Equivalent Circulating Density (ECD) in ppg

Equivalent Circulating Density (ECD) is the effective density that combines current mud density and annular pressure drop. ECD is vital for drilling engineering since it limits how depth of each section to be drilled and leads to losses.

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The equivalent circulating density formula is shown below

Equivalent Circulating Density (ECD) in ppg = (annular pressure loss in psi) ÷ 0.052 ÷ true vertical depth (TVD) in ft + (current mud weight in ppg)

Example:

Annular pressure loss = 400 psi
True Vertical Depth = 8,000 ft
Current mud weight in ppg = 10 ppg

ECD in ppg = (400 psi ÷ 0.052 ÷ 8,000 ft) + 10.0 ppg

ECD = 11.0 ppg

Please find the Excel sheet to calculate equivalent circulating density (ECD)

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 Engineer

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.

Pump Output Calculation for Duplex Pump and Triplex Pump

Rig pump output, normally in bbl per stroke, of mud pumps on the rig is important figures that we really need to know because we will use pump out put figures to calculates many things such as bottom up strokes,  wash out depth, tracking drilling fluid, etc. In this post, you will learn how to calculate pump out put for triplex pump and duplex pump.

Triplex Mud Pump

Triplex Pump Output Formula

Triplex Pump Output in bbl/stk = 0.000243 x (liner diameter in inch) 2 X (stroke length in inch)

Example: Determine the pump output in bbl/stk at 100% and 97% efficiency
Linner size = 6 inch
Stroke length = 12 inch
Triplex pump output:
PO @ 100% = 0.000243 x 62 x 12
PO @ 100% = 0.104976 bbl/stk

Adjust the triplex pump output for 97% efficiency:
Decimal equivalent = 97 ÷ 100 = 0.97
PO @ 97% = 0.104976 bbl/stk x 0.97
PO @ 97% = 0.101827 bbl/stk

Duplex Mud Pump (Ref: http://www.sunmachinery.com/8214R_01.jpg)

Duplex Pump Output Formula

Duplex Pump Output in bbl/stk = 0.000162 x S x [2(D)2 – d2]

Where:
D = liner diameter in inch
S = stroke length in inch
d = rod diameter in inch

Example: Determine the duplex pump output in bbl/stk at 100% and 85% efficiency

Liner diameter = 6 inch
Stroke length = 12 inch
Rod diameter = 2.0 in.

Duplex pump efficiency = 100 %.
PO @ 100% = 0.000162 x 12 x [2 (6) 2 -22 ]
PO @ 100% = 0.13219 bbl/stk

Adjust pump output for 85% efficiency:
PO @ 85% = 0.132192 bbl/stk x 0.85
PO @ 85% = 0.11236 bbl/stk

Please find the Excel sheet to calculate triplex pump output and duplex pump output

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.

Formation Integrity Test (FIT) Procedure and Calculation

Formation Integrity Test is the method to test strength of formation and shoe by increasing Bottom Hole Pressure (BHP) to designed pressure. FIT is normally conducted to ensure that formation below a casing shoe will not be broken while drilling the next section with higher BHP or circulating gas influx in a well control situation. Normally, drilling engineers will design how much formation integrity test pressure required for each hole section.

The formula below demonstrates you how to calculate required FIT pressure.

Pressure required for FIT (psi) = (Required FIT in ppg – Current Mud Weight in ppg) x 0.052 x True Vertical Depth of shoe in ft

Example:
Required FIT (ppg) = 14.5
Current mud weight (ppg) = 9.2
Shoe depth TVD (ft) = 4000 TVD
Pressure required for FIT = (14.5-9.2) x 0.052 x 4000 = 1,102 psi

Formation Integrity Test (FIT) guideline is listed below: (note: this is just only guide line. You may need to follow your standard procedure in order to perform formation integrity test):

1. Drill out new formation few feet, circulate bottom up and collect sample to confirm that new formation is drilled to and then pull string into the casing.

2. Close annular preventer or pipe rams, line up a pump, normally a cement pump, and circulate through an open choke line to ensure that surface line is fully filled with drilling fluid.

3.Stop the pump and close a choke valve.

4. Gradually pump small amount of drilling fluid into well with constant pump stroke. Record total pump strokes, drill pipe pressure and casing pressure. Pump until casing pressure reaches the pressure required for formatin integrity test. Hold pressure for few minutes to confirm pressure.

5. Bleed off pressure and open up the well. Then proceed drilling operation.

Please find the Excel sheetcalculate pressure required for formation integrity test.

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.

Leak Off Test (Procedures and Calcuation)

Leak Off Test is conducted in order to find the fracture gradient of certain formation at casing shoe depth. The results of the leak off test also dictate the maximum equivalent mud weight that should be applied to the well during drilling operations.

Leak Off Test (LOT) guide line procedures are as follows  (note: this is just only guide line.

You may need to follow your standard procedure in order to perform leak off test):

1.Drill out new formation few feet, circulate bottom up and collect sample to confirm that new formation is drilled to and then pull string into the casing.

2.Close annular preventer or pipe rams, line up a pump, normally a cement pump, and circulate through an open choke line to ensure that surface line is fully filled with drilling fluid.

3.Stop the pump and close a choke valve.

4.Gradually pump small amount of drilling fluid into well with constant pump stroke. Record total pump strokes, drill pipe pressure and casing pressure. Drill pipe pressure and casing pressure will be increased continually while pumping mud in hole. When plot a graph between strokes pumped and pressure, if formation is not broken, a graph will demonstrate straight line relationship. When pressure exceeds formation strength, formation will be broken and let drilling fluid permeate into formation, therefore a trend of drill pipe/casing  pressure will deviate from straight line that mean formation is broken and is injected by drilling fluid. We may call pressure when deviated from straight line as leak off test pressure.

5.Bleed off pressure and open up the well. Then proceed drilling operation.

Note:  the way people call leak off test pressure depends on each company standard practices.

Leak off test pressure can be calculated into equivalent mud weight in ppg as formula below:

Leak off test in equivalent mud weight (ppg) = (Leak off test pressure in psi) ÷ 0.052 ÷ (Casing Shoe TVD in ft) + (current mud weight in ppg)

Pressure gradient can be determined from Leak Off Test pressure by the following formula.

Pressure gradient in psi/ft = (Leak off test pressure in psi) ÷ (Casing Shoe TVD in ft)

Example:

Leak off test pressure = 1600 psi
Casing shoe TVD = 4000 ft
Mud weight = 9.2 ppg

Leak off test in equivalent mud weight (ppg) = 1600 psi ÷ 0.052 ÷ 4000 ft + 9.2ppg ppg = 16.9

Pressure gradient = 1600 ÷ 4000 = 0.4 psi/ft

Please find the Excel sheet to calculate leak off test

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.