Page 120 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 96

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1.4.22 Well Design

1.4.22. Wellheads: General Descriptions

Spool type surface wellhead. On a land or platform rig where the
wells are drilled from the platform, surface wellheads will generally be
used. The conductor pipe extends to surface (land rig cellar or plat-
form wellhead deck). Surface casing is cemented inside this, and a weld
or screw-on spool is attached after cutting the conductor to a conve-
nient height.
On a land rig, surface casing will generally be cemented to surface.
On a platform, small tubing is usually run in the casing-conductor
annulus and cement flushed out to seabed.
Subsequent casing strings are landed in the previous spool, and so
the surface casing spool will ultimately bear loads from all the casings
and the completion and Xmas tree.
Compact surface wellhead. The compact wellhead offers several
advantages over the spool type wellhead, including:

1. Reduced time nippling up/down
2. Safer—no need to flange up an extra spool after each casing job

The compact wellhead functions much like a subsea wellhead or
mudline suspension.
Mudline suspension system. A mudline suspension system may
be used when a well is drilled offshore for later completion after
installing a platform. It can be run into a template set on the seabed
that allows several wells to be drilled before the platform is installed. If
drilling and platform construction can take place together, the time to
get the field on stream is reduced.
The conductor is cemented in a drilled hole or driven to depth.
Below the mudline within the conductor is a landing ring that has an
internal profile allowing hangers to be set. As subsequent casings are
run they locate on top of the previous hanger. The hangers are run on
a running tool attached to a string of casing back to the rig.
To move the rig off location the casing strings above the hangers
are backed out and recovered, with a suspension cap put in place after
the last casing has been pulled. The conductor is cut above the landing
ring. This leaves the well suspended at the mudline. When the platform
is installed, the casing strings are rerun after recovering the suspension
cap and the well can be completed.

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