Page 95 - Practical Well Planning and Drilling Manual

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Casing Design [ ]
1.4.11

Net axial force = 439 lbs.

3. Use vectors to calculate the net lateral force (Pythagoras, √(600 -
2
439 ). (See Fig. 1-14)
2

Net lateral
force = 409 lbs

Net upward
Net axial force force = 600 lbs
= 439 lbs

Fig. 1-14 Resolving Net Axial and Lateral Forces in an Inclined Wellbore

1.4.11. Casing Design Criteria: Definitions and Methods of Calculation

So far you have determined what the directional plan will be,
where the casing shoes will be set, and what hole and casing sizes are
needed. The next step is to calculate the physical forces that the cas-
ings will be subjected to so that these can be compared to the casing
strengths, as modified by safety and correction factors.
Refer to API Bulletin 5C2 for minimum performance properties of
casing, including burst, collapse, collapse under axial load (biaxial),
and tensile strengths.
Note that lower tensile grades of pipe are required for an H S environ-
2
ment at temperatures below 175˚F. Refer to 1.14.19, “Material Grades.”

1.4.12. Calculating Burst and Collapse Loads, Including Biaxial Effects

Burst and collapse loads can be applied to the casing from various
causes. Each situation should be calculated and combined to give the
net burst or collapse loading on the casing in that situation. Burst and

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