We’ve learned so many topics regarding wait and weight well control method and I would like to share what advantages and disadvantages of wait and weight method are.
Advantages of Wait and Weight Method
• When compared to driller’s method, the wait and weight will generate lower pressure at casing shoe while circulating.
• It will generate the lowest pressure on surface equipment.
• It requires less circulation than driller’s method therefore time of equipment exposed to pressure is less.
This topic will cover about pressure profile both drill pipe and casing pressure while kill a well with wait and weight method.
Drill Pipe Pressure
Firstly, we will take a look at the drillpipe pressure. When kill weight mud is displaced in the well, drill pipe pressure drops as per the drill pipe schedule. Once kill weight mud is to the bit, drill pipe pressure is maintained until the well is killed. A pressure profile will look like the following chart.
This example demonstrates how to determine drill pipe pressure schedule for wait and weight method.
Well Information
Current mud weight = 9.5 ppg
Pump output = 0.1 bbl/stroke
Well depth = 9000’MD/9000’TVD
Drill string capacity = 0.0178 bbl/ft
Surface line volume = 15 bbl.
Shut in casing pressure = 700 psi
Shut in drill pipe pressure = 500 psi
ICP = 1600 psi at 30 spm as kill rate
Please follow steps below to determine the drill pipe pressure schedule (step down chart).
This topic will explain you how wait and weight well control controls bottom pressure constant. There are 2 steps that must be took into consideration separately. The first one is when kill weight mud is displaced to the bit and the second one is when the kill weight mud from bit to surface.
1) Displace kill weight mud to the bit
Once kill weight mud is mixed and displaced into drill pipe, drill pipe pressure will be decreased due to increasing in hydrostatic pressure. In order to control bottom hole pressure, a drill pipe pressure schedule must be developed and followed until kill mud weight to the bit.
There are some well control formulas that you need to know for wait and weight method.
1. Kill Weight Mud
KWM = OMW + [SIDPP ÷ (0.052 x TVD)]
Where;
KWM is kill weight mud in ppg.
OMW is original mud weight in ppg.
SIDPP is shut in drill pipe pressure in psi.
TVD is true vertical depth of the well in ft.
Note: Read more about it>> Kill Weight Mud
