Page 383 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 359

3.3.2
Drilling Problems [ ]

3.3.2. Lost Circulation

In some areas there may be offset information or “Field operational
notes (Sec. 1.12),” which give specific guidance on how best to handle
losses in particular formations based on previous experience. While
this does not guarantee that past successful techniques will work again
even in close offset wells, it gives a good starting point which is better
than general guidance notes such as are given in the following topics.
Therefore, these should be the first point of reference, if they exist for
the problem formation.
Many instances of lost circulation are self-inflicted and avoidable.
Keep the mud in good shape with rheology and gels low to minimize
surge pressures and ECD. Trip in at moderate speed. Use good con-
nection practices as detailed in Section 3.3.7, “Making Connections to
Minimize Wellbore Instability and Losses.”
There are many causes of lost circulation and various techniques to
deal with them. Following are some of these techniques in detail,
under the situations leading to the type of losses.
Where severe or total losses occur in relatively unknown areas,
special attention must be paid to the possibility of taking a kick, either
due to loss of hydrostatic or while drilling ahead with an actual or
cured loss zone higher in the well. If an internal blowout is suspected,
then the losses have to be cured before the well can be killed. In this
situation, the drilling office will be closely involved in planning the
strategy to bring the well under control.
Losses to surface or seabed outside conductor. Where this occurs
the stability of bottom supported units can be seriously compromised.
Offshore, if returns are to seabed, this is very unlikely to happen, but
where a riser is in use the extra hydrostatic imposed can be enough to
cause this.
Drill ahead until the losses become severe (unless drilling with a
diverter—see last paragraph of this subsection). POH and run open-
ended drillpipe to 30 m below the shoe. Spot a weighted viscous pill
into the conductor and pull back to 5 m below the shoe.
Pump a neat cement slurry from 5 m below the shoe to 20-50 m
inside. POH and make up the drilling assembly. When the surface samples
are hard, run in and drill out the cement. The level should have dropped
and cement displaced into the loss channels around the conductor.

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