Driller’s method and wait and weight method (engineer’s method) are widely used to circulate wellbore influx while maintaining bottom hole pressure constant. There are a lot of opinions regarding which method is the best for well control operation therefore this article will discuss about pros and cons of both methods.
The driller’s method requires two circulations to kill the well. The first circulation is to circulate influx out of the well with original mud weight. The second circulation is to kill the well with kill weight fluid. During the first circulation, the bottom hole pressure remains constant due to maintain drill pipe pressure constant while circulating. For the second circulation, in order to maintain constant bottom hole pressure, casing pressure is held constant while circulating kill mud to the bit. Once the kill mud passes the bit, the drill pipe pressure will be held constant until the kill weight mud is on surface and there is no sign of influx in the annulus.
Wait and Weight Method
The Wait and Weight method requires only one circulation. The influx will be circulated out while the kill weight mud is displaced into the well simultaneously. While pumping the kill fluid from surface to the bit, drill pipe pressure schedule must be strictly followed. After that the drill pipe pressure is maintained constant until the kill mud returns back to surface. Some people call the Wait and Weight method as “Engineer’s Method” because there are more calculations compared to the Driller’s method.
Comparison between Driller’s Method and Wait and Weight Method
Kill Weight Mud or Kill Drilling Fluid Density is the mud weight required to balance formation pressure. The kill weight mud may be pumped into the well at different time depending on kill methods (Driller’s method, Wait and Weight, Bull head, etc).
How to determine kill weight mud?
With the following equation, you can determine this figure.
Kill Weight Mud (KWM) = Current Mud Weight + (SIDPP ÷ 0.052 ÷ Well TVD)
In the first circulation of driller’s method, driller circulates gas kick with 25 spm and the initial circulating pressure (ICP) is 1600 psi. The initial shut in drill pipe pressure is 450 psi. After shift change, another driller accidentally changes pump rate to 30 spm but he still holds drill pipe pressure constant.
Driller’s method is one of several methods to kill the well. The main idea of driller method is to kill the well with constant bottom hole pressure. The Driller’s Method of well control requires two complete and separate circulations of drilling fluid in the well. Learn about it via VDO multimedia.