American Oil and Gas Reporter - April 2019 - 69

SpecialReport: Drilling Technology
The gas reached an ignition source and
ignited, causing several million dollars'
worth of damage to the rig. Fortunately,
no one was hurt.
A Root Cause Analysis
Why did the driller follow orders and
not shut in the well when he first discovered minor flow? Either he:
· Acquiesced to the experience of
his superiors; or
· Was concerned about being fired
because he had been laid off work for a
year and had returned for only a few
months.
Why did the operations supervisor
and engineer think the well was ballooning?
· Since other wells in the field experienced ballooning, this well was likely
to balloon.
· The well acted as if it was ballooning, since the flow was minor.
· Even after shut in, low surface pressures were observed on the gauges.
Why did the rig crew not interpret
shut-in pressures?
· Members had not been trained how
to determine the status of a well based
on pressures.
· The shut-in pressures were lower
than the crew had seen in normal kick
situations.
Why did management choose to circulate the well through the flowline?
· Everyone was keen to reduce nonproductive time, so they did not circulate
the well through the blowout preventer,
choke and mud/gas separator.
· The flow was minor and pressures
were low, so it was assumed that there
was no gas in the well, since it was perceived to be ballooning.
Why was the well not fingerprinted, or
in the absence of fingerprinting, why was

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no ballooning flow analysis performed?
· Neither the engineer nor the operations supervisor were aware of the fingerprinting process.
· NPT increases if the rig stops for a
ballooning analysis; the process takes
time.
The incident's root cause probably
amounted to a perception by management
and the crew that the well was ballooning
because other wells in the field had ballooned, the flow was minimal and the
shut-in pressures were low. Management
did not determine with certainty that the
well was, in fact, ballooning by using
fingerprinting or flow analysis. Minimal
flow characteristics, low shut-in pressures
and field experience contributed to the
false conclusion that the well was ballooning. Relying on perception, instead
of determining the facts, led to the decisions behind the incident.
Fingerprinting, Flow Analysis
What would have eliminated the root
cause in this case history? As stated earlier,
fingerprinting or ballooning flow analysis
are two ways to accurately determine
whether a well is ballooning or kicking.
Fingerprinting is the process of graphically tracking any fluid losses into formation microfractures. Surface volume
losses are tracked while the pumps are
on. If the crew is not building mud to
replace the volume needed to fill the
drilled hole, the potential ballooning
losses are total volume lost minus drilled
hole needs. If the drilled hole fill is 1.5
barrels a stand and the total losses are
5.0 barrels, the formation took 3.5 barrels.
If the well gives back approximately
3.5 barrels at connection, determined
by graph, the well is probably ballooning.
This give and take of fluid usually will
be consistent from connection to connection (Figure 2).
Flow analysis for ballooning involves
a process whereby fingerprinting has not
been performed or can be used to verify
fingerprinting. Flow analysis involves
several steps:
· If the well is flowing, shut it in.
· Record the shut-in pressures.
· Slowly bleed off fluid for a given
time into an easily measured tank (be
certain to bleed no more total fluid than
the kick tolerance).
· Time the flow back, shut the choke
and measure the amount of volume flowed
and again record pressures.
· Bleed the same amount of time

again recording the pressures and flowed
volume.
· Repeat the process several times
until a flow pattern can be established.
If a well is ballooning, the flow volume
will decrease on each cycle. Accordingly,
the wellbore pressures will decline.
If the flow volume or gauge pressures
increase, the well is kicking. The kick
should then be circulated out through the
BOP, choke and mud/gas separator.
In today's land drilling operations,
we see wells balloon more often because
of the close proximity of lateral wells
and production enhancement practices,
even in fields that previously never experienced ballooning. To press on because
of nothing more than perception is a
recipe for disaster. What rig crews and
supervisors believe by perception may
not always be fact. Without careful well
analysis leading to certainty, the well
should be considered to be kicking, not
ballooning. Determining the difference
between a ballooning and a kicking well,
objectively, through facts ascertained by
fingerprinting or flow analysis, is the
only way to proceed safely.
❒

STEVE L.
RICHERT

Steve L. Richert is manager of instructor and course development at
Wild Well Control in Houston, where
he leads education and development
for well control instructors, including
knowledge progression, certification,
and course and instructional materials
development. He has 20 years of industry experience, coupled with a 20year adult education background in
the pedagogical study of human
knowledge acquisition. Richert joined
Wild Well Control in 2012 after previously serving as a driller at Ensign
Energy Services, and as a financial
specialist at U.S. Bank and TD Ameritrade. He studied mechanical engineering at the University of Oklahoma
and holds a B.A. in history and philosophy from Grace University.
APRIL 2019 69

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