110
through a compromised well casing or a poorly-executed cement job. These incidents are quite rare, however, with only ten documented as of 2017 among the
thousands of wells completed in the Marcellus Shale (HEI 2019). One of the best
known cases was the reported 2015 contamination of several domestic water supply
wells in Pennsylvania following the drilling and fracking of five Marcellus Shale
wells within a distance of 2 km (Llewellyn et al. 2015). Stray gas and a foaming
agent were reported in the water wells, and laboratory analysis detected the presence of 2-n-butoxyethanol, a surfactant commonly used in hydraulic fracturing
fluid. The shale wells had been completed without intermediate casing, and the
frack fluids were thought to have moved vertically up the borehole until encountering a natural fracture system in the uncased interval that allowed them to migrate
into the aquifer.
The produced water from shale gas and tight oil wells is often hypersaline with
very high levels of TDS. The TDS is typically composed of chlorides, bromides,
sodium, calcium, magnesium, barium, strontium, and other salts. Produced water
also commonly contains the radioactive element radium (Ra), and natural gas from
these formations often contains the radioactive gas radon (Rn). USGS publications
on the Ra content in produced water from Marcellus Shale wells (Rowan et al.
2011) and a companion report on Rn in Marcellus Shale natural gas (Rowan and
Kraemer 2012) show that these radionuclides have been known about for quite
some time, but they are occasionally “rediscovered” by the news media. Ra is a
decay product of uranium (U), which is associated with the organic carbon in black
shales. Black shales are identified by a kick in the gamma ray well log, and drill
cuttings occasionally contain enough U to require special handling at landfills. U is
typically not very mobile in water, but Ra is quite soluble. Rn is a decay product of
Ra, and most isotopes have a short half-life (source: https://www.epa.gov/radiation/
tenorm-oil-and-gas-production-wastes).
Radium is an alpha emitter that is of particular risk if ingested – it is in the same
family of chemical elements as Ca and Mg, and tends to lodge in the bones. However,
no one is drinking ultra-saline produced water. Current practices for handling produced water, such as recycling it into subsequent fracks or disposing of it down UIC
wells have effectively kept most of the Ra out of the environment, but of course
people do get sloppy and spill things.
Not surprisingly, higher radium in produced water appears to correlate with
higher TDS levels, and also with a brine source in U-bearing black shale.
Measurements on produced water from the Marcellus Shale found a mean Ra value
of 2460 picocuries per liter (pC/l) compared to 1011 pC/l in non-Marcellus, conventional oilfield brines (Rowan et al. 2011). For reference, the maximum Ra limit in
industrial effluent is 60 pC/l, and the EPA drinking water limit is 5 pC/l. The highest
concentration of Ra in oil and gas well operations appears to be in the mineral precipitate or “scale” that forms inside pipes, where it readily substitutes for Ca in
calcite deposits.
Radon gas is a decay product of radium. It is a non-reactive, noble gas like
helium or neon with a half-life of only a couple of days. No one worried much about
Rn when natural gas spent weeks in a pipeline coming up north from the Gulf Coast,
6 Fracking and Water
through a compromised well casing or a poorly-executed cement job. These incidents are quite rare, however, with only ten documented as of 2017 among the
thousands of wells completed in the Marcellus Shale (HEI 2019). One of the best
known cases was the reported 2015 contamination of several domestic water supply
wells in Pennsylvania following the drilling and fracking of five Marcellus Shale
wells within a distance of 2 km (Llewellyn et al. 2015). Stray gas and a foaming
agent were reported in the water wells, and laboratory analysis detected the presence of 2-n-butoxyethanol, a surfactant commonly used in hydraulic fracturing
fluid. The shale wells had been completed without intermediate casing, and the
frack fluids were thought to have moved vertically up the borehole until encountering a natural fracture system in the uncased interval that allowed them to migrate
into the aquifer.
The produced water from shale gas and tight oil wells is often hypersaline with
very high levels of TDS. The TDS is typically composed of chlorides, bromides,
sodium, calcium, magnesium, barium, strontium, and other salts. Produced water
also commonly contains the radioactive element radium (Ra), and natural gas from
these formations often contains the radioactive gas radon (Rn). USGS publications
on the Ra content in produced water from Marcellus Shale wells (Rowan et al.
2011) and a companion report on Rn in Marcellus Shale natural gas (Rowan and
Kraemer 2012) show that these radionuclides have been known about for quite
some time, but they are occasionally “rediscovered” by the news media. Ra is a
decay product of uranium (U), which is associated with the organic carbon in black
shales. Black shales are identified by a kick in the gamma ray well log, and drill
cuttings occasionally contain enough U to require special handling at landfills. U is
typically not very mobile in water, but Ra is quite soluble. Rn is a decay product of
Ra, and most isotopes have a short half-life (source: https://www.epa.gov/radiation/
tenorm-oil-and-gas-production-wastes).
Radium is an alpha emitter that is of particular risk if ingested – it is in the same
family of chemical elements as Ca and Mg, and tends to lodge in the bones. However,
no one is drinking ultra-saline produced water. Current practices for handling produced water, such as recycling it into subsequent fracks or disposing of it down UIC
wells have effectively kept most of the Ra out of the environment, but of course
people do get sloppy and spill things.
Not surprisingly, higher radium in produced water appears to correlate with
higher TDS levels, and also with a brine source in U-bearing black shale.
Measurements on produced water from the Marcellus Shale found a mean Ra value
of 2460 picocuries per liter (pC/l) compared to 1011 pC/l in non-Marcellus, conventional oilfield brines (Rowan et al. 2011). For reference, the maximum Ra limit in
industrial effluent is 60 pC/l, and the EPA drinking water limit is 5 pC/l. The highest
concentration of Ra in oil and gas well operations appears to be in the mineral precipitate or “scale” that forms inside pipes, where it readily substitutes for Ca in
calcite deposits.
Radon gas is a decay product of radium. It is a non-reactive, noble gas like
helium or neon with a half-life of only a couple of days. No one worried much about
Rn when natural gas spent weeks in a pipeline coming up north from the Gulf Coast,
6 Fracking and Water