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Drilling Fluid:
Cooling the system
Another of the
fluids many tasks if to keep the string and bit cool and well lubricated. Working with small
surface volumes of drilling fluid can save money. How ever
there must be sufficient volume to keep the string and hole cool. Long bit
runs and the constant circulation add to the problems. It is well
understood the all need to make a profit but at what cast and to hume
Some
years ago while drilling an 18000 foot hole in the Middle
East the rig was using a base oil mud. Due to the fact
there was a lot of H2S in the area the volume was kept as
low as possible.
The
constant friction created by the pipe and bit using a PDC
soon bought the mud temperature up. Having such a low
surface volume never gave it a chance to cool. Pumps that
had never given problems before started to go down and it
became impossible to work on them. Cooling water was spray
over the pump and fluid ends started to crack
Piping began to warp and bend under their own weight. This was finally
capped of with an accident, when the de-sander piping now so hot
came loose spraying scolding fluid into the face of one of the men had it
not been for the fact he was wearing classes he would have been blinded
but even this never stopped him spending a lot of time in hospital.
Considerable heat is
generated by friction at the bit and where the drill string is in contact
with the formation. This heat must be absorbed by the fluid so that it
can be transmitted to the surface and dissipated. Small volumes are
quickly re-circulated and in the case of an oil base drilling fluid are
extremely hard to keep cool.
It must also be pointed out that oil mud's get far hotter
than water base mud's This in turn can have a devastating effect on the
other mud properties. In the case mention we found the fluid density
could not be maintained. Thus allowing the salt zone to close in
and a constant need to short trip.
The fluid also works to lubricate the bit and drill string. If additional lubricity is needed, there are several lubricating products which can be added to the system. The lubricity of the fluid helps to decrease torque, increase bit life, reduce pump pressure and reduce bit balling.
Liquid soap is a good lubricant and is also handy for washing down the
rig, hint. |