BAKER HUGHES - Drilling Fluids Reference Manual

PRESSURE PREDICTION AND CONTROL
Graphical Analysis of Pumping Schedule – Divide the time (strokes) to displace the drillstring
into even increments on the bottom of graph. Use 50, 100, or 200 stroke increments to utilize
the maximum amount of graph. Plot initial circulating pressure at time or strokes 0. Plot final
circulating pressure at time or strokes required to displace the drillpipe. Draw a straight line
between the two points.
When ready to circulate, open the choke slightly until there is some flow through the choke and
then start up the pump. Break circulation and bring the pump up to the predetermined kill rate.
While the pump is being brought up to speed, hold the casing pressure at the shut-in value with
the adjustable choke.
Note:
On rigs with subsea Blow-Out Preventer (BOP) stacks, the casing
pressure is allowed to drop by the amount of the pressure loss in the
choke line.
When the pump is up to the kill rate, the drillpipe pressure should be adjusted to the initial
circulating pressure by using the adjustable choke.
As the new fluid is being pumped down the drillpipe, reduce the drillpipe pressure according to
the graph on the worksheet. The pump pressure will drop from the initial circulating pressure to
the final circulating pressure over the time that the new fluid takes to fill the drillpipe (the
surface to bit travel time). If there is gas in the kick, the annular pressure can be expected to
rise and pit volume will increase as the gas comes to the surface.
When kill fluid is at the bit, the final circulating pressure should be maintained constant by
keeping the pump strokes constant and adjusting the choke as required. Continue to circulate
holding the final circulating pressure until the new fluid is circulated around. If calculations
and procedures have been followed correctly, the well should be dead.
After the new fluid reaches the surface, the pumps should be shut down, and the well checked
for flow. If no flow occurs, the well is dead. Depending upon the operating company, the well
may be circulated for a time, a short trip may be made, drilling may commence, etc. If the well
continues to flow, it should be shut in and kill procedures initiated again.
SPECIAL PROBLEMS
There are numerous well kill situations which develop that may require the use of special
techniques to bring under control. These are typical problems that may develop.
• Nearing fracture gradient limitations
• Plugged bit
• Plugged choke
• Lost circulation
• Well flows while tripping or out of the hole, etc.
It is not the scope of this chapter to cover these problems. The operator's representative is
normally responsible for handling these situations.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 12-34