Kick Detection – Drilling Process Safety
There is no issue more central to the discipline of drilling process safety (DPS) than kick
detection and yet there has been a chronic lack of focus on exactly this. Case in point, look at
the myriad of SPE papers and other industry writings on kick tolerance and you see not only
confusion in what kick tolerance defines (some say volume, some say underbalance density)
and yet they all simply give an arbitrary volume as a minimum for kick volume (we will define
kick tolerance as a volume for important reason).
Now the history of the arbitrary rule of thumb (ROT) for minimum kick volume stems from its
early adoption in our industry back on land rigs. The volume of kick, it was determined, was
noticeable in a typical land rig’s pits after it reached 15 bbls. Why? Go back and ask them! No
clue here except for probably the guy that wrote the first technical article looked at a rig and
found that only after a 15 bbl kick, on that rig, was it determined to be “noticeable”. So they
also, declared, well how long after noticing the kick will the well be closed in? Again, they
decided for a 8-1/2” and smaller hole this would be 10 bbls later. Okay, so they added 15 bbls
to the 10 bbls and said, “the minimum kick tolerance for a 8-1/2” and smaller hole size is 25
bbls. They then said for larger than 8-1/2” hole sizes we will double that and make it 50 bbls.
Good? Maybe not!
Get it wrong and a kick may not be able to be killed without breaking down your shoe or the
weakest zone and possibly creating an underground blowout that may broach to surface and
hence potentially deadly yet definitely costly and perhaps costing you the entire well.
No contradictions to the broad and fine preceeding comments and yet one addition makes real
sense and that is in regards to the need to make kick tolerance specific to both your operating
conditions and geologic assessments and not to an arbitrary standard in a company manual or
drilling
book.
The reason is simply in the concept of time to detect a kick and the variable influx rate of the
sands your well will penetrate. Let's say one operation is circulating at 1200 gpm and another at
300 gpm and another 600 gpm and you are going to set a kick tolerance. Doesn't it seem
arbitrary to pick say 25 bbl or 50 bbl kick volume? You're right it is. Your casing seat and casing
design will be dependent on your selection and yet it may be impossible to detect a 25 bbl kick
or it may be impossible to detect a 50 bbl kick. Kick detection time is a function of several things
that we must consider or else our casing design is meaningless. The kick tolerance (kick
volume) should be selected based on an accurate probability of the time to detect the kick, the
probability of the kick intensity (geological PP upper limit estimate with error bars), the planned
flowrate at the time of drilling the hole section, as accurate of an assessment of the range of
permeability of the sands to be penetrated, an estimate of the inflow using an appropriate inflow
equation and the kick intensity. A tight sand might take an hour to kick 25 bbls and yet a very
permeable one 5 minutes and the intensity is the other variable where it might take twice as
long to take the same size kick. We learned all of this in petroleum engineering school and we
need
to
use
it
now
in
this
case.
This isn't simple and yet why use an oversimplified notion that kick volume can arbitrarily taken
as 25 bbls in a 6-1/2" hole and 50 bbls in larger hole sizes ignoring formation properties,
uncertainty in sand pressure predictions and the range of times to detect? Go to most best
practices and standards manuals and you will see maximum kick volumes given to you and they
are arbitrary. This may work in low risk, development drilling areas and yet its not so much a
good idea in high risk, exploration drilling; where an arbitrary kick volume will not be sufficient to
prevent
loss
of
the
hole
or
worse.
This is the best approach as well since it gives you more of a sense of the importance of quick
detection and you can pass this sense of urgency along to your team.
Let's add to that since this question and answer are important in refocusing our industry's scope
on kick detection specifically in regards to drilling process safety in general, since your question
included, "What makes kick tolerance such a big problem in drilling, especially offshore?"
Reaction times are even more vital in offshore since it is harder to run away from an explosion
and in deepwater the BOPE is closer to the kick and so there is less reaction time before the
kick rises above this control device and it takes longer to close the BOPE on the kick because
the closure control lines are longer. Also, with subsea BOPE, a gas kick in SOBM can be harder
to detect until the gas kick "flashes" out of solution and this "flash point" approaches the
pressures at the depth of the BOPE, especially as water depths increase.
In general, minimum kick tolerance limits must be based on robust assessments of the
particular rig, crew and equipment to assess a minimum kick detection time. Also, there are
dimensional influences on your teams ability to detect a kick quickly and they are:
Personality (Reaction), Character (Response), Mood (Capacity), Competence (Capability),
Environment(Complexity)
Examples, from drilling experiences, of the influence on kick detection of each one of those
dimensions:
Personality - Pit man was interviewed after a kick was allowed to reach over 150 bbls while it
was his job to empty the trip tank and record the volume. He was asked later, "Didn't you see
the pits were overflowing?" He answered, "I was told only to empty the trip tank and record it. I
was too busy emptying the trip tank to see the main pit was overflowing". Example of seeing the
details
and
yet
not
the
big
picture.
Character - Toolpusher did not train the pit man and it was his first day. He gave the pit man
only a detail instruction and not the big picture that he was the first line of defense in detecting a
kick and his trip tank monitoring was a detailed part of the big picture of making sure the casing
going in the hole was displacing the correct amount of fluid. The pitman's reaction was to detail
yet he might have responded to the increasing pace that the trip tank needed emptying if only
the toolpusher had trained him properly to see the big picture and if the toolpusher had ever left
his
post
during
the
critical
trip
to
supervise
the
pit
man.
Mood - The company man was stressed and busy finishing filling out his morning report and
didn't notice the pits were overflowing despite indications within his line of sight he simply was
too
stressed
on
finishing
his
morning
report
to
notice.
Competence - The company man was not the regular one and was a replacement since
ironically the regular company man was sent to town to take mandatory well control school.
Environment - Many otherwise competent people do not realize the complexity of oil based mud
(OBM) in HTHP wells and the diffusivity of gas into the oil phase and the effect of lifting fluid in a
wellbore while running casing in the hole causing OBM much laden with gas from diffusivity
across a pay sand to be lifted to a lower pressure and sometimes after this pressure decreases
below the bubble point of the OBM laden with gas the well will kick. This is a complex system
that not every engineer and rig crew knows the ambiguities of. Most well control training warns
us of kicks being mostly caused by TRIPPING OUT of the hole with drillpipe and casing and yet
the fact is the in OBM with gas in HTHP wells kick all too often while TRIPPING INTO the hole.
So with that in mind the Kick Tolerance of our well designs must be tied to kick detection and
kick detection must consider the worse case scenario; or better yet make sure your crew is
trained properly in regards to the dimensions influencing kick detection and provide safeguards:
Personality (Reaction), Character (Response), Mood (Capacity), Competence (Capability),
Environment (Complexity)