Methane Emissions from the Marcellus Shale in Southwestern Pennsylvania and Northern West Virginia Based on Airborne Measurements

Abstract

Natural gas production in the United States has increased rapidly over the past decade, along with concerns about methane (CH4) fugitive emissions and its climate impacts. Quantification of CH4 emissions from oil and natural gas (O&NG) operations is important for establishing scientifically sound policies for mitigating greenhouse gases. We use the aircraft mass balance approach for three flight experiments in August and September 2015 to estimate CH4 emissions from O&NG operations over the southwestern Marcellus Shale. We estimate a mean CH4 emission rate as 21.2 kg/s with 28% coming from O&NG operations. The mean CH4 emission rate from O&NG operations was estimated to be 1.1% of total NG production. The individual best‐estimate emission rates from the three flight experiments ranged from 0.78 to 1.5%, with overall limits of 0% and 3.5%. These emission rates are at the low end of other top‐down studies, but consistent with the few observational studies in the Marcellus Shale region as well as the U.S. Environmental Protection Agency CH4 inventory. A substantial source of CH4 (~70% of observed CH4 emissions) was found to contain little ethane, possibly due to coalbed CH4 emitted either directly from coal mines or from wells drilled through coalbed layers in O&NG operations. Recent regulations requiring capture of gas from the completion‐venting step of hydraulic fracturing appear to have reduced the atmospheric release of CH4. Our study suggests that for a 20‐year time scale, energy derived from the combustion of natural gas extracted from this region likely exerts a net climate benefit compared to coal.

Estimating Methane Emissions From Underground Coal and Natural Gas Production in Southwestern Pennsylvania

“…From the results of this study, we estimate emissions from UNG production and gathering facilities in SWPA to be equivalent to 0.5 ± 0.3% of production, in agreement with published top‐down emission estimates from northeast PA (0.36 ± 0.09%) and SWPA (0.0–3.5%) and site‐level measurements at well sites in northeast PA (0.44 ± 0.15%) and SWPA (0.57 ± 0.23%; Alvarez et al, ; Barkley et al, ; Omara et al, ; Ren et al, ). These emission rates as a percent of production are lower than rates found from top‐down studies performed in other gas basins, with the next lowest rate measured in the Haynesville shale at 1.3% (Alvarez et al, ; Karion et al, ; Peischl et al, ; Pétron et al, ; Schwietzke et al, ; Smith et al, ).…”

Top‐Down Estimates of NOx and CO Emissions From Washington, D.C.‐Baltimore During the WINTER Campaign

“…The measured 5‐second precision for UMD CO 2 and CO measurements were ± 20 ppbv and ± 8 ppbv, respectively. Other instrumentation installed in the UMD Cessna has been discussed by He et al () and Ren et al ().…”

Unmanned aerial vehicle observations of cold venting from exploratory hydraulic fracturing in the United Kingdom

“…However fugitive emissions can occur (Wigley 2011, Alvarez et al 2012, with potential for higher leakage than from conventional gas extraction (Howarth et al 2011). Leaks of over 2.4% can overwhelm the climate benefit (over a 20 year horizon) of the use of gas for fuel, over coal (Ren et al 2019). Fracking emissions occur during three major phases (Allen et al 2013): recovery of fracking fluid prior to gas retrieval (flow-back), fluid recovery from well clearing during production (unloading) and leaks from gas refinement and distribution.…”

“…Fracking emissions occur during three major phases (Allen et al 2013): recovery of fracking fluid prior to gas retrieval (flow-back), fluid recovery from well clearing during production (unloading) and leaks from gas refinement and distribution. Net gas loss from shale regions in the USA varies, from zero up to the order of a 10% leak rate, depending on the prevalence of fracking and the presence of processing facilities (Schneising et al 2014, Omara et al 2016, Barkley et al 2019, Ren et al 2019. Omara et al (2016) observed higher average emissions from 13 unconventional than 18 conventional gas extraction sites in the Marcellus shale formation in the USA, though unconventional extraction had a lower leak rate due to better productivity.…”