TCP Level 2 Training MaterialReperforation
True shear pin value = 485 psi
Brine, 8.75 lb/gal
1.25 in. OD
BHP = 1,750 psi
BHT = 260°F
Bottom Hole Pressure at Firing (BHP at firing).
For this specific case, we have a flowing condition so the well has already been perforated.
BHP at firing = P well flowing = 1,750 psi
Total CT Pressure at Firing (PCT-pump).
Maximum pump pressure (PCT pump) to shear CBF/BCF pins
Note: If no firing pressure has been specified, use 1,500 psi as a first approximation.
Include in the CT firing head design an overkill pressure equals to 500 psi
PCT-pump = P firing + P overkill
PCT-pump = 1,500 + 500 = 2,000 psi
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Calculate the hydrostatic pressure of the Coiled Tubing String (PCT-Hydrostatic).
This is the fluid column inside the CT when the ball lands into the ball seat of the firing head.
PCT-Hydrostatic = fluid wt (lb/gal) x depth (ft) x 0.052
PCT-Hydrostatic = 8.75 x 7,260 x 0.052 = 3,303 psi
Determine the differential pressure (dP Bleeder Hole) across the bleeder holes at firing.
dP Bleeder Hole = PCT-Hydrostatic + PCT-pump – BHP at firing – (PCT-Friction)
dP Bleeder Hole = 3,303 + 2,000 – 1,750 – (PCT-Friction)*
dP Bleeder Hole = 3,553 psi – (PCT-Friction)*
The CT friction pressure is a function of the flow rate through the bleeder holes and unknown. For the first iteration, the friction pressure is neglected and the estimated differential pressure will be higher than the true value.
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Job Design and Calculations
Determine the empirical data for (Q Bleeder Holes) taking in consideration the dP already calculated:
dP Dp Bleeder Hole = 3,553 psi
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Averaged empirical data for Q Bleeder Holes = 0.4 bbls/ min.
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Job Design and Calculations
Determine the approximate friction pressure drop (P drop/ 1,000 ft) for the CT size used.
For (P drop/ 1,000 ft) enter the flow rate and read the pressure drop per 1,000 ft.
The graphs, which can be found in the Coiled Tubing Handbook – Varco (InTouch ID 3314629), are provided by the Tubing Manufacturer for the most common fluids.
Here P drop/ 1,000 ft = 100 psi
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46.bin
Job Design and Calculations
Calculate the total friction pressure loss of the CT string (PCT-Friction).
PCT-Friction = CT-Length x P drop/ 1,000 ft
PCT-Friction = 18,000 x 100 psi / 1,000 ft = 1,800 psi
Calculate the total internal CT pressure at firing (PCT at firing) corrected for the friction pressure loss.
PCT at firing = PCT-Hydrostatic + PCT-pump – (PCT-Friction)
PCT at firing = 3,303 + 2,000 – 1,800 = 3,503 psi
Correction of differential pressure across the bleeder holes (dP* Bleeder Holes) due to high friction loss in 1.25 in. CT.
dP* Bleeder Hole = PCT at firing – BHP at firing
dP* Bleeder Hole = 3,503 – 1,750 = 1,753 psi
* Values corrected for friction loss due to bleeder holes
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Job Design and Calculations
Having the new value for dP Bleeder Holes called dP* Bleeder Holes, determine the NEW empirical rate.
dP Dp Bleeder Hole = 1,753 psi
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So the new averaged empirical data for Q Bleeder Holes = 0.3 bbls/ min.
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Job Design and Calculations
At this time use the chart and determine the new approximate friction pressure drop (P drop/ 1,000 ft) for CT OD = 1.25 in.
P drop/ 1,000 ft = 60 psi
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Job Design and Calculations
Calculate the total friction pressure loss of the CT string (PCT-Friction).
PCT-Friction = CT-Length x P drop/ 1,000 ft
PCT-Friction = 18,000 ft x 60 psi/ 1,000 ft = 1,080 psi
Calculate the total internal CT pressure at firing (PCT at firing) corrected for the friction pressure loss
PCT at firing = PCT-Hydrostatic + PCT-pump – PCT-Friction
PCT at firing = 3,303 + 2,000 – 1,080 = 4,223 psi
Calculate the Maximun High Shear Value (HSV max).
HSV max = PCT at firing – BHP at firing – P overkill
HSV max = 4,223 – 1,750 – 500 = 1,973 psi
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Job Design and Calculations
Determine for a given (BHT) the temperature correction fcator (G BHT).
BHT = 260° F , GBHT = 0.91.
Determine the Nominal Shear Value (NSV).
Nominal Shear Value = HSV max ÷ (GBHT x 1.05)
Nominal Shear Value = 1,973 ÷ (0.91 x 1.05) =
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37.bin
Job Design and Calculations
The number of pins required is calculated from the firts approximation of the HSV max:
Nominal Shear Value = HSV max ÷ (GBHT x 1.05)
Nominal Shear Value = 1,973 ÷ (0.91 x 1.05 x ) = 2,065 psi
(Where 1.05 is the safety factor and GBHT is the temperature correction factor).
Number of Pins = Nearest Whole Number = NSV/ True Shear Value of Pin
Number of Pins = 2,065 psi/ 485 psi
Number of Pins = 4.26 pins = 4 pins
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Verification of shear pin selection
Nominal Shear Value = Number of pins x True Shear Value of Pin x GBHT
Nominal Shear Value = 4 x 485 x 0.91 = 1,765 psi
High Shear Value= NSV x 1.05
High Shear Value = 1,765 x 1.05 = 1,853 psi
Low Shear Value = NSV x 0.95
Low Shear Value = 1,765 x 0.95 = 1,677 psi
Verification of required pump pressure at firing PCT-pump
PCT-pump = HSV + BHP at firing – PCT-Hydrostatic + PCT-Friction +P overkill
PCT-pump = 1,853 + 1,750 – 3,303 + 1,080 + 500 = 1,880 psi
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Now compare the last calculation with the originally estimated PCT-pump.
PCT-pump = HSV + BHP at firing – PCT-Hydrostatic + PCT-Friction +P overkill
PCT-pump = 1,853 + 1,750 – 3,303 + 1,080 + 500 = 1,880 psi
VS
PCT-pump = P firing + P overkill
PCT-pump = 1,500 + 500 = 2,000 psi
If the value is significantly different from the original estimated PCT-pump pressure, review the calculations.
This is the maximum value requiered at surface to activate the firing head as soon as the ball is in position.
The minimun pump pressure at wich teh head can be activated is:
PCT-pump min = LSV + BHP at firing – PCT-Hydrostatic + PCT-Friction
PCT-pump min = 1,677 + 1,750 – 3,303 + 1,080 = 1,204 psi