WO2018096345A1

WO2018096345A1 - Fail-safe actuator to control a downhole safety valve

Info

Publication number: WO2018096345A1
Application number: PCT/GB2017/053533
Authority: WO
Inventors: Iain Maclean; Kenneth Sears
Original assignee: Zilift Holdings Limited
Priority date: 2016-11-28
Filing date: 2017-11-24
Publication date: 2018-05-31

Abstract

A wellbore formation fluid pump (30) and downhole safety valve system (20) includes a wellbore formation fluid pump (30) operable by a motor for lifting fluid entering the wellbore to the surface. A hydraulic fluid pump (10) is operably connected to the wellbore formation fluid pump (30). The hydraulic fluid pump (10) is configured to produce a selected fluid pressure sufficient to open a hydraulically operated wellbore device (20) when the wellbore formation fluid pump (30) is operated at at least a threshold rate. The hydraulic fluid pump (10) has a least one backflow feature (10C, 10D) to enable automatic stopping of operation of the hydraulically operated wellbore device (20) when the wellbore formation fluid pump (30) is operated below the threshold rate.

Description

FAIL-SAFE ACTUATOR TO CONTROL A DOWNHOLE SAFETY VALVE

FIELD

This disclosure relates to the field of downhole safety valves (DSVs) used in subsurface wells to close the well to fluid flow when the wellbore is intended to have fluid production stopped. More specifically, the disclosure relates to DSVs used in connection with downhole fluid pumps such as electric submersible pumps (ESPs).

BACKGROUND

Wellbore fluid pumps, such as ESPs are frequently disposed in wellbores to lift fluid to the surface when natural pressure in a subsurface reservoir is insufficient to lift the fluid unassisted. Wellbore fluid pumps are also used to increase fluid production rate from subsurface wells. Such wellbores often include downhole safety valves (DSVs) to enable fluid closure of the well at a selected depth to prevent uncontrolled release of fluid from the well in the event subsurface fluid pressure becomes sufficient to naturally lift the wellbore formation fluid to the surface.

For conventional tubing-deployed ESPs it is common for the DSV to be set at a shallower depth than the ESP. In this configuration the ESP cable is outside the production tubing as is the hydraulic control line for the DSV. A cable deployed ESP will have the ESP cable is inside the production tubing. Because the cable is inside the production tubing it would not be possible for a conventional shallow-set DSV to close.

A DSV is typically operated by hydraulic pressure provided by a system located at the surface. Because of the hydrostatic pressure of the column of hydraulic fluid from surface to the vertical depth of the DSV, systems known in the art must be pre- calibrated such that the hydrostatic pressure of the hydraulic fluid is lower than the operating pressure of the DSV actuator. Thus, each DSV deployment is pre-configured for the installation depth of the DSV. DSV systems known in the art also require separate controls to operate the DSV than the control use to operate the ESP or other well pump.

What is needed is a system where the DSV can be placed below a through tubing- conveyed ESP and can be installed at any wellbore vertical depth without the need to pre-calibrate the hydraulic system for wellbore depth, and that operates automatically, and passively (i.e., without the need for a separate energy source) to close the DSV when the ESP or other well pump is not operating.

SUMMARY

A wellbore formation fluid pump system according to one aspect of the present disclosure includes a wellbore formation fluid pump operable by a motor for lifting fluid entering the wellbore to the surface. A hydraulic fluid pump is operably connected to the wellbore formation fluid pump. The hydraulic fluid pump is configured to produce a selected fluid pressure sufficient to open a hydraulically operated wellbore device when the wellbore formation fluid pump is operated at at least a threshold rate. The hydraulic pump has at least one backflow feature to enable automatic stopping operation of the hydraulically operated wellbore device when the wellbore formation fluid pump is operated below the threshold rate. In some embodiments, the hydraulically operated wellbore device may comprise a downhole safety valve.

In some embodiments, the downhole safety valve may comprise a linear sleeve actuator operably coupled to a piston in fluid communication with an outlet of the hydraulic fluid pump so as to move the linear sleeve actuator to open the downhole safety valve when the wellbore formation fluid pump is operated at at least the threshold rate.

In some embodiments, the hydraulic fluid pump may comprise at least one of a metal to metal progressive cavity pump, a centrifugal pump, a gear pump, a vane pump and a trochoid pump.

In some embodiments, the at least one backflow feature may comprise an internal passage to enable backflow of fluid through an interior of the hydraulic fluid pump.

In some embodiments, the at least one backflow feature may comprise at least one of a chamfer of gear teeth on a gear pump and one or more passages on a gear face of a gear pump. In some embodiments, the at least one backflow feature may comprise a selected size fluid line connected between an outlet of the hydraulic fluid pump and an inlet of the hydraulic fluid pump. In some embodiments, an actuator operable to open and close the downhole safety valve may comprise a piston having a biasing device to close the downhole safety valve when hydraulic pressure on a side of the actuator used to open the safety valve falls below a selected threshold. In some embodiments, the biasing device may comprise a spring disposed between one side of the piston and an end of an actuation cylinder.

In some embodiments, the wellbore formation fluid pump may comprise a rotary motor.

In some embodiments, the wellbore formation fluid pump may comprise an electrically operated submersible pump.

In some embodiments, the downhole safety valve may comprise a wireline retrievable safety valve. In some embodiments, the hydraulic fluid pump may be part of a closed circuit hydraulic system having a reservoir compensated for ambient fluid pressure in the wellbore at the location of the reservoir in the wellbore. In some embodiments, the closed circuit hydraulic system may include a flexible bladder, bellows or flexible diaphragm exposed on one side to ambient wellbore formation fluid pressure and on another side to the closed circuit hydraulic system.

In some embodiments, the backflow feature may enable closure of the downhole safety valve within a selected time limit when the wellbore formation fluid pump is operated below the selected threshold rate.

In some embodiments, the hydraulic fluid pump may comprise a pressure relief valve operable to maintain a maximum pressure output of the hydraulic pump when the hydraulic fluid pump is operated above a selected threshold speed. A method for operating an hydraulically operated wellbore device according to another aspect of the present disclosure includes operating a hydraulic fluid pump using energy from operation of a wellbore formation fluid pump, the hydraulic fluid pump having a backflow feature such that pressure on an outlet of the hydraulic fluid pump is returned to an intake side of the hydraulic fluid pump at a predetermined rate. A hydraulically operated wellbore device is operated using pressure generated by operating hydraulic fluid pump at at least a threshold rate. The hydraulically operated wellbore device automatically stops operating when the hydraulic fluid pump is operated below the threshold rate such that the backflow feature reduces hydraulic pressure below an amount required to open the downhole safety valve.

In some embodiments the hydraulically operated wellbore device may comprise a downhole safety valve. In some embodiments, an actuator operable to open and close the downhole safety valve may comprise a piston having a biasing device to close the downhole safety valve when hydraulic pressure on a side of the actuator used to open the safety valve falls below a selected threshold. Some embodiments may further comprise compensating a pressure in a hydraulic fluid system connected to the hydraulic fluid pump for ambient wellbore fluid pressure.

In some embodiments, the energy from operation of the wellbore formation fluid pump may comprise rotational energy used to rotate the wellbore fluid pump coupled to a rotating energy input of the hydraulic fluid pump.

An aspect of the present disclosure relates to a downhole hydraulically operated wellbore system, such as a downhole safety valve system. The system may comprise a hydraulically operated wellbore device, such as a downhole safety valve. The system may comprise a hydraulic fluid pump configured to produce a selected fluid pressure sufficient to open the hydraulically operated wellbore device. The hydraulic pump may have at least one backflow feature to enable automatic stopping operation of the hydraulically operated wellbore device when the hydraulically operated pump develops a pressure below a threshold magnitude. The hydraulically operated pump may be operably connected to a wellbore formation fluid pump. The hydraulic fluid pump may be configured to produce a selected fluid pressure sufficient to open the hydraulically operated wellbore device when the wellbore formation fluid pump is operated at at least a threshold rate. The at least one backflow feature may enable automatic stopping operation of the hydraulically operated wellbore device when the wellbore formation fluid pump is operated below the threshold rate.

Features defined in relation to one aspect may be provided in accordance or in combination with any other aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example embodiment of a fluid pump used to operate a downhole safety valve (DSV). FIG. 2 shows an example embodiment of a gear from the fluid pump in FIG. 1 which has chamfer on the gear teeth to enable flow-back of pressurized fluid when the pump is stopped or operates below a selected threshold rotary speed.

FIG. 3 shows another example embodiment of a gear from the pump in FIG. .

FIG. 4 shows an example embodiment of a 'leaky' fluid pump and hydraulic fluid system connected to operate a DSV. The fluid pump in the present example embodiment may be rotationally coupled to a pump shaft from an electric submersible pump (ESP) above.

FIG. 5 shows a cross section of FIG. 4 at the axial position of the fluid pump. DETAILED DESCRIPTION

The following is an example of how an appropriately "leaky" hydraulic fluid pump could be configured to operate a wellbore device using hydraulic fluid pressure to effect its operation. One example of such a wellbore device is a downhole safety valve (DSV) such as a wireline retrievable DSV. Other examples may include, without limitation, inflatable packers, control valves and the like. The "leaky" hydraulic fluid pump may be, for example, a metal to metal or other type of PCP, centrifugal pump, gear pump, vane pump, trochoid pump or other type of fluid pump suitable to generate hydraulic fluid pressure used to operate the DSV. The present example embodiment uses a gear pump, however, the type of pump in the present embodiment is not a limit on the scope of the present disclosure. Referring to FIG. 1 , a hydraulic fluid pump such as a gear pump 10 may comprise a drive gear 10A rotated by a drive shaft 1 1 , which may be rotationally coupled to an electric submersible pump (ESP) shaft, as will be further explained with reference to FIG. 4. A driven gear 10B is rotated by the drive gear 10A. The gears 10A, 10B may be disposed in a housing (not shown) such that fluid is pumped by rotation of the gears 10A, 10B. "Leaky" in the present context means that the leaky hydraulic fluid pump is intentionally designed to allow pressure leakage from the pump outlet to the pump inlet. When the leaky hydraulic fluid pump 10 components are operated, e.g., rotated at a speed below a selected threshold speed, or are stopped, pressurized fluid at the pump outlet may flow back through the leaky hydraulic fluid pump 10 to the fluid inlet of the hydraulic fluid pump 10. Such back flow may enable a device operated by fluid pressure from the hydraulic fluid pump 10 to reverse operation passively, that is, the leaky hydraulic fluid pump 10 and hydraulic fluid pressure operated device are configured such that slowing or stopping operation of the leaky hydraulic fluid pump causes the fluid pressure operated device to return to its normally non-actuated state. In the present example embodiment, the fluid pressure operated device is a downhole safety valve (DSV) which closes on its own when hydraulic fluid pressure to its actuator is removed. In the present embodiment, the fluid pressure is removed by the above described back flow through the leaky hydraulic fluid pump 10. FIG. 2 shows an example of the leaky hydraulic fluid pump drive gear 10A, in which a chamfer 10C is formed on longitudinal edges of the gear teeth. Such chamfer 10C may enable fluid under pressure at the pump outlet to back flow through the hydraulic fluid pump (10 in FIG. 1) thus relieving the hydraulic fluid pressure at the leaky hydraulic fluid pump outlet and in the present example embodiment, allows the DSV to close passively as will be explained with reference to FIG. 4. FIG. 3 shows another embodiment of one of the leaky hydraulic fluid pump gears, in which a channel 10D is formed on the face of at least one of the gear teeth to provide a back flow passage through the leaky hydraulic fluid pump 10. In selecting features for the leaky hydraulic fluid pump 10, the following parameters may be taken into account. A hydraulic fluid pump input shaft speed range may be from 0 to 3600 revolutions per minute (rpm). Within such speed range, the leaky hydraulic fluid pump (10 in FIG. 1) may produce enough hydraulic pressure to keep the hydraulic pressure operated device (e.g., the DSV) open or otherwise actuated in a speed range of 50 to 3600 rpm. The DSV "held open" hydraulic fluid pressure range may be 200 pounds per square inch absolute (psia) to 400 psia. The DSV may close when the hydraulic pressure applied to its actuator (FIG. 4) is less than 100 psia. The wellbore formation fluid pump does not generate pressure and/or lift fluid when operating at very low speed. For example, a typical ESP needs to operate at several hundred rpm before it generates sufficient centrifugal forces to lift wellbore fluids. It is important that the wellbore formation fluid pump does not lift fluid at lower rpm, because otherwise the wellbore formation fluid pump would cavitate until the DSV is open.

The hydraulic fluid pump hydraulic system may be closed and comprise clean oil as the hydraulic motive fluid. An example upper limit of the time to open the DSV is less than 30 seconds. Correspondingly, the time to close the DSV when hydraulic pressure drops below the above selected threshold may be less than 30 seconds. Typical dimensions of the DSV (excluding connections) may be 2.5 inches outer diameter, 12 inches long with a 1 inch internal diameter bore for produced fluids.

Referring to FIG. 4, the DSV 20 in the present embodiment may be a wireline retrievable safety valve (WRSV) which includes a flapper valve 20A actuated by a sliding sleeve 20G. Examples of wireline retrievable safety valves include one sold under the trademark OPTIMAX, which is a trademark of Weatherford International, pic. Similar WRSVs may be obtained from, for example and without limitation, Halliburton Company, Baker Hughes Incorporated and Schlumberger Technology Corporation. WRSVs are typically operated by hydraulic pressure controlled by or provided from surface equipment. The DSV 20 in the example illustrated is located in wellbore 20D (e.g., cased or lined) and sealed via packer 22 The present example embodiment of a DSV (WRSV) operating system opens the DSV 20 by applying hydraulic fluid pressure to a valve actuator 20C. In the present example embodiment, the source of hydraulic fluid pressure, i.e., the leaky hydraulic fluid pump (10 in FIG. 1 ) may be rotationally coupled (or otherwise functionally coupled) to a wellbore formation fluid pump 30, e.g., an electric submersible pump (ESP). By such configuration and by having a leaky hydraulic fluid pump 10 to provide hydraulic pressure to actuate the DSV 20, the DSV 20 closes automatically when the wellbore formation fluid pump (ESP) 30 is stopped or slowed to below a selected rotational speed threshold, examples of which are provided above. The DSV 20 opens when the ESP 30 is operating at at least the threshold operating rate. No separate control system is required for the correct and fail-safe operation of the DSV 20.

A flapper 20A is mounted on a pivot 20H, and has a spring (not shown separately) to move the flapper 20A to the closed position when fluid pressure on the actuator 20C is relieved.

A sliding sleeve 20G can move axially in the through bore 20E so that in an upper position (upper means closer to the surface of the wellbore) the sleeve 20G is clear of the flapper 20A, and the flapper 20A will move to the closed position under the action of its spring. In the lower position (lower means closer to the downhole end of the wellbore) the sleeve 20G traverses the location of the flapper 20A, thereby opening the flapper 20A and allowing wellbore formation fluids 19A to pass to the ESP 30 and thence to surface. The sleeve 20G may be actuated by hydraulic pressure from the pump (10 in FIG. 1) acting on an annular piston 20C in an annular bore 20B, the piston 20C being in contact with the sleeve 20G. The piston 20C has a spring 20F which moves the piston 20C and the sleeve 20G to the upper position when there is insufficient hydraulic pressure to enable the piston 20C compress the spring 20F.

In this way, the DSV 20 is opened whenever more than a minimum hydraulic pressure is applied, and the DSV 20 is closed whenever less than a minimum hydraulic pressure is applied. In the present example embodiment, the hydraulic pressure is provided by the leaky hydraulic fluid pump (10 in FIG. 1 ) which may be rotationally driven by the ESP 30, thereby ensuring that the DSV 20 is closed when the ESP 30 is not turning, and the DSV 20 will be open when the ESP 30 is turning at more than a predetermined rotational speed (examples of which are provided above). A cross section of the assembly shown in FIG. 4 through the leaky hydraulic fluid pump 10 is shown in FIG. 5.

The following calculations are at an outline level only and do not include factors such as pump efficiency and friction. However, the calculations confirm the practicality of the concept, which leaves adequate scope for optimization of leaky hydraulic fluid pump size and characteristics, etc. to accommodate these effects.

A positive displacement pump is considered, for example, a gear pump, although other types of pump may be used. Gear pumps are well known industrial equipment, are compact and robust, and typically capable of generating pressures up to several hundred bar if and as required.

The axial travel of the sleeve (20G in FIG. 4) may be somewhat greater than the diameter of the bore which the flapper (20A in FIG. 4) will close. In the present example, the bore may be 1 inch. The sleeve 20G travel is taken to be 1.25 inch. Considering a cross-section through the piston 20C which operates the sleeve 20D, the piston may have an outer diameter (OD) of 2.0 inches and an inner diameter (ID) of 1.75 inches. The piston area is A = π(ρ² - d²) I 4 = π(2² - 1.75²) / 4 = 0.74 in². The volume of fluid required to displace the piston 20C and thus the sleeve 20G by 1.25 inches is 0.74*1.25 = 0.92in³, or approximately 1 cubic inch.

To obtain full longitudinal displacement of the sleeve 20G in at most 30 seconds when the leaky hydraulic fluid pump is turning at 50 rpm the leaky hydraulic fluid pump must deliver 1 in³ in 25 revolutions.

Hydraulic fluid pump displacement = 1/25 = 0.04in³ per rev. = 0.66cm³ per rev.

Hydraulic force on piston = pressure x area. Taking the example of 200 psi hydraulic pressure to open the DSV 20, 200 psi x 0.74in² = 148 pounds force (Ibf). This force has to overcome the total spring (20F) force, which is the preload of the installed spring + spring rate x displacement. Taking the example of the flapper 20A closing when the hydraulic pressure is <100 psi: Force on piston = 100psi x 0.74in² = 74lbf

Therefore, spring 20F preload may be more than 74 Ibf to ensure that the spring will overcome the hydraulic force of 0Opsi acting on the piston. In the present example, the spring preload may be 100 Ibf.

Spring rate x displacement = 148 - 100 = 48 Ibf

Displacement = 1.25 inch, therefore, rate = 48 / 1.25 = 38.4 Ibf/in.

10OIbf preload equates to 100 / 38.4 = 2.6 inch spring precompression.

Having displaced the piston 20C to the end of its possible travel, the pump (10 in FIG. 1 ) will continue to displace fluid in direct proportion to rotational speed.

At 3600rpm, the example hydraulic fluid pump will displace 3600 x 0.74 = 2664in³ per minute = 2664 / 61 liters/min = 43.7 liters/min.

This flow may spill back to a fluid reservoir 13 through a return passage. A pressure relief valve may allow flow to spill while maintaining the pressure required to keep the DSV open (in this example, 400 psi). In the situation where the pump is rotating at 3600 rpm and keeping the safety valve open, the pump will be discharging 43.7 liters/min at 400 psi. Pump power is given by the expression:

Power (kW) = (flow liters/min x pressure bar)/ 600 = (43.7 x 400/14.7) / 600 = 2 kW.

This power is not realized as useful work, and will therefore be dissipated as heat through the structure of the hydraulic fluid pump and DSV. An all metal construction pump, such as a gear pump, would be a good choice as such pumps can operate at very high temperatures.

Other embodiments may include a torque-limiting clutch in the hydraulic fluid pump drive, to limit the discharge pressure. Such a clutch could be, for example and without limitation a magnetic coupling or a freewheel. A clutch arrangement would allow the hydraulic fluid pump to maintain pressure to actuate the sleeve, but not increase displacement, and may serve to limit excess heat generation. The hydraulic fluid pump and piston may operate as a closed fluid circuit, completely filled with hydraulic fluid such as oil. A reservoir 13 is provided as shown in FIG. 4. Thermal expansion of the hydraulic fluid (e.g., oil) may be accommodated by a flexible bladder 13A, which may also provide pressure compensation for the ambient wellbore formation fluid pressure. In some embodiments the reservoir 13 could be canned (sealed), potentially using a magnetic coupling between the ESP shaft and the leaky hydraulic fluid pump shaft and a metal bellows for oil thermal expansion which would remove the need for the pressure balance/ bladder assembly 13A. Other devices for compensating the pressure in the hydraulic fluid system may comprise bellows and a flexible diaphragm such as an elastomer diaphragm.

In various embodiments of a pump/DSV system according to the present disclosure, when the wellbore formation fluid pump stops, or is turning slowly (less than a threshold rate, e.g., 50 rpm in the present example case) the spring 20F will return the piston 20C and sleeve 20G to the upper (flapper closed) position, and the safety valve is thus closed, within 30 seconds. This requires a return flow through the leaky hydraulic fluid pump 10 of 1 in³ in 30 sec = 2in³ / min with a nominal pressure differential of 100 psi.

The above fluid back flow rate can be obtained by providing a small additional clearance in the leaky hydraulic fluid pump. For example, in the case of a gear pump, a small chamfer may be provided on an outermost corner of one or both gears. This would of course reduce the efficiency of the leaky hydraulic fluid pump, which for normal pump applications is highly undesirable. However, because the flow rate required from the hydraulic fluid pump according to the present disclosure is not a limiting characteristic of the design, such a loss of efficiency is not a disadvantage. The exact dimensions of the chamfer can be optimized, for example, by computer simulation (CFD) and confirmed by physical experiments. In some embodiments, a small bore passage which connects the hydraulic fluid pump discharge (outlet) to the hydraulic fluid pump inlet may be provided.

Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

CLAIMS:

1. A wellbore formation fluid pump system, comprising:

a wellbore formation fluid pump operable by a motor for lifting fluid entering the wellbore to the surface; and

a hydraulic fluid pump operably connected to the wellbore formation fluid pump, the hydraulic fluid pump configured to produce a selected fluid pressure sufficient to operate a hydraulically operable wellbore device when the wellbore formation fluid pump is operated at at least a threshold rate, the hydraulic fluid pump having a least one backflow feature to enable ending operation of the hydraulically operable wellbore device when the wellbore formation fluid pump is operated below the threshold rate.

2. The system of claim 1 , wherein the hydraulically operable wellbore device comprises a downhole safety valve.

3. The system of claim 2, wherein the downhole safety valve comprises a linear sleeve actuator operably coupled to a piston in fluid communication with an outlet of the hydraulic fluid pump so as to move the linear sleeve actuator to open the downhole safety valve when the wellbore formation fluid pump is operated at at least the threshold rate.

4. The system of any preceding claim, wherein the hydraulic fluid pump comprises at least one of a progressive cavity pump, a centrifugal pump, a gear pump, a vane pump and a trochoid pump.

5. The system of any preceding claim, wherein the at least one backflow feature comprises an internal passage to enable backflow of fluid through an interior of the hydraulic fluid pump.

6. The system of any preceding claim, wherein the at least one backflow feature comprises at least one of chamfer of gear teeth on a gear pump and passages on a gear face of a gear pump.

7. The system of any preceding claim, wherein the at least one backflow feature comprises a selected size fluid line connected between an outlet of the hydraulic fluid pump and an inlet of the hydraulic fluid pump.

8. The system of any preceding claim, wherein an actuator operable to open and close the downhole safety valve comprises a piston having a biasing device to close the downhole safety valve when hydraulic pressure on a side of the actuator used to open the safety valve falls below a selected threshold.

9. The system of claim 8 wherein the biasing device comprises a spring disposed between one side of the piston and an end of an actuation cylinder.

10. The system of any preceding claim, wherein the wellbore formation fluid pump comprises a rotary motor.

1 1. The system of any preceding claim, wherein the wellbore formation fluid pump comprises an electrically operated submersible pump.

12. The system of any preceding claim, wherein the downhole safety valve comprises a wireline retrievable safety valve.

13. The system of any preceding claim, wherein the hydraulic fluid pump is part of a closed circuit hydraulic system having a reservoir compensated for ambient fluid pressure in the wellbore at the location of the reservoir in the wellbore.

14. The system of claim 13 wherein the reservoir pressure compensation is provided by at least one of a flexible bladder, a bellows and a flexible diaphragm exposed on an exterior to ambient wellbore formation fluid pressure and on another side to the closed circuit hydraulic system.

15. The system of any preceding claim, wherein the backflow feature enables closure of the safety valve within a selected time limit when the wellbore formation fluid pump is operated below the selected threshold rate.

16. The system of any preceding claim, wherein the hydraulic fluid pump comprises a pressure relief valve operable to maintain a maximum pressure output of the hydraulic pump when the wellbore formation fluid pump is operated above a selected threshold speed.

17. A method for operating a downhole safety valve, comprising:

operating a hydraulic fluid pump using energy from operation of a wellbore formation fluid pump, the hydraulic fluid pump having a backflow feature such that pressure on an outlet of the hydraulic fluid pump is returned to an intake side of the hydraulic fluid pump at a predetermined rate;

operating a hydraulically operated wellbore device using pressure from the operating hydraulic fluid pump at at least a threshold rate; and

automatically stopping operation of the hydraulically operated wellbore device when the hydraulic fluid pump is operated below the threshold rate such that the backflow feature reduces hydraulic pressure below an amount required to operate the hydraulically operated wellbore device.

18. The method of claim 17, wherein the hydraulically operated wellbore device comprises a downhole safety valve.

19. The method of claim 18, wherein the downhole safety valve comprises an actuator operable to open and close the downhole safety valve comprises a piston having a biasing device to close the downhole safety valve when hydraulic pressure on a side of the actuator used to open the safety valve falls below a selected threshold.

20. The method of any one of claims 17 to 19, further comprising compensating a pressure in a hydraulic fluid system connected to the hydraulic fluid pump for ambient wellbore fluid pressure.

21. The method of any one of claims 17 to 20, wherein the backflow feature enables closure of the safety valve within a selected time limit when the wellbore formation fluid pump is operated below the selected threshold rate.

22. The method of any one of claims 17 to 21 , wherein the energy from operation of the wellbore fluid pump comprises rotational energy used to rotate the wellbore fluid pump coupled to a rotating energy input of the hydraulic fluid pump.