Coil Tubing Calculations

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Calculate ID:

OD – (2 * Wall)

1.75 – (2 * .156) = 1.438 in

Calculate Area of Tubing Wall:

( OD2 – ID2 ) * p / 4 NOTE: (p/4 =.7854)

( 1.752 – 1.4382 ) * .7854 = .781 in2

Calculate Tubing Weight Per Foot (Wall Thickness Unknown)

((((OD2 – ID2) * .7854) * 12)/ 231) * 65.5

((((2.8752 – 2.4412) * .7854) * 12) / 231) * 65.5 =

Calculate Tubing Weight per foot:

p * ( OD – Wall ) * Wall * 12 * .2833

p * ( 1.75 – .156 ) * .156 * 12 * .2833 = 2.656 lbs/ft

Calculate Buoyancy Factor:

( 65.447 – Fluid Weight, lbs/gal ) / 65.447

( 65.447 – 8.33 ) / 65.447 = .873

Calculate Weight of Tubing in Fluid:

Weight in Air * Buoyancy Factor

2.656 * .873 = 2.319 lbs/ft

Calculate Load Capacity @ Minimum Yield:

( OD2 – ID2 ) * .7854 * Yield * SF

( 1.752 – 1.4382 ) * .7854 * 80,000 * .8 = 49,997 psi

Calculate Pressure Capacity:

2 * ( Wall – .005 )* Yield / OD

2 * (.156 – .005 ) * 80,000 / 1.75 = 13,806 psi

Calculate Pipe Capacity in Barrels per Linear Foot:

ID2 * .0009714

1.4382 .0009714 = .002009 bbls/ft

Multiply by Total Length for Total Capacity in Barrels

Calculate Annular Volume in Barrels per Linear Foot:

(IDprod2 – ODcoil2 ) * .0009714

( 2.4412 – 1.752 ) * .0009714 = .00281316 bbls/ft

Multiply by Total Length for Total Capacity in Barrels

Calculate Annular Velocity, Ft/Min:

GPM * 24.51 / (IDprod2 – ODcoil2 )

84 * 24.51 / ( 4.8922 – 1.752 ) = 98.7 ft/min

Time to Displace:

Total Volume ,bbls / Pump Rate, bbl/min = Minutes

or

Total Volume ,gal / Pump Rate, gal/min = Minutes

Calculate Fluid Pressure Gradient:

Down Hole Pressure / Depth = psi/ft

or

Fluid Weight, lbs/gal * .05195 = psi/ft

Calculate Hydrostatic Pressure:

Weight, lbs/gal * .05195 * Depth

9.6 * .05195 * 11,200 = 5591 psi

Calculate Bottom Hole Pressure:

Well Head Pressure + Hydrostatic Pressure

2200 + ((9.6 * .05195 * 11,200)) = 7785.664 psi

Calculate Kill Fluid Weight:

Weight, lbs/gal + [ Well Head Pressure / ( .05195 * Depth ) ]

9.6 + ( 2200 / ( .05195 * 11,200 ) ) = 13.4 lbs/gal

Calculate Stretch due to Weight in hole, feet :

.0567 * ( Length / 1000 )2

.0567 * (12000 / 1000)2 = 8.1648 Feet

Calculate a “Free Point” for stuck tubing or the length of free pipe

L = Stretch in inches*(30000000*Area)/Force/12

Stretch = inches, from over-pull force

Area = cross-sectional area of CT pipe wall

Force =applied weight over weight of pipe in air to stretch the CT

Example:

CT OD = 1.5

CT ID = 1.282

Stretch = 120 inches

Force = 15000 lbs (Weight Indicator)

120 * 30,000,000 * .476 / 15000 /12 = 9520 feet.

Calculate Elongation Due to Temperature, feet :

Average Temperature :

( Surface Temperature + Bottom Hole Temperature ) / 2

( 70 + 210 ) / 2 = 140 Deg. F

DT :

Average Temperature – Surface Temperature

140 – 70 = 70 Deg. F

Depth * .0000828 * DT / 12

9650 * .0000828 * 70 / 12 = 4.7 ft

Calculate Specific Gravity of oil from API :

141.5 / ( 131.5 + API )

141.5 / ( 131.5 + 30 ) = .876

Calculate thermal gradient, Deg F / ft

(Bottom hole Temperature – Suface temperature) / Depth

( 195 – 60 ) / 9800 = .00138 Deg F / ft

or .138 Deg F / 100 ft

or 1.38 Deg F / 1000 ft

Calculate Pressure drop due to friction

.000077 * MW .8 * Q 1.8 * PV 2 * L / D 4.8

.000077 * 8.33 .8 * 42 1.8 * 1 2 * 10000 / 1.438 4.8 = 613.2 psi

For spooled tubing on the reel: add 10 % or x 1.1

  • * 1.1 = 674.5 psi or 67.4 psi /1000 ft

MW = Fluid weight in lbs/gal

Q = Flow rate in gal / min

PV = Plastic viscosity in centipois

L = Length of pipe to flow through in feet

D = Diameter of pipe to flow through in inches

*NOTE: This is conservative compared to the Quality Charts

PHYSICAL CONSTANTS:

Viscosity of water = 1 centipoise

API gravity of water = 10 Deg. API

Fresh water n’ and k’ = 1.0 and .00002

Fresh water weighs 8.33 lbs/gal

1 cu. ft = 7.4805 gal

Water weighs 8.33 * 7.4805 = 62.312565 lbs/cu. ft

1 cu. ft = 12 in * 12 in * 12 in = 1728 cu. in

Pressure = Force / Area

62.312565 lbs / 144 sq in = .4327261458 lbf / sq in / ft or psi/ft

.4327261458 psi/ft / 8.33 lb/gal = .05194791666 (.05195) thus the constant born .052

1 bbl = 5.615 cu. ft = 42 gal

1 gal of Liquid (Cryogenic) N2 expands to 93.11 SCF

N2 expands 697 times ( more exact: 696.4 times)

Calculate KCL in pounds for % Needed:

Gallons x (Fluid weight) x % KCL wanted = lbs

80 bbl x 42 = 3360 gallons

3360 x 8.6 lbs/gal x 2% = 578 lbs KCL

Calculate rate of travel with coiled tubing

(Total bbl ÷ Pump rate in bbls/min = Total Minutes)

(Total Interval in feet ÷ minutes = ft/min)

150 bbls Acid

200 ft Interval to Place Acid

150 bbls÷ 2 bbl/min = 75 mins.

200 ft Interval ÷75 minutes = 2.6 fpm

To make 3 passes using same problem

75 minutes ÷ 3 = 25 minutes

200 ft Interval ÷ 25 minutes = 8 ft/min each pass

 

To Calculate Pump Rate

(Bore2 x .7854 x Stroke x # of plungers)

42 x .7854 x 8 x 3 = 301.6 in3

= 301.6 in3 x (1gal ÷ 231 in3) x (1 bbl ÷ 42 gals)

= .0312 bbl/rev

= 1 ÷ .0312 = 32.05 rev/bbl

Assume Operating range in the 80 to 90 % Efficiency Range

32.05 rev/bbl x .85% = 27.2 rev/bbl

2 bbl/min x 27.2 rev/bbl = 54.4 strokes/min

 

 

Kill Wt Fluid: PPG = PSI / .05195 X depth

(O.D. 2 – I.D. 2) X .7854 X .05195 X 65.447 =

(O.D. 2 – I.D. 2 )X 2.6703 = wt. per ft