Page 84 - Well Control for Completions and Interventions

Well Construction and Completion Design 75

Some of the more common upper completion configurations are illus-
trated and discussed in the next few pages.

2.2.7 No tubing: Flow through production casing

Tubingless completions, if completion is indeed the right word, are still in
use in many places. They are popular first and foremost because they are
cheap and simple. They are primarily used on land locations where con-
ditions are benign. There are clear disadvantages to this type of
“completion.”
• Well integrity—The production casing and wellhead is exposed to res-
ervoir pressure. There are no barriers in the event of a loss of wellhead
integrity. Quite simply, they are not safe.
• The casing is exposed to wellbore products, and is at risk of erosion
and corrosion leading to well integrity problems.
• Flow stability concerns in larger casing sizes.
• Well kill (when necessary) is complicated by the absence of a tubing
string. Bullheading is the only option, unless coil tubing or a snubbing
unit is used to create a circulation path.
From a well integrity and well control standpoint, these wells fall far
short of the ideal and are not allowed by some regulatory authorities—
particularly if the well is capable of flow to surface without reliance on
artificial lift (Fig. 2.8).

2.2.8 Tubing only completion: no production packer
Running a string of completion tubing gives number of distinct advan-
tages over the tubingless configuration.
• Although the casing is still exposed to hydrocarbons and other well-
bore products, the annulus between the tubing and casing is static.
The risk of erosion is virtually eliminated, and whilst corrosion is still
possible it will be at a much reduced rate since the fluids in the annu-
lus are static (not being replenished by flow), unless the well is deliber-
ately produced through the annulus.
• Worn or corroded tubing can be recovered and replaced—whereas the
repair of corroded casing would be more complex and costly, perhaps
requiring a side track or even abandonment.
• Tubing can be correctly sized to stabilize flow.
• Well kill is simplified—reverse circulation or conventional circulation
now becomes possible.