In order to get more understanding about driller’s method, there are some quizzes that will help you get clear picture of it.
1st example –
Before start circulating, you have the following information
Original Shut in Drill Pipe Pressure = 500 psi
Initial Circulating Pressure (ICP) = 1500 psi
After end of 1st circulation of Driller’s Method, the drillpipe pressure gauge and the casing pressure gauge shows that the circulating drill pipe pressure = 1500 psi and casing pressure = 650 psi (see the figure below).
Do you think what is happening with the well?
When we perform the first circulation of driller’s method, the casing pressure will increase due to gas expansion and the maximum casing pressure will be observed when the gas influx reaches surface.
When gas is moved upward during circulation, the gas will expand due to pressure decrease (refer to Boyle’s gas law P1V1 = P2V2). The higher gas is moved up inside annulus, the higher expansion will be. Therefore, the system hydrostatic pressure will be decreased. For this reason, the casing pressure will increase in order to maintain constant bottom hole pressure.
The mud pumps can be shut down after the total volume of the well has been displaced with kill mud. Practically, you need to check mud weight out several times to ensure that the mud weight out equates to the kill weight mud. Otherwise you may have misinterpretation once the well is shut in and flow checked.
Once shutting down the mud pumps, the choke should be gradually closed in order to hold casing pressure constant. The drill pipe pressure will be slowly dropped to zero as the pump speed is reduced. Please always remember every time that you either bring the pumps up to speed or slow down pump speed, you must hold casing pressure constant.
Once you finish weighing up your mud system to required kill mud weight, you need to do the 2 nd circulation of driller’s method. This post will describe how to do the 2nd circulation of driller’s method.
The second circulation of the driller’s method will be started after drilling fluid is weighted-up to required kill weight.
First, when you establish the desired pump rate you must hold casing pressure constant while bringing the pump up to speed, killing rate +/- 2-5 bpm. Please always hold this pump rate constant throughout the killing process.
After kick has been circulated out of the well, the mud pumps can be shut down and the well must be secured. While shutting down the pumps, it is a good practice to gradually close the choke instead of suddenly shut in.
You must keep in mind that while shutting down pumps, you must keep casing pressure constant achieved by manipulating the choke. This procedure is to ensure that constant bottom hole pressure is maintained during the shutdown.