Page 406 - Fundamentals of Gas Shale Reservoirs

386 GAS SHALE ENVIRONMENTAL ISSUES AND CHALLENGES

are either naturally occurring gas in water sands or problems that shale gas production has a GHG footprint that is 20–50%
caused by mistakes in well design—improper cementing— lower than for coal.
not related to fracking. In the 2012 Massachusetts Institute of Technology (MIT)
No one is saying that there are no potential risks to water study, researchers argue that the amount of methane emis-
resources from hydraulic fracturing. However, available sions caused by shale gas production has been largely exag-
scientific literature appears to support a cautiously opti- gerated (O’Sullivan and Paltsev, 2012). Their analysis was
mistic view of the dangers posed by fracking to freshwater based on data from each of the approximately 4000 wells
supplies. Studies have thus far failed to establish any drilled in the five main U.S. shale‐drilling sites during 2010.
systematic relationship between drilling activity and water Wells in two of those sites, Texas’ Barnett shale and the
pollution. Others caution that although the studies do not Haynesville shale on the Texas‐Louisiana boarder, had been
confirm any cases of drinking water contamination caused studied by Robert Howarth from Cornell University last
by fracking, which does not mean that such contamination is year when he looked at potential emissions released by the
impossible or that hydraulic fracturing chemicals cannot get industry.
loose in the environment in other ways such as through spills In studying potential emissions, where Howarth found
of produced water. 252 mg of methane emissions per well in the Barnett site and
Definitive evidence may have to wait until the EPA com- 4638 mg per well in the Haynesville site, the MIT researchers,
pletes in 2014 its study of hydraulic fracturing and its poten- using their comprehensive well dataset, found that the poten-
tial impact on drinking water resources (EPA, December tial emissions per well in the Barnett and Haynesville sites
2012a). Nonetheless two things are clear: in areas of frack- were in fact 147 mg of methane (273 thousand cubic meters
ing, in order to trace the source of contamination, there is a of natural gas) and 633 mg (1,177 thousand cubic meters of
need to know what chemicals are being used in the fracking gas), respectively. When accounting for actual gas handling
process before fracking starts. Secondly, proper baseline field practices, these emission estimates were reduced to
water sampling needs to be conducted prior to the start of about 35 mg per well of methane from an average Barnett
drilling. well and 151 mg from an average Haynesville well. The
MIT study found that companies are already capturing about
70% of potential “fugitive” emissions.
18.5 METHANE EMISSIONS In April 2013, EPA dramatically lowered its estimate of
how much of a potent heat‐trapping gas leaks during natural
Methane emissions from natural gas extraction, especially gas production in its latest GHG inventory to less than half
shale gas, has been getting a lot of attention as environmen- of what had been previously estimated (EPA, April 2013).
talists focus on the full life cycle of energy production and Among the key findings of the analysis:
use and the amount of natural gas that is released into the
atmosphere unburned as part of the hydraulic fracturing pro- (i) The effective natural gas emissions rate per unit of
cess, transportation by pipelines, and from compressors and natural gas production is 1.5%. This emissions rate
processing units. The issue of methane leaks has caused a is lower than earlier estimates of 2.2–2.4% using
major split between environmental groups. Since power data from prior EPA inventories for 2009 and 2010.
plants that burn natural gas emit about half the amount of the (ii) The EPA revised its estimates of natural gas system
greenhouse gases as coal‐fired power plants, the recent shift methane emissions downward 33% for 2010, from
to gas‐fired generation has allowed the United States to 215.4 million metric tons of carbon dioxide
become the only major industrialized country to signifi- equivalent in the 2012 inventory to 143.6 MMTe in
cantly reduce greenhouse emissions. But others believe the the 2013 inventory.
methane leaks during the production of shale gas negate any (iii) The long‐term trend for methane emissions from
benefits over coal substitution, since methane is a highly natural gas systems is downward. Annual methane
potent greenhouse gas. emissions have dropped 10% since 1990 and are
A controversial paper by Cornell’s Robert Howarth jump‐
started this debate (Howarth et al., 2011). He argued that 17% below the all‐time peak set in 2007.
natural gas from fracking operations can be worse for the (iv) Distribution system methane emissions have
atmosphere than coal because of methane seepage into dropped 16% since 1990, even as the industry added
the atmosphere. Another Cornell study also suggested that nearly 300,000 miles of distribution mains to serve
life cycle greenhouse gas emissions from shale gas are 17 million more customers, an increase of 30% in
20–100% higher than coal on a 20‐year timeframe basis. both cases.
Studies by DOE’s National Energy Technology Laboratory
(NETL), The Worldwatch Institute, Carnegie Mellon, and In August 2013, scientists with the National Oceanic and
Deutsche Bank challenged these conclusions and showed Atmospheric Administration (NOAA) and the University of