Drillers Method for Killing a Well
the drillers Method for killing a well is an alternative to the one circulation Method. In this method the influx is first circulated out of the well with the original mud. the heavyweight kill mud is then circulated into the well in a second stage of the operation. As with the one circulation method, the well will be closed in and the circulation pressures in the system are controlled by manipulation of the choke on the annulus. This procedure can also be divided conveniently into 4 stages:
Phase I (circulation of influx to surface)
during this stage the well is circulated at a constant rate, with the original mud. Since the original mudweight is being circulated the standpipe pressure will equal Pdp + Pc1 throughout this phase of the operation. If the influx is gas then Pann will increase significantly (Figure 18). If the influx is not gas the annulus pressure will remain fairly static.
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Figure 18 Summary of standpipe and annulus pressure during the "Drillers" method |
Phase II (discharging the influx)
As the influx is discharged the choke will be progressively opened. When all the influx has been circulated out Pann should reduce until it is equal to the original shut in drillpipe pressure Pdp so that Pann + pmd = Pf
Phase III (filling the drillstring with heavy mud)
At the beginning of the second circulation, the stand pipe pressure will still be Pdp + Pc1, but will be steadily reduced by adjusting the choke so that by the end of phase III the standpipe pressure = Pc2 (as before).
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Phase IV (filling the annulus with heavy mud)
In this phase Pann will still be equal to the original Pdp, but as the heavy mud enters the annulus Pann will reduce. By the time the heavy mud reaches surface Pann = 0 and the choke will be fully opened. The pressure profiles for the drillers method are shown in Figure 17.
Exercise 4 Well Killing Technique
a. Briefly explain the essential differences between the "one circulation method" and the "drillers method" for killing a well.
b. Briefly explain how and why the wellbore pressure is monitored and controlled throughout the well killing operation (assuming that the "one circulation method" is being used to kill the well).