1. Lesson 10 Drilling Hydraulics (cont’d)
PETE 411 Well Drilling
Lesson 10 Drilling Hydraulics (cont’d)

2. 10. Drilling Hydraulics (cont’d)
Effect of Buoyancy on Buckling
The Concept of Stability Force
Stability Analysis
Mass Balance
Energy Balance
Flow Through Nozzles
Hydraulic Horsepower
Hydraulic Impact Force

3. READ: ADE, Ch. 4 to p. 135 HW #5: ADE # 4.3, 4.4, 4.5, 4.6
due September 27, 2002

4. Partially buckled slender pipe Slender pipe suspended in wellboreFh
Buckling of Tubulars
Fh - Fb
Neutral Point
Partially buckled slender pipe
Slender pipe suspended in wellbore
Neutral Point Fb

5. Buckling of Tubulars
Long slender columns, like DP, have low resistance to bending and tend to fail by buckling if...
Force at bottom (Fb) causes neutral point to move up
What is the effect of buoyancy on buckling?
What is NEUTRAL POINT?
Neutral Point
Neutral Point Fb

6. What is NEUTRAL POINT?
One definition of NEUTRAL POINT is the point above which there is no tendency towards buckling
Resistance to buckling is indicated, in part, by:
The Moment of Inertia
Neutral Point
Neutral Point

7. Consider the following:
19.5 #/ft drillpipe
Depth = 10,000 ft.
Mud wt. = 15 #/gal.
DPHYD = (MW) (Depth)
= * 15 * 10,000
DPHYD = 7,800 psi
Axial tensile stress in pipe at bottom
= - 7,800 psi
What is the axial force at bottom?

8. Axial compressive force = pA Can this cause the pipe to buckle?
What is the axial force at bottom?
Cross-sectional area of pipe
= (19.5 / 490) * (144/1) = 5.73 in2
Axial compressive force = pA
= 44,700 lbf.
Can this cause the pipe to buckle?

9. Axial Tension: FT = W1 - F2 FT = w x - P2 (AO - Ai )
At surface, FT = 19.5 * 10, ,800 (5.73)
= 195, ,694
= 150,306 lbf.
At bottom, FT = 19.5 * ,800 (5.73)
= - 44,694 lbf
Same as before! F2

10. Stability Force: FS = Aipi - AO pO FS = (Ai - AO) p (if pi = pO)
At surface, FS = * 0 = 0
At bottom, FS = (-5.73) (7,800) = - 44,694 lbs
THE NEUTRAL POINT is where FS = FT
Therefore, Neutral point is at bottom!
PIPE WILL NOT BUCKLE!! Ai

11. Depth of Zero Axial Stress Point =
Compression Tension , ,306 FS FT
Zero Axial Stress
Neutral Point
Depth of Zero Axial Stress Point =

12. Length of Drill Collars
Neutral Point
Neutral Point

13. Length of Drill Collars
In Air:
In Liquid:
In Liquid
with S.F.: (e.g., S.F =1.3)

14. State of stress in pipe at the neutral point?

15. At the Neutral Point:
The axial stress is equal to the average of the radial and tangential stresses.

16. Stability Force: FS = Ai Pi - Ao PoFT
Stability Force: FS FT
FS = Ai Pi - Ao Po
If FS > axial tension then the pipe may buckle.
If FS < axial tension then the pipe will NOT buckle.

17. At the neutral point: FS = axial load To locate the neutral point:
Plot FS vs. depth on “axial load (FT ) vs. depth plot”
The neutral point is located where the lines intersect.

18. NOTE:
If pi = po = p,
then Fs = AS
or, Fs = - AS p

19. Axial Load with FBIT = 68,000 lbf

20. Stability Analysis with FBIT = 68,000 lbf

21. Nonstatic Well Conditions
FLUID FLOW
Physical Laws
Rheological Models
Equations of State

22. Physical Laws Conservation of mass Conservation of energy
Conservation of momentum

23. Rheological Models
Newtonian
Bingham Plastic
Power – Law
API Power-Law

24. Equations of State Incompressible fluid Slightly compressible fluid
Ideal gas
Real gas

25. Average Fluid Velocity Pipe Flow Annular Flow
WHERE
v = average velocity, ft/s
q = flow rate, gal/min
d = internal diameter of pipe, in.
d2 = internal diameter of outer pipe or borehole, in.
d1 =external diameter of inner pipe, in.

27. Law of Conservation of Energy
States that as a fluid flows from point 1 to point 2: {
In the wellbore, in many cases Q = 0 (heat)
r = constant

28. In practical field units this equation simplifies to:
where
p1 and p2 are pressures in psi
r is density in lbm/gal.
v1 and v2 are velocities in ft/sec.
Dpp is pressure added by pump
between points 1 and 2 in psi
Dpf is frictional pressure loss in psi
D1 and D2 are depths in ft.

29. Determine the pressure at the bottom of the drill collars, if
(bottom of drill collars)
(mud pits)

30. Velocity in drill collars
Velocity in mud pits, v1

31. Pressure at bottom of drill collars = 7,833 psig
NOTE: KE in collars
May be ignored in many cases

33. Fluid Flow Through Nozzle
Assume:

34. This accounts for all the losses in the nozzle.If
This accounts for all the losses in the nozzle.
Example:

36. For multiple nozzles in //
Vn is the same for each nozzle even if the dn varies!
This follows since Dp is the same across each nozzle.
&

37. Hydraulic Horsepower of pump putting out 400 gpm at 3,000 psi = ?
In field units:

38. What is Hydraulic Impact Force
developed by bit?
Consider:

39. Impact = rate of change of momentum