Note: Descriptions are shown in the official language in which they were submitted.
~ CA211 7296
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~j DOWNHOLE SAFETY VALVE
Wells in gas and oil fields are usually built with
~ downhole safety valves, sometimes referred to as sub-
,l surface safety valves, which close to contain the well
pressure in emergency situations. Such valves may be
~ constructed as flapper or ball valves and are usually held
;~, open against normal well pressure by hydraulic pressure
applied down from the surface through a control line. Such
control lines are vulnerable and liable to damage which can
result in complicated and lengthy workover situations.
The present invention is concerned with the
retrofitting of a well with a downhole safety valve.
Conventionally this has involved installing at the wellhead
an intermediate flange and a piggy back hanger either to
give the facility of installing a control line or to create
an annulus down which control fluid can be pumped to supply
pressure to a downhole safety valve. However, these
solutions involve the killing of the well and pulling of
the completion in order to install the valve, and still
result in the need to provide for the feeding of control
fluid down the well to operate the valve.
The inventors have now appreciated that the above
problems can be overcome by setting a downhole closure
valve a short distance, say between 2 and 15, preferably
between 3 and lO and most preferably substantially 5 metres
below the wellhead, and to operate the valve by means of a
piston in the wellhead which is coupled directly and
mechanically to the valve by a stinger, preferably rigid
with the piston.
Accordingly, in accordance with the present invention,
a downhole valve assembly for a well comprises a closure
valve which is, or is arranged to be, secured within tubing
~ in a completed well; an annular member which is, or is
.~ arranged to be, built into a wellhead; a piston which is
:: axially slidable within the annular member; means for
~ displacing the piston axially within the annular member;
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TECHSOURCE Classification 1994/07/14
IPC & CPC List for an Application 13:26:24
Type an application number and press ENTER.
Application Number . 2117296_
~ Title : DOWNHOLE SAFETY VALVE
~i MORE:
IPC Code CPC Code
' P 5 E 21 B 34 / 10 166 / 44
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and a stinger depending Erom the piston down to the valve
to operate the valve upon axial move~ent of the piston.
The piston may be subjected to a variety of forces to
s provide the valve control. Thus the displacement means may
'q comprise at least one fluid space to which fluid under
pressure can be applied through a gallery in the annular
member to urge the piston in a respective axial direction.
The fluid under pressure applied to one fluid space may
then be arranged to hold the piston and stinger against the
10 action of a spring in a position in which the valve is held
open; the spring providing a fail safe closing of the valve
upon reduction in the fluid pressure.
The fluid pressure might be provided by a hand pump
and the pressure locked in within an integral needle valve.
However, when a more permanent reliable pressure source is
required, this could be provided by an hydraulic
accumulator. For security purposes it is proposed that the
accumulator be secured within the annular member behind a
tamper proof cover.
In an alternative arrangement, one fluid under
pressure applied to one fluid space is arranged to hold the
piston and stinger against the action of normal well
pressure applied to another fluid space, in a position in
which the valve is held open. The piston and stinger being
arranged to be moved by the well pressure applied to the
second fluid space upon reduction of the first fluid
pressure, to cause closing of the valve.
The invention also includes a method of retrofitting
~1 a completed well with a downhole safety valve, without
pulling the completion, the metllod comprising plugging the
tubing to seal the well, Eitting the wellhead with an
additional annular member such as a flange or spool,
unplugging the tubing, running in and securing a downhole
pressure valve within the tubing, and running into the
annular member a piston having a depending stinger which
reaches down to the valve assembly, the piston being
~- CA2117296
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axially movable relatively to the annular member to operate
the valve via the stinger.
~The advantage of the new system is that the means of
iactuating the valve, whether it be applied hydraulic
pressure, well bore pressure, or spring force, or a
combination of combination of these, is located at the
surface, say 5 metres above the valve installed in the
existing tubing. This removes the need for pressure lines
in the tubing or casing annulus which is a source of
problem and failure.
Three examples of valve assemblies constructed in
accordance with the present invsntion are partially
illustrated in half axial section in respective ones of the
three figures of the accompanying drawings.
In the arrangement shown in figure 1, a spool 4 is
shown built into a wellhead, to another part 5 of which it
is bolted by a ring of bolts with the usual interposed seal
7.
The inner periphery of the spool 4 is prepared to
receive a piston hanger 8 which is screwed into the spool
at g and sealed to the spool by six annular seals loA, los,
lOC, lOD, lOE and lOF. Between the seals lOA and lOB a
gallery 11 extending radially through the spool leads into
an annular groove 12. A similar gallery 13 leads radially
through the spool to an annular groove 14 between the seals
lOD and lOE.
Slidable within the piston hanger 8 is a tubular
piston 15 having an outer radial projection 16 forming an
annular piston head provided with plastic bearings 17 and
a seal 18, which slide against a cylindrical outer portion
of the piston hanger 8. Below the piston head 16 and
between the pis-ton ancl piston hanger is provided a fluid
space 19, the lower end of which is closed by seals 20
`carried by the lower portion of the piston hanger and
sliding against a cylindrical external surface of the
piston. The piston hanger also carries a plastic bearing
21 against which the same cylindrical portion of the piston
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f 4
slides. The annular groove 12 communcates with the fluid
space 19 through radial ports 22.
Above the piston head 16 is a second fluid space 23, ~-
shown axially much shorter than the space 19 only because
the piston is shown in its uppermost position. The upper
end of the space 23 is sealed by seals 24 which, together
with a further plastic bearing at 25, are carried by the
upper portion of the piston hanger and slide against an
external cylindrical surface at the top of the piston.
1 n Screwed to the bottom of the piston is a tubular
stinger 26, which may be of 2 inch diameter and
approximately 5 metres long~ This extends into the 3 inc'h
tubing 27 and terminates adjacent to a safety valve unit
28, which is sealed within the tubing by packers 29. In
this case thef valve is shown as a flapper valve having a
closure flap 30 which, under the action of a small torsion
spring and well pressure from below tends to pivot upwardly
to the horizontal position shown in full lines in figure 1
in which it abuts against an annular seating to close the
passsageway through the tubing. At this time the piston 15
is in its illustrated raised position so that the lower end
of the stinger 26 does not interfere with the flap. The
piston is held in this raised position by hydraulic
pressure applied through the line 11. When the valve is to
be opened, the line 11 is vented and hydraulic pressure is
applied through the line 13 to force the piston and hence
the stinger 26 downwardly so that the lower end of the
stinger engages and forces the flap 30 downwards to the
dotted line position. A piston stroke of about ~ inches is
sufficient for this purpose.
il The conversion of a well by the fitting of such a
; safety valve may typically involve the following steps.
First, a blow out preventer (BOP) stack is fitted on top of
~,x the exlsting tree and a back pressure valve ~BPV~ is set in
the existing 3~f inch tubing hanger. ~fter testing the tree
~: is lifted and the new spool 4 is fitted. Thereafter -the
,~ tree i5 re-made-up and all the connections are tested. The
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BOP stack is reinstalled and the BPV pulled. The flapper
valve unit 28 can the be installed by wireline through the
~, BOP at a known and required depth by setting the packers
29. Two inch nominal tubing to form the stinger 26 is then
cut to the required length and fitted to the piston 15
which is assembled with its hanger 8. These are then run
into the wellhead under pressure control and the hanger
rotated by the engagement of dogs of the running tool with
slots 31 at its upper end so that the screw connection 9 is
made with the spool. The running tool is then withdrawn
and the ~OP stack removed.
The arrangement shown in figure 2 utilises a spool 4A
which will be built into the wellhead. The spool is
prepared to locate therein a screwed in piston hanger 8A.
A piston 15A having concentric cylindrical upper portions
32 and 33 is sealed to external cylindrical portions of the
spool, against which it slides, by means of seals 34 and
35. The piston is also sealed to cylindrical portions of
the piston hanger 8A against which it slides, by means of
seals 36 and 37. A helically coiled compression spring 38
is located between the spool 4A and piston 15A and urges
the piston upwardly to the illustrated position. The
spring may be overcome to lower the piston by fluid
pressure contained within an hydraulic accumulator 39 and
fed to a fluid space 40 between the piston and piston
hanger via a gallery 41 in the spool and a gallery 42 in
the piston hanger.
In use a stinger will be connected at a wireline set
latch groove 26A to, and extend down through, the bottom of
the piston 15A for operating a valve such as the flappex
valve unit shown in figure 1. Otherwise installation an*
operation of the valve are analogous to the figure 1
example. The accumulator 39 is shown mounted within a
cavity portion 43 of the spool the cavity being closed by
an armoured glass cover 44 secured by tamper proo~ bolts
45. It is envisaged that, within the cavity 43, there
would also be provided necessary valving and pressure
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gauges, visible through the window 44. The cavity could
also form a fluid reservoir or dunk tank if the applied
pressure is to be relieved in case of emergency, for
example upon fusion of a fusible pipe.
The arrangement shown in figure 3 is similar in many
respects in that shown in figure 1. Thus a spool 4B as
screwed into it a piston hanger 8B. A piston lsB slides
upwardly and downwardly relatively to complementary
~;~cylindrical surfaces of the piston hanger 8B and spool 4B
by means of plastic bearings 46 carried by the piston
hanger and 47 carried by a radially outwardly enlarged
annular piston head 48 of the piston. A fluid space 49
provided above the piston head 48 is sealed by seals 50, 51
and 52. A gallery 53 through the spool 4B opens into the
fluid space 49.
A second fluid space s4 is provided below the piston
head 48 between the spool 4B and piston, and communicates
with the interior of the piston and hence downhole through
a ring of radial ports 55. The lower end of the piston is
provided with a screw thread 56 for connection of the
stinger 26.
~;~Installation and operation of the figure 3 example are
analogous to the previous examples except that in this case
:~the piston 15B will be forced downwardly to hold open the
~i~ flapper valve when sufficiently high pressure is applied
through the gallery 53 to the fluid space 49 to overcome
the upward force provided by the well pressure acting in
the fluid space 54 on the underside of the piston head 48.
~,The valve will then close if the gallery 53 is vented or if
there is an excessively high surge in well pressure.
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