Methane emissions from contrasting production regions within Alberta, Canada: Implications under incoming federal methane regulations

Abstract

Aggressive reductions of oil and gas sector methane, a potent greenhouse gas, have been proposed in Canada. Few large-scale measurement studies have been conducted to confirm a baseline. This study used a vehicle-based gas monitoring system to measure fugitive and vented gas emissions across Lloydminster (heavy oil), Peace River (heavy oil/bitumen), and Medicine Hat (conventional gas) developments in Alberta, Canada. Four gases (CO2, CH4, H2S, C2H6), and isotopic δ13CCH4 were recorded in real-time at 1 Hz over a six-week field campaign. We sampled 1,299 well pads, containing 2,670 unique wells and facilities, in triplicate. Geochemical emission signatures of fossil fuel-sourced plumes were identified and attributed to nearby, upwind oil and gas well pads, and a point-source gaussian plume dispersion model was used to quantify emissions rates. Our analysis focused exclusively on well pads where emissions were detected >50% of the time when sampled downwind. Emission occurrences and rates were highest in Lloydminster, where 40.8% of sampled well pads were estimated to be emitting methane-rich gas above our minimum detection limits (m = 9.73 m3d–1). Of the well pads we found to be persistently emitting in Lloydminster, an estimated 40.2% (95% CI: 32.2%–49.4%) emitted above the venting threshold in which emissions mitigation under federal regulations would be required. As a result of measured emissions being larger than those reported in government inventories, this study suggests government estimates of infrastructure affected by incoming regulations may be conservative. Comparing emission intensities with available Canadian-based research suggests good general agreement between studies, regardless of the measurement methodology used for detection and quantification. This study also demonstrates the effectiveness in applying a gaussian dispersion model to continuous mobile-sourced emissions data as a first-order leak detection and repair screening methodology for meeting regulatory compliance.

Methane emissions from conventional and unconventional oil and gas production sites in southeastern Saskatchewan, Canada

“…Using the same method as O'Connell et al (2019) to assess the distribution of site-level emissions rates in conventional and unconventional developments, we found that the emissions can be described using lognormal statistics, as previously observed by Zavala-Araiza et al (2015) and Zavala-Araiza et al (2018). As expected with lognormal distributions, a Lorenz curve shows that a small percent of sites is responsible for a large percentage of measured emissions ( figure 3).…”

“…The survey data was analyzed to isolate CH 4 -rich plumes from the varying ambient atmospheric levels using ratios of super-ambient (or 'excess', denoted by 'e') CO 2 and CH 4 (eCO 2 :eCH 4 ). The gas ratio approach has been used previously by Atherton et al (2017), Williams et al (2018), andO'Connell et al (2019), though the most complete explanation is presented in Hurry et al (2016). Ambient atmospheric CO 2 and CH 4 vary spatiotemporally due to factors such as atmospheric stability, land-use types, and topography.…”

Repeated leak detection and repair surveys reduce methane emissions over scale of years

“…The average production normalized leakage rate for satellite pads and well sites is 0.21%, while that for super pads is 0.03%. These proportional loss rates are lower than many recent studies of methane emissions in Canada [6,8]. Figure 2(b) shows the absolute methane leakage volumes as a function of production for the same set of sites in figure 2(a).…”

“…Both ground-based and aerial-measurements in Alberta showed higher vented and total methane emissions compared to provincial regulatory estimates [5,6]. Similarly, mobile measurements using truck-mounted sensor systems in British Columbia and Alberta have consistently shown that a majority of the emissions are dominated by a small number of high-emitting sites, often identified as 'super-emitters' [5,7,8]. This is not unique to oil and gas activity in Canadameasurements of methane emissions across different shale basins in the US demonstrate evidence of superemitters, widespread underestimation compared to US EPA inventory, and significant spatial and temporal variability [9][10][11][12].…”

Methane Mitigation: Methods to Reduce Emissions, on the Path to the Paris Agreement

“…Deliberate venting of unwanted gas is a major source of emission in many oilfields. O'Connell et al () studied heavy oil wells around Lloydminster, Canada. Over 40% of sampled well pads were emitting detectable methane, and of these, 40% emitted above the venting threshold beyond which mitigation was required by Canadian federal regulations.…”