American Oil and Gas Reporter - August 2015 - 81

SpecialReport: Hydraulic Fracturing Technology
the wellbore," DeGeare says. "NCS saw
a need for a new kind of float-in system
that could help overcome friction between
the pipe and formation.
"To meet that need, we developed the
AirLock casing buoyancy system," he relates. "With this system, the vertical casing
section is filled with fluid, while a unique
seal keeps the lateral section filled with
air. This enhances the buoyancy of the
lateral section, reducing friction as much
as 50 percent. With that friction reduction,
the weight of the vertical section can push
the casing all the way to the toe."
After casing is landed, increased pressure fragments the seal, leaving a fulldrift wellbore. Seal fragments are captured
by a debris collar, and circulation and
cementing proceeds as usual, DeGeare
describes.
The system has enabled some operators
to run casing in previously impossible
wells, but DeGeare says an additional
benefit is saving time. "In many applications, we have been able to cut two days
off the time it takes to run casing to bottom," he reports.
DeGeare adds that the buoyancy system
also can eliminate the need to rotate the
casing. "If well conditions permit, operators
can change from premium connections to
lower cost standard connections," he notes.

Degradable materials continue to get
more reliable and versatile, Rosenholm
says. "For example, Bubbletight has introduced a degradable composite polymer
(DCP) that can degrade in lower temperatures than standard polyglycolic acid
(PGA). This degradable composite dissolves in ambient freshwater, whereas
PGA needs at least 180 degrees Fahrenheit
to degrade."
Rosenholm adds that DCP offers a

tensile strength of 20,000 psi, some 4,000
psi higher than PGA.
"Tensile strength provides a useful
reference value, but engineers should
look at other qualities as well when evaluating degradable materials," Rosenholm
advises. "For example, with a frac ball,
they also should look at modulus, which
is somewhat synonymous with stiffness,
because a ball that is too stiff will fracture,
and one that is too soft will extrude.

Degradable Tools
Interest in degradable completion tools
is on the rise, suggests Andy Rosenholm,
the chief technology officer for Bubbletight
LLC. "As refracturing becomes more
prevalent, operators are looking for ways
to ensure there is no obstruction left in
the casing that could interfere with a second completion," he says. "As a result,
we are seeing a drive to make everything
left in the hole degradable, including
balls, plugs, seats and sleeves."
Rosenholm says that goal will soon
be achievable. He points out that degradable technology has proven successful in
a range of applications, from frac balls
to plugs for zonal pressure isolation.
Degradable polymer powders can be
applied along with degradable diverter
balls to plug existing perforations during
a refrac, he adds. "The powder is pumped
down with the fluid, where it packs off
existing fractures for hours or days, then
degrades to allow the fractures to reopen. This tool can increase the effectiveness of diverter balls, and the combination of the two may be less expensive
than mechanical alternatives such as
bridge plugs," he says.

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American Oil and Gas Reporter - August 2015

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