I completed about well control formulas from previous blog post and then I would like to continue about driller’s method in details.
You can read previous about driller’s method here!!!
Today, I post about 1st step of establishing circulation in driller’s method, bring the pumps up by holding casing pressure constant.
The idea of holding casing pressure constant while bring up pumps is to maintain constant bottom hole pressure.
Bring pump up to circulating rate, typically about 2-5 BPM, by holding constant casing pressure. The reason why we need to hold constant casing pressure is to maintain constant bottom hole pressure.
Let’s me explain more by showing you some equations.
Note: Acronyms are listed below;
BHP = Bottom Hole Pressure
HP = Hydrostatic Pressure
CP = Casing Pressure
FrP = Frictional Pressure
At static condition: BHP = HP in the annulus + CP
At dynamic condition: BHP = HP in annulus + CP + FrP
In the dynamic environment, if we pump as slowly as possible, FrP can be ignored. The equation above tells us that when you hold CP constant, the BHP will be maintained the same.
After you bring pump to kill rate, you will get circulating pressure called Initial Circulating Pressure (ICP). ICP is summation of shut in drill pipe pressure (SIDPP) and pressure to overcome friction called Slow Circulating Rate Pressure (SCR pressure). Hence, we can write the relationship in term of equation below.
ICP = SIDPP + SCR pressure
SCR pressure = ICP – SIDPP
Note: Kill rate is normally about 2-5 BPM.
Before performing this operation, you must ensure these following items;
1. Ensure that team members know their role and responsibility. You should have a pre job safety meeting before killing operation.
2. Eliminate all ignition sources that are close to the rig and vent lines of mud-gas separator.
3. Ensure that a circulating system is lined up properly.
4. Zero strokes counter and record time every activity.