HYDRAULIC FRACTURING ADVANCES
Metal-seal dissolvable frac plugs
use simplified design to improve
reliability during plug and perf
BY JINLU WANG, VERTECHS GROUP
Compared with composite frac plugs, dis-
solvable frac plugs currently only have less
than 20% of the market share of the plug-
and-perf completion method. Frequently
cited disadvantages include casing ero-
sion and issues with dissolving too fast
or too slow, leading to increased costs and
longer completion times. However, newer
and more simplified dissolvable frac plugs
could help to address these challenges and
have the potential to achieve efficiency
and cost savings in major unconventional
plays around the world.
One source of limitation with frac plugs
is the elastomer. The oil and gas industry
has used elastomers as a material for
frac plugs – both in traditional composite
frac plugs and dissolvable frac plugs – in
zonal isolation for years. However, recent
research and observations made through
the use of downhole cameras indicate that
elastomers can sometimes fail or extrude,
leading to leakage and casing erosion. The
chemical nature of elastomers tends to
cause them to extrude under high pressure
and temperature conditions.
Still, elastomers can provide reliable
isolation when properly designed with
anti-extrusion mechanisms. These can be
made of overlapping plates or rings that are
compressed and flattened into a disc-like
shape, blocking the elastomer from slipping
through the gap of slip segments. In com-
plex downhole conditions, however, these
anti-extrusion mechanisms can sometimes
fail or not deploy fully, leaving weak points
that allow for extrusion to occur.
To address the issues associated with
elastomers, metal-seal dissolvable frac
plugs have been developed. These plugs
use a metal-to-metal seal to provide reli-
able isolation under high pressure and
temperature conditions, eliminating the
need for anti-extrusion mechanisms. As
a result, the design of the plug is sim-
plified, requiring fewer components and
materials. This can also make clean-out
runs faster and more efficient. In addition,
metal seals can eliminate running risks in
high annular velocities.
In challenging situations, hybrid seals
can also be used; it combines both an elas-
tomer ring and a metal-seal mechanism.
The elastomer serves as the initial pres-
sure barrier during stimulation, while the
metal seal undergoes plastic deformation
and fully engages with the casing wall
as the pressure increases. This not only
provides reliable isolation of the casing,
but the metal seal also serves as a robust
anti-extrusion component
Compared with these newer and more
simplified plugs, traditional dissolvable
frac plugs are typically made of complex
components that can be prone to failure
risks. These components may be sensitive
to temperature, pressure and other factors,
which can make it difficult to predict and
control the rate at which the plug dissolves.
Another potential limitation of tradi-
tional dissolvable frac plugs is that they
are often heavily customized to dissolve
at specific rates, which can be difficult to
predict and control. This can make it chal-
lenging to use these plugs in a wide range
of wellbores and production scenarios, as
the specific conditions and requirements
of each well can vary significantly.
Using dissolvable technology can be
both beneficial, but it does comes with its
challenges. To customize plugs that are
suitable for different conditions, a thor-
ough understanding of both application
challenges and engineering are neces-
sary. The tool supplier must consider all
operational details, including the condi-
tions and requirements, to design, simu-
late, validate and optimize the plug in
order to achieve optimal performance and
results for end users. This requires a care-
ful balance between tool performance and
dissolvability. Striking a balance between
the trade-offs in different applications and
scenarios is crucial for success. DC
LEFT: Vertechs’ traditional dissolvable frac plug design (left) versus its new design (right).The metal-seal dissolvable frac plugs
use a metal-to-metal seal, eliminating the need for anti-extrusion mechanisms. RIGHT: A metal-seal dissolvable frac plug is
rigged up before being run in hole. The plug’s simplified design meant fewer components and materials were needed.
36 M A R C H/A P R I L 2023 • D R I L L I N G C O N T R AC T O R