Abstract:
A method, system and apparatus is provided for a partially retrievable safety valve to control a well. The method includes securing a normally closed valve in the well. The valve may be a self-equalizing flapper valve. Following this, an actuator system operable to open the valve is run into the well. The actuator system is removable from the well while the valve remains closed and secured in the well. A submersible pump and motor may be secured to the actuator system before the actuator system is run into the well. The submersible pump and motor are also removable from the well while the valve remains closed and secured in the well. Therefore the actuator system, submersible pump and motor can be replaced or redressed, while the valve remains closed, keeping the well under control at all times.

Description:
BACKGROUND OF THE INVENTION 
     1. Area of the Invention 
     The present invention relates to deep-set safety valves used in subterranean well production. More specifically, the present invention relates to deep-set safety valves used in connection with submersible pumps for controlling a well. 
     2. Description of the Related Art 
     In subsurface wells, such as oil wells, an electrical submersible pump with a motor (an “ESP”) is often used to provide an efficient form of artificial lift to assist with lifting the production fluid to the surface. ESPs decrease the pressure at the bottom of the well, allowing for more production fluid to be produced to the surface than would otherwise be produced if only the natural pressures within the well were utilized. 
     There may be times when an operator of a well would want or need to retrieve an ESP from within the well. In order to do so, the operator must have a means for closing off the well so that the production fluid does not still flow to the surface, while the ESP is retrieved. Killing the well may be accomplished by pumping heavy fluids into the well to overbalance the subterranean pressure. But that method can cause formation damage so it is therefore more desirable to control the well than to kill it. Maintaining control of a well with an umbilical-deployed ESP would normally require the use of a deep set subsurface safety valve (SSSV) or other shut-off valve that would be set below the ESP to shut-in the well first so that the ESP could be retrieved. Normally deep-set safety valves are controlled via a single ¼″ OD hydraulic umbilical to the surface, but at deep depths, the hydraulic pressures are very high and even when the hydraulic system fails, the magnitude of residual hydraulic pressure can be significant. In such a system, the springs that return the valve to the closed position must be capable of overcoming the residual hydrostatic pressure in order to shut-in the well in an emergency situation. Therefore, the deeper the well, the higher the pressure, and the stronger the spring system must be to lift the hydraulic fluid column to close the valve and shut-in the well. There will also come a point when the hydraulic pressures would be so great that a spring system would become very difficult to implement and eventually become unfeasible. Springs can generally be constructed as either plain mechanical or mechanical plus gas-charge assisted. 
     One way to solve this deep setting problem is to use an electrically activated subsurface safety valve (E-SSSV). E-SSSVs are usually powered via a ¼″ tubing encased conductor (TEC) which is a hydraulic umbilical with one or more electric wires inside, Electrical wet connectors can be a source of failure in a well system and can be cumbersome to work with so it would be advantageous for a system to operate without the need for a wet connector if the components that activate the E-SSSV need to be retrieved, for example, for maintenance or repair. 
     Also, a typical failure mode of most flapper-type safety valves is the flow tube becomes stuck to the valve mandrel, sticking the valve open. This is because typical deep-set safety valve systems do not have excessive force available to push the flow tube upward and free it from wellbore contaminants such as asphaltines, scale, and packed fines. 
     Prior art safety valves are configured in only two methods; either wireline retrievable or tubing retrievable. Both the prior art hydraulic and electrical safety valves are provided with a dedicated method of control, that is, the connection between the surface and the valve is not shared with any other downhole component. This creates additional time and cost associated with requiring multiple connection components and may also raise design issues in finding space to route multiple control lines downhole. 
     Some prior art flapper safety valves also require the pressure to be equalized on either side of the valve before it can be opened. This requires passageways that connect the space above and below the flapper. This in turn creates additional components, including a valve means for opening and closing this passageway and a means for activating such valve. It would be advantageous to avoid the need for such equalization. 
     In addition, with the prior art methods, normally the well must be killed and a full rig used to pull the tubing string when an ESP replacement is required. It would be advantageous to neither to kill the well, nor require a rig to replace an ESP completion. 
     Therefore a problem exists of how to provide fail-safe well control for a live well intervention on an assisted ESP artificial lift, which was umbilical deployed. 
     SUMMARY OF THE INVENTION 
     Applicants appreciate the importance of providing a reliable deep-set safety valve and have provided methods and apparatuses that can be instrumental in providing such a valve while also providing for a method and apparatus that allows the efficient retrieval, removal and replacement of an actuator system, and an ESP, consisting of a submersible pump and motor, used in connection with such valve. 
     The present concept provides for a very reliable means for a safety valve, allowing the actuator system to be removed and redressed periodically with the ESP during routine rigless replacement of the actuator system and ESP. The system can be installed and removed without a rig. 
     The current application provides a solution where there is no need or opportunity to open the valve if the ESP or actuator system is not functional. Instead, the ESP, if any, and actuator system would simply be removed and redressed. The ESP and actuator system can be replaced or redressed, while the valve remains closed, keeping the well under control at all times. The system of the current application provides a safety valve that can be controlled with the same communication conduit that controls the ESP. 
     After a subterranean well is cased, a packer may be run and set in the well. The packer may comprise a polished bore receptacle and the valve of one of the embodiments of this application. Next, an upper tubing string is run into the well and secured to the packer via a polished bore receptacle with tubing seals. Alternatively, the embodiments of the current application can be used in an uncased subterranean well. 
     In one embodiment of the current application, a normally closed valve is secured in the well. The valve may be a self-equalizing flapper valve or a member of the generic globe valve family. A globe valve may be, for example, a butterfly valve or a ball valve. Following this, an actuator system operable to open the valve is run into the well. The actuator system is removable from the well while the valve remains closed and secured in the well. An ESP may be secured to the actuator system before the actuator system is run into the well. The ESP is also removable from the well while the valve remains closed and secured in the well. 
     The actuator system may include a communication conduit. The communication conduit may be, for example, a three-phase electrical umbilical, a single electrical umbilical, or hydraulic line. If the communication conduit comprises a three phase electrical umbilical, the communication conduit can be used for sending a signal to activate the ESP. 
     In one embodiment, the actuator system may include a normally disengaged clutch, a normally unlocked locking system and a communication conduit. The communication conduit may used to engage the locking system and secure the actuator system in the well. A loss of signal in the communication conduit will caused the valve, the locking system, and clutch to return to their respective normal positions. 
     In an alternative embodiment, the actuator system further comprises a return spring and a flow tube. A signal sent through the communication conduit will cause the flow tube to move to a lower position to come in contact with and open the valve. Upon a loss of a signal in the communication conduit, the return spring will return the flow tube to an upper position and the valve will close. 
     Either upon the loss of a signal in the communication conduit or by the operator sending a signal by way of the communication conduit for the locking system, valve and clutch to return to their respective normal positions, the actuator system and the ESP can be retrieved from the well. The actuator system and ESP can then be maintained, repaired, or replaced and returned to the well as discussed above. The actuator system and the ESP can be retrieved from the well by spooling the communication conduit out of the well with a wireline truck. An over-pull on the communication conduit may be required to release the actuator system and the ESP from the well. Similarly, the running of the actuator system and the ESP into the well can also be performed with a wireline truck. No rig is required for either operation. 
     In another embodiment, the partially retrievable safety valve system for controlling a subterranean well includes a normally closed valve and an actuator system operable to open the valve. The actuator system is removable from the well while the valve remains closed and secured in the well. An ESP may be secured to the actuator system. The ESP is also removable from the well while the valve remains closed and secured in the well. 
     The actuator system may comprise a communication conduit, an actuator motor, a clutch, and a locking system. The valve may be either a flapper valve or a valve from the generic family of globe valves. The communication conduit may comprise either an electrical umbilical or a hydraulic line. The communication conduit communicates with the ESP motor, the actuator motor, the clutch, and the locking system. The actuator system is removable from the well by the communication conduit. 
     In an additional embodiment, the actuator system further comprises an actuator and a flow tube. The communication conduit is operable to transfer a signal to the actuator motor to move the actuator to a lower position. The actuator, when moving to its lower position, causes the flow tube to move to a lower position and the flow tube, when in its lower position, maintains the valve in an open position. 
     In an alternative embodiment, the actuator system further comprises a return spring operable to return the flow tube to an upper position upon the loss of communication in the communication conduit. 
     In another embodiment, the partially retrievable safety valve for controlling a subterranean well comprises a packer comprising a polished bore receptacle and a normally closed valve, an actuator system operable to open the valve, and a normally unlocked locking system securing the actuator system in the well. The actuator system is removable from the well while the valve remains closed and secured in the well. 
     The actuator system may comprise an actuator motor, a normally disengaged clutch, a flow tube, and a communication conduit. The communication conduit is capable of communication with the actuator motor, locking system, and clutch. The clutch and valve are in their respective normal positions when a signal in the communication conduit is lost. 
     In an additional embodiment, the actuator system further comprises a flow tube. The flow tube has an upper position and lower position such that when the flow tube is in the upper position, the valve is closed and when the flow tube is in the lower position, the valve is open. The actuator system may further comprise a return spring operable to return the flow tube to an upper position when a signal in the communication conduit is lost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the invention, as well as others which will become apparent are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only an embodiment of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a sectional view of an embodiment of the present system and method. 
         FIG. 2  is another sectional view of an embodiment of the present system and method. 
         FIG. 3  is another sectional view of an embodiment of the present system and method. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the Present System and Method Include 
     As seen in  FIG. 1 , the system may be employed in a cased well  10  with casing  12 . Components installed in such a well  10  may include a packer  14  with integral valve  16 . Valve  16  is shown as a flapper valve but may alternatively be any valve in the generic globe valve family. A globe valve may be, for example, a butterfly valve, a gate valve or a ball valve. Packer  14  has a polished bore receptacle  18  at its upper end. A tubing string  20  is connected to the polished bore receptacle  18 . This connection may be made as the tubing string  20 , which has a lower outer diameter slightly smaller than the inner diameter of the polished bore receptacle  18 , comes into sliding engagement with the polished bore receptacle  18  as the tubing string  20  is lowered into the well  10 . The bottom of tubing string  20  has a reduced diameter compared to the upper portion of the tubing string  20 , to allow for this sliding engagement with the polished bore receptacle  18 . Seals  22  create a seal between the base of the outside diameter of the base of the tubing string  20  and the inside diameter of the polished bore receptacle  18 . 
     Turning to  FIG. 2 , the ESP assembly is shown to include, an ESP, which comprises a submersible pump and motor  26 , and an actuator system. Seals  30  create a seal between the ESP assembly and the tubing string  20 . The actuator system includes a communication conduit  24 , a safety valve actuator motor  34 , clutch and locking system  36 , actuator  32 , return spring  38 , and flow tube  40 . The locking system may comprise an anchor, as it is referred to herein, but it may also be an alternative locking means known in the art. Actuator  32  may be a ball screw actuator or alternative appropriate actuator known in the art. The return spring  38  may be a power spring. The ESP assembly as show in  FIG. 2  is in the closed position. Valve  16  is closed so that the production fluid in the lower portion of well  10  cannot enter the inlet  42  (shown in  FIG. 3 ) in the bottom of the flow tube of the ESP assembly. The communication conduit  24  is communicatively connected to each of the submersible pump and motor  26 , the actuator motor  34 , and the clutch and anchor  36 , and the communication conduit  24  can transfer a signal to each of these components. Therefore this single source can effectively operate the ESP  26 , the actuator system, and the valve  16 . 
     The ESP assembly is shown in  FIG. 3  in the open position. Actuator  32  is holding the flow tube  40  in a lower position, forcing valve  16  open and putting return spring  38  in a stressed mode, with stored potential energy. With valve  16  in the open position, production fluid enters the inlet  42 . The production fluid is artificially lifted by the submersible pump and motor  26  and leaves the ESP assembly at exit  44 . If a signal to the ESP assembly is lost, the clutch will disengage, the anchor will unlock, the actuator  32  will no longer hold the flow tube  40  in the lower position, and the return spring  38  will force the flow tube  40  to an upper position, causing the valve  16  to close and the ESP system to return to the embodiment shown in  FIG. 2 . 
     In operation, a well  10  is drilled and lined with casing  12  by traditional means. After the well  10  is lined with casing  12 , the packer  14  with the valve  16  is run into the well  10  and secured to the casing  12  by traditional means. Next, the tubing string  20  is run into the well  10  and stabbed into the polished bore receptacle  18  in the packer  14 . When the tubing string  20  is fully engaged with the polished bore receptacle  18 , seals  22  create a fluid tight seal between the outer diameter of the tubing string  20  and the inner diameter of the polished bore receptacle  18 . After the tubing string  20  has been fully run into the well  10 , a rig is no longer required to perform any other step in this method. Contrary to the requirements of prior art, where pumps and valves are run into and out of the well on tubing strings, for the embodiments of the present application, the rig may be released, if desired, and the rig will not be required in order to remove the ESP assembly, including the ESP and actuator components, for maintenance or repair. 
     The next step of the current method is to lower the ESP assembly into the well  10 . The ESP assembly may be lowered into the well  10  on a communication conduit  24  using a wireline truck. The ESP assembly lands in the seal bore  28 , adjacent to the seals  30  as seen in  FIG. 2 . The anchor is then activated to lock the ESP assembly into the seal bore  28 . Seals  30  create a fluid tight seal between the ESP assembly and the tubing string  20 . 
     Next, the clutch and the actuator motor  34  are activated and the actuator  32  is operated to move the flow tube  40  down to its lower position. The actuator motor  34  will allow for control of the actuator  32 , enabling the operator to move the actuator  32  to and from its upper position and its lower position. The clutch is a normally unengaged device and a signal must be maintained in the communication conduit for the clutch to remain engaged. When the actuator  32  is in its lower position, it applies force to the return spring  38 , storing potential energy in the return spring  38 . When the actuator  32  is in its lower position, it forces the flow tube  40  downward and the flow tube  40  comes into contact with the valve  16 , causing the valve  16  to open and to remain open for so long as the flow tube  40  is in its lower position. If a signal in the communication conduit is lost, the return spring  38  has sufficient force and stored energy to reposition the flow tube  40  to its upper position causing the valve  16  to close. 
     After the valve  16  has been opened, production fluids will enter through the inlet  42  and exit through the exit  44 . If there is sufficient natural pressure, the production fluids will continue traveling upwards through the tubing string  20  to the surface. After the valve  16  has been opened the submersible pump and motor  26  may be started and will provide artificial lift to the production fluids to further force the production fluid up the tubing string  20  to the surface. The submersible pump and motor  26  will only continue to run and supply artificial lift to the production fluid if the signal in the communication conduit is maintained. Signals to the ESP assembly, including the clutch and anchor  36 , the actuator motor  34 , and the submersible pump and motor  26  are all provided by communication conduit  24 . 
     In the case of a loss of a signal the communication conduit, the submersible pump and motor  26  stop, the anchor unlocks, and the clutch disengages. Although the anchor unlocks, it remains engaged. A slight over-pull is required for the anchor to become unengaged. With the clutch disengaged, the return spring  38  strokes flow tube  40  to its upper position, allowing valve  16  to close. This method thus provides a fail-safe closed device. 
     If the operator desires to close the valve  16  purposefully, a command can be sent by way of the communication conduit  24  to the actuator motor  34 , causing the actuator  32  to be stroked to its upper position, which in turn causes the flow tube  40  to move to its upper position, and close the valve  16 . Upon reestablishment of a signal to the ESP assembly via the communication conduit  24 , the clutch and anchor  36  is reengaged, the actuator motor  34  causes the actuator  32  to move to its lower position, forcing the flow tube  40  downward, while also applying force to the return spring  38 . The flow tube  40  comes into contact with the valve  16 , causing the valve  16  to open and to remain open for so long as the flow tube  40  remains in its lower position. 
     As discussed above, a loss of a signal in the communication conduit  24  will unlock the anchor. Alternatively, the operator may send a signal via the communication conduit  24  to unlock the anchor. In either case, if the operator wishes to then remove the ESP assembly, a slight over-pull on the communication conduit  24  will release the ESP assembly from the seal bore  28 , allowing the ESP assembly to be spooled out of the well  10  via the communication conduit  24 . If over-pull on the communication conduit  24  is unsuccessful to remove the ESP assembly, then the communication conduit  24  will be further pulled and a weak point at the top of the ESP assembly, called a rope socket, will release the communication conduit  24 , permitting it to be retrieved. Next a rig will be brought on and a workover string run with an overshot to latch onto the ESP rope socket and retrieve it from the well. When the ESP assembly is removed, the valve  16  remains closed, keeping well  10  under control. If the operator wishes to return the ESP assembly to the well  10 , the same procedure used to set the ESP assembly in the well  10  initially can be repeated. 
     The foregoing has broadly outlined certain objectives, features, and technical advantages of the present invention and a detailed description of the invention so that embodiments of the invention may be better understood in light of features and advantages of the invention as described herein, which form the subject of certain claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages is better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that such description and figures are provided for the purpose of illustration and description only and are not intended as a definition of the limits of the present invention.