American Oil and Gas Reporter - June 2016 - 52

SpecialReport: Permian Basin Update

Bottom-Hole Pressure

FIGURE 1B
Diagnosing Gas-Lift Performance Issue using BHP Data

Gas-lift valve
replaced & well
producing

Unplanned
shut-in &
pressure
buildup

Time

For wells using ESPs, the method for
measuring BHP is simple. ESP systems
typically measure and record downhole
pump intake pressure, easily satisfying
the engineer's desire for accurate and
high-frequency BHP data.
For gas-lift wells, measuring real-time
BHP is more complex, and requires installing a gauge and a method for transmitting data to the surface. Gas-lift wells
in this study incorporate a unique system
where a gauge installed at the end of the
tubing string measures tubing pressure
while a tubing-encapsulated conductor

52 THE AMERICAN OIL & GAS REPORTER

(TEC) line is run from the gauge up the
annulus to surface. The TEC line is run
through the wellhead and connects to a
surface box, which records high-frequency
pressure/temperature data and transmits
them to engineering offices daily or ondemand.
The real-time nature of these data
makes them extremely valuable for optimizing and trouble-shooting the gaslift system. These retrievable gauge assemblies can be used for the life of a
gas-lift system and reused on subsequent
wells.

Optimizing Well Performance
Figure 1A shows how measured BHP
data were used to troubleshoot a potential
artificial lift issue on an ESP well. Pump
intake pressure revealed that the ESP
was unable to adequately draw down the
well, as seen in the flattening of BHP at
an unacceptably high pressure.
After attempts to improve drawdown
by adjusting ESP settings were unsuccessful, an acid flush was performed, resulting in increased drawdown. Production
tests performed during the week before
and the week after the acid flush revealed
average rate increases from 460 to 1,125
barrels of fluid per day.
Without measured BHP, the initial
production underperformance may have
been interpreted simply as a bad well.
With downhole pressure data, the problem
was easily identified and fixed, resulting
in greatly improved well performance.
It is common practice in the Wolfcamp
Shale to test wells on a periodic basis
after initial flowback, which helps reduce
capital associated with installing production trains for each well. Figure 1B shows
how measured BHP was used as a surveillance tool in the absence of daily
production tests and identified artificial
lift issues on a gas-lift well. In this case,
wells were being tested on a monthly
basis, and the well in question was assumed to be producing normally when
the BHP started building, which is indicative of the well not flowing or flowing
at a significantly reduced rate.
A subsequent production test revealed
the fluid rate had dropped from 430 to
eight bbl/d. Casing pressure, gas-lift injection rate, and standard surface diagnostics suggested gas was injecting successfully into the bottom gas-lift valve
and the well was fine.
Bottom-hole pressure, as a unique diagnostic measurement, was the only
reason to pull equipment out of the well
and search for an issue. After pulling the
tubing, a shallow gas-lift injection valve
failure was discovered. The valve was
replaced and the well was reopened, producing an average 800 bbl/d of fluids
during the first week.
These examples are only two of many
instances where real-time BHP monitoring
has allowed for rapid trouble-shooting
and optimization of artificial lift systems
in Wolfcamp horizontals, some of which
may never have been understood fully
without pressure data. They show how
the value of having the downhole gauges

American Oil and Gas Reporter - June 2016

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