American Oil and Gas Reporter - June 2017 - 93

SpecialReport: Artificial Lift Technology

Method Improves Gas Lift Economics
By Stuart L. Scott,
Renato P. Coutinho
and Paulo J. Waltrich

BATON ROUGE, LA.-Gas lift is the
second most popular form of artificial
lift for U.S. wells, injecting compressed
gas to decrease the density of the fluids
in the wellbore and reduce flowing bottom-hole pressure to allow the produced
fluid column to flow to the surface.
A new and transformational gas lift
method termed liquid assisted gas lift
(LAGL) has been developed that utilizes
the co-injection of liquid with lift gas to
reduce surface pressure requirements for
the kick-off of gas lift and simplify well
completions. This method dramatically
reduces injection pressure requirements,
and has the potential to reduce or even
eliminate the need for additional gas
compression when gas lift is installed.
In fact, in demonstration testing at
Louisiana State University's Petroleum
Engineering Research & Technology
Transfer Laboratory, the technology reduced gas lift injection pressures from
1,200 to 300 psi. Moreover, LAGL utilizes
a single gas lift valve, which reduces
system costs compared with the traditional
use of multiple valves and mandrels while
also dramatically reduces the risk of tubing-to-casing leaks.
Gas lift is a mature artificial lift method
technology that has been successfully
used to boost or maintain production
where reservoir energy is insufficient for
the well to flow at economic rates. Injecting gas into the tubing lightens the
weight of the fluid column especially as
the gas approaches the surface and expands
as a result of decreased pressure. However,
the pressure of the injection gas source
limits the depth that gas can be injected
into a well. The wellhead gas injection
pressure must overcome the liquid column
in the tubing in order for gas to "U-tube"
into the tubing, since the hydrostatic pressure created by the column of gas in the
annulus contributes very little to allowing
the gas to "turn the corner" from the annulus to the tubing.
When a single valve is used, the gas
lift method is termed single-point injection.
To expand the benefits of gas lift, multiple
unloading valves are typically installed
in side-pocket mandrels that are included
in the tubing string (Figure 1). For a

given surface gas pressure, multiple unloading valves enable gas injection at
depths far greater than single-point injection, as illustrated in the unloading
sequence.

Emerging Application Areas
Gas lift has been successfully applied
in a diverse range of operating environments. Emerging application areas that
can benefit from a different and more
cost-effective approach to gas lift include
both onshore unconventional and deepwater wells.
Gas lift already is being utilized for
higher gas-to-liquid ratio unconventional
wells to boost production following the
typically strong initial flow period after
hydraulic fracturing, and the pad-based
nature of unconventional reservoir development provides advantages for gas lift
in much the same way it provides advantages for offshore platform installations.
Gas lift increases gas velocity in the
wellbore to also delay the onset of liquid
loading. An added benefit is that it is
largely insensitive to proppant flowback,
which can accelerate pump wear and fail-

ure rates when electric submersible pumps
or sucker rod systems are utilized. However, onshore unconventional well applications are very sensitive to both capital
and lifting costs, and an approach that
can reduce both is expected to add value.
Offshore, gas lift is attractive in some
deepwater developments since it can both
improve estimated ultimate recoveries
and boost mid-life production rates and
cash flows. It provides the least expensive
in-well artificial lift method for deepwater
wells, but reservoir fluids must be compatible with the injected gas and not
create deposition of solids in the wellbore.
For deepwater, using multiple unloading
valves is not attractive from the tubing
integrity point of view as multiple valves
increase the likelihood that one of these
valves will leak, forcing a well intervention
to restore the tubing well barrier. Considering the high intervention costs in
deep water, this makes single-point injection a much more attractive method.
Key Limiting Factors
While widely utilized (10 percent of
all U.S. wells on artificial lift are gas

FIGURE 1
Gas Lift Unloading Sequence Using Multiple Unloading Valves

Gas

Liquid

Gas

JUNE 2017 93

American Oil and Gas Reporter - June 2017

Table of Contents for the Digital Edition of American Oil and Gas Reporter - June 2017