Chemical Engineering May 2013 - 13

Improved coating for hydraulic fracturing proppants
T
wo new coating products for sand
proppants used in hydraulic fracturing
operations in the oil and gas
industry overcome the challenges of
traditional phenolic coatings, which
can leach environmentally hazardous
chemicals. The coatings, developed
by Preferred Sands LLC (Radnor, Pa.;
www.preferredsands.com), are based on
a specialized polyurethane developed
over the past three years with partner
The Dow Chemical Company (Midland,
Mich.; www.dow.com).
In hydraulic fracturing, sand used as
a proppant increases the contact area
between particles, which effectively
strengthens them against the crushing
pressures inside the fractures. Also,
coated proppants keep particle fines from
the sand grains in place when water and
oil or gas flows back up the well.
Proppant coatings based on phenolic
resins leach phenol, formaldehyde and
others, explains Michael O'Neill,
CEO of Preferred Sands LLC.
Further, current proppant coatings
require activator compounds
to help curing once the proppants
are injected into the well, with
the intention that they will cure
fully inside the fractures of the deposit.
" But if the fractures close before
the coatings cure, then they lose their
ability to bond, " says Bob McDaniel, of
Preferred Sands.
The company's new coatings have the
ability to adhere to other particles, independent
of temperature, and without
the need for activator compounds, " McDaniel
says. " The phenolics require that
a good deal of chemistry happen downhole,
and that is the toughest environment
to make coatings work well. " The
Preferred Sands formulation requires
the closure stress of the fractures to
fully cure, which allows the coated sand
to penetrate fractures in the deposit
before curing. This feature allows the
coated proppant to maintain 100% of
its ability to prevent sand from flowing
back into the well when extraction begins,
says O'Neill. " This is a new type of
chemistry that hasn't been used for this
purpose before, " said McDaniel.
The company's coating-application
method requires lower temperatures
than that for phenolics, and does not
produce volatile organic compounds
(VOCs). These features allow for a lowercost
process, because you don't need as
much energy and don't need scrubbers,
says O'Neill.
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Circle 13 on p. 72 or go to adlinks.che.com/45772-13
CHEMICAL ENGINEERING WWW.CHE.COM MAY 2013 13
CAS-190H.indd 1
4/19/11 8:10 AM
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Chemical Engineering May 2013

Table of Contents for the Digital Edition of Chemical Engineering May 2013
