Page 64 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 40

[ ] Well Design
1.4.1

you to pull out the casing once it is cut. However, in some areas, gov-
ernment regulations may force you to cement off all exposed forma-
tion when abandoning the well (even if impermeable). If this is the
case then it may incur substantial extra cost on abandonment to get
cement in place and this may prevent the option to sidetrack under the
previous shoe.
On deeper vertical wells, buckling in intermediate casing may be a
consideration. Further, during production, intermediate casings may
be subjected to burst or collapse pressures as stated for surface casing.
Several intermediate casings may be required in a deep well.
Production casing. Production casing may be run at the total depth
of the well or it may be set above the reservoir prior to drilling to TD
without setting another full casing string. In the latter case, liner(s)
may be run or the well produced through an uncased hole or through
a sand control screen.
The completion tubing is run inside the production casing. If the
completion tubing were to leak, the production casing would be sub-
jected to extra internal pressure. During its design lifetime this casing
may need to resist high burst pressures from leaking completions,
injection of gaslift gas or other fluids through valves in the completion
string, frac job support pressure, etc. There may be significant effects
from temperatures, wear, corrosion, and reactions to produced materi-
als such as H2S or mobile formations (massive salts).
If it is set across the reservoir, the production casing must with-
stand collapse loads due to drawdown during production. On deeper
vertical wells, buckling in production casing may be a consideration.
Drilling liner. A drilling liner is run inside production casing but
is set above the reservoir. This is to permit deeper drilling without the
expense of running another full casing string. It forms part of the pro-
duction “pressure vessel” as it could be subjected to all the loads (pre-
viously discussed in “Production casing” of this section), but not the
collapse loads due to production drawdown as detailed below. It might
also be set above the reservoir for a barefoot, slotted liner, or prepacked
screen completion.
Production liner. This is set inside the production casing or inside
the drilling liner if one has been run. It is set across the reservoir zones
to provide zonal isolation and, if necessary, may incorporate sand con-
trol measures such as internal or external gravel packs. Apart from
loads (previously discussed in “Production casing” of this section), the
production liner will have to resist collapse loads due to the pressure

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