Page 93 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 69

1.4.10
Casing Design [ ]

sectional area at 5000 ft.; this will be 3000 psi x (15.55 - 11.45) in 2
= 12,300 lbs. Hydrostatic force will also apply downwards at 4000
ft. This will be 2400 psi x (15.55 - 11.45) in = 9840 lbs.
2
To calculate axial force F at 9000 ft, subtract forces down from
a
forces up:
F = [68,700] - [1000 x 40] = 28,700 lbs (positive, so in compression).
a
To calculate axial force at 3000 ft, subtract forces down from forces up:

F = [68,700 + 12,300] - [(5000 x 40) + (1000 x 53.5) + (1000 x 40) +
a
(9840)] = -222,340 lbs (negative, so in tension).

4. Calculate hydraulic force acting sideways only.

If the side force exerted by a casing lying in an inclined wellbore is
to be considered, then the hydraulic forces acting perpendicular to
the axis need to be calculated. This may be needed for instance to
calculate drags or torques when running in a deviated well. Refer to
Figure 1-13.

Equal
Equal hydraulic
hydraulic force
force
Case 2
Greater
hydraulic
Case 1 force from
below
Greater
hydraulic
force from
below
Casing
extends to
surface
Case 4
Case 3

Greater Greater hydraulic
hydraulic force laterally up;
force laterally same as Case 3
up Greater Greater hydraulic
hydraulic force axially up
force axially up
Fig. 1-13 Applying Hydraulic Forces in an Inclined Wellbore

69