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Problem 1 Hooking load
A blanking plug is stuck in the tail pipe of a latch type seal assembly. If the seal assembly requires 5000 lbs tension to release, what is the required hook-load?
Well Data:
Packer Depth = 7200 ft
Tubing Size = 23/8" 4.7 lbs/ft
Packer Seal Bore = 4.000"
Annulus Fluid = 9.0 lbs/gal water
Tubing Fluid = 44° API Oil
Pressure Below Plug = 2200 psi
No applied pressure
Both the tubing and annulus are full.
From the Engineering Tables:
Tubing Fluid Gradient, (fgi) = 0.350 psi/ft
Annulus Fluid Gradient, (fgo) = 0.468 psi/ft
Tubing I.D. Area, (Ai) = 3.126 in2
Tubing O.D. Area, (Ao) = 4.430 in2
Packer Seal Bore Area, (Ap) = 12.566 in2
Tubing Calculations:
1. Tubing Pressure at the plug (Pi).
Pi = fgi × h = 0.350 × 7200 = 2520 psi - down
2. Tubing I.D. area
(Ai) = 3.126 in2
3. Force ‘F1’:
F1 = Pi × Ai = 2520 × 3.126 = 7878 lbs - down
Annulus Calculations:
4. Annulus Pressure at the packer (Po).
Po =fgo × h = 0.468 × 7200 = 3370 psi
5. Difference between packer seal bore area and tubing O.D.
area (A2).
A2 = Ap – Ao = 12.566 – 4.430 = 8.136 in2
6. Force ‘F2’:
F2 = Po × A2
= 3370 × 8.136 = 27418 lbs
7. Pressure Below Plug
(Ptrap) = 2200 psi
8. Force ‘F3’.
F3 = Ptrap × Ap = 2200 × 12.566 = 27645 lbs
9. Tubing String Weight (Wt).
Wt = w × L = 4.7 × 7200 = 33840 lbs
10. Hook-Load (Whl).
Whl = Wt + F1 + F2 + F3 + Release Tension
= 33840 + 7878 + 27418 + (–27645) + 5000 = 46491 lbs
The hook load to release the seal assembly is 46491 lbs.
After calculations please answer the following questions:
1. What is difference between retrievable and permanent packer?
The main advantages of permanent packers are lower cost and greater sealing and gripping capabilities. In situations where a packer must be easily removed from the well, such as secondary recoveries, re-completions, or to change out the production tubing, a retrievable packer must be used. To unset the tool, either a metal ring is sheared or a sleeve is shifted to disengage connecting components. Retrievable packers have a more complicated design and generally lower sealing and gripping capabilities, but after removal and subsequent servicing, they can be reused.
2. How you can describe the piston and ballooning effects?
If a tubing string is freely suspended in a cased hole with no fluid inside the casing, the lower end of the tubing string may be subjected to either a tensile force or a compressive force. The tensile force will elongate the tubing while the compressive force shortens and buckles the tubing.
The ballooning effect is caused by the change in average pressure inside or outside the tubing string. Internal pressure swells or "balloons" the tubing and causes it to shorten. Likewise, pressure in the annulus squeezes the tubing, causing it to elongate. This effect is called "reverse ballooning."