Page 165 - Well Control for Completions and Interventions

Well Control Surface Equipment 157

Most annular preventers are designed for a maximum recommended
closing pressure of 1500 psi (10,342 kPa). Some annular preventers operate
with a higher chamber working pressure of 3000 psi (20,684 kPa). The
minimum pressure necessary to obtain a seal is dependent on several factors
such as bore size, outer diameter (OD) of the pipe, and the wellbore pres-
sure. In general, the greater the difference between annular BOP bore size
and pipe OD, the more closing pressure is required to ensure a seal.
Annular preventers have a doughnut shaped multi-segment seal ele-
ment with integral bonded steel reinforcement. Closure of the seal occurs
when a hydraulically actuated piston is driven upwards. This extrudes the
seal into the wellbore and compresses it around any pipe in the well.
Closure pressure is hydraulically regulated and most systems are configured
to allow control fluid to flow in both directions, so closure pressure remains
constant as pipe (and tool joints) are stripped through the seal. For surface
installations, the API recommend a maximum closure time of 30 s for
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annular preventers smaller than 18/4 in. and 45 s for equipment of 18/4 in.
and larger. For subsea installations closure time should not exceed 60 s.
Most of the annular preventers currently in use are made by three
manufacturers, or will be copies of these basic types, made in the emerg-
ing markets of India and the Far East.
• Cameron cooper:
• Type D and DL.
• Hydril (a subsidiary of GE):
• Model GK.
• Model GL.
• Model GX.
• Shaffer:
• Shaffer spherical.
• Shaffer “Spherical” annular preventer.
Since the annular preventer is part of the BOP stack, and therefore
normally provided by the drilling contractor, operating company supervi-
sors will not always have adequate knowledge of the workings of the
annular preventer. A brief description of the most commonly used annu-
lar preventers follows.

4.7.1 Cameron (Sclumberger) D and DL annular preventers
The Cameron Model “D” preventer is available in sizes between 7(1/16) in.
and 21/4 in., with working pressures between 2000 and 10,000 psi. It uses a
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