Driller’s Method:

To regain control of a well using the ‘Driller's Method,’ it is necessary to perform two complete circulations of the drilling fluid within the well. The initial circulation uses the same mud density in the hole when encountering the kick to remove the influx from the well.

As the circulation starts, the pressure in the casing is maintained constant at ‘Shut-In Casing Pressure (SICP)’ until the pump reaches the kill rate. After that, the pressure in the drill pipe is kept constant to ensure that the bottom hole pressure is equal to or slightly higher than the fluid pressure in the formation.

Maintaining a steady pump rate and pressure in the drill pipe during the first circulation is essential to ensure that the bottom hole pressure does not fall below the formation pressure, thus avoiding a secondary kick situation.

Should the kick contain gas, it will undergo controlled expansion within the annulus as it approaches the surface during circulation. This will occur under regulated conditions. Due to the gas expansion, an increase in casing pressure and pit volume will be seen during the first circulation.

The well can be shut-in after pumping the calculated number of strokes to complete the first circulation. The pressure reading on the drill pipe after the completion of the first circulation will be the same as it was on the initial shut-in. Assuming that all the influx has been completely removed from the well and that the hydrostatic pressure of the mud inside the drill pipe and the annulus is the same, the shut-in pressures inside the drill pipe and the casing will be the same after the completion of the first circulation.

The Kill Weight Mud density is calculated by converting the initial Shut-In Drill Pipe pressure (SIDP) to the equivalent mud weight and adding it to the original density of the drilling fluid in the well to balance the formation pressure at the bottom of the well. The second circulation is carried out with kill-weight mud.

During the second circulation, the choke is manipulated to keep the casing pressure constant while pumping kill-weight mud through the drill pipe. This ensures that the bottom hole pressure remains constant. Once the predefined number of strokes are pumped to fill the drill pipe, the control turns to ensure that the drill pipe pressure remains constant while the annulus is filled with heavy mud. When the kill mud reaches the surface, the pressure on the choke should be minimal. The pumps can be stopped while holding casing pressure constant and the well checked for flow.

If all the influx is out of the well and there wasn’t any secondary kick due to the bottom hole pressure falling below the formation pressure during the well killing, the drill pipe and casing pressures should read zero.

There could be situations where the circulation needs to be stopped and started again during the well killing. The processes for starting up and shutting down pumps should be done with utmost care. Every time, the casing pressure must be maintained at the same level as it was just before the pump speed change was commenced to ensure that the bottom hole pressure is constant. It is acceptable to use this approach because the pressure inside the casing remains the same regardless of whether the pumps are on or off. Meanwhile, the pressure in the drill pipe changes depending on the frictional pressure loss in the system during circulation.