Page 399 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 375

Drilling Problems [ ]
3.3.8

hole size, BHA configuration, and any packing off around the BHA
drillpipe OD). Significant swab pressures can be created by pulling out
too fast or stopping the pumps too quickly. The amount of pressure
decrease on a connection will depend on how fast the pumps are
stopped, depth, mud density, mud rheology, and hydraulic diameter.

3.3.8. Preplanned Wiper Tripping

In certain circumstances, wiper trips are programmed into the
drilling program:

1. Where offset experience shows that certain formations will deform
plastically into the wellbore and a wiper trip, after a certain time
period, justifies the costs involved because it reduces time later
spent tripping and running casing. Massive salts are one example
(such as the North Sea Zechstein, where wiper trips back to the
previous wiper trip depth, after 18 hours drilling, prevent further
tripping overpulls and stuck pipe).
2. In deviated wells, wiper tripping may disturb cuttings beds before
they become great enough to cause a problem.

Wiper trips cost time (money) and help to destabilize the wellbore
(increased open-hole time; surge and swab pressures), thereby initiat-
ing or worsening many common hole problems.
The decision to wiper trip can be summarized as: “Will the time
taken to wiper trip lead to a greater time savings when tripping, logging,
and running casing?” Experience has shown that most wiper trips are at
best only time consuming and at worst may cause significant problems,
without giving any benefits in return. This decision is best left to the
discretion of the drilling supervisor, however, this must be justified with
a properly engineered analysis of the costs and expected benefits.
If you do program in “routine” wiper trips, at least analyze whether
any benefit has been obtained. If on your wiper trip you saw no drags
or holdups then it is reasonable to say that the wiper trip probably had
no beneficial effect. Therefore, on the subsequent well, you could
extend the period between such wiper trips if the hole angle and mud
properties are similar. Even if some drags or resistance were seen, it is

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