Page 425 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 401

Cementing [ ]
3.5.4

1. On the down stroke, annular velocities are increased.
2. As the casing is moved, it will tend to move laterally in the well-
bore. Thus, if the casing is not perfectly centralized, the “narrow”
and “larger” flow-by areas will move around, improving displace-
ment in areas that may otherwise be dead. This may happen
whether the casing is rotated or reciprocated.

Reciprocation has been found to be more efficient from field expe-
rience. It may be because in reciprocation, both of the above mecha-
nisms are present whereas in rotation only the second one is. With a
solid mandrel hanger, only attempt this if the hole is completely trou-
ble free. Land the casing shortly before bumping the plug. If using a
slip and seal hanger, position the casing on depth and stop movement
shortly before bumping the plug.
Liners cannot usually be reciprocated, since the hanger is set
before cementing. Some liner hangers are designed to permit rotation
during displacement and while this is not as effective as reciprocation,
it is better than no motion at all. If a liner is to be rotated, check the
torque on the last trip out at liner hanger depth, and limit the torque
while cementing to this value plus the make-up torque of the liner.
Cementing casing with plugs. Normally, two slurries are used; an
extended lead slurry and a neat or heavy tail. It is vital to get compe-
tent, high-strength cement at the shoe for drilling ahead or at the inter-
vals for perforating.
Batch mixing is the preferred method for producing high-quality,
homogenous slurry. For normal casing jobs if a batch tank is available
on the rig, the tail slurry can be batch mixed first. Since the setting time
is applicable at downhole rather than surface temperature, the
pumpable time from starting to displace the cement should not be seri-
ously shortened. This allows you to pump the lead slurry in a recircu-
lating mixer, switch lines, and immediately start to displace the tail
slurry without having to pump as slowly as you can accurately mix
with the recirculating mixer.
After pumping the slurry, drop the top plug, displace the lines from
the cement pump to the rig floor with water, then use the rig pumps to
pump mud behind. (On smaller jobs the cement pump may be used to
displace the slurry.) Do not over-displace by more than half the shoe-
track volume because if the top plug leaks, mud will exit the casing
shoe and the shoe will not be well cemented. Monitor for losses and

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