HOW - Hydrofracking: What Everyone Needs to Know - page 24

What Are Hydrofracking Fluids?
Having drilled a directional well, we can turn to what gets injected into them. I've
mentioned some of the chemicals, as well as the “proppant” that is carried into the
shale formation to help release the oil or gas trapped there.
First, acid scours the borehole and the fractures in the rock. Then fluid is in-
jected into the borehole, with the pressure greater than the fracture gradient of the
rock. The fluid includes water-soluble gelling agents, such as guar gum, which in-
crease viscosity and help deliver proppant to the bottom of the well. 19 As the frac-
turing proceeds, viscosity-reducing agents—such as oxidizers and enzyme break-
ers—are added to the fluid to deactivate the gelling agents.
The components of fluid vary, depending on the specifics of the site, but are
typically 99 percent water and sand and 0.5 to 1 percent chemicals. 20
Drillers usually begin by pumping hydrochloric acid or acetic acid to dissolve
rubble, clean the borehole, and reduce pressure on the surface. Then the proppant
is added to the fracking fluid and sent down the well. Proppants are small par-
ticulates—typically grains of silica sand, resin-coated sand, or man-made ceramic
balls—that are used to prop open the fractures in shale rock and keep them open,
even after fracking is completed. In essence, proppants make shale artificially per-
meable.
Drillers use two methods to deliver proppants to the bottom of a well: high rate
and high viscosity. High-rate, or slickwater, fracturing causes small spread-out mi-
crofractures. High-viscosity fracturing tends to cause large dominant fractures in
the rock.
The chemicals in the fluid are tailored to the specific geology of the site, so as
to protect the borehole and improve the flow of oil or gas to the surface. 21 They
include fresh water, salt water, foams, friction reducers, and gelling chemicals. The
friction reducer is usually a polymer, which reduces pressure loss caused by fric-
tion, allowing pumps on the surface to work at a higher rate without adding greater
pressure.
A number of chemicals are used to increase the viscosity of the fracturing fluid,
which carries proppant into the formation. But to stop the fluid from pulling prop-
pants out of the formation, a chemical known as a “breaker”—usually an oxidizer
or enzyme—is pumped with gel or cross-linked fluids to reduce the viscosity. For a
complete list of the chemicals used in hydrofracking, see the appendix at the back
of this topic.