Mismeasuring Methane - Estimating Greenhouse Gas Emissions from Upstream Natural Gas Development - Private Report

Published 2011 / 08
Summary This report reacts to new estimates by EPA (Environmental Protection Agency) of methane emissions from unconventional gas drilling sites in the US. It argues that these estimates are wildly overstated. According to the report the operators of a gas well have three fundamental concerns: Safety Health Economics All three of these concerns give an incentive to recover as much of the fugetive methane as possible, first in order to sell it, or if this is not possible to flare it (burn it, releasing CO2 instead of methane), because venting methane (i.e. releasing it into the atmosphere) would cause a serious health and safety risk. The report describes current industry practice to reduce methane emissions during drilling, well completion and flowback of 'fraccing material'. It also cites various reasons why gas has to be flared or vented: The (initial) gas may to be too contaminated for the pipelines. When the flow of gas is sporadic it may be hard to sustain the flame on a flare. Scheduling delays of tie-in pipelines can cause initial gas production to be flared instead of sold. Flaring does not have a 100% efficiency of converting methane to CO2, it is assumed that 2% of methane is still emitted when flared. Water from the flowback can have up to 35mg of methane per liter (at surface temperature and pressure), this is very little, but has led to a reduction in open-pit flowback and towards enclosed tanks The new EPA methodology to estimate methane emissions at well drilling sites is argued by the report to be grossly overstated. EPA based the estimate of emissions per site on an average of 4 data points from several presentations, out of which 3 data points described methane captured from green wells for sale, instead of emitted. EPA assumed that gas produced during completion is vented, rather than flared, unless flaring is required by state regulation. This claim is not backed by industry practice according to the report, since operators have an incentive to sell the gas first (economics) or flare it (safety and health). During flowback the emissions of methane are lower than during production, because the gas stream builds up slowly during completion. The EPA estimate comes to 9175 Million Cubic Feet per well during completion. According to the report this would create a hazardous and toxic environment around the well site. Since accidents are rare around gas wells shows that the estimate cannot be the average emissions per well. The report does not give it's own estimate, but at one point compares its own calculation of all methane being vented during a 10 day flowback period of 43 MtCO2e methane emissions against the EPA estimate of 130 MtCO2e of methane emissions (i.e. a 3 times lower estimate assuming all methane was vented, which it is not in reality). The report concludes that even though EPA overstates the estimate, one part of its new proposed standard is a good idea: measuring and monitoring emissions will provide for much better data on actual emissions.
Keywords methane, unconventional gas, drilling, well, EPA
File name IHS CERA_20110823_Mismeasuring Methane - Estimating Greenhouse Gas Emissions from Upstream Natural Gas Development.pdf