Page 81 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 57

1.4.7
Casing Design [ ]

Gumbo
Clay Conductor; driven
to refusal depth
Soft Sand
Soft Clay Surface Casing
Sand Kick off depth
Build up in competent formation
Shale
Sand End of build
Intermediate Casing;
set in transition zone
& protects build
Shale

Salt
Production Casing;
Reservoir set just above the
Sand reservoir
Sump below reservoir for logs
TD
Shale

Fig. 1-8 Example of Casing Point Selection

1.4.7. Mechanical Properties of Steel
Steel is an elastic material, up to a limit. If a tensile load is applied
to steel (stress), the steel will stretch (strain). If you double the load,
you will double the amount that the steel stretches.
Stress is defined as load ÷ cross-sectional area. Units are usually
pounds per square inch. Stress is usually given the symbol S.
Strain is defined as the amount of stretch ÷ the original length. Stress
does not have any units, being a ratio. Strain is usually given the symbol e.
Strain can be due to applied stress or it can be due to thermal expansion.
Hooke’s Law states that, up to the elastic limit, stress is proportion-
al to strain If this is the case, then stress ÷ strain is a constant. This con-
stant is called Young’s Modulus of Elasticity, symbol E, and for steel is
6
approximately 30,000,000 (or 30 x 10 ). E for aluminum is approxi-
6
mately 10,500,000 (or 10.5 x 10 ).
Within the elastic limit, a load will stretch steel by a calculated dis-
tance. Removal of the load will restore the steel to its original dimen-
sions. Once the elastic limit is exceeded, the structure of the steel is
changed and it will not return to its original dimensions once the load
is removed. Its behavior is now termed plastic. If more load is applied
the steel will deform further and eventually fail (see Fig. 1–9).

57