Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIE:LD OF INVENTION
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This invention relates to blowout preventers
used near the bottom of a well duriny drilling of the well.
BACKGRO~ND OF THE INV~NTION
The bottom hole blowout preventer is a
device used to control backflow or displacement of
drilling fluids within the drill string by high pressure
gas or hydrocarbons encountered while normal drilling or
well servicing activities are in progressD
Downhole blowout preventers are known which
include a housing engagable in a drill string and which
use a ball valve pivotally mounted in the bore of the
housing, where the ball valve is rotated from an open to a
closed position by means of a cooperating cam sleeve, the
cooperating cam sleeve being operated by a solenoid valve
in response to a signal received by a downhole unit. The
solenoid valve opens up a pa~sage into a chamber above a
flanged end oE the cam .sleeve, and mud pressur~ entering
the chamber Eorces the cam sleeve down, khus closi.ng the
ball valve. Such a downhole blowout preventer is operated
~rom lnstructions ~rom the surface, and i~ described, for
example, in European Patent Application No. 86304179.4,
published December 17, 1986.
Surface controllable rotary valves, actuated
by a sleeve, have also been used in the oil industry in
production. That is, in the production of well fluids,
such as oil or gas from wells, it has been the prac~ice to
provide automatically closeable shut-off or safety valves
which are located downhole in the well which are held open
by control fluid pressure, the valves closing
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automatically when control fluid pressure is purposely
reduced to allow the valves to close or when damage occurs
to the control fluid system at the well head or on an
offshore pla~form. ~n example of such a safet~v valve
which includes a lateral opening for ease of installing
the valve, is described in United Kingdom Patent No.
1,416,085.
However, there does not exist an adequate
automatic downhole blowout preventer useable for drilling
purposes. Autornatic rotary valves tend to close at times
when closure is not desired, for example, from excess
running-in rates, which interferes with pipe fill-up or
drainage.
SUMMARY OF Tf~E: INVENTION
_
The inventor has provided an automatic down
hole blowout preventer for a drill string, the blowout
preventer comprising:
a rotary valve pivotally mountable in a
drill string:
an actuatlng sleeve disposed ahout the ball
valve within the drill string and having a ~low passage,
the actuating sleeve being slideable in relation to the
drill string in response to downhole over pressure
conditions from a first position in which the ball valve
is open to a second position in which the ball valve is
closed;
reset means disposed against the actuating
sleeve for biasing the actuating sleeve to the open
position; and
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means connected to the actuating sleeve to
regulate the closure rate of the rotary valve.
Further summary of the invention may be found in the
claims.
BRIEF DESCRIPTION OF TE~E FIGURE:S
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There will now be described a preferred
embodiment of the invention, with reference to the figures
in which like elements are indicated by like numerals, by
way of example, and in which:
Figure 1 is a schematic section of a ball
valve type bottom hole blowout preventer;
Figure 2 is a schematic section of a ball
valve type blowout preventer depicting a vertical
cross-section at 90 degrees to the section of Figure l;
Figure 3A i4 an end view of a ball valve for
a bottom hole blowout preventer accordirlg to the
invention: and
Fiyure 3B is a side view, par~i.ally broker
away, o~ the ball valve o~ Figure 3A.
I)!:SCRIPTION OF T~E PREFERRE:D EMBODIMENT
Referring to Figures 1 and 2, the bottom
hole blowout preventer 10 includes a cylindrical sleeve 56
having a bore 24 for the passage of drilling fluids and
suitably disposed within the drill string sub 94. The
sleeve 56 has a top cap 70, and a bottom cap 28~ with
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suitable threaded connections to enable thern to be
threaded onto sleeve 56. In the sleeve bore 24 there is a
valve ball 40 which is rotatably mounted on pivot pins 36,
which allow it to rotate on a single axis only norrnal to
the bore 24. The valve ball pivot pins 36 fit in suitably
drilled holes 76 in collets 80 fitted to either side of
the ball valve 40, and facing up to flats 78 machined on
either side of the ball valve 40.
The collets 80 fit into suitably machined
sockets 82 in the sleeve 56.
The ball valve 40 seats spherically between
the upper seat 42 and the lower seat 30 in the bore 24 of
the sleeve 56. The valve ball 40, and the seats 42 and 30
are retained within the sleeve 56 by the threaded bottom
cap 28. There is a bore in the valve ball 40 extending
perpendicular to the pivotal axis of the valve ball 40.
Machined into the flats 78 of valve ball 40
are slots 34 extending radially at 45 degrees from the
vertical axis as shown in Figure 3~, and as shown in the
broken away portion 35 in Fiyure 3B. Each slot 34 is
designed to be engaged by an actuating pin 32 attached to
the drill striny sub 94 and ~rav~lling within a rn~lled
slot 38 in the sleeve 56. ~n identical set of slots and
actuating pins (not shown) are on the other side of the
valve to the side seen in Figure 2.
Fitted over the upper outsid~ diameter of
sleeve 56 is a retainer 58 with a machined collar 84 on
its inside diameter, made to have a close tolerance fit
over-the sleeve 56 and with an O-ring seal 86 between the
sleeve outside diameter and the retainer inside diameter.
The retainer 58 lirnits the vertical movement of the sleeve
56. Two drilled channels 88 connect a lower hydraulic
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chamber 44 to an upper hydraulic oil chamber 66 throuyh a
ball check valve 90 that meters oil flow in the upper
direction ~towards chamber 66) and allows free oil passage
in the opposite direction. The size of the orifice in the
check valve may be varied according to the desired closure
rate of the ball valve 40. The two channels 88 and the
chambers 44 and 66 comprise means to regulate the closure
rate of the ball valve 40. They are hydraulically
connected to the actuating sleeve 56 and it will be
understood that "connected" as used in the claims includes
hydraulic connection.
The outside diameter of the retainer 58 is
threaded at 52 over the lower half of its length and has
O-ring seal grooves 22 in its outside diameter above and
below the threads 52. The retainer 58 threads into a sub
94 or other sub that becomes an intagral part of the drill
string and retains the entire blowout preventer assembly
in place within the sub.
O-ring seals 14 and molded lip seals 16 help
seal the chambers 44 and 66. Opposing compression springs
50 and 62 bias the sleeve 56 to a ready position (not
shown) in which the valve baLl ~0 is neither EulLy C1OE~
nor fully open. Pressure from drilling 1uid c.lurincJ
drilling forces the sl~eve S6 to the first position shown
in Figure 1, in which the valve bal:L 40 is Eul:ly open.
The spring 62 is held between shoulder 60 of
the retainer 58 and the shoulder 64 of the sleeve 56. The
spring 50 is held between shoulder 46 of the sleeve 56 and
shoulder 54 of the retainer 58. Together the springs 50
and 62 constitute reset means disposed against the
actuating sleeve 56.
The manner of operation of the bottom hole
blowout preventer is as follows.
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Forces resulting from a bottom hole over
pressure condition act on the lower surfaces 20 of the
sleeve 56 and cause it to move vertically within the drill
string sub 94 and retainer 58. This upward motion causes
the actuating pins 32 to move downward within the milled
slots 38 of sleeve 56. The engagement of the actuating
pins 32 with the machine slots 34 and the valve ball 40
causes the valve ball 40 to rotate 90 degrees around the
pivot pin 36 between the open position shown in Figure 1
and the closed position shown in Figure 2.
As the sleeve 56J top cap 70 and bottom cap
28 traverse vertically up within the sub 94, a chamber 66
is created between the bottom shoulder 68 of the top cap
and the top shoulder 72 of the retainer 58. At the same
time, the lower hydraulic fluid chamber 44 closes, and
forces hydraulic fluid through channel 88 and the
check valve 90, into the top chamber 66. As these
chambers 44 and 66 are sealed to ensure fluid tight
integrity one from the other, and from the outer well
fluids, the flow of hydraulic oil 96 from the lower
chamber 44 through the metering efEect o check valve 90
inhibits the rotating closure rate o:E the valve ball 40.
In the event oE a well kick or blowout,
pressure ~orc~s actlng on the lower blowout preventer
surfaces ~orce valve closure at a predetermined rate, and
ensure a delayed closure. As pressure i9 equaliæed across
the valve, the valve is automatically reset by the springs
50 and 62 to an open position. By allowing limited flow
at the surface, bottom hole pressures can readily be
taken.
If the drill string is run in the hole at an
excess rate, bottom hole pressures will tend to urge the
valve ball 40 towards closure, but will re-open as the
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drill pipe ~ills. The mekering effect oE the check valve
90 avoids unwanted closure.
Drilling ahead procedures retain the valve
in the fully open position with fluid pressures acting
upon the upper surfaces of the sleeve 56. During normal
running in procedures, the ball valve 40 will normally
stay in the half-open pOSitiOIl.
In summary, in the absence of forces from
pressure on either of the top or bottom surfaces of the
sleeve 56, the compression springs 50 and 62 bias the ball
valve 40 in a central half-open position. Forces acting
on the upper surfaces of the sleeve, for example during
drilling, will bring the valve to a fully open position.
Forces acting on the lower surfaces of the sleeve 56 will
bring the ball valve 40 to a fully closed position. With
the relaxation of either the upward or downward force, the
blowout preventer will always return to the ready position.
It would be understood by persons skilled ln
the art that immaterial modiEications can be made to the
invention described here and these are intended to b~
covered by the scope o~ the claims that ~ollows
