A new look at methane and nonmethane hydrocarbon emissions from oil and natural gas operations in the Colorado Denver‐Julesburg Basin

Abstract

Emissions of methane (CH 4 ) from oil and natural gas (O&G) operations in the most densely drilled area of the Denver-Julesburg Basin in Weld County located in northeastern Colorado are estimated for 2 days in May 2012 using aircraft-based CH 4 observations and planetary boundary layer height and ground-based wind profile measurements. Total top-down CH 4 emission estimates are 25.8 ± 8.4 and 26.2 ± 10.7 t CH 4 /h for the 29 and 31 May flights, respectively. Using inventory data, we estimate the total emissions of CH 4 from non-O&G gas-related sources at 7.1 ± 1.7 and 6.3 ± 1.0 t CH 4 /h for these 2 days. The difference in emissions is attributed to O&G sources in the study region, and their total emission is on average 19.3 ± 6.9 t/h, close to 3 times higher than an hourly emission estimate based on Environmental Protection Agency's Greenhouse Gas Reporting Program data for 2012. We derive top-down emissions estimates for propane, n-butane, i-pentane, n-pentane, and benzene from our total top-down CH 4 emission estimate and the relative hydrocarbon abundances in aircraft-based discrete air samples. Emissions for these five nonmethane hydrocarbons alone total 25.4 ± 8.2 t/h. Assuming that these emissions are solely originating from O&G-related activities in the study region, our results show that the state inventory for total volatile organic compounds emitted by O&G activities is at least a factor of 2 too low for May 2012. Our top-down emission estimate of benzene emissions from O&G operations is 173 ± 64 kg/h, or 7 times larger than in the state inventory.

Natural gas facility methane emissions: measurements by tracer flux ratio in two US natural gas producing basins

“…Peischl et al (2015) report basin-level emission rates from three shale plays that make up over 50% of 2013 US gas production: the Haynesville (West Texas & Louisiana), Fayetteville (Arkansas) and Marcellus (Pennsylvania portion only) shale formations. They find that loss rates as a percentage of methane produced were lower than the previously studied Denver-Julesburg (Colorado) (Pétron et al, 2012;Pétron et al, 2014) and Uinta (Utah) plays (Karion et al, 2013). This paper describes dual tracer flux ratio measurements of methane emissions from oil and natural gas facilities.…”

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

“…In addition to these aircraftbased studies, one study uses the SCIAMACHY instrument on the Envisat satellite to estimate CH 4 emissions from the Eagle Ford and Bakken Shale regions in Texas and North Dakota, respectively . Several of these studies find leakage rates that greatly exceed the EPA's estimated emission factors (e.g., Karion et al, 2013;Pétron et al, 2014;Schneising et al, 2014), while other studies estimate leakage rates that are comparable to the EPA's numbers (e.g., Caulton et al, 2014;Peischl et al, 2015). Differences in drilling technology and practices from one basin to another may account for these contrasting results (e.g., Peischl et al, 2015).…”

“…Furthermore, Brantley et al (2014) explain that these leaks do not correlate with production and can vary greatly in time. Different oil and gas drilling basins also have different overall leakage rates -from 0.3 % in Pennsylvania's Marcellus Shale region to 8.9 % in Utah's Uintah Basin (e.g., Karion et al, 2013Karion et al, , 2015Pétron et al, 2014;Peischl et al, 2015). These factors make it challenging to create consistent, generalizable EFs that can translate activity data into emissions.…”

“…For example, several top-down studies indicate that the California state inventory is likely too low by a factor of 1.2 to 1.9 (Jeong et al, 2013Wecht et al, 2014b), and several top-down studies estimate emissions for oil and gas drilling regions of Utah and Colorado that are up to 3 times bottom-up estimates (e.g., Karion et al, 2013;Pétron et al, 2014). Overall, total US CH 4 emissions are likely ∼50 % larger than estimated by EDGAR or the US EPA Wecht et al, 2014a;Turner et al, 2015).…”

The global methane budget 2000–2012

“…Indeed, the practice of high-volume hydraulic fracturing (fracking) for oil and gas extraction is a growing sector of methane and other hydrocarbon production, especially in the US. Most recent studies M. Saunois et al: The global methane budget 2000709 al., 2014Olivier and Janssens-Maenhout, 2014;Jackson et al, 2014b;Howarth et al, 2011;Pétron et al, 2014;Karion et al, 2013) albeit not all Cathles et al, 2012;Peischl et al, 2015) suggest that methane emissions are underestimated by inventories and agencies, including the USEPA. For instance, emissions in the Barnett Shale region of Texas from both bottom-up and top-down measurements showed that methane emissions from upstream oil and gas infrastructure were 90 % larger than estimates based on the USEPA's inventory and corresponded to 1.5 % of natural gas production (Zavala-Araiza et al, 2015).…”