Environmental Engineering Reference
In-Depth Information
controlled to ensure that it does not have an adverse effect on other users.
It should be noted that in some of the areas where shale gas deposits are
located, such as the North West of England, there is abundant water and
therefore the quantities of water used will have little impact on the overall
water supply situation.
The cost of water, as well as its availability, will ensure that the shale gas
industry is constantly attempting to reduce the volumes used by improving
the hydraulic fracturing process, as well as re-using the water wherever
possible to mitigate overall water requirements.
2.2.2.3 Hydraulic Fracturing Fluids
While the majority of the fluids used for hydraulic fracturing consist of more
than 99.5% water and sand, companies do use a small quantity of additional
chemicals to assist in the process. Although the percentage of chemical
additives is small, this still equates to some 1000-3000 tonnes of chemicals
for hydraulically fracturing a typical eight-well pad. The water and additives
are blended on site and, when mixed with the proppant, usually sand, are
pumped into the wellbore. Chemicals performmany functions in a hydraulic
fracturing job. Although there are dozens to hundreds of chemicals which
could be used as additives, there are a limited number which are routinely
used in hydraulic fracturing. Table 2 shows a list of the chemicals used most
often in America.
19
One of the problems associated with identifying chemicals is that some
chemicals have multiple names. For example, ethylene glycol (antifreeze) is
also known by the names ethylene alcohol, glycol, glycol alcohol, Lutrol 9,
Macrogol 400 BPC, monoethylene glycol, Ramp, Tescol, 1,2-dihydroxy-
ethane, 2-dydroxyethanol, HOCH
2
CH
2
OH, dihydroxyethane, ethanediol,
ethylene gycol, Glygen, Athylenglykol, ethane-1,2-diol, Fridex, MEG, 1,2-
ethandiol, Ucar 17, Dowtherm SR 1, Norkool, Zerex, aliphatic diol, Ilexan E,
ethane-1,2-diol and 1,2-ethanediol.
These additives are there for a number of reasons, such as helping dis-
solve minerals and initiate fissures; preventing scale deposits in the pipes;
eliminating bacteria in the water; minimising friction between the fluid and
the pipe; preventing precipitation of metal oxides; and thickening the water
to suspend the sand which is used to hold the fissures generated apart.
While many of the chemicals used are found in common household and
commercial products, such as table salt, food additives and cosmetics, some,
used in small quantities, are toxic. The number of additives used varies
between 3 and 12 as the composition of the fracturing fluid is individually
designed for the shale formation being fractured. In the USA the com-
position of the hydraulic fracturing fluid has not always been disclosed, with
some of the companies maintaining that this is commercially sensitive in-
formation. This has led to suspicion by members of the public, particularly
where health issues have occurred close to shale gas extraction sites. How-
ever, in the UK the composition of the fracturing fluid together with all of the
