CUTTING SLIP VELOCITY CALCULATION METHOD 2

This is another method to determine cutting slip velocity. The process of calculation is quite different from the first method however it is still straight forward calculation. It still gives you the following answers: annular velocity, cutting slip velocity and net velocity.

Let’s get started with this calculation method.

1. Determine n:

Where: n is the power law exponent.
Θ600 is a value at 600 viscometer dial reading.
Θ300 is a value at 300 viscometer dial reading.

2. Determine K:
Where:

K is the fluid consistency unit
Θ300 is a value at 300 viscometer dial reading.
n is the power law exponent.


3. Determine annular velocity with following equation:
Where:


AV is annular velocity in ft/min.
Q is flow rate in gpm (gallon per minute).
Dh is diameter of hole in inch.
Dp is diameter of drill pipe in inch.

4. Determine cutting slip velocity with following equation:
Where:

Vs is cutting slip velocity in ft/min.
PV is plastic viscosity in centi-poise.
MW is mud weight in ppg.
Dp is diameter of cutting in inch.
DenP is cutting density in ppg.


5. Determine net rise velocity with following equation:


Net rise velocity = AV – Vs


Where:


AV is annular velocity.
Vs Cutting Velocity


This figure indicates that cuttings are being lifted by mud or are still falling down.
If net rise velocity is positive, it means that you have good flow rate which can carry cuttings in the wellbore.


On the other hand, If net rise velocity is negative, your current flow rate is NOT engough to carry cuttings.


Example: Please use the following information to determine annular velocity, cutting slip velocity, net rise velocity, and tell us if the flow rate is good for hole cleaning.

Flow rate = 300 gpm
Hole Diameter = 6.3 inch
Drillpipe OD = 4 inch
PV = 15 cps
MW = 10 ppg
Diameter of cutting = 0.20 inch
Density of cutting = 20.0 ppg

1. Determine annular velocity:

AV = 310.3 ft/min

2. Determine cutting slip velocity:

Vs = 35.4 ft/min

3. Determine net rise velocity with following equation:

Net rise velocity = 310.3 – 35.4 = 274.9 ft/min

Conclusion: This flow rate is good for hole cleaning because annular velocity is more than cutting slip velocity.