Oil & Gas

     Natural gas is mostly methane (CH4), the prized ingredient.  Some waste gases (CO2, H2S, etc.) are removed from natural gas sent into pipelines, while others (He, Ar, C2H6, C3H8 and C4H10 - helium, argon, ethane, propane and butane) are separated for resale.

     This Earth justice map shows US shale formations suitable for fracking, active and potential.  The Bakken formation is in Norh Dakota, Marcellus in Appalachia, Eagle Ford etc. in Texas, Utica+ in Michigan, Monterrey in California, Fayetteville in Arkansas, etc.
    Earthjustice identifies 35 "fraccidents" outside the Marcellus area and 41 inside it, including 38 in Pennsylvania.  They include poisoned drinking water, polluted air, mysterious animal deaths, industrial disasters, and explosions.

Methane Emissions at US Natural Gas Production Sites - Allen 0913 - PDF

     This multi-university study, sponsored in part by EDF and several gas companies, measured methane leakage rates at 190 sites.  These included 27 well completion flowback sites, where leakage ranged from 0.01 to 17 tonnes per completion (5 to 339 hours per completion).  These averaged 1.7 tonnes, a small fraction of EPA's estimate of 81 tonnes per completion.  To explain this, Allen found that operators captured 98% of potential emissions (including 99% where equipment for methane capture and control was used) rather than the 50% EPA assumed.

     The 190 sites also included 9 "unloadings," a periodic process to clear out liquids that clog wells.  The average leak per unloading was 1.1 tonnes, compared to EPA's estimate of 5.2.

     Routine continuous operations (150 wells) released 1.23 grams of methane per minute (about 1.2 tonnes per year for continuous operation) through various pneumatic controllers, roughly 14% less than EPA estimates.

     In all, methane leakage in the study sample is 20% less than estimates using EPA guidelines at the time.  The study attributes this reduced leakage rate to emerging regulatory requirements and improved operating practices.  The study summarizes the overall methane leakage rate as 0.42% of gross natural gas production (extraction), though some of that 0.42% could be attributed to the oil (and propane / NGL) production from the well, instead of all of it to natural gas.  In April 2013, EPA cut its estimate of methane release from natural gas production by about 20%, presumably relying on a pre-publication version fo the study.

     EPA's old and new estimates, as well as Allen's study results, are similar to natural gas leakage rates from transmission and distribution mains.  Error bars are appreciable for extraction, transmission, and distribution leakage rates.

     Caveats: The sample is chosen from the best-managed wells, where more money and resources are devoted to capturing emissions ("green completions"), compared to typical wells.  Leakage rates at old wells are probably (much) higher.  Also, if "unloadings" happen often, they can dominate emissions.

Limiting Methane Leaks Critical to Gas 0513 - see sample of the interactive trade-off graphs, below.
www.climatecentral.org/news/limiting-methane-leaks-critical-to-gas-climate-benefits-1020
    If leakage is too high, fracked natural gas is worse than coal for climate change, at least in the early decades.  If leakage is low, natural gas is much better than coal on climate change.  Allen's 0913 study, below, found only small leaks.
    The lower right leak rate graph (2%/5%) probably best describes the situation.  In fact, the GHG advantage of gas over coal can closely approach 50% even sooner than it shows, if gas production operations continue improving, cutting leaks, even at old wells.

Section Map: Fossil Fuels & Nuclear Energy