buoyancy forces in ct applications

8/7/2019 Buoyancy forces in CT applications

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Buoyancy Forces In Coiled Tubing Applications

Pressure:

Pressure = Force / Area => Force = Pressure x Area

Buoyancy Force:

When a coil is immersed in a fluid, the hydraulic pressure of the fluid applies an

upward force to the coil. This effect is the force of buoyancy.

OR

Resistance to RIH the coil is called buoyancy force.

It is opposite to the snubbing force, and is directly related with the weight of theCoil, OD of BHA and Hydrostatic pressure.

In High pressure Well the Buoyancy value is high. Buoyancy force is determined

by the volume of fluid displaced by the length, width, and height of the immersed

coil.

Buoyant Force upw ard = Hydros t a t i c Pressure o f t he Flu id x Cross -

s ec t i ona l A rea o f t he Ob jec t ( i n a h o r i z on t a l p l ane )

CALCULATIONS/FORMULA:

Hanging weight = Weight in Air B.F

Weight in Air = CT weight/ft X total depth

Buoyancy force = crass-sectional area X H.PBuoyancy force = /4 X (OD)2 X H.PBuoyancy force = 0.785 X (OD)2 X H.P.

And O.D = O.D of B.H.A


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Example :

Suppose a well having 5000 ft depth, fluid weight is 8.5 ppg , coil spincat OD is1.69and CT weight/ft is 2.1lb.

Now in order to calculate the hydrostatic pressure we have the formula,

H.P = Depth (ft) x mud weight x 0.052

= 5000 x 8.5 x 0.052

H.P = 2210 psi

Now to calculate the weight of coil in Air,

1. Weight in Air = CT weight/ft x total depth

= 2.1 x 5000

= 10500 lb/ft2. Buoyancy Force =(OD)2 x 0.785 x H.P

= (1.69)2 x 0.785 x 2210

= 2.856 x 0.785 x 2210

Buoyancy Force = 5522 lbs

Now by putting these value in formula we get,

Hanging wt =Weight of the CT actual B.F

=10500 5522

= 4978 lbs

In case of Live well, formula of CT changes to,flowing while the RIHHanging wt of CT = weight in air (OD)2 x 0.785 x Flowing pressure

Example :


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Suppose a well having 8500 ft depth, simple nozzle OD is 1.75 Well head

pressure is 2500 and CT weight/ft is 2.48lb.CT is empty

Now in order to calculate the hydrostatic pressure we have the formula Hanging wt of CT= weight in air (OD)2 x 0.785 x F.P

1. Weight in Air = CT weight/ft x total depth

= 2.48 lb/ft x 8500ft

= 21080 lb

2. Buoyancy Force =(OD)2 x 0.785 x F.P

= (1.75)2 x 0.785 x 2500

= 3.06 x 0.785 x 2500

Buoyancy Force = 6010 lbs

Now by putting these value in formula we get

3. Hanging wt = Weight of the CT actual B.F

4. Weight indicator gauge show this wt = 15070 lbs

If buoyancy forces increases it cause several problems which are as

follow,

If buoyancy forces increases it cause several problems which are as follow, Injector goes upward then load Cell. Weight goes to negative value. Can not run the CT in high /high Gear. We have to increase the out side tension. Force increases on injector chain.

buoyancy forces in ct applications

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