1. Chapter VIII
Packer and Tubing
Forces

2. Types of Packers Retrievable Permanent
Packer body, slips and rubber packing elements are rigidly attached to the tubing string
Can unseat and move
Permanent
Set into casing with wireline
Sealing elements on tubing

3. Retrievable Packers
Weight set
Tension set
Hydraulically set

4. Weight-set Packers Simplest Slips point down preventing movement
J-slot prevents movement until at depth
Rotate tubing to disengage J-slot then apply downward force (weight) to compress sealing element

5. Permanent Packers Run in on wireline Charge fired to set slips
Slips point up AND down preventing movement
Can also be set using tubing and hydraulic pressure
Tubing seals to inside with sealing sub

7. Forces acting on Packer-Tubing Systems
Tubing movement occurs or forces are induced when the following changes are made to the well
Running the packer
Placing the well on production
Swabbing the well
Acidizing the well
Fracing the well
After the packer is set each subsequent operation must be evaluated against the original setting conditions
Exceeding the original setting forces might cause:
Retrievable packer to move
Sealing sub to slide out of permanent packer

8. Forces acting on Packer Body
Pressure changes in the tubing or the annulus will result in forces being applied to the packer body
Pressure is the SAME at the packer (hydrostatic) BUT the dimensions of the top and bottom of the packer body are different.
Let’s examine this condition:
Assume a well with a weight-set packer is being acidized
Packer was set with 7000 lbs of downward force (weight-set)
Casing annulus pressure acts on the top of the packer cross-section
Tubing pressure acts on the bottom of the packer cross section
See next slide/

9. Top of packer is 14.81 sq in cross section
Bottom of packer is sq in cross section

10. When the packer was set the tubing and annulus contain 9 lb/gal saltwater
For a packer set at 6,500 ft this results in a hydrostatic pressure in the annulus of 3042 psi
9 lb/gal X X 6500 ft = 3042 psi
At this pressure the top of the packer has a force of:
3042 psi X sq in = 45,052 lbs
At the same pressure the bottom of the packer has a force of
3042 psi X sq in = 49,007 lbs
This 3,955 lb difference is buoyancy in the UP direction

11. When we acidize the well we pump acid down the tubing with the packer set.
The acid weighs 6.9 lb/gal
The acid changes the tubing hydrostatic pressure to:
6.9 lb/gal X X 6,500 ft = 2,332 psi
Assuming we pump the acid at 1000 psi at the surface the total pressure at the bottom of the tubing is:
2,332 psi psi = 3,332 psi.
The annulus remains unchanged at 3,042 psi because the packer is set

12. Let’s now look at the force on the packer
DOWNWARD force is:
7,000 lbs + (3,042psi X 14.81sq.in.) =
7, ,050 = 52,050 lbs
UPWARD force is:
3,332 psi X 16.11sq.in. = 53,680 lbs
The resulting total force on the packer is the DIFFERENCE and pointe UP = 1,630 lbs

13. BUT we set the packer with 7,000 lbs of DOWNWARD force
Clearly the packer will UNSEAT at 1,630 lbs of UPWARD FORCE
What can we do?
Apply 8,630 lbs in the downward direction from the surface (might buckle the tubing) – BAD idea
Apply 583 psi to the casing annulus to achieve the same 8,630 lbs in the downward direction
583psi X sq.in = 8,630 lb

14. FORCES ACTING ON TUBING
Forces are caused by pressure and temperature changes
Four main causes of forces on tubing
Piston Effect (pressure pushes sealing sub out of permanent packer)
Pressure (Helical) Buckling (Corkscrew of tubing shortens length)
Ballooning Effect (expansion of tubing diameter shortens length)
Temperature Effect (lower temp shortens tubing hotter temps lengthen tubing)

15. Piston Effect and Pressure (Helical) Buckling
mainly concern Permanent Packers
Ballooning Effect and Temperature Effect
mainly concern Retrievable Packers

16. Forces change length of tubing
Same mechanism as a spring.
Pull on spring and it lengthens. Release tension and spring returns to original length
Description of this effect is called:
Hooke’s Law
F = -kx where F is force, k is spring constant and x is the length
This is for ONE DIMENSIONAL objects (long and skinny)

17. Elastic and Plastic Deformation
Hooke’s Law only works for elastic deformation
Pull the spring too hard and it will NOT return to original length = plastic deformation
plastic F
elastic
Pull too hard and break
Longer than before stretch x

18. E = Young’s Modulus (psi) For steel = 3x107 psi
For three-dimensional solids Hooke’s Law changes
STRESS = F/A (equivalent of force)
STRAIN = ∆L/L (fractional change in length)
STRESS = -E x STRAIN
(lbs)
(sq.in.)
(in)
E = Young’s Modulus (psi)
For steel = 3x107 psi

19. Example: 10’ long steel rod being pulled on with 1000 lbs force that has a cross section of 1 sq. in. (about the size of your index finger)
1000 ft rod pulled by 1000 lbs would stretch by 0.4”

20. If we look at the acidizing job described in the text (Figure 8.9):
Initial conditions
Packer set at 14,400 feet
Tubing and annulus filled with 9 lb/gal saltwater
No PUMP pressure on either tubing or casing
Acidizing conditions
Annulus – no change to fluid – 2,500 psi pump pressure
Tubing – 9.5 lb/gal acid pumped at 6,000 psi on surface

21. Piston Effect
Change in length due to pressure difference above and below the packer:
116.6”
About 10 feet.

22. Helical (pressure) Buckling
Change in length due to “squirm” in the tubing
33.1”
About 3 feet.

23. Ballooning
Change in length due to “bulge” in the tubing (like a balloon)
24.3”
About 2 feet.

24. Temperature Effect (Thermal Expansion)
Where β is the Coefficient of Thermal Expansion
For steel β = 6.9 x 10 -6
Take note of these expansion joints when looking at piping runs

25. Back to the acid job: = 10.1 feet = - 121.6 in
We work with the AVERAGE temperature of the tubing:
Before Tavg = 182 °F
After Tavg = 80 °F
= 10.1 feet = in
290 °F
90 °F
Before
During

26. Total length change of tubing during acid job:
= – 33.1 – 24.3 – 121.6
= ”
= feet

27. Tubing is latched to the packer
Anchored Tubing
Tubing is latched to the packer Or
Packer is retrievable
In BOTH cases the length change you calculate is converted into a FORCE using the defining equation for the Young’s Modulus
PISTON EFFECT and HELICAL BUCKLING are IGNORED

28. becomes

29. Back to our Acidizing Example
If tubing is latched: Calculated change in length (ignoring piston effect and helical bucking) is:
∆L = =
This means that the force on the tubing (tension) is

30. Back to our Acidizing Example
The weight of the tubing is given by:
W = 14,400ft x 6.5 lb/ft : (tubing weight from table)
= 93,600 lbs
The tension pulls UP on the tubing at the bottom of the well BUT the tension pulls DOWN at the tubing hanger
Recall that if this were a weight set packer set with a force of 7000 lbs the 45,000 tension force would pull the packer free of the casing.

31. Back to our Acidizing Example
At the tubing hanger then:
The total force on the tubing is:
45, , 600 = 139,000 lbs
The yield strength is only 145,000 lbs which is too close to the edge.

32. Permanent Packer Calculations
If the tubing is NOT latched then ∆L must be calculated to make sure you have enough sealing sub length.
Temperature changes cause length changes and all such changes need to be calculated using ∆T expression
Prevent helical buckling by applying pressure to the casing annulus