Note: Descriptions are shown in the official language in which they were submitted.
115B~9
BAC~GROUND OF THE I~VENTION
Field of the Invention
This invention relates to hydraulic valve con-
trol circuits, and more particularly to valve operating
circuits for providing positive opening and closing of
surface-controlled, sub-surface safety valves while pre-
venting leakage of fuel to the outside environment. ~-
Description of the Prior Art
Crude oil and gas wells are often drilled and
tubing is installed at locations where the internal pres-
sure of the petroleum deposit is quite high so that
precautions must be taken to prevent a blowout of the
well. Such blowouts are not only costly in terms of loss
of oil or gas but in addition a blowout is highly
dangerous and the cost of controlling a blowout at an
oil or gas well is rather high. As a result, many
devices including safety valves and associated control
circuits have been developed and many such devices have
been installed in association with gas and oil wells.
One such device that is frequently employed is a surface-
controlled, sub-surface safety valve (SCSSV) which can be
installed within the tubing of a well either prior to
running the tubing into the well, or afterward by means of
well-known wire line techniques. Such valves are generally
positioned 200 or 300 feet below the wellhead, and are
always of the "fail-close" design. The construction of
these valves resembles a conventional ball valve wherein
positive actuation against a spring is-required to open it,
for example by applying hydraulic pressure to a small
diameter control line and to a valve actuator which can be
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conveniently located within the well. In some of the
installations the valve actuator can be positioned outside
the tubing.
The hydraulic pressure applied to the control
S line must be sufficient to develop a force on one face of
the piston of the actuator greater than the combination
of the opposing force developed by gas or oil pressure in
the tubing acting on the opposite face of the piston and
the spring-generated valve closing force. B~cause of the
depth of the safety valves, there is a substantial fluid
head in the control line which provides a significant
amount of pressure acting on the piston of the actuator,
so that the spring force, the valve depth, and the loca-
tion of the safety valve must be carefully selected to
ensure complete closure of the valve when the pressure in
the control line is relieved by action taken at the sur-
face.
Another type of SCSSV hydraulic circuit in common
use involves a hydraulic balance and requires both a
hydraulic control line to open and close the valve and a
balance line which communicates with the opposing face of
the piston of the actuator. By means of this arrangement,
the control line pressure needs only to overcome the
spring force since otherwise the forces are equal but op-
posite as developed by the head in both the control lineand in the balance line.
Whether a balanced type SCSSV or a non-balanced
type is used, it is common practice to pass the control
and/or balance lines through the wellhead and its connector
and then exit the christmas tree below the master valve.
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The control and/or balance lines, after leaving the
christmas tree, are connected to a control system to
enable operation of the SCSSV.
The previously proposed control systems have the
disadvantage that if a leak or other malfunction occurs
in the SCSSV, which results in connecting the tubing bore
to the control line, a high pressure leakage path is then
formed to the outside environment. Such a leak can damage
the control system and also allow oil or gas to pollute
the environment. This problem has already been appreciated
and with a view to solving it, shut-off valves have been
provided where the control andfor balance lines leave the
christmas tree. By this provision, if a leak shoula occur,
the shut-off valves can be closed manually but further
problems arise if the christmas tree is installed below
the surface of the sea because the shut-off valves will
then require actuators, for example, hydraulic actuators
- so that the shut-off valves can be remotely opened or
closed.
It will be apparent that the shut-off valves in
the control and/or balance lines must be open when it is
desired to open the associated SCSSV so that fluid can be
foxced under pressure to the actuating cylinder of the
SCSSV. Even more important, the shut-off valves must
remain open until the SCSSV has completely closed. Once the
latter has closed it is desirable to close fully the shut-
off valves~ However, if the shut-off valves are allowed to
close before the SCSSV has completely closed, the shut-off
valves will not allow fluid to flow away from the actuator
of the SCSSV, and therefore the latter will remain open or
1 1~6139
partial~y open. It follows that for fully safe operation
there must be proper co-operation between the actuator
of the SCSSV and the shut-off valves particularly for
remote or sub-sea surface locations. In order more fully
to take into account the difficulties outlined above,
control systems such as hy~raulic sequencing or electro-
hydraulic multiplexing systems have been proposed so that
the shut-off valves are connected to separate hydraulic
output lines of the control system and are actuated inde-
pendently of the SCSSV control line. These proposed con-
trol systems are generally satisfactory but do not provide
for the sudden loss of hydraulic pressure in the control
system. Such loss in hydraulic pressure will result in
the well becoming shut down because all the valves from the
christmas tree including the SCSSV will close because of
their "fail-close" characteristics. However, the loss of
hydraulic pressure will provide no assurance that the
shut-off valves will remain open long enough to allow
complete closure of the associated SCSSV.
As an alternative to the complexities of hydrau-
lic sequencing or electro-hydxaulic multiplexing, a simple
hydraulic time delay circuit has been proposed which com-
prises simply a restrictor valve and an accumulator which
ensures that the SCSSV closes before the shut-off valve is
timed to close. This system has the merit of simplicity
but does not provide a complete answer to the problems
involved. In particular it is neither possible readily to
know the exact closing time of the SCSSV after installation
nor is it possible to ensure that it will remain constant
over long periods of time. To ensure that the system is
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basically safe, it has been proposed simply to make the time
constant long enough to accommoda~e the longest possible closing
times for the SCSSV. However, such long time constants require
either very small orifice restrictor valves which are liable to
clog or large accumulators which cannot readily be accommodated
in the limited space available.
Another hydraulic valve operating circuit, disclosed
in United States Patent No. 4,193,449 issued to Lochte et al,
includes a plurality of shut-off valves mounted in the wall of
a well and connected to provide positive opening and closing of
a SCSSV while isolating the safety valve from the outside
environment. The shut-off valves prevent leakage of well fluids
to the outside environment if a leak should occur between the
inside of the well and the hydraulic lines which are connected
to the safety valve actuator. The shut-off valves also insure
that the safety valve will close properly by relieving the fluid
pressure applied to the safety valve actuator when it is desired
to close the safety valve.
The present invention provides a hydraulic valve
operating system for opening and closing a surface-controlled,
sub-surface safety valve, said system connected for use with a
source of pressurized hydraulic fluid and a surface-controlled,
sub-surface safety valve mounted in a petroleum well having a
wall, said safety valve including a valve actuator having an
inlet port, said well including a block valve mounted to a
christmas tree atop said well to connect the safety valve
actuator to an outside hydraulic pressure source and to a
pressure sink while isolating the safety valve from the outside
environment by preventing fluids from being discharged to the
outside environment, said system comprising:
a normally closed block valve having an inlet port and
an outlet port;
1 3 9
a fluid accumulator having a variable volume fluid
chamber and an inlet port connected to said fluid chamberi
means for decreasing the volume of said accumulator
fluid chamber in response to an increase in hydraulic fluid
pressure;
means for connecting said block valve outlet port and
said accumulator inlet port to said safety valve actuator inlet
port while preventing fluid flow to the outside environment;
means for selectively connecting said block valve inlet
port and said accumulator volume varying means to said hydraulic
pressure source;
means for opening said block valve when said block
valve inlet port is connected to said hydraulic pressure source;
and
means for selectively connecting said block valve inlet
port and said accumulator volume varying means to said pressure
sink.
The present invention also provides an accumulator
actuator for decreasing the volume of said accumulator chamber
in response to pressure applied to an accumulator actuator
inlet port.
Thus according to the present invention t.here is
provided a surface-controlled, sub-surface fail-close safety
valve, an actuator positively operable to open the safety valve,
and a control line communicating with the safety valve actuator
through a normally closed shut-off valve and through a fluid
accumulator to hold the valves open when the control line is
pressurized. A reduction in pressure on the control line allows
fluid from the safety valve actuator to be directed into the
accumulator, whereby the safety valve is free to close by virtue
of its fail-close characteristics.
1 ~56~ 3'~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic side elevation of a
subsea well in which the present invention may be used, with
portions being broken away.
Figure 2 is a vertical section of a shut-off valve
used in the present invention.
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1 156139
Figures 3-5 are circuit diagrams of one embodi-
ment of the present invention showing a sequence of opera=
tion.
DESCRIPTION OF T~ PREFERRED EMBODIMENT
Referring now to the drawings, Fig. 1 illustrates
a petroleum well, of the type that is used to produce oil
and gas, completed with a christmas tree 10 and a pair of
control modules 11,12 mounted on a mounting plate 15.
The christmas tree 10 is mounted atop the well by a tree
connector 16 and a plurality of casing strings 17a,17b
are suspended in a bore hole 20 drilled into the sea floor
21. The casing strings 17a,17b are anchored in position
by cement 22 which is pumped into the annulus between the
bore hole 20 and the outermost string of casing.
A surface-controlled, sub-surface safety valve
24 and a safety valve actuator 25 are positioned inside
- the inner string 17b several feet below the christmas tree
10 to provide positive control of fluid through a tubing
string 26. The safety valve actuator 25 is coupled to a
hy~raulic fluid source P and to a sink S (Figs. 3-5) by
hydraulic lines 27,28, by a shut-off or gate valve 29
located in the wall of the christmas tree 10, and by a
three-way valve 30. The source of pressure P, the sink
S and the three-way valve 30 are located at a control cen-
ter 33 at the ocean surface. A pair of valve operators
34,35 (Fig. 1) control the operation of a pair of christ-
mas tree valves (not shown) inside the tree to control a
flow of oil from the tree through a pair of tree flow
lines 39,40. Each of the flow lines 39,40 is in the
form of a loop having sufficient radius to facilitate
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1156~39
passage of conventional "through-flow-loop" tools (not
shown) therethrough. Operation of the valve operators 34,35
is controlled by the control modules 11,12.
A circuit which provides control of the SCSSV
24 (Figs. 3-5) includes the safety valve actuator ~5
having an annular body 41 with a piston 45 mounted therein.
The piston 45 is biased toward the upper end of the actua-
tor by a spring ~6 which closes the valve when the piston is
adjacent the upper end of the body ~1~ The hydraulic con-
trol line 28 provides hydraulic fluid under pressure tomove the piston 45 downward, thereby opening the surface-
controlled, sub-surface safety valve 240
The single gate valve 29 of the present inven-
tion, shown in detail in Figure 2, can be used to control
the SCSSV when connected in the hydraulic circuit shown
in Figures 3-5. me gate valve 29 includes a base 49, a
- fluid flow passage 50 extending transversely through the
base, a gate chamber 51 extending through a portion of the
base and intersecting the passage 50, and a pair of
~ enlarged flow passage portions 50a,50b adjacent the cham-
ber 51. Fitted into each of the enlarged passage portions
50a,50b is a tubular insert 55,56, respectively, each in-
sert having an external annular groove 57 in its outer wall
61,62, and an annular sealing mem~er 62 positioned in the
groove to provide a fluid-tight seal between the insert
and the enlarged portion of the passage. Each of the in-
serts extends into the gate chamber 51 where it makes
sliding contact with a flat valve gate 63 having a through-
port 67. When the valve gate 63 is in the deenergized
positionshown in Figure 2 the flow of fluid between the
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1 15~13g
right and left portions of the passage 50 is blocked.
The lower portion of the base includes a fluid
accumulator ACl (Fig. 2) comprising a chamber 68 and a
fluid-actuated piston 69. The chamber 68 includes an
enlarged portion 68a, and the piston includes a radially
outward extending flange 69a. An annular sealing member
73, located in an annular groove 74 in the piston flange
69a, provides a fluid-tight seal between the flange 69a
and the walls of the enlarged chamber 68a, and an annular
sealing member 75, located in an annular groove 76 in
the body of the piston 69, provides a fluid-tight seal
between the piston body and the wall of the chamber 68.
A fluid passageway 50 interconnects the chamber 68 and the
flow passage 50.
The base 49 of the gate valve can be fastened to
a christmas tree adaptor 80 (Figs. 1-2) by capscrews (not
shown) or other suitable means, in which case an annular
seal 81 in grooves 85,86 provides a fluid-tight barrier
between the base and the tree adaptor. Alternately, the
base 49 may be formed as part of the wall of the christmas
tree adaptor, or the entire valve can be machined into a
portion of the tree adaptor.
A cover plate 87 (Fig. 2) is secured to the valve
base 49 by a plurality of studs 91, each of which projects
through a hole 92 in the cover plate 87 and into a threaded
bore 93 in the base 49, and a like plurality of nuts 97
threaded into the outer ends of the studs 91. A control
~unction line 27a is connected to the outer end of a
threaded bore 50c in the cover plate, and an annular metal
seal 99 surrounding the flow passage 50 in annular grooves
llS~l~9
103,104, provides a fluid-tight barrier between the cover
plate 87 and the base 49.
An accumulator actuator housing 105 is secured to
the base 49 (Fig. 2) by a plurality of studs 109 and nuts
115 (only one of each being shown), each stud projecting
through a hole 110 in the actuator and into a threaded bore
111 in the base 49. A passage 116, extending be~ween the
accumulator chamber's enlarged portion 68a and the outside
of the actuator housing 105, vents the chamber 68a to the
outside of the gate valve 29, and hydraulic line 27b is
threaded into a bGre 117 which extends into the enlarged
chamber 68a. Because the surface area 69b of the piston's
flange 69a is greater than the surface area 69c of the
piston's other end, the piston will move in the direction
of the arrow X when fluid pressures are substantially equal
in the chamber 68 and the hydraulic line 27b.
A gate valve actuator base 121 (Fig. 2) is
attached to the valve base 49 by a plurality of capscrews
122 (only one being shown) threaded into bores 123 in the
base 49. The actuator base 121 includes a longitudinal
bore 127 having a lower portion 127a and an enlarged upper
portion 127b.
An elongated actuator cap 129 (Fig. 2) is secured
to the actuator base 121 by a plurality of capscrews 134
(only one shown) each extending through a hole 135 into
threaded engagement with a bore 139 in the base 121. The
cap 129 has a central bore 133 with a first section 133a,
a second section 133b with a reduced diameter, and a third
section 133c of further reduced diameter. The outer end of
the bore 133 is closed and sealed from the atmosphere by
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11561~9
means of a capscrew 146 threaded into the bore section
133c, and an elongated plug 1~0, with an annular sealing
element 141 in an annular groove 145, is positioned in the
bore section 133b. In the bore section 133a is a piston
147 that is connected to the valve gate 63 by a rod 153,
and this piston is biased toward the plug 140 by a coil
spring 152. The rod 153 extends through an annular packing
spacer 157 that is sealed to the actuator bore 127b and
the actuator cap 129 by annular seal elements 158,159,
respectively, and an annular packing 163 provides a
dynamic seal between the base 121 and the rod 153.
The actuator cap 129 includes another axial bore
164 with its inner end communicating with the bore section
133a and its outer threaded end 164a connected to a
hydraulic control line 27c. A radially extending bore
165, having a threaded outer portion 165a, extends into the
bore section 133a to provide space for air when the piston
147 moves toward the actuator base 121. A plug 169 in the
threaded portion of the bore 165 is removed in order to
vent the bore 133a to the outside during normal operations.
The gate valve 29 is connected to the surface con-
trol center 33 by the single control line 27 (Figs. 3-S) to
provide operation of this valve and the SCSSV 24. The
three-way valve 30 at the control center is biased toward
the right by a spring 170 to connect the B~section between
the hv~raulic line 27 and a hydraulic line 171 as shown in
Figure 5. In the "B-position" of the valve 30 (Fig. 5)
the hydraulic lines 27a-27c are each connected to the sink
S by the line 171 and valve 30 allowing the safety valve
actuator 25 to close the SCSSV 24.
115613g
To open the SCSSV a spool 174 of the three-way
valve is moved to the left until the A-sectlon (Fig. 3) of
the valve connects the pressure source P to the hydraulic
control lines 27, 27a-27c. Pressure on the control line
27b moves the accumulator actuator piston 69 to the right
forcing fluid from the accumulator chamber 68 through the
passage 77, valve outlet port 50d and input hydraulic line
28 into the SCSSV actuator 25 and moving the piston to the
right end of the chamber 68 as seen in Figure 4. Pressure
on the control line 27c moves the valve actuator piston
147 downward until the valve gate port 67 (Fig. 4) is
aligned with the fluid flow passage 50 and fluid moves from
passage 50 into the SCSSV actuator 25 forcing the pistGn 45
downward against the spring 46 and opening the SCSSV 24.
To close the SCSSV the spool 174 of the three-way
valve is released and the valve moved back to the "B-
position" by the spring 170 thereby connecting the control
line 27 to the sink S and relieving the pressure on line 27.
The actuator piston 147 (Figs. 2-5) is moved upward (Fig.
5) and the valve gate 63 blocks the fluid flow passage 50
in the gate valve 29. The SCSSV actuator spring 46 forces
the piston 45 upward (Fig. 5) moving the fluid out of the
actuator body 41, through the hydraulic line 28 and passage
77 into the accumulator chamber 68 and moving the accumula-
tor piston 69 to the left. As the piston 45 in the SCSSV
actuator 25 moves upward the SCSSV 24 closes.
It is believed that the hereinbefore described
safety valve manifold system will insure proper operation
of a SCSSV while providing isolation of the SCSSV from the
environment outside an oil or gas well. Only one hydraulic
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control line is required to operate the SCSSV and the shut-
off valve. The system is very simple and requires few
components.
Although the best mode contempla~ed for carrying
5 out the present inven-tion has been herein shown and
described, it will be apparent that modification and varia-
tion may be made without departing from what is regarded
to be the subject matter of the invention.
LBG:cds
