PETE 411 Well Drilling

1
PETE 411Well Drilling

• Lesson 10Drilling Hydraulics (contd)

2
10. Drilling Hydraulics (contd)

• 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
READADE, Ch. 4 to p. 135

• HW 5
• ADE 4.3, 4.4, 4.5, 4.6
• due September 27, 2002

4
Buckling of Tubulars
Fh
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 0.052 (MW) (Depth)
• 0.052 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

• 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

• FT W1 - F2
• FT w x - P2 (AO - Ai )
• At surface, FT 19.5 10,000 - 7,800 (5.73)
• 195,000 - 44,694
• 150,306 lbf.
• At bottom, FT 19.5 0 - 7,800 (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 - 5.73 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
Compression Tension
44,770 0 150,306
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
FT
0
FS
FT

• FS Ai Pi - Ao Po
• If FS gt axial tension then the pipe may
  buckle.
• If FS lt 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 withFBIT 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 VelocityPipe 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.

26
(No Transcript)
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
32

33
Fluid Flow Through Nozzle
Assume

34
If
This accounts for all the losses in the nozzle.
Example
35
(No Transcript)
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 ?
• Power

In field units
38
What is Hydraulic Impact Force

• developed by bit?
• Consider

39
Impact rate of change of momentum