This is a precis of a talk about fracking given by a Dr. Ingraffea, who is a professor in the School of Civil and Environmental Engineering at Cornell University in the US and an expert in fracking.
Here is the link to his bio at Cornell.
Deep fracking is done by drilling long laterals holes at great depth. The technology is fifteen years old and it is still being developed.
The sheer length of the piping necessitates that water is injected at very high pressure. Water resists being pumped, so chemicals (eight million gallons of chemicals in the case of some wells) are added to make the water flow more easily – this mix is the so-called slickwater.
Once the hole is drilled a cement case is built around it. The cement case around the piping prevents methane from escaping into the the surrounding rock and travelling wherever it will, rather than being extracted via the piping.
The cement is pumped in as a liquid, and if it doesn’t make good contact with the surrounding rock, then methane will escape.
Reasons why it might not make good contact are
- The cement went in too dry
- The cement wasn’t pushed down properly
- Not enough cement was pumped in to reach above existing shallow shale deposits
- The centralisers that makes sure cement is put all around the pipe are not placed correctly or at all.
If centralisers – a series of ‘o’ rings that are placed over the pipes – are not placed correctly, then the pipe will not be central in the bore hole and there will not be any cement where it is needed to keep the methane from escaping into the surrounding rock.
The failure rate for inland fracking wells of this type, which are just a few years old – as determined by Schlumberger in one review and by Watson and Bauhu in another – is more than 6%.
The experience from offshore wells is that wells of all kinds have an increased failure rate as they get older – up to 60% for thirty-year-old wells.
The chemicals pumped in to make slickwater include hydrochoric acid,acetic acide, sodium chloride, polyacrylamide, ethylene glycol, borates, carbonates, glutaraldehyde, guar gum, citric acid, isopropanol, and ethylene glycol.
The Wikipedia page on polyacrylamide says:
Concerns have been raised that polyacrylamide used in agriculture may contaminate food with the nerve toxin acrylamide. While polyacrylamide itself is relatively non-toxic, it is known that commercially available polyacrylamide contains minute residual amounts of acrylamide remaining from its production, usually less than 0.05% w/w.