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BACKGROUND OF THE INVENTION 
     The present invention relates to a safety device for a fluid production well, of the type comprising:
         a valve housing intended to be fixed tightly inside a fluid flow conduit, the housing delimiting a fluid flow passage and comprising:
           a valve used to seal the passage, and which can move between an open position of the passage and a closed position of the passage;   means for permanently biasing the valve towards its closed position; and   means for connecting the housing to a coupling member for a working wire line intended to move and anchor the housing in the conduit;   
           means for holding the valve in the open position against the permanent biasing means, said holding means comprising at least one movement element for the valve, which can move in the valve housing between a rest position and an active valve biasing position, and an element for permanently returning the movement element to its rest position; and   means for hydraulically actuating the holding means, which can be controlled by a control signal to actuate the holding means upon receipt of a valve open control signal by the actuating means, and to deactivate the holding means in the absence of said signal.       

     Such a device is used to secure a well for the production of oil or another fluid (notably gas, vapour or water), in particular when said well is eruptive and can be sealed rapidly in case of failure of the surface installation, said failure producing the disconnection of the open control signal. 
     A device of the above-mentioned type is known from U.S. Pat. No. 4,002,202, said device being lowered in a production casing of an oil well by means of a working wire line. Said device comprises a valve housing, a rod for holding the valve in the open position and electromagnetic coils for actuating the support rod. The coils are fixed to the outside of the casing at a determined point thereon on, and are connected electrically to the surface by electric cables. 
     When an electric control signal is received by the electromagnetic coils, the valve is held in the open position by the support rod, against a return spring. 
     In the absence of a control signal, the return spring is deployed to move the rod, which allows rapid sealing of the valve. 
     A safety device of the same type is also known, driven by a hydraulic control line extending outside the casing from the surface. 
     Such devices are not entirely satisfactory. The safety device must be positioned at a determined point of the well, opposite the actuating coils, and the coils must be connected to the surface by electric power supply lines, or must be positioned opposite the inlet of the hydraulic conduit. 
     SUMMARY OF THE INVENTION 
     An object of the invention is therefore to provide an autonomous safety device, comprising a safety valve that can be installed and anchored at any point of the well whatever the finished architecture thereof, and that can be controlled from the surface. 
     Accordingly, the invention relates to a device of the above-mentioned type, characterised in that the holding means and actuating means are connected to the housing in such a way that they can be moved simultaneously under the control of the working wire line. 
     The device according to the invention may comprise one or more of the following characteristics, taken in isolation or in a technically feasible combination:
         actuating means comprising a hydraulic cylinder and a hydraulic unit for controlling the cylinder;   the hydraulic unit projects at least in part in relation to the housing, outside the flow passage, the flow passage being clear between the connection means and the valve;   the hydraulic unit can be removed from the valve housing, said valve housing comprising means for receiving the unit;   the cylinder comprises a chamber for pressurising control fluid, said chamber receiving a portion of the movement element of the valve; and a tank for reserving and discharging control fluid,
 
and the hydraulic control unit comprises a pump for feeding the control fluid into the pressurising chamber, a pressurising conduit connecting the pressurising chamber to the discharge tank, a first discharge conduit connected to the pressurising conduit provided with a discharge valve that is open in the absence of the control signal and closed in the presence of said signal;
   the return element loads a piston for pressurising the tank;   the actuating means comprise a rapid discharge conduit, connected to the pressurising conduit, the rapid discharge conduit being provided with a sealing element that can be released when the discharge valve is open;   the maximum cross-section of the first discharge conduit and of the upstream portion of the pressurising conduit situated upstream of the releasable sealing element is less than the minimum cross-section of the rapid discharge conduit and of the downstream portion of the pressurising conduit situated downstream of the releasable sealing element;   the actuating means comprise a control fluid accumulator connected to the pressurising chamber;   the actuating means comprise a zero-leakage non-return valve, interposed between the pump and the pressurising chamber;   the hydraulic unit comprises means for controlling the cylinder, said control means comprising a receiver, a control unit suitable for driving the cylinder to actuate the holding means upon receipt of a valve open control signal by the receiver and to deactivate said holding means in the absence of said signal;   the control unit is suitable for driving the cylinder to actuate, at least temporarily, the holding means in the absence of a valve open signal, after reception of a silence signal by the receiver; and   the device comprises releasable means for anchoring the housing in the conduit, carried by the housing.       

     The invention also relates to a safety installation for a fluid production well comprising a fluid flow conduit, said installation comprising:
         a device as defined above; and   means for deploying said device in the conduit comprising a working wire line connected releasably to the connection means.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on reading the description that follows, given solely by way of an example and with reference to the accompanying drawings, in which: 
         FIG. 1A  is a cross-sectional view along a vertical mid-plane of an oil well equipped with a safety device according to the invention, during operation of the well; 
         FIG. 1B  is a similar view to  FIG. 1A , when the device is installed in the well; 
         FIG. 2  is a side view of the safety device illustrated in  FIG. 1A  and in  FIG. 1B ; 
         FIG. 3  is a cross-sectional view along a vertical mid-plane of a detail of the device in  FIG. 2 ; 
         FIG. 3A  is a view of a detail marked IIIA in  FIG. 3 ; 
         FIG. 4  is a lateral cross-sectional view along the plane IV-IV of  FIG. 3 ; 
         FIG. 5  is a diagrammatic view of the hydraulic actuating means of the device in  FIG. 2 ; and 
         FIG. 6  is a similar view to  FIG. 3  in which the valve of the safety device is sealed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Throughout the remaining text, the term “proximal” means relatively closer to the ground surface, whereas the term “distal” means relatively closer to the bottom of a well made in the ground. 
     The autonomous safety device  10  according to the invention, illustrated in  FIGS. 1 to 6 , is intended to be lowered into an oil well  12  using wire deployment means  14 . The device  10  is placed at a chosen point in the well  12 , for example situated at a depth of between 10 m and 1000 m, to replace a faulty safety valve, or to add an intermediate safety valve. 
     As illustrated in  FIGS. 1A and 1B , the well  12  comprises a first conduit  16  known as the “casing” made in the sub-soil  18  and a second conduit or pipe  20  known as the “production casing” secured substantially in the centre of the first conduit  16 . 
     The well  12  further comprises a wellhead  22  at the surface to seal selectively the first conduit  16  and the second conduit  20 . 
     The second conduit  20  is not as long as the first conduit  16 . It opens at a point  23  into the first conduit  16  situated in a distal portion of the well  12 . Annular packing elements  24  are arranged between the first conduit  16  and the second conduit  20  in the vicinity of the point  23 . 
     These elements  24  seal tightly the annular space  25  defined between the conduits  16  and  20 . 
     The second conduit  20  defines internally a plurality of circular engagement grooves or annular engagement recesses  26 A,  26 B, designated by the term “landing nipple”. Said recesses  26 A,  26 B are situated at points spaced longitudinally along the conduit  20 . 
     In a variant, the second conduit  20  is not provided with recesses  26 A,  26 B, and the device  10  is anchored directly against a smooth wall of the conduit  20 . 
     As illustrated in  FIG. 1B , for the installation of the device  10  in the well  12 , the deployment means  14  of the device  10  comprise a working wire line  30 , a surface hoist  32  enabling the line  30  to be deployed or retracted in the well  12 , and pulleys  34  for orienting the line  30  mounted on the wellhead  22 . 
     The line  30  is formed for example by a smooth single strand wire of the “piano wire” type, commonly referred to by the term “slickline”, with or without electrical insulation on its outer surface. The line  30  comprises, at its distal end, an installation gear  31  for the device  10 . 
     In a variant, the line  30  is a mechanically reinforced electric cable, commonly referred to by the term “electric line”, or a hollow spiral cable, commonly referred to by the term “coiled tubing”. 
     The hoist  32  and the pulleys  34  allow the working line  30  to be deployed successively in the second conduit  20 , then in the first conduit  16  via the wellhead  22 . 
     As illustrated in  FIG. 1A , when operating the well  12 , the deployment means  14  have been withdrawn and the well  12  comprises means  35  for emitting a signal for controlling the safety device  10 . In the example illustrated, the control signal is an electromagnetic signal and the means  35  are arranged at the surface. In a variant, said signal is an acoustic signal. 
     As illustrated in  FIG. 2 , the safety device  10  comprises a safety valve housing  40 , means  42  for holding the safety valve in an open position, and a hydraulic cylinder  44  for actuating the holding means  42 . The device  10  also comprises a hydraulic unit  46  fixed removably at a distal end of the housing  40 , the unit  46  comprising means  48  for controlling the cylinder  44 , and batteries  49  for supplying electrical power to the unit  46 . 
     As illustrated in  FIG. 3 , the valve housing  40  comprises a tubular body  50  with a longitudinal axis X-X′ delimiting internally a longitudinal through-flow passage  52  for circulating an oil fluid, means  54  for connecting to the installation gear  31 , mounted at a proximal end of the body  50 , and means  56  for anchoring the device  10  in the second conduit  20 . 
     The housing  40  further comprises, in the vicinity of its distal end, a valve  58  for sealing the passage  52 . 
     When moving from a proximal end, to the right in  FIG. 3 , to a distal end, to the left in  FIG. 3 , the body  50  comprises a proximal tubular portion  60 , a portion  62  for guiding and holding the valve, and a distal portion  64  for connecting to the hydraulic unit  46 . 
     As illustrated in  FIG. 3A , the mid-portion  62  defines a proximal sheath  66  mounted in the tubular portion  60  and delimiting an annular transverse surface  68  directed towards the body  60 . 
     The mid-portion  62  also delimits a distal annular shoulder  70  directed towards the distal portion  64  and a cylindrical guide surface  72  extending between the proximal surface  68  and the distal shoulder  70 . 
     The cylindrical surface  72  delimits, between the distal shoulder  70  and the proximal surface  68 , an annular recess which receives a proximal sealing gasket  73 . 
     By moving distally along the axis X-X′ in  FIG. 3 , the distal tubular portion  64  delimits a lateral valve retraction opening  74 , which opens into the passage  52 , an annular shoulder  76  oriented towards the distal end of the body  40 , and a lateral passage  78  (i.e., a receiving portion) for assembling the hydraulic unit opening into the flow passage  52 . The portion  64  has at its distal end a distal opening which opens into the flow passage  52 . 
     The connection means  54  comprise a head  80  for receiving the installation gear  31  delimiting an internal recess  82 . The head  80  is screwed to the proximal end of the tubular portion  60 . 
     The recess  82  opens distally into the passage  52  and proximally through a proximal opening  84 . A fluid may thus penetrate into the passage  52  of the housing  40  when the installation gear  31  is arranged at a distance from the housing  82 . 
     The anchoring means  56  comprise lateral locking mandrels or “dogs” referred to by the term “lock mandrel”. The dogs  86  project radially outside of the head  80  and have a form complementary to that of the engagement recesses  26 A,  26 B arranged in the second conduit  20 . 
     The anchoring means  56  also comprise compressible annular packing (not illustrated) intended to form a seal between the wall of the conduit  20  and the head  80 . 
     The sealing valve  58  comprises an annular seat  88  mounted integrally with the body  50  in the passage  52 , and a shutter  90  that can move between an open position of the passage  52  and a sealed position of the passage  52 . The valve  58  also comprises a spring  92  for returning the shutter  90  to its sealed position. 
     The valve seat  88  is fixed in the passage  52  and forms a mechanical connection between the mid-portion  62  and the distal tubular portion  64 . As illustrated in  FIG. 3A , a proximal annular surface  93  of the seat extends opposite the distal surface  70  of the mid-portion  62 . A distal conical annular surface  94  of the seat  88  is flush with the wall of the distal portion  64  in the region of the lateral reception opening  74 . 
     The shutter  90  can rotate about a horizontal axis perpendicular to the axis X-X′ situated in the vicinity of the distal surface  94  of the seat  88 . 
     In the open position of the shutter  90 , said shutter  90  extends substantially in the extension of the tubular portion  64  to seal the lateral opening  74  and free the passage  52 . 
     In the sealed position, illustrated in  FIG. 6 , the shutter  90  extends in a plane that is substantially perpendicular to the longitudinal axis X-X′ of the valve housing  40 . It rests on the distal conical annular surface  94  to seal the passage  52 . 
     The spring  92  permanently biases the shutter  90  towards its sealed position. 
     The means  42  for holding the valve in its open position comprise a cylindrical sleeve  98  mounted movably in translation along the axis X-X′ in the passage  52 , between a proximal rest position and a distal open position of the valve  58 . The means  42  further comprise, mounted on the sleeve  98 , a distal pressurisation piston  100 , a proximal end stop  102  for guiding the sleeve, and a spiral spring  104  for returning the sleeve to its proximal position. 
     The sleeve  98  extends longitudinally in the body  40  opposite the proximal tubular portion  60 , the mid-portion  62  and, in its proximal position, the distal portion  64 . As illustrated in  FIG. 4 , it comprises an outer surface  106  of transverse cross-section substantially complementary to the guide surface  72  of the mid-portion  62  in such a way that the mid-portion  62  guides the sleeve  98  when it moves between its proximal position and its distal position. 
     As illustrated in  FIG. 3A , the surface  106  delimits with the seat  88 , an annular space  107 . It comprises an annular rib  107 B which delimits a distal recess oriented towards the seat  88 . The recess receives a sealing gasket  108  which distally seals the annular space  107 . The space  107  is sealed proximally by the proximal gasket  73 . 
     The distal annular piston  100  is mounted slidingly on the sleeve  98  between the outer surface  106  and the proximal tubular portion  60 . It delimits a distal annular surface  110  which extends opposite the proximal surface  68 . It further delimits a proximal annular surface  112  on which a distal end of the spring  104  rests. 
     The proximal annular end stop  102  is mounted integrally with the proximal end of the sleeve  98 . It extends between the sleeve  98  and the tubular portion  60 . The end stop  102  slides in the tubular portion  60  and delimits a distal annular surface  114  on which the proximal end of the spring  104  rests. The end stop  102  comprises a wiper gasket  115  arranged resting on the tubular portion  60 . 
     In the proximal position of the sleeve  98 , illustrated in  FIG. 6 , the gasket  108  extends in the vicinity of the proximal surface  93  of the seat  88 . In addition, the end stop  102  is situated in the vicinity of the receiving head  80 . The distance separating the piston  100  and the end stop  102  is then at the maximum. The spring  104  is pre-stressed in such a way that it exerts a minimal return force on the piston  100  and on the end stop  102 . In this position, the annular rib  107 B of the sleeve  98  rests against the shoulder  70 . 
     In this position, the distal edge of the sleeve  98  is arranged opposite the seat  88 , proximally in relation to the shutter  90 . 
     In the distal position of the sleeve  98 , illustrated in  FIG. 3 , the distance between the piston  100  and the end stop  102  is minimal and the compression of the spring  104  is at the maximum in such a way that it exerts maximum return force on the piston  100  and on the end stop  102 . 
     In this position, a distal portion of the sleeve  98  extends opposite the lateral opening  74 . The distal edge of the sleeve  98  rests on the end stop shoulder  76  of the distal portion  64 . The sleeve  98  covers the shutter  90 . In addition, the gasket  108  is at a distance distally from the proximal surface  93  of the valve seat  88 . 
     As illustrated in  FIGS. 3 to 6 , the hydraulic cylinder  44  comprises a pressurising chamber  120  and a reserve and discharge tank  122  which are connected hydraulically to the unit  46  by the respective connection conduits  124 A,  124 B. The tank  122  and the chamber  120  contain a hydraulic fluid for controlling the cylinder  44 . 
     The chamber  120  comprises an intermediate space  121  of constant volume and the annular space  107  of variable volume. 
     The intermediate space  121  extends between the body  50  and the sleeve  98 . It is delimited proximally by the distal shoulder  70  of the mid-portion  62 , by the proximal surface  93  of the seat  88 , and by the outer surface  106  of the sleeve. The space  121  is connected to the annular space  107 . 
     In the proximal position of the sleeve  98 , the distance between the proximal gasket  73  and the distal gasket  108  is minimal and the volume of the chamber  120  is minimal. In the distal position of the sleeve  98 , this distance is at the maximum and the volume of the chamber  120  is at the maximum. 
     The tank  122  extends between the body  50  and the sleeve  98  proximally in relation to the chamber  120 . It is delimited by the proximal tubular portion  60 , by the proximal surface  68  of the mid-portion  62 , by the surface  106 , and by the distal surface  110  of the piston  100 . 
     The volume of the tank  122  depends on the longitudinal position of the piston  100  along the sleeve  98  and along the body  50 . 
     As illustrated in  FIG. 2 , the conduits  124 A,  124 B extend outside the body  50  along said body. They open out distally in the region of the lateral passage  78  for assembling the unit  46 . In addition, the distal connection conduit  124 A opens proximally in the intermediate space  121  of the chamber  120  via the mid-portion  62 . 
     The proximal connection conduit  124 B opens proximally in the tank  122  through the mid-portion  62 . 
     As illustrated in  FIG. 5 , the unit  46  comprises a tubular housing  125  receiving a hydraulic electric pump  126  and a conduit  128  for selectively pressurising the chamber  120 , connecting the electric pump  126  to the distal connection conduit  124 A. 
     The tubular housing  125  projects distally outside the body  50  along the axis X-X′. The proximal end thereof is introduced into the distal opening of the distal portion  64  and received in the assembly passage  78  in order to be fixed to the distal portion  64  of the body  50 . 
     The electric pump  126  connects the proximal connection conduit  124 B to an inlet of the conduit  128  so as to connect the tank  122  to the conduit  128 . 
     The pressurising conduit  128  comprises, from upstream to downstream, from the electric pump  126  to the chamber  120 , a zero-leak non-return valve  130  and an upstream portion  128 A on which are fastened a safety conduit  132  and a first discharge conduit  134  received in the housing  125 . The conduit  128  also comprises a downstream portion  128 B on which are connected a rapid discharge conduit  136  and an accumulator  138 , received in the tubular housing  125 . 
     The safety conduit  132  is connected on the upstream portion of the pressurising conduit  128  at the outlet of the valve  130 . It opens at the inlet of the proximal connection conduit  124 B. The safety conduit  132  is provided, from upstream to downstream, with a pressure switch  140  and a pressure relief valve  142 . 
     The first discharge conduit  134  is fastened on the upstream portion  128 A of the conduit  128  downstream of the conduit  132 . The conduit  134  is provided with a controlled safety solenoid valve  144 , which is normally open, and which opens into the proximal connection conduit  124 B. 
     The solenoid valve  144  is connected electrically to the control means  48 . 
     The rapid discharge conduit  136  is connected on the pressurising conduit  128  by means of a bypass valve  146 , delimiting the upstream portion  128 A and the downstream portion  128 B on the conduit  128 . 
     The valve  146  comprises a primary inlet  148  and a primary outlet  150  opening respectively into the upstream portion  128 A of the pressurising conduit  128  towards the electric pump  126 , and into the downstream portion  128 B of the conduit  128  towards the chamber  120 . The valve  146  also comprises a secondary outlet  152  connected to the rapid discharge conduit  136 . 
     When the pressure that prevails in the region of the primary inlet  148  is greater than or substantially equal to the pressure that prevails in the region of the primary outlet  150 , the secondary outlet  152  is sealed in such a way that the primary inlet  148  is connected hydraulically to the primary outlet  150 . 
     On the other hand, when the pressure that prevails in the region of the primary inlet  148  is less than the pressure that prevails in the region of the primary outlet  150 , the primary inlet  148  is sealed and the primary outlet  150  is connected hydraulically to the secondary outlet  152  and thus to the tank  122  by means of the conduit  124 B. 
     The minimum flow cross-section through the downstream portion  128 B, the secondary outlet  152  and through the rapid discharge conduit  136  is very much greater than the maximum flow cross-section through the upstream portion  128 A, the solenoid valve  144  and through the first discharge conduit  134 , for example at least twice as great. 
     As illustrated in  FIG. 2 , the control means  48  are received in the tubular housing  125 . They comprise a receiver  154  and a unit  156  for controlling the cylinder  44 . The receiver  154  is able to receive a valve open control signal emitted from the surface and to transmit an order to the control unit  156  to hold the shutter  90  in its open position, for as long as the control signal is received by the receiver  154 . 
     The receiver  154  is also able to receive a temporary silence signal for the well  12  and to transmit an order to the control unit  156 , to hold the shutter  90  temporarily in its open position even in the absence of a valve open signal. 
     The control unit  156  is connected electrically to the solenoid valve  144 , to the electric pump  126 , and to the pressure switch  140  for controlling the cylinder  44 . 
     The operation of the autonomous safety device  10  according to the invention to replace a defective valve in the well  12  will now be described. 
     Initially, a valve housing  40  is selected of suitable dimensions for insertion into the second conduit  20 . 
     A hydraulic unit  46  common to valve housings  40  of different diameters is fixed in the lateral passage  78  and is connected hydraulically to the distal ends of the conduits  124 A and  124 B. 
     The autonomous device  10  according to the invention is thus formed. 
     Then, with reference to  FIG. 1B , the deployment means  14  are arranged on the wellhead  22 . The installation gear  31  is mounted on the receiving head  80  at the proximal end of the valve housing  40 . 
     The valve housing  40 , the holding means  42 , the hydraulic actuating cylinder  44  and the hydraulic unit  46  connected to the housing  40 , forming the device  10 , are then introduced into the second conduit  20  and are thus lowered simultaneously under the control of the working wire line  30 . 
     When the device  10  reaches the desired position in the second conduit  20 , for example when the anchoring means  56  are arranged opposite an engagement recess  26 B, the working wire line  30  is halted. 
     The anchoring means  56  are then actuated by the operator to lock the housing  40  in position in the conduit  20 . 
     Accordingly, the engagement dogs  86  are inserted in the recesses  26 B and a sealed connection is formed between the housing  40  and the second conduit  20 . Then, the installation gear  31  is released from the connection means  54 , to free the opening  84  at the inlet of the passage  52 . The deployment means  14  are then withdrawn ( FIG. 1A ). 
     The shutter  90  is maintained in the position in which it seals the passage  52 , the sleeve  98  being in its proximal position. 
     The safety device  10  then tightly seals the second conduit  20 . 
     When the well operator wishes to open the second conduit  20 , he actuates the emission means  35  at the surface to emit a valve open control signal. 
     When the receiver  154  receives the valve open control signal, it transmits an actuation order to the control unit  156 . The unit  156  then actuates the electric pump  126  and the solenoid valve  144  to introduce a portion of the liquid contained in the tank  122  into the chamber  120 . The volume of the tank  122  reduces, which causes the distal movement of the piston  100 . 
     In this regard, the priming of the electric pump  126  is assisted by the presence of the pre-stressed return spring  104  which rests on the piston  100  when the sleeve  98  is in its proximal position, to compress slightly the fluid contained in the tank  122 . 
     Once the electric pump  126  is primed and the solenoid valve  144  is closed, the pressure in the chamber  120  increases and is applied in the annular space  107 , between the proximal gasket  73  and the distal gasket  108 , which causes the sleeve  98  to move towards its distal position, against the return spring  104  which is compressed between the piston  100  and the end stop  102 . 
     During this movement, the distal edge of the sleeve  98  pushes the shutter  90 , and moves it from the sealed position to its open position, against the biasing spring  92 . 
     When the sleeve  98  has reached the position in which it comes to a stop against the end-stop shoulder  76 , the shutter  90  is secured against the distal portion  64  and seals the lateral opening  74 , as illustrated in  FIG. 3 . 
     Moreover, the pressure in the chamber  120  increases to a threshold value which is detected by the pressure switch  140  and transmitted to the unit  156 . When the control unit  156  determines that the pressure in the chamber  120  is greater than the threshold value, it disconnects the electric pump  126 . 
     The solenoid valve  144  is kept sealed for as long as the receiver  154  receives a valve open control signal. 
     If the pressure in the chamber  120  falls below a re-start value for the electric pump  126 , the control unit  156  actuates the electric pump  126  once again to raise the pressure in the chamber  120  to the threshold value. 
     However, the presence of a zero-leak non-return valve  130  reduces the operating time of the electric pump  126  and increases the autonomy of the device  10 . 
     The accumulator  138  allows pressure variations in the chamber  120 , due in particular to temperature variations in the housing  40 , to be compensated. 
     In the event of an incident at the surface, the valve open control signal emitted by the emission means  35  is disconnected. 
     Once the receiver  154  no longer receives said signal, the control unit  156  determines whether a temporary silence signal has been emitted before disconnecting the valve open control signal. In the absence of such a silence signal, the control unit  156  deactivates the solenoid valve  144  and then resumes its normally open position. 
     With reference to  FIG. 5 , the fluid contained in the upstream portion  128 A of the conduit  128 , upstream of the primary inlet  148  of the rapid discharge valve  146  is then reintroduced into the tank  122  via the first discharge conduit  134  and the proximal connection conduit  124 B. 
     The pressure that prevails in the region of the primary inlet  148  thus reduces to a value below that which prevails at the primary outlet  150 . 
     As a follow-up, the secondary outlet  152  of the rapid discharge valve  146  opens, and the primary inlet  148  closes. The fluid contained in the pressurising chamber  120  is therefore discharged very rapidly into the tank  122  via the downstream portion  128 B of the conduit  128 , the primary outlet  150 , the secondary outlet  152 , the rapid discharge conduit  136  and the proximal connection conduit  124 B. 
     As the pressure in the chamber  120  falls rapidly, the return spring  104  moves the sleeve  98  towards its proximal position very rapidly. It will be noted that only one spring  104  is necessary to pressurise the tank  122  when the pump  104  is deactivated, and to allow the sleeve  98  to return towards its proximal position in the event of an incident at the surface. The length of the housing  40  is thus reduced. In addition, since the volume of the tank  122  increases after the rapid discharge valve  146  opens, the difference in length of the spring  104  resting proximally on the piston  100  between the proximal position and the distal position of the sleeve  98  is less than the travel of the sleeve  98  between said positions. 
     The biasing spring  92  then returns the shutter  90  to its sealed position across the passage  52 , as illustrated in  FIG. 6 . The well  12  is thus made safe. 
     However, if the operator has issued a previously programmed silence signal, before the disconnection of the valve open signal, the control unit  156  maintains the solenoid valve  144  sealed and the chamber  120  under pressure for a determined period of time, despite the absence of a control signal. The shutter  90  therefore remains in the open position. 
     This operating method maintains production of the well  12 , even if an intervention requiring the absence of any control signal must be carried out on another nearby well. 
     If a control signal is once more emitted, the control unit  156  is reinitialised, such that the disconnection of the control signal causes the shutter  90  to close once more. 
     With the aid of the invention that has just been described, it is possible to have an autonomous safety device  10  that is easily installed and anchored in a well  12  by a working wire line  30 . Said device comprises a valve housing  40 , means  42  for holding the valve in an open position, and hydraulic actuating means  44 ,  46  holding means  42 , connected to the housing  40 , for the simultaneous movement thereof in the well  12 . 
     Such a device  10  can be used at any point in the well  12 , without the need to introduce hydraulic or electric control lines, either to replace an existing defective valve in the well  12 , or to install a new valve in the well  12  without having to raise the production casing. 
     The arrangement of the hydraulic unit  46  in the valve housing frees the fluid flow passage  52  inside the valve housing and opens a passage  52  of sufficient diameter for the production of hydrocarbons or the passage of tools as far as the shutter  90 . 
     The structure of the hydraulic unit  46  is suitable for connection thereof to valve housings  40  of different diameters. In addition, the structure thereof consumes little energy, for autonomous operation of the device  10  over a long period of between six months and two years without the need to raise the device  10  to the surface.

Summary:
The invention relates to a safety device for an oil well and to the associated safety installation. The inventive device comprises a valve housing ( 40 ) which defines a fluid flow passage ( 52 ). The aforementioned housing ( 40 ) comprises a valve ( 48 ) which is used to seal the passage and which can move between an open position and a closed position and means for permanently biasing the valve towards the closed position thereof. The housing ( 40 ) also comprises releasable means ( 54 ) for connecting same to a working line with tubing that is intended to move the housing ( 40 ) in the conduit. In addition, the device comprises retractable means ( 42 ) for supporting the valve ( 58 ) in the open position and hydraulic means ( 44, 46 ) for actuating the support means ( 42 ) in order to activate same upon reception of a valve open control signal. The aforementioned support means ( 42 ) and actuation means ( 44, 46 ) are solidly connected to the housing ( 40 ) such that they can be moved simultaneously under the control of the line.