American Oil and Gas Reporter - June 2021 - 71

SpecialReport: Artificial Lift Technology
change that through an integrated gas lift
system with downhole valve stations that
send data to the surface and receive commands
through a tubing-encased conductor.
" With this system, we have the equivalent
of a flowing gradient survey across the
tubing at all times. This lets production
engineers calibrate multiphase flow models
and gain a much clearer view of what is
happening down hole. "
If something needs to change, an engineer
can open or close valves with the
push of a button, Johnson reports. " A
paper presented at an Artificial Lift Research
and Development Council meeting
by Mike Johnson and Tony Hord of
ExxonMobil suggests that optimizing gas
lift systems generally increases production
5%-20%, " he says. " By using our system
to automate decision making, we can
keep wells optimized while avoiding the
cost, downtime and safety risks associated
with bringing a wireline unit on site to
adjust valves manually. "
Because each downhole valve station
can contain several valves that can be
opened and closed in various combinations,
the system offers fine-tuned control
over injection rates, Johnson says. He
adds that it is easy to open valves to
unload wells after a frac hit.
" Because the valves are controlled
electronically, the system accelerates
initial unload times and can inject gas
deeper without requiring more compression, "
Johnson says. " With a conventional
gas lift completion, when the injection
point moves past the top station, 30-50
psi of injection pressure must be spent to
keep its valve closed. This has to be done
for every valve, so by the time injection
reaches the final station, several hundred
psi has been lost.
" Our system uses the full casing pressure
to move gas, " he contrasts. " How
much that matters varies widely, but we
often see it increase injection depths
from 850 to 1,200 feet. For example, it
enabled a major operator in the Permian
to get gas 1,000 feet deeper without
adding compression. "
Future Applications
Soon, Silverwell will deploy the system
in extended reach wells on Alaska's
North Slope, Johnson reveals. " The cost
savings from adjusting injection without
interventions are especially significant
there, " he reports. " Offshore, where intervention
costs and risks are magnified
a hundredfold, we are working on variants
for use on tension leg platforms and in
subsea developments. "
Johnson acknowledges that the digital
gas lift system is more expensive than
traditional gas lift completions with
pressure operated valves. " We are an
investment, but the business case is
powerful, " he says. " In a typical Permian
Basin unconventional, the system pays
for itself in months. In some of the
more extreme applications, such as dual
string wells in the Middle East and
Southeast Asia, payback can be as quick
as a few days or weeks.
" When capital is especially tight, we
do hybrid systems where most stations
have traditional pressure operated valves
but the stations that will see the greatest
activity use ours, " Johnson says. " That
involves some trade-offs, but it lets operators
get many of the benefits at a
lower cost. "
The system has proven to be reliable,
Johnson assures. " The core downhole
technology is a binary actuator, " he describes.
" We have never had one fail,
and across all our valves, we have logged
almost 60,000 operating days. The longest
system will have been down hole for
four years in August.
" The system is designed to run for
the life of the well, " he says. " It takes
Surface
Controller
Closed
To Separator
To Separator
Injection
Gas
Valve Closed
Valve Closed
Valve Closed
Valve Closed
Operating
Valve Closed
(A) Immediately Before
Gas Injection
Surface
Controller
Open
To Separator
Injection
Gas
Valve Closed
Valve Closed
Valve Closed
Valve Closed
Operating
Valve Open
(B) During Gas Injection
little power to operate, which is important
because the biggest threat to downhole
electronics' life is the heat they generate
while powering up. The valves also
have been engineered to minimize the
chance debris will get stuck inside them.
In fact, operators can even pump proppant
through the system, then proceed
directly to production. "
Each device takes temperature and
pressure measurements, so it is usually
possible to detect scale buildup and
address it before a valve fails, Johnson
adds. If mitigation falls short, the operator
can switch to another valve at the same
location in the string.
" Right now, we are able to automatically
unload and optimize individual
wells, " Johnson reports. " Our endgame
vision is to fully automate multiple gaslifted
wells in a field. We are not there
yet, but we are close. "
End-Of-Life Gas Lift
Intermittent gas lift (IGL) is an extremely
cost-effective technique for managing
production from mature wells, says
A. Stan Logie, president of Logie Gas
Lift Consulting, who has 28 years' experience
optimizing production at ChevronTexaco
and independents such as Pioneer
Natural Resources and Energen Resources.
" Like continuous gas lift, IGL is an
extremely reliable and affordable way to
Surface
Controller
Closed
To Separator
Injection
Gas
Valve Closed
Valve Closed
Valve Closed
Valve Closed
Operating
Valve Open
(C) Injection Gas Entering
Tubing Through Valve
After Controller Closed
Injection
Gas
Valve Closed
Valve Closed
Valve Closed
Valve Closed
Operating
Valve Closed
(D) After Gas Injection
Surface
Controller
Closed
According to Logie Gas Lift Consulting, most gas lift wells should transition to intermittent
gas lift rather than gas-assisted plunger lift once their production falls below 350 barrels
of fluid a day. In IGL, high-pressure gas brings accumulated liquids to surface through
isothermal expansion. Logie says the technique combines strong production with
extremely low operating costs.
JUNE 2021 71

American Oil and Gas Reporter - June 2021

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