American Oil and Gas Reporter - April 2019 - 67

SpecialReport: Drilling Technology

Ballooning Perception May Be Flawed
By Steve L. Richert
HOUSTON-Well bore ballooning or
breathing during drilling has become a
greater challenge in horizontal resource
plays. Ballooning is a formation anomaly
whereby pumped fluids' circulating friction
pressure forces drilling fluid from the
wellbore into the rock's microfissures,
which open only enough to contain fluid,
but not enough to permanently fracture
the rock. When the fluids cease to be
pumped and the circulating friction pressure is lost, the overburden of the rock
forces the contained fluid back into the
wellbore.
In short, circulating friction causes
fluid losses at the surface. The formation
takes drilling mud when the pumps are
on, but when the pumps stop, the fluid
returns to the surface. The process is
similar to how a balloon holds air then
returns it to the atmosphere when reopened
(Figures 1A and 1B).
Identifying ballooning effects is critical
because the well will behave as if it were
taking a kick. The question boils down
to whether a well is ballooning or kicking.
Is the formation merely returning injected
drilling fluid or is a blowout imminent?
Sometimes what we perceive may not
correspond with the facts.
Considering that well ballooning can
be confused with a kick or an even more
serious well control situation, which of
the following case histories is an example
of well ballooning?
In the first case history, a driller noticed
partial losses of approximately seven barFIGURE 1A

rels. When the time arrived for a bit
change, the operator shut down, lined up
returns to the trip tank and conducted a
flow check. The flow check was negative,
so the crew began to pull out of the hole
using continuous fill. The trip tank volume
began dropping. After several stands were
pulled, a derrick hand noticed steadily
increasing trip tank volume. Even so, the
volume was manageable and equal to the
losses recorded while drilling.
In the second case history, crew members that were drilling a new hole section
that projected to be a ballooning shale
formation were warned to keep their eyes
open for signs of ballooning. After making
a few connections, the crew noticed a
slight increase in flowback. The volume
was small and increased only slightly
during the next few connections.
The third case history dealt with mud
losses that began to occur while drilling
through soft shale. The driller stopped
circulation to flow check and observed a
pit volume gain. When drilling resumed,
fluid losses were observed. Every time
the pumps were shut off to make a connection, the well gave mud back with
only a slight increase in flow rate.
Which well was ballooning? The answer is none of them. Each well was
taking an influx (that is to say, kicking).
Although it seems arguable that one of
the wells was ballooning, all the wells'
subsequent ballooning analysis showed
a flow increase. Kicking wells indicate a
flow increase, while ballooning wells
show a decrease.
Lacking either well "fingerprinting"

or a ballooning flow test, wells in such
situations should be considered kicking.
Too often, drilling crews, management
and engineers perceive a well to be ballooning without performing a requisite
investigation. Decisions are executed
based on perceptions instead of facts:
Those decision makers believe the well
is ballooning when, in fact, it is kicking.
Serious Consequences
Misdiagnosing a kick as ballooning
can have disastrous consequences. Careful
analysis of ballooning characteristics can
prevent a catastrophe, potentially damaging
life, limb, equipment, the environment,
company finances and the industry's reputation.
Consider another example: In a field
known to balloon around 30 barrels, the
drilling crew was tripping out of the hole.
The driller kept an accurate trip sheet,
which showed the fluid volume needed
to replace the steel volume removed from
the well. The total drilled depth was
16,000 feet; 6,000 feet of it vertical and
the remaining 10,000 feet horizontal.
After tripping 8,000 feet of pipe from
the well's horizontal section and with
another 8,000 feet left to trip, the driller
noticed less fluid volume was needed to
replace the pipe's steel volume. The volume in the trip tank had increased approximately 20 barrels since the operation
began.
The driller stopped tripping and performed a flow check, which showed a
slight flow-about the diameter of a small

FIGURE 1B

In a ballooning well, fluid is temporarily lost to the formation (FIGURE 1A). If a formation is ballooning, returns will be nearly equivalent
to losses (FIGURE 1B).

APRIL 2019 67

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