Page 128 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 104

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1.4.24 Well Design

Table 1-5 Casing Design Criteria—Drilling Liner

Drilling Criteria

Burst 1. Resist the anticipated formation breakdown pressure at the shoe
with a gas gradient to top of liner (0.1 psi/ft inside).
2. Liner test pressure and mud hydrostatic inside, mud and cement
as planned outside.

Safety factor 1.1.
Collapse 1. Calculate collapse pressure at shoe when cement is displaced. Use
planned fluid heights and densities inside and out.
2. Assume losses taken at next hole TD. Normal external pressure
(0.465 psi/ft) at the loss zone; planned mud in use drops to height
supported by thief zone pressure. Maximum collapse likely to be
at the top of the liner. Calculate external pressure exerted by mud
in hole when the casing was run.
3. If there are any plastic squeezing formations, resist 1 psi/ft outside
less normal pressure inside (0.465 psi/ft) at the relevant depth(s).

Safety factor 1.1.

Tension 1. Weight of liner in air plus overpull allowance of 100,000 lbs.
Safety factor 1.1.

2. Axial loads due to buoyant weight plus test pressure.
Safety factor 1.75 if deviated along liner length or 1.5 if vertical.

3. Axial loads due to buoyant weight plus test pressure plus and
bending stress if deviated along liner length.

Safety factor 1.5.
4. Triaxial analysis incorporating temperature correction for yield
strengths.
Safety factor 1.25.

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