil and gas facilities provide a prime example; scientists may not know about some leaks and therefore may not measure them, other leaks may be in inaccessible locations (e.g., Subramanian et al, 2015), and the largest leaks often come from ephemeral equipment failures at a small number of facilities that are difficult to identify (e.g., Brantley et al, 2014;Allen, 2014;Allen et al, 2015). Cost also limits facility-level, continuous emission monitoring; it is typically only used for large point sources like power plants (National Research Council, 2010).…”

Diagnostic methods for atmospheric inversions of long-lived greenhouse gases

“…For example, point sources of anthropogenic emissions can be measured directly at discrete times (e.g., Allen et al, 2015;Subramanian et al, 2015;Zimmerle et al, 2015),…”