During hydraulic fracturing, fracturing fluid is released at high pressure into the underground rock formation to create millimetre-sized cracks through which natural gas trapped in the shale can flow.
Before fracturing takes place, the Environment Agency must approve the proposed composition of Cuadrilla’s fracturing fluid. The fracturing fluid Cuadrilla used at the Preese Hall exploration well site and plans to use at future exploration well sites is composed almost entirely of fresh water and sand. We also have approval to use the following additives:
● Polyacrylamide (friction reducer )
● Sodium salt (for tracing fracturing fluid)
● Hydrochloric acid (diluted with water)
● Glutaraldehyde biocide (used to cleanse water and remove bacteria)
So far, as additives to fracturing fluid, Cuadrilla has only used polyacrylamide friction reducer along with a miniscule amount of salt, which acts as a tracer. We have not needed to use biocide as the water supplied by United Utilities to our Lancashire exploration well sites has already been treated to remove bacteria, nor have we used diluted hydrochloric acid in fracturing fluid. Additives proposed, in the quantities proposed, have resulted in the fracturing fluid being classified as non-hazardous by the Environment Agency.
In our hydraulic fracture at Preese Hall, polyacrylamide was used to reduce friction between water and the pipe wall, which allows us to reduce the pressure required during fracturing. At our Preese Hall well, this friction reducing additive made up 0.04% of the fracturing fluid – translating to 3.7 m3.
Polyacrylamide is a non-hazardous, non-toxic substance. For example, polyacrylamide is used as a flocculant (to remove suspended solids) in drinking and wastewater plants, and for soil remediation.
Cuadrilla will disclose on its website details of any additives it is approved to use and any additives used in hydraulic fracturing fluid used in fracturing shale. The Environment Agency also discloses on its website details of any additives approved for use.
Click here to view the overall composition of our fracturing fluid used in 2011.
Fracturing fluid together with water that may be stored underground in the shale rock return up the bore with the gas and this is known as “returned water” or “flowback Fluid”. Typically about 40% of the fracturing fluid used during the fracturing process flows back to the surface in returned water within the first few weeks of well flow.
Much of the fracturing fluid returns to the surface over the producing lifetime of the well.
Returned water is tested as it comes to surface both by the Environment Agency and Cuadrilla, and is treated and disposed of in EA approved waste water treatment plants according to Environment Agency rules.
Returned waters contain very low levels of “naturally occurring radioactive materials” (NORM) – such as those found around the UK at surface outcrops of granite and shale rock.
We apply for a Radioactive Substances Regulation (RSR) permit as per Environmental Permitting Regulations 2010 for any fracturing or well-testing programme. The Environment Agency has classified as non-hazardous the returned water composition seen in Lancashire Bowland shale wells
To find out more about returned water and regulation, please visit the Environment Agency Website.