Page 124 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 100

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1.4.24 Well Design

Table 1-2 Casing Design Criteria—Surface Casing
Drilling Criteria

Burst 1. Resist the anticipated formation breakdown pressure at the
shoe with a gas gradient to surface (0.1 psi/ft inside).
Maximum burst at surface; depth (ft) x [formation
gradient - 0.1 psi/ft].
2. Casing test pressure at top of casing.
3. Casing test pressure plus mud hydrostatic to shoe less
normal external pressure (0.465 psi/ft) at shoe.

Safety factor 1.1.
Collapse 1. Calculate collapse pressure at shoe when cement 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 may be at the top of the mud column or at the shoe.
Calculate external pressure exerted by mud in hole when the
casing was run.

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

Safety factor 1.1

2. Buoyant weight plus test pressure.
Safety factor 1.75 if deviated or 1.5 if vertical.

3. Buoyant weight plus test pressure plus bending stress if deviated.
Safety factor 1.5.

4. Triaxial analysis incorporating temperature correction for
yield strengths.

Safety factor 1.25.
Compression N/A.
Buckling N/A; cemented to seabed or surface.

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