HYDRAULIC ACTUATOR WITH PRESSURE-BASED PISTON POSITION FEEDBACK

Abstract

A hydraulic actuator includes a piston housing having a head end and a base end opposite the head end and a drive piston movable between a first piston position proximate to the head end and a second piston position proximate to the base end. The hydraulic actuator further includes a control valve positionable between a first control valve position, in which the control valve directs fluid into the base end, and a second control valve position, in which the control valve directs fluid into the head end. A pressure-based position feedback system configured to facilitate transition of the control valve between the first control valve position and the second control valve position in response to predetermined head end and base end pressures.

Description

BACKGROUND

The field of the disclosure relates generally to oil and gas downhole pump assemblies and, more specifically, to hydraulic actuators for use in oil and gas pumping operations.

At least some known rod pumps are used in oil and gas wells, for example, to pump fluids from subterranean depths towards the surface. In operation, a pump assembly is placed within a well casing, well fluid enters the casing through perforations, and mechanical lift forces the fluids from subterranean depths towards the surface. For example, at least some known rod pumps utilize a downhole pump with complicated geometry, which by reciprocating action of a rod string, lifts the well fluid towards the surface.

In some known oil and gas well pump systems, one or more actuators may be used to facilitate the reciprocating action required for pumping fluid. In certain known systems, such actuators rely on one or more electronic components for providing power and/or control. However, due to the harsh conditions inherent in downhole pumping operations, electronic components can be subject to reduced reliability, significantly reducing the operational life of the actuator and increasing costs and downtime for repairs and replacements. Moreover, operators must rely on batteries with limited lifespans, expensive downhole generators, and/or long power supply lines to provide adequate power to the electronic components. Accordingly, a reliable actuator without the limitations associated with electronic power and control systems is desirable.

BRIEF DESCRIPTION

In one aspect, a hydraulic actuator for a downhole pump is provided. The hydraulic actuator includes a piston housing having a head end and a base end opposite the head end and a drive piston disposed within the piston housing. The drive piston is movable between a first piston position proximate to the head end and a second piston position proximate to the base end. The hydraulic actuator further includes a control valve positionable between a first control valve position and a second control valve position. In the first control valve position, the control valve is configured to direct fluid into the base end. In the second control valve position, the control valve is configured to direct fluid into said head end. The hydraulic actuator further includes a pressure-based position feedback system including a first pressure actuated valve coupled in fluid communication with the head end and a second pressure actuated valve coupled in fluid communication with the base end. The first pressure actuated valve is configured to facilitate transition of the control valve from the first control valve position to the second control valve position in response to a predetermined head end pressure. The second pressure actuated valve is configured to facilitate transition of the control valve from the second control valve position to the first control valve position in response to a predetermined base end pressure.

In a further aspect, a downhole pump system is provided. The downhole pump system includes a piston rod pump assembly and a hydraulic actuator coupled to the piston rod pump assembly. The hydraulic actuator includes a piston housing having a head end and a base end opposite the head end and a drive piston disposed within the piston housing. The drive piston is movable between a first piston position proximate to the head end and a second piston position proximate to the base end. The hydraulic actuator further includes a control valve positionable between a first control valve position and a second control valve position. In the first control valve position, the control valve is configured to direct fluid into the base end. In the second control valve position, the control valve is configured to direct fluid into said head end. The hydraulic actuator further includes a pressure-based position feedback system including a first pressure actuated valve coupled in fluid communication with the head end and a second pressure actuated valve coupled in fluid communication with the base end. The first pressure actuated valve is configured to facilitate transition of the control valve from the first control valve position to the second control valve position in response to a predetermined head end pressure. The second pressure actuated valve is configured to facilitate transition of the control valve from the second control valve position to the first control valve position in response to a predetermined base end pressure.

In another aspect, a method of controlling a hydraulic actuator is provided. The hydraulic actuator includes a piston housing having a head end and a base end opposite the head end. Thy hydraulic actuator further includes a drive piston disposed within the piston housing and movable between a first piston position proximate to the head end and a second piston position proximate to the base end. The hydraulic actuator also includes a control valve positionable between a first control valve position and a second control valve position. The method includes determining, using a first pressure actuated valve coupled in fluid communication with the head end, a head end pressure exceeds a predetermined head end pressure threshold. The method further includes transitioning, in response to determining the head end pressure exceeds the predetermined head end pressure threshold, the control valve into the second control valve position. The method also includes determining, using a second pressure actuated valve coupled in fluid communication with the base end, a base end pressure exceeds a predetermined base end pressure threshold. The method further includes transitioning, in response to determining the base end pressure exceeds the predetermined base end pressure threshold, the control valve into the first control valve position.

DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a perspective schematic illustration of an exemplary downhole pump system;

FIG. 2 is a schematic view of an exemplary hydraulic actuator that may be used in the downhole pump system of FIG. 1;

FIG. 3 is a schematic illustration of the hydraulic actuator shown in FIG. 2; and

FIG. 4 is a flow chart illustrating a method for controlling a hydraulic actuator, such as the hydraulic actuator of FIGS. 2 and 3.

Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of the disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of the disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

The actuator assemblies and associated methods described herein facilitate extending pump operation in harsh oil and gas well environments. Specifically, actuator assemblies described herein include a control valve configured to induce reciprocating motion of piston assemblies. To do so, the control valve alternately directs pressurized hydraulic fluid into a head end and base end of the piston assembly, inducing corresponding movement of a drive piston disposed within the piston assembly. The control valve is switched between two configurations, each configuration corresponding to a different fluid flow path, in response to feedback provided by a pressure-based position feedback system. The pressure-based position feedback system is configured to induce transition of the control valve in response to pressure at the base end and head end of the piston assembly exceeding a predetermined pressure threshold. In the exemplary embodiment, a first predetermined pressure threshold corresponds to a pressure at the head end of the piston assembly when the drive piston is substantially in the first piston position and a second predetermined pressure threshold corresponds to a pressure at the base end of the piston assembly when the drive piston is substantially in the second piston position.

FIG. 1 is a perspective schematic illustration of an exemplary downhole pump system 100. In the exemplary embodiment, pump system 100 includes a well head 102, production tubing 104 coupled to well head 102, and a pump assembly 110 coupled to production tubing 104 and positioned within a well bore 106. Well bore 106 is drilled through a surface 108 to facilitate the production of subterranean fluids such as, but not limited to, water and/or petroleum fluids. As used herein, “petroleum fluids” may refer to mineral hydrocarbon substances such as crude oil, gas, and combinations thereof.

Pump assembly 110 includes a piston rod pump assembly 112 and a hydraulic actuator 114 configured to actuate piston rod pump assembly 112. Hydraulic actuator 114 generally includes a hydraulic power section 116, a control section 118, and a piston section 120. During operation, a drive piston 122 disposed within piston section 120 is driven by hydraulic power section 116 subject to control by control section 118. More specifically, power section 116 provides pressurized hydraulic fluid to drive piston 122 while control assembly 118 dynamically redirects the pressurized hydraulic fluid provided by power section 116 to facilitate reciprocation of drive piston 122.

FIG. 2 is a schematic view of an exemplary hydraulic actuator 114 that may be used in downhole pump system 100 (shown in FIG. 1). FIG. 3 is a schematic illustration of hydraulic actuator 114. In the exemplary embodiment, hydraulic actuator 114 includes power section 116, control section 118, and piston section 120. Power section 116 includes an actuator motor 224 and an actuator pump 226. Actuator pump 226 is coupled in fluid communication with control section 118 and, more specifically, a valve manifold 228 including a control valve 230 disposed within control section 118. Control section 118 further includes a first pressure actuated valve 232 and a second pressure actuated valve 234 coupled in fluid communication with control valve 230 through a first hydraulic control line 258 and a second hydraulic control line 260, respectively. In the exemplary embodiment, first pressure actuated valve 232 and second pressure actuated valve 234 are pilot-operated sequence valves. For example, pressure actuated valves 232 and 234 are direct-acting sequence valves having an integral check valve to provide reverse flow from a sequence port (not shown) to an inlet port (not shown). Pressure actuated valves 232 and 234 supply a secondary circuit (e.g., hydraulic control lines 258 and 260) with fluid flow once the pressure at the inlet port has exceeded a predetermined pressure threshold. In alternative embodiments, first pressure actuated valve 232 and a second pressure actuated valve 234 are any suitable valves configured to actuate in response to detecting a predetermined pressure.

In certain embodiments, valve manifold 228 is a unitary valve manifold that includes first pressure actuated valve 232 and second pressure actuated valve 234. In such embodiments, valve manifold 228 may be manufactured using various techniques, including, without limitation, additive manufacturing. Hydraulic actuator 114 further includes piston section 120 including a piston housing 236 and drive piston 122 disposed within piston housing 236. In addition, hydraulic actuator 114 includes a compensator bag or compensator 244 that functions as a fluid volume storage device for hydraulic actuator 114 as well as actuator pump 226. Compensator 244 facilitates damping of pump pulsations transmitted through the fluid as well as energy storage, shock absorption, and other reservoir functions (e.g., fluid leakage make-up and fluid volume compensation due to temperature changes, etc.). In alternative embodiments, hydraulic actuator 114 further includes an accumulator 242 to facilitate accounting for variations in fluid volume during operation of hydraulic actuator 114, and in particular during a transition of control valve 230.

During operation, with reference to FIG. 3, drive piston 122 reciprocates between a first piston position 250 proximate to a head end 246 of piston housing 236 and second piston position 252 proximate to a base end 248 of piston housing 236. To facilitate reciprocation of drive piston 122, control valve 230 is configured to alternately direct fluid from actuator pump 226, which is driven by actuator motor 224, to head end 246 and base end 248 in response to the position of drive piston 122. More specifically, control valve 230 is configured to operate in a first control valve position in which pressurized fluid provided by actuator pump 226 is directed into head end 246 and a second control valve position in which the pressurized fluid is directed into base end 248. As the pressurized fluid is provided into head end 246, drive piston 122 is moved to second piston position 252 proximate to base end 248. Similarly, as pressurized fluid is provided into base end 248, drive piston 122 is moved to first piston position 250 proximate to head end 246. Accordingly, as control valve 230 alternates between the first control valve position and the second control valve position, drive piston 122 reciprocates within piston housing 236.

Control valve 230 switches between the first control valve position and the second control valve position in response to positional feedback provided by first pressure actuated valve 232 and second pressure actuated valve 234. First pressure actuated valve 232 is coupled in fluid communication with head end 246 of piston housing 236 and second pressure actuated valve 234 is coupled in fluid communication with base end 248. In the exemplary embodiment, first pressure actuated valve 232 is coupled in fluid communication with a head end hydraulic line 238 for providing hydraulic fluid from actuator pump 226 to head end 246 of piston housing 236, and second pressure actuated valve 234 is coupled in fluid communication with a base end hydraulic line 240 for providing hydraulic fluid from actuator pump 226 to base end 248 of piston housing 236. In alternative embodiments, first pressure actuated valve 232 and second pressure actuated valve 234 are otherwise coupled in fluid communication to each of head end 246 and base end 248 to detect hydraulic fluid pressure corresponding to each of head end 246 and base end 248, respectively. For example, in certain embodiments, first pressure actuated valve 232 and second pressure actuated valve 234 are coupled in fluid communication with head end 246 and base end 248, respectively, through pressure taps installed in head end 246 and base end 248 of piston housing 236.

Each of first pressure actuated valve 232 and second pressure actuated valve 234 are configured to actuate in response to experiencing a predetermined fluid pressure. In the exemplary embodiment, first pressure actuated valve 232 is configured to actuate in response to a head end pressure exceeding a predetermined head end pressure threshold, and second pressure actuated valve 234 is configured to actuate in response to a base end pressure exceeding a predetermined based end pressure threshold. More specifically, first pressure actuated valve 232 is coupled in fluid communication with head end 246 by head end hydraulic line 238 and actuates in response to a pressure within head end hydraulic line 238 corresponding to a head end pressure exceeding the predetermined head end pressure threshold. For example, as drive piston 122 is moved to first piston position 250 (i.e., drive piston 122 dead ends against head end 246), a pressure in the hydraulic fluid is increased, or spikes, to a pressure exceeding the predetermined head end pressure threshold. Similarly, second pressure actuated valve 234 is coupled in fluid communication with base end 248 by base end hydraulic line 240 and actuates in response to a pressure within base end hydraulic line 240 corresponding to a base end pressure exceeding the predetermined base end pressure threshold.

During operation, when control valve 230 is in the first control valve position, control valve 230 directs fluid provided by actuator pump 226 into base end 248 and drive piston 122 moves towards head end 246. As drive piston 122 moves towards head end 246, pressure within head end hydraulic line 238 increases until the predetermined head end pressure threshold is exceeded. When the predetermined head end pressure threshold is exceeded, first pressure actuated valve 232 actuates, causing pressurized fluid to flow to control valve 230 via hydraulic control line 258 to translate control valve 230 into the second control valve position. In the exemplary embodiment, the predetermined head end pressure threshold is selected such that first pressure control valve 232 actuates when drive piston 122 is located substantially in first piston position 250, thereby providing positional feedback corresponding to the position of drive piston 122 within piston housing 236. In the second control valve position, control valve 230 directs fluid provided by actuator pump 226 into head end 246 and drive piston 122 moves towards base end 248. As drive piston 122 moves towards base end 248, pressure within base end hydraulic line 240 increases until the predetermined base end pressure threshold is exceeded. When the predetermined base end pressure threshold is exceeded, second pressure actuated valve 234 actuates, causing pressurized fluid to flow to control valve 230 via hydraulic control line 260 to translate control valve 230 into the first control valve position. In the exemplary embodiment, the predetermined base end pressure threshold is selected such that second pressure actuated valve 234 actuates when drive piston 122 is located substantially in second piston position 252. The foregoing process of control valve 230 redirecting fluid alternately into head end 246 and base end 248 may be repeated to facilitate reciprocating motion of drive piston 122.

In the exemplary embodiment, control valve 230 is a two-position, detented, four-way directional valve. Alternatively, control valve 230 may be a three-position, detented, four-way valve or any other valve configuration that enables pump system 100 to function as described herein. In the exemplary embodiment, control valve 230 includes an internal mechanical detent that facilitates holding the valve in position until a minimum pilot fluid pressure is applied to a pilot port (not shown) of control valve 230. For example, in the exemplary embodiment, control valve 230 is switched between the first control valve position and the second control valve position by applying the minimum pilot fluid pressure to one of the pilot ports, where control valve 230 remains in that position, with no pilot fluid pressure applied, until a new pilot fluid pressure signal is temporarily applied to the opposite pilot port. As such, control valve 230 is configured to remain in either the first control valve position or the second control valve position until either first pressure actuated valve 232 or second pressure actuated valve 234 is actuated, respectively. Accordingly, control valve 230 continues to direct fluid into head end 246 and base end 248 until drive piston 122 is substantially in second piston position 234 and first piston position 232, respectively.

In certain embodiments, hydraulic actuator 114 includes features configured to reduce forces of components as drive piston 122 reciprocates within piston housing 236. Drive piston 122 is configured to dead end in head end 246 and base end 248 of piston housing 236, and as such, hydraulic actuator 114 includes deceleration features configured to facilitate decelerating drive piston 122 to facilitate increasing its longevity. For example, piston housing 236 defines a plurality of longitudinal grooves 266 proximate to head end 246 and base end 248 such that as drive piston 122 approaches head end 246 and base end 248, a pressure differential across drive piston 122 is reduced due to leakage of the fluid through grooves 266, causing deceleration of drive piston 122. In alternative embodiments, piston housing 236 includes other deceleration features including, without limitation, springs and bumpers disposed in head end 246 and base end 248 to facilitate deceleration of drive piston 122 and/or hydraulic cushioning features including a tapered piston bore and similar tapered features on drive piston 122.

FIG. 4 is a flow chart illustrating a method 400 for controlling a hydraulic actuator, such as hydraulic actuator 114 (shown in FIGS. 2 and 3). Referring to FIG. 2, FIG. 3, and FIG. 4, hydraulic actuator 114 generally includes piston housing 236 having head end 246 and base end 248 opposite head end 246, drive piston 122 disposed within piston housing 236 and movable between first piston position 250 proximate to head end 246 and second piston position 252 proximate to base end 248. Hydraulic actuator 114 further includes control valve 230 positionable between a first control valve position and a second control valve position. Control valve 230 is positionable between the first control valve position and the second control valve position based, at least in part, on positional feedback provided by first pressure actuated valve 232 and second pressure actuated valve 234. More specifically, first pressure actuated valve 232 is configured to actuate in response to a fluid pressure within head end 246 exceeding a predetermined head end pressure threshold and, upon actuation, to cause control valve 230 to translate into the second control valve position. Similarly, second pressure actuated valve 234 is configured to actuate in response to a fluid pressure within base end 248 exceeding a predetermined base end pressure threshold and, upon actuation, to cause control valve 230 to translate into the first control valve position. In the exemplary embodiment, each of first pressure actuated valve 232 and second pressure actuated valve 234 are pilot-operated pressure sequence valves.

Method 400 includes determining 402, using first pressure actuated valve 232, that a head end pressure within head end 246 exceeds a predetermined head end pressure threshold. For example, in the exemplary embodiment, first pressure actuated valve 232 is coupled in fluid communication with head end 246 by a head end hydraulic line 238 and is configured to respond to pressure within head end 246 through head end hydraulic line 238. As drive piston 122 moves within piston housing 246, pressure within head end hydraulic line 238 varies. More specifically, as drive piston 122 moves towards head end 246, pressure within head end 246, and by extension head end hydraulic line 238, increases until first pressure actuated valve 232 actuates in response to the pressure within head end 246 exceeding the predetermined head end pressure threshold. In the exemplary embodiment, the predetermined head end pressure threshold corresponds to a head end pressure when drive piston 122 is substantially in first piston position 250.

Method 400 further includes transitioning 404, in response to determining the head end pressure exceeds the predetermined head end pressure threshold, control valve 230 into the first control valve position. In the first control valve position, control valve 230 is configured to direct fluid into head end 246 of piston housing 236. In actuator assembly 114, for example, first pressure actuated valve 232 is coupled in fluid communication with control valve 230 via hydraulic control line 258 such that when first pressure actuated valve 232 is actuated when the head end pressure exceeds the predetermined head end pressure threshold, first pressure actuated valve 232 facilitates transition of control valve 230 into the second control valve position.

Method 400 also includes determining 406, using second pressure actuated valve 234, that a base end pressure within base end 248 exceeds a predetermined base end pressure threshold. For example, in the exemplary embodiment, second pressure actuated valve 234 is coupled in fluid communication with base end 248 by a base end hydraulic line 240 and is configured to respond to pressure within base end 248 through base end hydraulic line 240. As drive piston 122 moves within piston housing 246, pressure within base end hydraulic line 240 varies. More specifically, as drive piston 122 moves towards base end 248, pressure within base end 248, and by extension base end hydraulic line 240, increases until second pressure actuated valve 232 actuates in response to the pressure within base end 248 exceeding the predetermined base end pressure threshold. In the exemplary embodiment, the predetermined base end pressure threshold corresponds to a base end pressure when drive piston 122 is substantially in second piston position 252.

Method 400 further includes transitioning 408, in response to determining the base end pressure exceeds the predetermined base end pressure threshold, control valve 230 into the second control valve position. In the second control valve position, control valve 230 is configured to direct fluid into base end 248 of piston housing 236. In actuator assembly 114, for example, second pressure actuated valve 234 is coupled in fluid communication with control valve 230 via hydraulic control line 260 such that when second pressure actuated valve 234 is actuated when the second fluid pressure exceeds the predetermined base end pressure threshold, second pressure actuated valve 234 facilitates transition of control valve 230 into the second control valve position. In the exemplary embodiment, control valve 230 is configured to latch into the first control valve position upon transitioning. As indicated in FIG. 4, after the step of transitioning 408 control valve 230 into the second control valve position, steps 402-408 may repeat, thereby resulting in a reciprocating action of drive piston 122.

In the exemplary embodiment, control valve 230 is configured to latch into the first and second control valve positions upon transitioning. For example, in the exemplary embodiment, control valve 230 is a detent valve configured to stay in either the first or second control valve position until drive piston 122 completes its stroke and the pressure thresholds at each end are exceeded, which triggers control valve 230 to unlatch to move to a different position.

The actuator assemblies described herein facilitate extending pump operation in harsh oil and gas well environments. Specifically, the actuator assemblies described herein facilitate reciprocation of a drive piston based on a pressure-based position feedback system. The pressure-based position feedback system is configured to translate a control valve to alternately direct fluid into a head end and a base end of a piston housing. As the drive piston reaches either the head end or the base end, the position feedback system switches the control valve to direct fluid into the piston housing to facilitate movement of the drive piston in the opposite direction.

An exemplary technical effect of the methods, systems, and assembly described herein includes at least one of: (a) improving reliability of actuator assemblies as compared to electronically controlled actuator assemblies; (b) improving the operational life of actuator assemblies; (c) improving the service life of downhole pump systems including actuator assemblies; and (d) reducing downhole pump operating costs.

Exemplary embodiments of methods, systems, and apparatus for actuator assemblies are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods, systems, and apparatus may also be used in combination with other pumping systems outside of the oil and gas industry. Rather, the exemplary embodiment can be implemented and utilized in connection with many other applications, equipment, and systems that may benefit from improved reciprocating actuator assemblies.

Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

1. A hydraulic actuator comprising:

a piston housing having a head end and a base end opposite said head end;

a drive piston disposed within said piston housing and movable between a first piston position proximate to said head end and a second piston position proximate to said base end;

a control valve positionable between a first control valve position and a second control valve position, wherein: in the first control valve position, said control valve is configured to direct fluid into said base end; and in the second control valve position, said control valve is configured to direct fluid into said head end; and

a pressure-based position feedback system comprising: a first pressure actuated valve coupled in fluid communication with said head end, said first pressure actuated valve configured to facilitate transition of said control valve from the first control valve position to the second control valve position in response to a predetermined head end pressure; and a second pressure actuated valve coupled in fluid communication with said base end, said second pressure actuated valve configured to facilitate transition of said control valve from the second control valve position to the first control valve position in response to a predetermined base end pressure.

2. The actuator in accordance with claim 1, wherein at least one of said first pressure actuated valve and said second pressure actuated valve is a pilot-operated pressure sequence valve.

3. The actuator in accordance with claim 1 further comprising at least one deceleration feature proximate to at least one of said first piston position and said second piston position.

4. The actuator in accordance with claim 3, wherein said at least one deceleration feature comprises at least one of a groove defined by said piston housing, a spring, a hydraulic cushion, and a bumper.

5. The actuator in accordance with claim 1, wherein said control valve comprises at least one of a two-position, detented, four-way directional control valve and a three-position, detented, four-way directional control valve.

6. The actuator in accordance with claim 1 further comprising a unitary valve manifold comprising each of said control valve, said first pressure actuated valve, and said second pressure actuated valve.

7. A downhole pump system comprising:

a piston rod pump assembly; and

a hydraulic actuator coupled to said piston rod pump assembly, said hydraulic actuator comprising: a piston housing having a head end and a base end opposite said head end; a drive piston disposed within said piston housing and movable between a first piston position proximate to said head end and a second piston position proximate to said base end; a control valve positionable between a first control valve position and a second control valve position, wherein: in the first control valve position, said control valve is configured to direct fluid into said base end; and in the second control valve position, said control valve is configured to direct fluid into said head end; and a pressure-based position feedback system comprising: a first pressure actuated valve coupled in fluid communication with said head end, said first pressure actuated valve configured to facilitate transition of said control valve from the first control valve position to the second control valve position in response to a predetermined head end pressure; and a second pressure actuated valve coupled in fluid communication with said base end, said second pressure actuated valve configured to facilitate transition of said control valve from the second control valve position to the first control valve position in response to a predetermined base end pressure.

8. The downhole pump system in accordance with claim 7 further comprising:

an actuator pump configured to provide fluid to said piston housing through said control valve; and

an actuator motor coupled to said actuator pump and configured to drive said actuator pump.

9. The downhole pump system in accordance with claim 8 further comprising at least one of an accumulator and a compensator bag, coupled in fluid communication with said actuator pump.

10. The downhole pump system in accordance with claim 8, wherein said actuator pump is a positive displacement pump.

11. The downhole pump system in accordance with claim 7, wherein at least one of said first pressure actuated valve and said second pressure actuated valve is a pilot-operated pressure sequence valve.

12. The downhole pump system in accordance with claim 7 further comprising at least one deceleration feature proximate to at least one of the first piston position and the second piston position.

13. The downhole pump system in accordance with claim 12, wherein said at least one deceleration feature comprises at least one of a groove defined by said piston housing, a spring, a hydraulic cushion, and a bumper.

14. The downhole pump system in accordance with claim 7, wherein said control valve comprises at least one of a two-position, detented, four-way directional control valve and a three-position, detented, four-way directional control valve.

15. The downhole pump system in accordance with claim 7 further comprising a unitary valve manifold comprising each of said control valve, said first pressure actuated valve, and said second pressure actuated valve.

16. The downhole pump system in accordance with claim 7, further comprising a piston rod extending from said drive piston, said piston rod coupling said drive piston to said piston rod pump assembly.

17. A method of controlling a hydraulic actuator, the hydraulic actuator including a piston housing having a head end and a base end opposite the head end, a drive piston disposed within the piston housing and movable between a first piston position proximate to the head end and a second piston position proximate to the base end, and a control valve positionable between a first control valve position and a second control valve position, said method comprising:

determining, using a first pressure actuated valve coupled in fluid communication with the head end, a head end pressure exceeds a predetermined head end pressure threshold;

transitioning, in response to determining the head end pressure exceeds the predetermined head end pressure threshold, the control valve into the second control valve position;

determining, using a second pressure actuated valve coupled in fluid communication with the base end, a base end pressure exceeds a predetermined base end pressure threshold; and

transitioning, in response to determining the base end pressure exceeds the predetermined base end pressure threshold, the control valve into the first control valve position.

18. The method in accordance with claim 17 further comprising latching the control valve in at least one of the first control valve position and the second control valve position after translating the control valve into the first control valve position and second control valve position, respectively.

19. The method in accordance with claim 17, wherein at least one of the first pressure actuated valve and the second pressure actuated valve is a pilot-operated pressure sequence valve.

20. The method in accordance with claim 17, wherein the first predetermined fluid pressure corresponds to a fluid pressure within the head end when the drive piston is substantially in the first piston position, and the second predetermined fluid pressure corresponds to a fluid within the base end when the drive piston is substantially in the second piston position.