105
6.2 Additives and Produced Water
Some of the chemicals added to frack fluid are relatively benign, such as ethylene
glycol used for corrosion control or polyacrylamide added as a friction reducer, but
others are not. For example, the biocides added to control downhole bacteria growth
are definitely something that one does not want to encounter in drinking water.
At least four sources of chemical contaminants associated with the development
of tight oil and shale gas may present water quality risks to groundwater and surface
water. These are, in approximate chronological order of use:
1. The various drilling fluids, lubricants, cement compounds, and “drilling mud”
employed when constructing the borehole (Soeder and Kent 2018).
2. The concentrated chemicals, conditioners, and performance enhancers stored on
the well pad in large volumes and blended into the frack fluid (Soeder et al. 2014).
3. The fluids produced out of the well after fracking, including flowback of the
original frack fluid and water produced from the formation itself. Produced water
consists of high TDS brine, hydrocarbons, dissolved solids like barium extracted
from the rock (Renock et al. 2016), and new chemicals formed by downhole
reactions between the frack fluid additives and the formation (Orem et al. 2014).
4. Black shale drill cuttings, drilling mud residue, contaminated soil, and other solids left behind on the drill pad that may oxidize, weather and leach inorganic and
organic chemicals, heavy metals, radionuclides, and other potentially toxic substances into shallow groundwater (Phan et al. 2015).
The contamination risks to water from the frack chemicals are poorly defined,
because little is known about the natural breakdown paths of the different organic
chemical additives in groundwater, or the persistence of inorganic compounds in
streams. A few natural attenuation (NA) lab studies have been done with microcosms using analog mixtures of organic chemicals to represent “typical” frack fluids (e.g. Cluff et al. 2014). A few reactive transport modeling studies have been
done to try to define NA pathways, but with little more than generalities available
on the chemical additives, these have not been very useful (HEI 2019). Much
remains unknown given the number of possible chemical additives, the variety of
new chemicals constantly being introduced, and the proprietary nature of the
formulations.
After a broken pipeline spilled produced water from the Bakken Shale into a
North Dakota creek, the USGS found itself conducting an impromptu field experiment to measure the dilution and dispersal of inorganic dissolved solids in a stream.
The general consensus was that contaminants from a surface water spill would dissipate fairly quickly after an incident because the pollutants are rapidly washed
downstream. Surprisingly, the USGS found that measurable levels of contaminants
were still present in the stream 6 months after the pipeline break had been repaired.
The contaminants had become trapped in the stream sediment, and were slowly diffusing into the water over time (Cozzarelli et al. 2017).
6.2 Additives and Produced Water
6.2 Additives and Produced Water
Some of the chemicals added to frack fluid are relatively benign, such as ethylene
glycol used for corrosion control or polyacrylamide added as a friction reducer, but
others are not. For example, the biocides added to control downhole bacteria growth
are definitely something that one does not want to encounter in drinking water.
At least four sources of chemical contaminants associated with the development
of tight oil and shale gas may present water quality risks to groundwater and surface
water. These are, in approximate chronological order of use:
1. The various drilling fluids, lubricants, cement compounds, and “drilling mud”
employed when constructing the borehole (Soeder and Kent 2018).
2. The concentrated chemicals, conditioners, and performance enhancers stored on
the well pad in large volumes and blended into the frack fluid (Soeder et al. 2014).
3. The fluids produced out of the well after fracking, including flowback of the
original frack fluid and water produced from the formation itself. Produced water
consists of high TDS brine, hydrocarbons, dissolved solids like barium extracted
from the rock (Renock et al. 2016), and new chemicals formed by downhole
reactions between the frack fluid additives and the formation (Orem et al. 2014).
4. Black shale drill cuttings, drilling mud residue, contaminated soil, and other solids left behind on the drill pad that may oxidize, weather and leach inorganic and
organic chemicals, heavy metals, radionuclides, and other potentially toxic substances into shallow groundwater (Phan et al. 2015).
The contamination risks to water from the frack chemicals are poorly defined,
because little is known about the natural breakdown paths of the different organic
chemical additives in groundwater, or the persistence of inorganic compounds in
streams. A few natural attenuation (NA) lab studies have been done with microcosms using analog mixtures of organic chemicals to represent “typical” frack fluids (e.g. Cluff et al. 2014). A few reactive transport modeling studies have been
done to try to define NA pathways, but with little more than generalities available
on the chemical additives, these have not been very useful (HEI 2019). Much
remains unknown given the number of possible chemical additives, the variety of
new chemicals constantly being introduced, and the proprietary nature of the
formulations.
After a broken pipeline spilled produced water from the Bakken Shale into a
North Dakota creek, the USGS found itself conducting an impromptu field experiment to measure the dilution and dispersal of inorganic dissolved solids in a stream.
The general consensus was that contaminants from a surface water spill would dissipate fairly quickly after an incident because the pollutants are rapidly washed
downstream. Surprisingly, the USGS found that measurable levels of contaminants
were still present in the stream 6 months after the pipeline break had been repaired.
The contaminants had become trapped in the stream sediment, and were slowly diffusing into the water over time (Cozzarelli et al. 2017).
6.2 Additives and Produced Water