## Pressure Required to Break Circulation in Annulus

From the previous post, we learn about how to determine break circulating pressure inside drill string. This post we will learn about how to calculate pressure required to break circulation in annulas.

Formula to calculate pressure required overcoming the mud’s gel strength in the annulus as follow:

Pgs = y ÷ [300 x (Dh, in. – Dp, in.)] x L

where Pgs = pressure required to break gel strength, psi

L = length of drill string, ft

y = 10 mm. gel strength of drilling fluid, lb/100 sq ft

Dh = hole diameter, in.

Dp = pipe diameter, in.

Let’s take a look at the example below and understand how to determine pressure required to break circulation in the annulus by using following information

L = 11,500 ft

y = 12 lb/100 sq ft

Dh = 6.5 in.

Dp = 4.0 in.

Referring to the formula above, all parameters can simply input into the formula to get the break circulation pressure in the annulus.

Pgs = 12 ÷ [300 x (6.5 – 4.0)] x 11,500 ft

Pgs = 184.0 psi

Please find the Excel sheet for calculating the pressure required for break circulation in the annulus.

## Pressure Required to Break Circulation Inside Drillstring

When we need to break circulation after mud in static condition, we need certain pressure to break mud gel strength. You may see that higher gel strength of mud, the higher pressure is required breaking circulation. So this post demonstrates how to determine pressure required breaking mud gel strength inside a drillstring.

Formula to calculate pressure required overcoming the mud’s gel strength inside the drill string as follow:

Pgs = (y ÷ 300 ÷ d) L

where Pgs = pressure required to break gel strength in psi

y = 10 mm gel strength of drilling fluid in lb/100 sq ft

d = inside diameter of drill pipe in inch

L = length of drill string in ft

Determine pressure required to break circulation inside the drill string by using following information

y = 12 lb/100 sq ft

d = 3.32 inch

L= 11,500 ft

Pgs = (12 ÷ 300 ÷ 3.32) x 11,500 ft

Pgs = 138.6 psi

Therefore, approximately 139 psi would be required to break circulation inside drill string.

Please find the Excel sheet for calculating the pressure required for break circulation inside drill string.

## Calcuate Annular Pressure Loss

From the previous post, Equivalent Circulating Density (ECD) in ppg, you may want to know how to determine annular pressure loss in order to calculate Equivalent Circulating Density (ECD) in ppg.

So use the following formula to calculate annular pressure loss. This formula will give you idea about how much annular pressure loss you will encounter.

P= [(1.4327 x 10-7) x MW x Lx V2] ÷ (Dh – Dp)

P = annular pressure losses, psi

MW = mud weight in ppg

L = length of annular in ft

V = annular velocity in ft/min

Dh = hole or casing ID in inch

Dp = drill pipe or drill collar OD in inch

Example:

Mud weight = 13.0 ppg

Length = 8000 ft

Circulation rate = 320 gpm

Hole size = 6.5 in.

Drill pipe OD = 4.0 in.

Determine annular velocity, ft/mm: v = (24.5 x 320) ÷ (6.52 – 4.02)

v = 299 ft/min

Determine annular pressure losses, psi: P = [(1.4327 x 10-7) x 13.0 x 8000 x 2992] ÷ (6.5 – 4.0)

P = 531.65 psi

Please find the Excel sheet to calculate annular pressure loss

PS, if you want to get the more accurate, you may need to contact your drilling fluid company to do it for you because they have the actual database and more complex formula that may help you get the good number.

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.

## Annular Velocity (AV) Calculation

Annular Velocity (AV) is how fast of fluid in annulus while pumping.

Three main factors affecting annular velocity are size of hole (bigger ID), size of drill pipe (smaller OD) and pump rate. This post will show you how to calculate annular velocity in feet per minute with different formulas.

## Formula#1: Annular velocity (AV) in ft/min

Annular velocity in ft/min = Flow rate in bbl/min ÷ annular capacity in bbl/ft

Example:
Flow rate = 10 bbl/min
Annular capacity = 0.13 bbl/ft
AV = 10 bbl/min ÷ 0.13 bbl/ft
AV = 76.92 ft/mim

## Formula#2: Annular velocity (AV) in ft/min

Annular velocity in ft/min = (24.5 x Q) ÷ (Dh2 – Dp2)

where
Q = flow rate in gpm
Dh = inside diameter of casing or hole size in inch
Dp = outside diameter of pipe, tubing or collars in inch

Example:
Flow rate (Q) = 800 gpm
Hole size = 10 in.
Drill pipe OD = 5 in.
AV = (24.5 x 800) ÷ (102 – 52)
AV = 261 ft/mim

## Formula#3: Annular velocity (AV) in ft/min

Annular Velocity in ft/min = Flow rate (Q) in bbl/min x 1029.4÷ (Dh2 – Dp2)

Example:
Flow rate (Q) = 13 bbl/min
Hole size = 10 in.
Drill pipe OD = 5 in.
AV = 13 bbl/min x 1029.4 ÷ (102 – 52)
AV = 178.43 ft/min

You also can back calculate how much flow rate you want for desired annular velocity in feet per minute as per following formulas.

Flow rate required in gpm = (AV in ft/min) x (Dh2 – DP2) ÷ 24.5

AV = desired annular velocity in ft/min
Dh = inside diameter of casing or hole size in inch
Dp = outside diameter of pipe, tubing or collars in inch

Example:
Desired annular velocity = 120 ft/mm
Hole size = 10 in
Drill pipe OD = 5 in.
Flow rate required in gpm = 120 x (102– 52) ÷ 24.5
Flow rate required in gpm = 367.4 gpm

Moreover, you can calculate strokes per minute (SPM) required for a given annular velocity in feet per minute as well. The idea is to use the formula above and devided by pump output in bbl/stk. Let’s review the fomula.

SPM = (AV in ft/min x annular capacity in bbl/ft) ÷ pump output in bbl/stk

AV = desired annular velocity in ft/min

Example
Desired annular velocity in ft/min = 120 ft/min
Dh = 12-1/4 in.
Dp = 4-1/2 in.
Annular capacity = 0.1261 bbl/ft
Pump output = 0.136 bbl/stk
SPM = (120 ft/mm x 0.1261 bbl/ft) ÷ 0.136 bbl/stk
SPM = 111.3 spm

Please find the Excel sheet  for calculating annular velocity

Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.