How wait and weight method controls bottom hole pressure

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.

Take a look at the equation:

Pressure in drillpipe side = BHP = Pressure in casing side

DPP + HP – Frictional P in drillstring = BHP = HP + CP + Frictional P in annulus


DPP is drill pipe pressure.

HP is hydrostatic pressure.

Frictional P is frictional pressure.

CP is casing pressure.


At drillpipe side:


DPP will drop when kill mud weight is displaced.

HP will increase due to kill mud weight in the drillstring.

Friction P in drillstring will not change so much.


At casing side:

HP will decrease due to gas expansion in the annulus.

CP will increase in order to compensate hydrostatic pressure loss.

Frictional P in annulus had minimal effect on bottom hole pressure due to slow flow rate while killing the well.


2) Displace kill weight mud from bit to surface

Once the kill weight mud comes out of the bit, there is one single column of hydrostatic in the drillstring. Therefore, in order to maintain bottom hole pressure constant, drill pipe pressure must be maintained while displacing.




• Use the drill pipe pressure schedule to control constant bottom hole pressure while displacing kill weight mud to the bit.

• After kill mud out of the bit, maintain drill pipe pressure until circulation complete.

Reference books: Drilling Formula BookFormulas and Calculations for Drilling, Production and Workover, Second Edition

 Well Control Books

Related Post

Hole Monitoring Procedures While Tripping This is the example of hole monitoring procedure while tripping and this will give you some ideas only. You need to adjust it to suit with your operat...
Drill Pipe Pressure Schedule Calculation for Wait ... This example demonstrates how to determine drill pipe pressure schedule for wait and weight method.   Well Information Current mud weigh...
Lubricate and Bleed in Well Control In some special well control cases, you will not be able to circulate kick out of the well then the kick is brought up to the surface using special we...
Maximum pit gain from gas kick in water based mud In water based mud, you can not only estimate the maximum surface casing pressure, but you are also be able to determine the maximum pit gain due to g...
Share the joy

About DrillingFormulas.Com

Working in the oil field and loving to share knowledge.
Tagged , . Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *