Safety valve with electrical actuator and tubing pressure balancing

A well tool for use with a subterranean well can include a flow passage extending longitudinally through the well tool, an internal chamber containing a dielectric fluid, and a flow path which alternates direction, and which provides pressure communication between the internal chamber and the flow passage. A method of controlling operation of a well tool can include actuating an actuator positioned in an internal chamber of the well tool, a dielectric fluid being disposed in the chamber, and the chamber being pressure balanced with a flow passage extending longitudinally through the well tool, and varying the actuating, based on measurements made by at least one sensor of the well tool.

BACKGROUND

This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in one example described below, more particularly provides a safety valve with an electrical actuator and tubing pressure balancing.

Actuators are used in various types of well tools. Unfortunately, fluids in wells can damage or impair operation of some well tool actuators. Therefore, it will be appreciated that improvements are continually needed in the arts of isolating well tool actuators from well fluids, and actuating well tools.

SUMMARY

In this disclosure, systems and methods are provided which bring improvements to the arts of isolating well tool actuators from well fluids, and actuating well tools. One example is described below in which an actuator is exposed to a dielectric fluid isolated from an interior flow passage. Another example is described below in which various sensors can be used to control actuation of the well tool.

In one aspect, this disclosure provides to the art a well tool for use with a subterranean well. In one example, the well tool can include a flow passage extending longitudinally through the well tool, an internal chamber containing a dielectric fluid, and a flow path which alternates direction. The flow path provides pressure communication between the internal chamber and the flow passage.

In another aspect, a method of controlling operation of a well tool can include actuating an actuator positioned in an internal chamber of the well tool, a dielectric fluid being disposed in the chamber, and the chamber being pressure balanced with a flow passage extending longitudinally through the well tool; and varying the actuating, based on measurements made by at least one sensor of the well tool.

In yet another aspect, a safety valve for use in a subterranean well is described below. In one example, the safety valve can include a flow passage extending longitudinally through the safety valve, an internal chamber containing a dielectric fluid, a flow path which alternates direction, and which provides pressure communication between the internal chamber and the flow passage, an actuator exposed to the dielectric fluid, an operating member, and a closure member having open and closed positions, in which the closure member respectively permits and prevents flow through the flow passage. The actuator displaces the operating member, which causes displacement of the closure member between its open and closed positions.

These and other features, advantages and benefits will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the disclosure hereinbelow and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers.

DETAILED DESCRIPTION

Representatively illustrated inFIG. 1is a system10and associated method which can embody principles of this disclosure. However, the system10and method comprise only one example of how the principles of this disclosure can be applied in practice, and so it should be clearly understood that those principles are not limited to any of the specific details of the system10and method described herein or depicted in the drawings.

In theFIG. 1example, a tubular string12is installed in a wellbore14lined with casing18and cement16. Well fluid20(in this case, produced from an earth formation22penetrated by the wellbore14) enters the tubular string12via a flow control device24(such as, a sliding sleeve valve, a variable choke, etc.). A packer26seals off an annulus28formed radially between the tubular string12and the wellbore14.

A well tool30selectively permits and prevents flow of the fluid20through a longitudinal flow passage32formed through the well tool and the substantial remainder of the tubular string12. In this example, the well tool30comprises a safety valve. However, in other examples, the well tool30could comprise a flow control device (such as the flow control device24) or another type of well tool (such as the packer26, a chemical injection tool, a separator, etc.).

The well tool30depicted inFIG. 1includes a closure member34, an electronic circuit36and an actuator38. The actuator38is used to displace the closure member34to and between open and closed positions in which flow of the fluid20is respectively permitted and prevented.

The closure member34in one example described below comprises a flapper which pivots relative to the flow passage32between the open and closed positions. In other examples, the closure member34could instead be a ball, gate, sleeve, or other type of closure member. Multiple closure members or multi-piece closure members could be used, if desired.

The electronic circuit36in the example described below comprises a hybridized circuit, in which semiconductor dies are mounted to a circuit board with little or no packaging surrounding the dies. This significantly reduces a volume requirement of the electronic circuit36, allowing a wall thickness of the well tool30to be reduced. However, other types of electronic circuits may be used, if desired.

The actuator38in the example described below comprises an electrical actuator, such as a direct current stepper motor. One advantage of such a motor is that a torque and/or force output of the motor can be conveniently regulated, and a position of an operating member displaced by the actuator38can be conveniently determined by monitoring a number of step pulses transmitted to the motor. However, other types of electrical actuators, and other types of actuators, may be used in keeping with the scope of this disclosure.

One or more lines40extend from the well tool30to a remote location (such as the earth's surface, a rig, a subsea location, etc.). The lines40can include one or more electrical conductors for conveying electrical power to the electronic circuit36, transmitting commands, data, etc. to the well tool30, receiving data, etc. from the well tool, etc. The lines40may include optical waveguides (such as optical fibers, ribbons, etc.), hydraulic conduits, and/or other types of lines, if desired.

In the example described below, the lines40extend internally through a conduit (for example, a conduit of the type known to those skilled in the art as a control line). The conduit protects the lines40during installation of the tubular string12in the wellbore14, and thereafter. However, use of the conduit is not necessary in keeping with the principles of this disclosure.

A control system42is located at the remote location, and is connected to the lines40. The control system42may include a computing device44and a display46, along with suitable memory, software, firmware, connectivity (e.g., to the Internet, to a satellite, to a telephony line, etc.), processor(s), etc., to communicate with and control operation of the well tool30. Alternatively, the control system42could be as simple as a switch to either apply electrical power, or not apply electrical power, to the well tool30.

An optional telemetry device48is included in the system10for relaying commands, data, etc. between the well tool30and the control system42at the remote location. For example, acoustic, electromagnetic, pressure pulse, a combination of short- and long-hop transmissions, or any other type of telemetry may be used. Wired or wireless telemetry, or a combination, may be used.

Since the fluid20is produced from the formation22through the tubular string12, those skilled in the art would refer to the tubular string as a production tubing string. The tubular string12could be jointed or continuous.

However, it should be understood that it is not necessary for the tubular string12to be a production tubing string, or for the fluid20to be produced from the formation22through the tubular string. In other examples, well tools incorporating the principles of this disclosure could be used in injection operations. Well tools incorporating the principles of this disclosure are not necessarily interconnected in a tubular string.

Referring additionally now toFIGS. 2A-10, a representative example of the well tool30is depicted in various longitudinal and lateral cross-sectional views. The well tool30ofFIGS. 2A-10may be used in the system10and method ofFIG. 1, or the well tool may be used in other system and methods.

InFIGS. 2A-D, a longitudinal cross-sectional view, taken along lines2-2ofFIG. 4is representatively illustrated. In this view, it may be seen that the well tool30includes a generally longitudinally extending flow path50.

One section50aof the flow path50is visible inFIGS. 2A-D. However, in this example, there are actually fourteen of the sections50a-n(seeFIG. 4) spaced apart circumferentially in a side wall52of the tool30.

Of course, any number and/or arrangement of flow path sections may be used in other examples incorporating the principles of this disclosure. For example, the flow path sections50a-ncould be helically and/or laterally arranged.

In theFIGS. 2A-10example, the sections50a-nare arranged so that they alternate direction when viewed as a continuous flow path50. The flow path50provides pressure communication between the flow passage32extending through the tubular string12and an internal generally longitudinally extending chamber62(seeFIG. 4).

The actuator38is positioned in the chamber62. A dielectric fluid54(e.g., a silicone fluid, etc.) surrounds the actuator38in the chamber62. The fluid54also fills a substantial majority of the flow path50.

A floating piston assembly56(seeFIGS. 9A & 10) isolates the dielectric fluid54from the well fluid20, which enters the flow path50via an opening58. The assembly56permits pressure to be balanced (e.g., at substantially equal levels) between the flow passage32and the chamber62via the flow path50, without any mixing of the fluids20,54.

In this manner, the chamber62is isolated from the well fluid20(which could interfere with operation of the actuator38, electronic circuit36, etc.), but the side wall52does not have to withstand a large pressure differential between the chamber62and the flow passage32. Thus, the side wall52can be made thinner, due to the chamber62being pressure balanced with the flow passage32.

Note that the floating piston assembly56is reciprocably and sealingly received in a radially enlarged section50iof the flow path50. This allows the floating piston assembly56to displace more volume per unit of translational displacement, thereby allowing more expansion of the dielectric fluid54with increased temperature, and allowing for a greater range of pressure transmission (although, if the dielectric fluid54is substantially incompressible, very little volume change would be expected due to pressure in a typical downhole environment). A pressure relief valve or other pressure relief device68is provided in the floating piston assembly56to relieve excess pressure in the flow path50due, for example, to increased temperature.

The chamber62is one of several chambers60,62,64,66in fluid communication with the flow path50. The electronic circuit36is positioned in the chamber66(seeFIGS. 8A& B).

A generally tubular housing70forms an enclosure72in which the electronic circuit36is contained, isolated from the fluid54in the chamber66. The housing70in this example comprises a pressure bearing weldment. However, if the electronic circuit36can withstand the pressure in the chamber66(substantially the same as the pressure in the flow passage32), then the housing70may not be used, or at least the housing may not have to withstand as much differential pressure.

Upper and lower manifolds72,74provide fluid communication between the flow path sections50a-oand chambers60,62,64,66.FIG. 5depicts a lateral cross-sectional view of the upper manifold72, andFIG. 6depicts a lateral cross-sectional view of the lower manifold74, taken along lines5-5and6-6ofFIGS. 3A& C, respectively.

Alternating opposite ends of adjacent ones of the flow path sections50a-nare placed in fluid communication with each other by the manifolds72,74. In addition, electrical conductors and/or optical waveguides can extend through openings in the manifolds72,74(seeFIG. 5).

For example, as depicted inFIG. 2A, the lines40can extend through the upper manifold72to a bulkhead connector76in the chamber60. The connector76isolates the chamber60from a conduit78extending external to the well tool30. The conduit78(and the lines40therein) could extend to, for example, another well tool (such as, another safety valve, the telemetry device48, etc.), a remote location, the control system42, etc.

In other examples, the bulkhead connector76may not be used, and the conduit78can be in fluid communication with the flow path50and chambers60,62,64,66. In this manner, the dielectric fluid54(or another fluid, such as, a chemical treatment fluid, etc.) could be injected into the flow path50and chambers60,62,64,66from a remote location via the conduit78.

For example, after installation of the well tool30in a well, dielectric fluid54could be pumped through the conduit78from the remote location to the flow path50and chambers60,62,64,66. Sufficient pressure could be applied to cause the pressure relief device68to open, thereby allowing the fluid to be pumped into the flow passage32from the flow path section50i.

This would ensure that the flow path50and chambers60,62,64,66are filled with the dielectric fluid54. This can also allow a chemical treatment fluid (such as, a corrosion inhibitor, a precipitate reducer, etc.) to be pumped into the flow passage32via the conduit78, flow path50and relief valve68.

Various sensors can be included with the well tool30. These sensors may be useful for monitoring well parameters, monitoring operation of the well tool, controlling the operation of the well tool, etc.

In the example ofFIGS. 2A-10, a pressure and/or temperature sensor80is disposed in the upper manifold72(seeFIG. 5). A position sensor82measures a position of an operating member84(seeFIGS. 2B-D), which is displaced by the actuator38against a biasing force exerted by a biasing device86, to thereby open or close the closure member34.

Magnets104are carried on the shaft90. A position of the magnets104is sensed by the position sensor82, thereby providing a measurement of the position of the operating member84.

Note that the position sensor82is not necessarily a magnetic-type position sensor. The position sensor82could instead be a linear variable displacement transducer, acoustic rangefinder, optical sensor, or any other type of position sensor.

A force sensor88(seeFIG. 3A) measures a force output by the actuator38. As mentioned above, the actuator38in this example comprises a stepper motor. A torque output, current draw, number of step pulses, and/or any other parameter may be measured by the sensor88, another sensor or any combination of sensors.

The motor (via suitable gearing, clutch, brake, etc., not visible inFIGS. 3A& B) displaces a shaft90upward or downward (as viewed in the drawings). A sealing rod piston92is displaced with the shaft90. The sealing rod piston92isolates the dielectric fluid54in the chamber62from the well fluid20in the flow passage32.

Note that, since the chamber62and the flow passage32are at substantially the same pressure, seals96on the piston92do not have to seal against a large pressure differential. Nevertheless, in this example, metal-to-metal sealing surfaces94are provided at each end of the piston's displacement for further sealing enhancement.

An alternative pressure transmission device could be a bellows98, as depicted in the example ofFIGS. 11A-C. Yet another alternative could be a diaphragm or membrane. Any type of pressure transmission device which can isolate the chamber62from the flow passage32, while transmitting force from the actuator38to the operating member84may be used.

The operating member84can be displaced to any position by the actuator38at any time. For example, the operating member84can be displaced to a position in which the closure member34is fully closed, a position in which the closure member is fully open, a position in which an equalizing valve100(seeFIG. 2D) is opened, etc.

When actuating the well tool30from its open to its closed configuration, the actuator38can displace the operating member84to its equalizing position (thereby opening the equalizing valve100), stop at the equalizing position (e.g., using a brake of the actuator) and then continue to the open position (in which the closure member34is fully open). The operating member84can remain stopped at the equalizing position until the sensor80indicates that pressure in the flow passage32above the closure member34has ceased increasing, until a certain time period has elapsed, until a differential pressure sensor (not shown) indicates that pressure across the closure member34has equalized, etc.

Measurements made by the sensor88can also be used to control operation of the well tool30. For example, the force and/or torque output by the actuator38could be limited to a predetermined maximum level. In some examples, this predetermined maximum level could be changed, if desired, via the control system42.

In other examples, the force and/or torque, current draw, etc., of the actuator38can be optimized for most efficient and/or effective operation of the well tool30. For example, the force output by the actuator38could be limited when displacing the operating member84from the closed position to the equalizing position, then increased to a greater level when the operating member begins opening the closure member34, and then reduced after the closure member has been rotated a sufficient amount. If greater force is needed to displace the operating member84in any of these situations (or in any other situations), an alert, alarm, etc. may be provided to an operator by the control system42(e.g., via the display46).

It may now be fully appreciated that significant improvements are provided to the arts by the principles set forth in this disclosure. In an example described above, electrical connections (e.g., the bulkhead connector76, connections at the position sensor82, sensor88, actuator38, etc.), a downhole electronics housing70weldment, a position sensor82and an electrical actuator38are installed inside of dielectric fluid54filled chambers60,62,64,66. All of the dielectric fluid54filled chambers60,62,64,66are pressure balanced to the flow passage32using a flow path50which alternates direction multiple times.

The illustrated configuration contains only one electric actuator, one downhole electronics housing weldment, and one position sensor. However, any number of these elements may be used, as desired.

There are seven alternating dielectric fluid filled gravity assisted “U” flow path sections (fourteen total sections) to separate the production fluid from the dielectric fluid, in the illustrated configuration. However, any number of flow path sections may be used, as desired.

The passageway ports that are used for the passage of the dielectric fluid balance pressure can also be used to route electrical conductors or other types of lines from chamber to chamber. These ports can be sealed with static double o-ring seals (which always have substantially no differential pressure across them).

If desired, these ports could be laser welded instead of being sealed with o-rings. However the pressure balance device in other examples could include a chamber where the dielectric fluid is separated from the well fluids by bellows or other types of seals.

No large magnetic coupling is used in the illustrated configuration. However, a magnetic coupling could be used, in keeping with the principles of this disclosure.

Typically, the main limitation on safety valve dimensions is the wall thickness needed for the actuator. The required wall thickness can be much smaller with the illustrated design, since the electric actuator can be smaller than conventional designs.

The electric actuator for the illustrated configuration does not have to be as powerful or as large as conventional electrical safety valve actuators. The actuator in the illustrated configuration must only be strong enough to overcome the force of the biasing device86and friction. Since there is no differential pressure on any seals, the friction should be minimal.

A conventional rod piston92with leak-proof seals96is used in the depicted safety valve example. Note that multiple rod piston seals (or even a bellows, diaphragm, etc.) could be used in place of the leak-proof seals, since there is preferably substantially no differential pressure across the seals.

Again, all of the seals in the design will preferably have little to no pressure differential across them. No pressure differential should equate to very little to no leakage past the seals for long periods of time.

A hybrid electronics package design that is long with a small OD is used in the depicted safety valve example. This hybrid circuit design provides a significant size reduction. Longevity at high temperatures is also increased.

In other examples, a hybrid circuit that holds high pressure and, therefore, does not need a high pressure housing may be used. This can further reduce the cost of constructing the well tool.

In the depicted example, there is no welding required on any body components which experience significant tension in operation. This enhances the structural integrity of the well tool, while also reducing costs.

The tubing pressure balancing feature is integrated into the depicted safety valve example. This can also result in substantial cost reductions. However, in other examples, the tubing pressure balancing feature could be provided by a separate component that is connected to the dielectric fluid filled chambers.

The illustrated safety valve example also provides for addition of a downhole electronic pressure and/or temperature gauge as part of the safety valve. Such a pressure/temperature gauge can be installed into one of the pressure balancing chambers which are maintained at the pressure in the flow passage. This downhole gauge could transmit pressure and temperature information to a remote location on a same line as is used to control operation of the safety valve.

Complete system redundancy can be provided in at least three ways, due at least in part to the reduced cost of the safety valve example described above:

a. Multiple safety valves could be installed. A secondary valve could be pinned or temporarily locked in an open position. The secondary valve could be actuated (e.g., via a wireline trip) when a primary safety valve fails.

b. Multiple safety valves could be operated all the time. If any one safety valve fails, it can be locked open.

c. A safety valve could include multiple actuators, multiple control lines, and multiple sets of electronics. In the illustrated configuration, the number of alternating flow paths may be reduced, if the multiple actuators, etc. are to fit in the same size wall of the safety valve. If dielectric fluid contamination is a concern, more “U” tubes could be added, or a metal bellows pressure balancing system could be used instead, etc.

The illustrated configuration uses a currently new Honeywell changing magnetic field sensing position sensor. As a small magnet assembly carried by the shaft90moves, the Honeywell position sensor accurately reports the position. This solid state sensor has no moving parts inside the pressure housing and it should be much more reliable than a potentiometer type sensor. However, a potentiometer or other type of position sensor may be used, if desired.

There might be concerns that well fluids could eventually reach the actuation chamber if the flow path is open to the flow passage (e.g., if the floating piston assembly56is not used). However, the multiple alternating direction flow path sections50a-nshould be effective to prevent migration of the well fluid20into the chambers60,62,64,66.

The floating piston assembly56forms a physical barrier between the well fluids and the dielectric fluid, thereby preventing mixing of the fluids. The floating piston could move inward and outward with changes in pressure, but its inward movement could be limited by the compressibility of the dielectric fluid, and its outward movement could be limited by the expansiveness of the dielectric fluid.

A basic combination described above is a chamber filled with a dielectric fluid, with one end of a flow path connected to the chamber, and another end of the flow path in communication with the flow passage. While this integral pressure balancing feature is primarily described for an electrically actuated safety valve, it could potentially be used with other well tools, such as sliding sleeves, chemical injection valves, separators, etc.

The depicted electric safety valve system can include an electric actuator with downhole electronic circuitry, a downhole telemetry device (transmitter and/or receiver), and a control system at a remote location (such as, at the earth's surface, a rig, an underwater facility, etc.).

A position sensor can report the relative position of the operating member from the start (or the fully closed position) to the end (or the fully open position) to the electronic circuitry. The electronic circuitry transmits this information to the telemetry device. The telemetry device then relays the position information to the control system. In some examples, an operator at the remote location can view the position of the operating member.

The control system can display when the safety valve should be fully open, for example, after a preset number of stepper motor steps have been executed. This control system computer display indication can be independent of the position sensor, so that a failure of the position sensor does not affect the opening/closing functions of the safety valve.

The control system can display when the valve is in the closed position, when the control system's computer program is running. The safety valve will preferably automatically close if the control system is shut down, electric power to the safety valve is lost, or a computer used to run the computer program fails.

In another example, the safety valve could go into a hold state if the control system fails or is shut down, instead of the safety valve automatically closing. The reason for the failure or shutdown could be a system maintenance issue that does not require the well to be shut-in.

The force sensor88periodically reports to the control system the measured force output by the actuator. These force measurements can comprise a secondary indication of the safety valve operation, which may be used in case the position sensor82fails.

If the safety valve is a self-equalizing type (e.g., comprising the equalizing valve100), the electronic circuitry or the control system can be preprogrammed to displace the operating member only to the equalizing position, and then set the brake until the operator issues a command to the control system to continue to open the safety valve to the fully open position.

The temperature, pressure, vibration, etc. of the electronic circuitry can be reported periodically to the control system. For example, this information can be displayed after the safety valve is closed. The temperature, pressure, vibration, etc. could also be displayed and/or recorded in real time.

The pressure and temperature in the tubular string12(e.g., as measured by the sensor80) may be reported periodically to the control system42(e.g., the safety valve is open), or after the valve is closed, and/or in real time. This can be accomplished with an integral downhole pressure/temperature gauge or other dedicated sensors.

If the force on the actuator or the force required to open the flapper exceeds a preset limit, indicating that pressure across the flapper is not equalized, the electronic circuitry can automatically command the safety valve to close (e.g., causing the actuator to reverse direction), and the force overload can be reported to the control system.

The operator can then set this force limit to a higher level, if desired. However, the stepper motor will likely dither and not open the safety valve if the maximum motor torque is reached. In this circumstance, the operator can increase the tubing pressure to equalize the pressure above the flapper to the pressure below the flapper.

The current and voltage supplied to the clutch, brake, and stepper motor are preferably reported periodically to the control system.

The torque output of the stepper motor can be increased by decreasing a frequency of electrical step pulses transmitted to the motor. The time to open the safety valve can be optimized by increasing the frequency of the pulses at the beginning of the displacement when the force output by the biasing device is lowest, and decreasing the frequency at the end of the displacement when the spring force is highest.

This functionality can be enhanced by monitoring the force sensor output. If the force sensor indicates an increased force, the frequency of the step pulses can be reduced.

In order to optimize electrical power usage, the safety valve can have a demand system, whereby the power is continuously monitored, and is maintained within a narrow range. The safety valve will likely have an optimum power at which it performs its function. This optimum power is sufficient to operate the valve, with a minimum amount of excess power. In this manner, smaller electrical components can be used and less heat is generated in the downhole electronic circuitry, actuator, etc.

In one example, if the flow passage32pressure is below or above a preset limit, the valve would automatically close. A warning with a predetermined override time limit could be displayed by the control system42before this happens, so the valve would not be closed unless circumstances warrant.

This would allow the operator to override the closure if the downhole pressure gauge failed or the pressure limits are incorrect. The pressure limits could be reset at the control system42. If the override command is not received during the given time period, the valve could automatically close.

The control system42could automatically alternate redundant clutches and/or brakes of the actuator38.

Note that the electric actuator38and other components used in the illustrated configuration could also be used to operate a downhole choke, sliding sleeve valve, etc., instead of a subsurface safety valve. For a downhole choke, other sensors such as resistivity and a differential pressure flow meter could be included in the design, so that operation of the choke could be controlled, based on the outputs of such sensors.

The electronic circuitry and/or telemetry device may be reprogrammed from the control system42.

Another self-equalizing function can be included as part of the safety valve. The operating member84can be displaced from the closed position to a predetermined equalizing position, at which the equalizing valve100opens. The brake would be set, holding the operating member84in the equalizing position. The pressure gauge could be monitored, until the pressure above the closure member34stops increasing for a predetermined time period, then the operating member84would be displaced to the open position.

A well tool30for use with a subterranean well is described above. In one example, the well tool30can include a flow passage32extending longitudinally through the well tool30, an internal chamber60,62,64,66containing a dielectric fluid54, and a flow path50which alternates direction, and which provides pressure communication between the internal chamber60,62,64,66and the flow passage32.

The well tool30can also include a floating piston102in the flow path50. The floating piston102may prevent the dielectric fluid54from flowing into the flow passage32. The floating piston102can be positioned in an enlarged section50oof the flow path50.

The well tool30may include an electrical actuator38in the dielectric fluid54. The actuator38can displace a pressure transmission device (e.g., piston92, bellows98, etc.) which isolates the chamber60,62,64,66from the flow passage32. The pressure transmission device may comprises a bellows98and/or a piston92.

The chamber60,62,64,66can be in fluid communication with a source of the dielectric fluid54via a conduit78extending to a remote location. A line40may extend through the conduit78to an actuator38in the chamber62.

The chamber60,62,64,66can be in fluid communication with a source of chemical treatment fluid via a conduit78extending to a remote location. In this example also, a line40may extend through the conduit78to an actuator38in the chamber62.

The well tool30can include a pressure relief device68. The pressure relief device68may permit the dielectric fluid54to flow into the flow passage32in response to pressure in the chamber60,62,64,66exceeding a predetermined pressure level.

The well tool30can include an actuator38in the dielectric fluid54, and a force sensor88which senses a force applied by the actuator38. The force applied by the actuator38may be controlled, based on measurements made by the force sensor88.

The force output by the actuator38can vary, based on a displacement of an operating member84of the well tool30by the actuator38. The well tool30can include a displacement or position sensor82which senses the displacement of the operating member84.

The displacement of the operating member84may cause displacement of a closure member34which selectively permits and prevents flow through the flow passage32. The displacement of the operating member84can actuate an equalizing valve100which equalizes pressure across the closure member34.

The well tool30can include at least one of the group comprising temperature, force, pressure, position, and vibration sensors in the dielectric fluid54. At least one of the sensors (e.g., vibration sensor106, seeFIG. 8B) and an electronic circuit36may be disposed in an enclosure71isolated from pressure in the chamber66.

A method of controlling operation of a well tool30is also described above. In one example, the method can include actuating an actuator38positioned in an internal chamber62of the well tool30, a dielectric fluid54being disposed in the chamber62, and the chamber62being pressure balanced with a flow passage32extending longitudinally through the well tool30; and varying the actuating, based on measurements made by at least one sensor80,82,88,106of the well tool30.

The actuating step can also include displacing an operating member84. The sensor82may sense displacement of the operating member84. The varying step can include changing a speed of the displacement, based on the sensed displacement of the operating member84.

The varying step can include changing a force and/or torque output by the actuator38, based on the sensed displacement of the operating member84.

The varying step can include varying a frequency of electrical pulses transmitted to the actuator38.

The varying step can include closing a closure member34, in response to the sensor88sensing that a force output by the actuator38exceeds a predetermined maximum force level.

The varying step can include ceasing displacement of an operating member84, and then resuming displacement of the operating member84. The ceasing displacement step may be performed when the actuator38has displaced the operating member84to an equalizing position, in which pressure is equalized across a closure member34. The resuming displacement step may be performed when the pressure has equalized across the closure member34, and/or in response to a predetermined period of time elapsing from the operating member84being displaced to the equalizing position.

The well tool30may comprise a safety valve. The actuator38may cause a closure member34to be alternately opened and closed to thereby respectively permit and prevent flow through the flow passage32.

In particular, the above disclosure describes a safety valve30for use in a subterranean well. In one example, the safety valve30can include a flow passage32extending longitudinally through the safety valve30, an internal chamber60,62,64,66containing a dielectric fluid54, a flow path50which alternates direction, and which provides pressure communication between the internal chamber60,62,64,66and the flow passage32, an actuator38exposed to the dielectric fluid54, an operating member84, and a closure member34having open and closed positions, in which the closure member34respectively permits and prevents flow through the flow passage32. The actuator38can displace the operating member84, which causes displacement of the closure member34between its open and closed positions.

In the above description of the representative examples, directional terms (such as “above,” “below,” “upper,” “lower,” etc.) are used for convenience in referring to the accompanying drawings. However, it should be clearly understood that the scope of this disclosure is not limited to any particular directions described herein.

Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of this disclosure. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the invention being limited solely by the appended claims and their equivalents.