Chemical Engineering February 2012 - 14

Newsfront
FRAC WATER REUSE
Reuse of water from fractured shale
formations is growing, but success
requires tailored treatment approaches
to water chemistry
P
roduction of natural gas from
shale formations presents key
water management challenges.
As the number of gas drilling
operations continues to grow in shale
plays around the world, and the practice
of hydraulic fracturing (frac or
fracing) of gas wells remains widespread,
efficient water use strategies
are becoming critical aspects of shale
gas operations. Fresh water supplies
for drilling and fracturing can be limited
by regional climate, transportation
logistics and competing industrial or
agricultural uses. Meanwhile, wastewater
disposal options are increasingly
difficult because of high trucking costs,
increased regulatory oversight and
limited suitable underground sites.
Given the supply and disposal challenges,
many gas producers are collecting
water used in fracturing operations
and treating it for reuse in a subsequent
gas well. These water recycling
approaches can reduce expenses, increase
efficiency and help protect the
surrounding environment; but several
factors, including the complexity of
shale gas production, the variability
of water chemistries in different areas,
and a host of regionally specific logistical
issues, make one-size-fits-all approaches
impossible. To arrive at viable
individualized solutions, engineers
need accurate assessments of local
water chemistry and geology and a
creative outlook toward applying available
water treatment technologies.
Treatment and reuse of water is becoming
the dominant approach now,
acknowledges Dave Grottenthaler,
general manager of Kroff Well Services
Inc. (Pittsburgh, Pa.; www.kroff.com).
" Most gas producers are reusing a
FIGURE 1. Analysis of
the microbial proile in
fracturing lowback water
is among the important
considerations of treating
water for reuse
large portion of their flowback water
- as much as 90% - for fracturing
other wells, " he says.
Experts agree that the wide range of
proven, available water-treatment technologies
allows water from fractured
shale wells to be recycled effectively.
" The prospects for treating flowback
water to a recyclable condition from
fracturing operations in shale-gas formations
appears very good, " remarks
Dave Manz, water engineer at Oasis
Filter International Ltd. (Calgary,
Alta.; www.oasisfilter.com). " Today's
treatment-and-reuse strategies are economically
competitive with currently
used deep-well disposal methods. "
" Whether you are going to reuse the
water [from fractured wells] or discharge
it to municipal facilities, some
degree of water treatment is required, "
says Bob Kimball, process engineer at
CDM Smith (Cambridge, Mass.; www.
cdmsmith.com). " Although research
and development continues to improve
water treatment, we focus on applying
current technologies in creative ways, "
says Kimball.
Water-based fracturing fluid
The current expansion of operations
to extract natural gas from shale formations
is largely the result of improvements
in hydraulic fracturing
technology, and refinement of horizontal
drilling practices. Together, the two
factors have made it economically viable
to locate gas operations in shale
14 CHEMICAL ENGINEERING WWW.CHE.COM FEBRUARY 2012
formations that were inaccessible or
uneconomical in the past. Hydraulic
fracturing - a technique that has
been employed in the oil and gas industries
since the 1950s - is a wellstimulation
technique in which fluid
is pumped at high pressure into the
formation to create cracks in the target
rock. The fractures are held open
by a proppant (usually sand) that is
included in the fracturing fluid to facilitate
gas escape into the wellbore.
Most industry estimates say that
typically around 2-4 million gal of
water (with additives) are required to
drill and fracture a single shale well,
although the volume can vary widely
(1-10 million gal), depending on specific
circumstances. Water accounts for
99.5% of the volume of conventional
fracturing fluid, to which a customized
mixture of chemicals is added (Figure
2). The additive mix in fracturing water
varies widely depending on the permeability
of the shale formation and other
factors, but typically includes biocides,
scale inhibitors and friction-reducing
compounds designed to allow the water
to maintain a high velocity in the well.
The high-velocity water better maintains
the proppant material in suspension
while transporting it to the fracture
network, explains Manz.
To effectively select the correct combination
and concentration of fracturing
fluid additives and proppants,
engineers need information about the
formation's geology - porosity, permeKroff
Well Services
http://www.oasisfilter.com http://www.cdmsmith.com http://www.kroff.com http://WWW.CHE.COM
Chemical Engineering February 2012

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