Annular BOP
1. Application
Used in conjunction with hydraulic control system,the annular BOP seals off the annulars of different sizes when drilling tool is
set in the hole,when there is no drilling tool in the hole,it can also seal off the wellhead.If well blowout happens during the
coring and measuring operation,it can seal off the annular spaces between the well barrel and Kelly,coring tool,cable and steel
rope etc.matched with pressure-relief valve and buffer tank,it can force-execute the running/retrieving drill operation through
butt-weld drilling rod at 18 degree without fine thread.
2. Working Principles
A hydraulic control system is used to close or open the annular preventer,when it is closed,high pressure oil is directed to the
closing chamber positioned in the lower side of the piston,causing the piston to move upward.The rubber core is compressed by the
moving piston.Because the annular BOP has a cap,the packing unit can not move upward and only can move toward the center of the
well to pack off a string or seal off the well.
When well open is required,operate the reversal valve to direct high pressure oil from the upper oil-port into the chamber in the
upper side of the piston so as to push the piston to move down,and then the closing chamber is relieved,the squeeze pressure at
the cone of rubber core is removed,the wellhead is opened.
3. Operating Requirements
a.The annular BOP can be used to seal off a well where the drill pipe is in use if the well blowout.However the annular BOP
cannot be closed for a long time,because the packing unit is easy to be damaged and the BOP itself has no locking mechanism.
b.It is necessary to use a drilling tool with 18degree bevel when running /retrieving drill of operation with
BOP,running/retrieving drill should be slow pass through the nipple and all the rubber protecting collar on the drilling tool
should be discharged off.
c.With the annular BOP in the closed position and shut-in pressure kept below 5MPa,the string can be moved either up or down,but
mustn’t be rotated.
d.It is forbidden to open the annular BOP to relieve the pressure out of the well to avoid rubber core damage.
e.Be sure to check whether the annular BOP is in the full open position or not every time after opened in order to prevent damage
to the packing unit.
f.Clean the inside of the BOP after well cementing operation is completed in order to keep its closings and openings flexible.
g.More attention shall be paid to ring gaskets and gasket grooves during installation of the BOP or its removal from the service.
h.After entering the destination layer,running/retrieving drill once should be accompanied with test of well-enclosed with
drilling tool once,and inspect the effect of well enclosed with rubber core,if beyond the requirement,it should be replace.
i.Periodically perform pressure test on the annular BOP in accordance with applicable standards.