Not all boreholes are the same. Scientists of the Karlsruhe Institute of
Technology (KIT) used mobile measurement equipment to analyze gaseous
compounds emitted by the extraction of oil and natural gas in the USA.
For the first time, organic pollutants emitted during a fracking process
were measured at a high temporal resolution using a vapor capture
system. The highest values measured by this process exceeded typical
mean values in urban air by a factor of about one thousand, as was
reported in the ACP journal.
Emission of trace gases by oil and gas fields was studied by the KIT
researchers in the USA (Utah and Colorado) together with US institutes.
Background concentrations and the waste gas plumes of single extraction
plants and fracking facilities were analyzed. The air quality
measurements of several weeks duration took place under the "Uintah
Basin Winter Ozone Study" coordinated by the National Oceanic and
Atmospheric Administration (NOAA).
The KIT measurements focused on health-damaging aromatic hydrocarbons
in air, such as carcinogenic benzene. Maximum concentrations were
determined in the waste gas plumes of boreholes. Some extraction plants
emitted up to about a hundred times more benzene than others. The
highest values of some milligrams of benzene per cubic meter air were
measured downstream of an open fracking facility, where returning
drilling fluid is stored in open tanks and basins. Much better results
were reached by oil and gas extraction plants and plants with closed
production processes. In Germany, benzene concentration at the workplace
is subject to strict limits: The Federal Emission Control Ordinance
gives an annual benzene limit of five micrograms per cubic meter for the
protection of human health, which is smaller than the values now
measured at the open fracking facility in the US by a factor of about
one thousand. The researchers published the results measured in the
journal Atmospheric Chemistry and Physics ACP.
"Characteristic emissions of trace gases are encountered everywhere.
These are symptomatic of gas and gas extraction. But the values measured
for different technologies differ considerably," Felix Geiger of the
Institute of Meteorology and Climate Research (IMK) of KIT explains. He
is one of the first authors of the study. By means of closed collection
tanks and so-called vapor capture systems, for instance, the gases
released during operation can be collected and reduced significantly.
"The gas fields in the sparsely populated areas of North America are a
good showcase for estimating the range of impacts of different
extraction and fracking technologies," explains Professor Johannes
Orphal, Head of IMK. "In the densely populated Germany, framework
conditions are much stricter and much more attention is paid to reducing
and monitoring emissions."
Fracking is increasingly discussed as a technology to extract fossil
resources from unconventional deposits. Hydraulic breaking of suitable
shale stone layers opens up the fossil fuels stored there and makes them
accessible for economically efficient use. For this purpose, boreholes
are drilled into these rock formations. Then, they are subjected to high
pressure using large amounts of water and auxiliary materials, such as
sand, cement, and chemicals. The oil or gas can flow to the surface
through the opened microstructures in the rock. Typically, the return
flow of the aqueous fracking liquid with the dissolved oil and gas
constituents to the surface lasts several days until the production
phase proper of purer oil or natural gas. This return flow is collected
and then reused until it finally has to be disposed of. Air pollution
mainly depends on the treatment of this return flow at the extraction
plant. In this respect, currently practiced fracking technologies differ
considerably. For the first time now, the resulting local atmospheric
emissions were studied at a high temporary resolution. Based on the
results, emissions can be assigned directly to the different plant
sections of an extraction plant. For measurement, the newly developed,
compact, and highly sensitive instrument, a so-called proton transfer
reaction mass spectrometer (PTR-MS), of KIT was installed on board of a
minivan and driven closer to the different extraction points, the
distances being a few tens of meters. In this way, the waste gas plumes
of individual extraction sources and fracking processes were studied in
detail.
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