Low power miniature hydraulic actuator

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit under 35 USC §119 of the filing date of international application PCT/US00/29972, filed Oct. 31, 2000, the disclosure of which is incorporated herein by this reference.

TECHNICAL FIELD

The present invention relates generally to methods and apparatus utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a compact electrohydraulic actuation system for downhole tools used in subterranean wells.

BACKGROUND

It would be desirable to be able to operate selected ones of multiple hydraulically actuated well tools installed in a well. However, it is uneconomical and practically unfeasible to run separate hydraulic control lines from the surface to each one of numerous well tool assemblies. Instead, the number of control lines extending relatively long distances should be minimized as much as possible. Additionally, it would be desirable to effect the operation of multiple hydraulically actuated well tools with a relatively low power consumption control system.

Therefore, it would be highly advantageous to provide a hydraulically-based control system and associated control methods which reduce the number of control lines extending relatively long distances between multiple hydraulically actuated well tools and the surface. The control system would preferably permit individual ones of the well tools to be selected for actuation as desired, and the selection of well tools should be convenient and reliable.

SUMMARY

In carrying out the principles of the present invention, in accordance with an embodiment thereof, a compact hydraulic actuator and associated methods are provided which solve the above problem in the art.

According to one aspect of the invention, a downhole well tool assembly, representatively a flow control device in the form of a variable inlet choke device, is controlled using a fluid power source connected thereto and including a first source of pressurized fluid operable to power the downhole well tool assembly via a first fluid circuit portion connectable to the downhole well tool assembly, and a second source of pressurized fluid having a second fluid circuit portion interposed in the first fluid circuit portion, the second source of pressurized fluid being operable to selectively alter the routing of pressurized fluid to the downhole well tool assembly. The fluid power source is preferably disposed entirely downhole, and is electrically operable.

In an illustrated embodiment of the actuator, the first source of pressurized fluid includes a reciprocating hydraulic primary pump which is coupled to the well tool assembly by the first circuit portion, and has a reversible electric drive motor. Check valves interposed in the first circuit portion the primary pump a double pumping action. The second source of pressurized fluid includes a reciprocating hydraulic switching pump used to control fluid pressure operable pilot check valves in the second fluid circuit portion and in a manner selectively reversing the fluid supply and return flow directions to the controlled well tool assembly via the first fluid circuit portion.

In the illustrated embodiment of the actuator, the actuator construction includes a body having first and second bores extending therethrough, the first and second bores respectively having radially enlarged first and second cylinder portions with opposite ends. First and second rods are reciprocably disposed in the first and second bores and have radially enlarged piston portions slidably received in the first and second cylinder portions and dividing each of them into opposing first and second hydraulic chambers that may be coupled to fluid circuitry. First and second drive portions extend outwardly from the body and have reversible electric motors respectively coupled to the first and second rods, to reciprocate them in the first and second body bores, via gearing and ball screw structures.

According to another aspect of the invention, a pilot check valve is carried in the first bore and is connectable to the first fluid circuit portion, the pilot check valve being selectively engageable ay an end portion of the first rod to disable the fluid flow blocking function of the pilot check valve.

In accordance with another aspect of the invention, a first accumulator is communicated with the first fluid circuit portion, is chargeable by the first source of fluid pressure, and is selectively communicatable with the controlled well tool assembly to rapidly open or close a control drive portion thereof. A second, smaller accumulator is preferably interconnected between the first accumulator and the first fluid circuit portion, and functions to maintain a minimum fluid pressure in the first fluid circuit portion.

In accordance with a further aspect of the present invention, a well completion is provided in the wellbore of which are provided a spaced series of downhole well tool assemblies which are representatively flow control devices in the form of variable fluid chokes. Each flow control device is operatively connected to one of the downhole hydraulic actuators, and, according to a method of the present invention, a control system is used to sense the magnitudes of predetermined operational parameters of the chokes and responsively control the operation of their associated first and second sources of pressurized fluid in a manner maintaining the magnitudes of the sensed operational parameters at predetermined levels.

Representatively, the sensed operational parameters are fluid pressure drops across the variable inlet opening areas of the chokes. In various representative embodiments of this control method, the control system is operative to maintain predetermined minimum fluid pressure drops across the inlet opening area, representatively by maintaining predetermined minimum positive exterior-to-interior fluid pressure drops across the inlet opening areas, or may be operative to maintain substantially equal fluid pressure drops across all of the variable inlet opening areas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a highly schematic cross-sectional view through a portion of a subterranean well completion in which a series of well tool assemblies, representatively flow control devices, are disposed and operated by specially designed electrohydraulic actuators embodying principles of the present invention;

FIG. 2

is a schematic circuit diagram of one of the actuators;

FIG. 3

a schematic control diagram for a representative one of the actuators; and

FIG. 4

is a highly schematic cross-sectional view through a portion of an alternate embodiment of the subterranean well completion shown in FIG.

1

.

DETAILED DESCRIPTION

Representatively and schematically illustrated in

FIG. 1

is a downhole portion of a subterranean well completion

10

which embodies principles of the present invention. In the following description of the well completion

10

and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used only for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention.

The portion of the well completion

10

schematically illustrated in

FIG. 1

representatively includes a generally vertical cased and cemented-in wellbore

12

which illustratively intersects three spaced apart subterranean production formations or zones

14

,

16

and

18

, with the usual wellbore perforations

20

communicating the production zones

14

,

16

and

18

with the interior of the wellbore. Production tubing

22

is extended through the wellbore

12

and forms therewith an annular space

24

. Annular packers

26

,

28

and

30

are used to sealingly divide the annular space

24

into longitudinal segments

24

a

,

24

b

, and

24

c

that are respectively communicated with the production zones

14

,

16

and

18

via the various wellbore perforations

20

.

While the apparatus and methods of the present invention described herein will be described in conjunction with the representatively vertical, cased wellbore

12

it is to be clearly understood that methods and apparatus embodying principles of the present invention may be utilized in other environments, such as horizontal or inclined wellbore portions, uncased wellbore portions, etc. Furthermore, the apparatus and methods of the present invention will be representatively described herein in terms of producing fluid from the well, but such apparatus and methods can also be utilized in injection operations without departing from principles of the present invention. As used herein, the term “wellbore” is intended to include both cased and uncased wellbores.

Still referring to

FIG. 1

, a plurality of well tool assemblies

32

a

,

32

b

and

32

c

, representatively hydraulically operable variable flow choke devices, are operatively installed in the production tubing

22

, with the choke

32

a

being disposed between the packers

26

,

28

and associated with the production zone

14

, the choke

32

b

being disposed between the packers

28

,

30

and associated with the production zone

16

, and the choke

32

c

being positioned below the packer

30

and associated with the production zone

18

. The chokes

32

a

-

32

c

are of conventional construction, with each of them having a schematically depicted inlet opening area

34

through which production fluid entering its associated wellbore annulus portion may inwardly flow for upward transport to the surface via the interior of the production tubing

22

. While three chokes

32

a

-

32

c

have been representatively illustrated herein, it will be readily appreciated that a greater or lesser number of such chokes could be incorporated in the well completion

10

without departing from principles of the present invention.

One of the variable chokes, representatively choke

32

a

, is schematically depicted in FIG.

2

and has a hydraulically operable drive portion

36

that is operable in a known manner to selectively vary the inlet opening area

34

of the choke. The drive portion

36

illustratively includes a hollow cylindrical body

38

through the opposite ends of which a rod

40

slidingly and sealingly passes. Rod

40

has a radially enlarged central portion which defines a piston

42

that slidingly and sealingly engages the interior side surface of the body

38

, is axially reciprocable therein, and divides the interior of the body

38

into opposite right and left chambers

44

and

46

.

When the hydraulic pressure in chamber

44

is greater than that in chamber

46

, the rod and piston structure

40

,

42

is shifted leftwardly relative to the body

38

to increase the opening area

34

of choke

32

a

. Conversely, when the hydraulic pressure in chamber

46

is greater than that in chamber

44

, the rod and piston structure

40

,

42

is shifted rightwardly relative to the body

38

to decrease the opening area

34

of choke

32

a

. AS schematically depicted in

FIG. 1

, each of the chokes

32

a

,

32

b

,

32

c

has a position sensing section

48

operable to output a control signal indicative of the position of the rod and piston structure

42

, and therefore indicative of the degree to which its associated choke is open or closed to fluid inflow. For purposes later described herein, the production tubing

22

(see FIG.

2

), adjacent each of the variable chokes

32

a

,

32

b

,

32

c

, has associated therewith exterior and interior pressure sensors

50

,

52

which respectively monitor the fluid pressure exterior to the production tubing

22

and the pressure within the production tubing

22

and generate a combinative signal indicative of the pressure drop across the inlet opening area

34

of their associated choke

32

.

According to a key aspect of the present invention, each of the chokes

32

a

,

32

b

,

32

c

is controlled by a specially designed low power miniature hydraulic actuator

54

(see

FIG. 1

) which is positioned downhole adjacent its associated choke and is electrically operable at a low peak wattage which is illustratively in the range of about 5-10 watts. one of the actuators

54

, representatively the one associated with the choke

32

a

, will now be described with reference to FIG.

2

.

Each actuator

54

includes an overall fluid power source that illustratively comprises a generally rectangularly shaped metal body

56

which carries a first fluid pressure source, representatively in the form of an electrically operable reciprocating hydraulic primary pump

58

, and a second fluid pressure source, representatively in the form of an electrically operable reciprocating hydraulic switching pump

60

.

Pump

58

includes a cylinder structure

62

defined by a radially enlarged portion of a circular bore

64

extending inwardly through the left end of the body

56

, the cylinder

62

having left and right ends

66

,

68

and slidingly and sealingly receiving an enlarged central piston portion

70

of a rod

72

reciprocably received in the bore

64

. Piston

70

divides the interior of the cylinder

62

into left and right opposing chambers

74

and

76

, and a left end portion of the rod

72

projects outwardly through the left end of the body

56

into a cylindrical housing structure

78

.

At the left end of the housing structure

78

is a reversible electric motor

80

which is drivingly connected, via a gear train

82

, to a schematically depicted ball screw

84

which, in turn, is drivingly connected to the rod

72

. Motor

80

is connected, via leads

86

and

88

, to an electrical power source which, as schematically depicted in

FIG. 1

, is representatively disposed on the surface and extended downhole via an electrical cable

90

. Alternately, the electrical power source may be disposed downhole (as schematically depicted in

FIG. 4

) in the form of, for example, one or more batteries

92

or another type of self-contained downhole electrical power source well known in this particular art.

A first fluid circuit portion is interconnected between the primary pump

58

and the choke drive portion

36

and includes hydraulic lines

94

-

99

which are interconnected as schematically shown in FIG.

2

. Four check valves

100

,

102

,

104

,

106

are respectively interposed as shown in the hydraulic lines

94

-

97

, with each of these four check valves permitting fluid flow therethrough only in the direction indicated by the flow arrow adjacent such valve.

For purposes later described herein, a main fluid pressure accumulator

108

and a smaller auxiliary fluid pressure accumulator

110

are incorporated in the actuator

54

. Accumulator

108

has a piston

112

slidingly and sealingly disposed therein and dividing the interior of the accumulator

108

into opposing left and right chambers

114

and

116

. A coiled compression spring

118

disposed in the chamber

116

resiliently biases the piston

112

toward the left end of the accumulator

108

. The smaller auxiliary accumulator

110

is of a similar construction, having a piston

120

slidingly and sealingly disposed therein and dividing the interior of the accumulator

110

into opposing top and bottom chambers

122

and

124

. A coiled compression spring

126

resiliently biases the piston

120

toward the upper end of the accumulator

110

.

Chamber

114

of the accumulator

108

is communicated with the right end of the body bore

64

by a hydraulic line

128

, and the chamber

116

of the accumulator

108

is communicated with the hydraulic line

97

, and with the chamber

122

of the accumulator

110

, by a hydraulic line

130

. For purposes later described herein, a mechanically operable pilot check valve

132

is disposed within the body bore

64

and is coupled between the hydraulic lines

95

a

and

128

as indicated. Under normal operation thereof the check valve

132

is open to flow therethrough from the line

95

a

to the line

128

(as indicated by the flow arrow adjacent the valve

132

) but blocks flow therethrough from the line

128

to the line

95

a

. However, when a mechanical pilot force is exerted on the left end of the valve

132

, its flow blocking function is disabled to permit fluid flow in either direction therethrough. This mechanical pilot force may be applied to the valve

132

by a reduced diameter right end portion

134

of the rod

72

which forcibly contacts the left end of the valve

132

when the primary pump piston

70

is stroked clear to the right or distal end

68

of the cylinder

62

as later described herein.

The switching pump

60

includes a cylinder structure

136

defined by a radially enlarged portion of a circular bore

138

extending inwardly through the left end of the body

56

, the cylinder

136

having left and right ends

140

,

142

and slidingly and sealingly receiving an enlarged central piston portion

144

of a rod

146

reciprocably received in the bore

138

. Piston

144

divides the interior of the cylinder

136

into left and right opposing chambers

148

and

150

, and a left end portion of the rod

146

projects outwardly through the left end of the body

56

into a cylindrical housing structure

152

.

At the left end of the housing structure

152

is a reversible electric motor

154

which is drivingly connected, via a gear train

156

, to a schematically depicted ball screw

158

which, in turn, is drivingly connected to the rod

146

. Motor

154

is connected, via leads

160

and

162

, to the previously mentioned electrical power source.

A second fluid circuit portion is interposed in the previously described first fluid circuit portion

94

-

99

and is operable as later described herein to selectively alter the routing of pressurized hydraulic fluid to the choke drive portion

36

. This second fluid circuit portion comprises four fluid pressure operated pilot check valves

164

,

166

,

168

,

170

and hydraulic lines

172

-

177

which are connected to the pump

60

, the pilot check valves

164

,

166

,

168

and

170

, and the first fluid circuit hydraulic lines

95

,

97

,

98

and

99

as schematically depicted in FIG.

2

.

Each of the pilot check valves

164

,

166

,

168

and

170

is normally operable to permit fluid flow therethrough in the single direction indicated by the flow arrow adjacent the valve, but to block fluid flow in the reverse direction therethrough. However, when pilot fluid pressure is exerted on the right end of any of the check valves

164

,

166

,

168

and

170

, its flow blocking function is disabled, and fluid may flow therethrough in either direction.

The switching pump

60

and its associated second fluid circuit portion just described provides the overall hydraulic circuitry of the actuator

54

with a mechanical switching logic that permits various control manipulations of the choke drive portion

36

to be carried out by selectively controlling the pilot check valves

164

,

166

,

168

and

170

to variably route pressurized hydraulic fluid to and from the chambers

44

and

46

of the choke drive portion

36

.

Switching pump

60

may be controlled to position its piston

144

in a selected one of three positions within its cylinder

136

—(1) a centered position (shown in

FIG. 2

) in which all of the pilot check valves

164

,

166

,

168

and

170

are operative to permit fluid flow leftwardly therethrough, but block fluid flow rightwardly therethrough; (2) a rightwardly shifted position in which pilot fluid pressure from the right cylinder chamber

150

is transmitted via hydraulic line

172

to the right ends of the check valves

164

and

170

to disable their fluid flow blocking functions and thereby permit both leftward and rightward fluid flow therethrough while the check valves

166

,

168

continue to preclude rightward fluid flow therethrough; and (3) a leftwardly shifted position in which pilot fluid pressure from the left cylinder chamber

148

is transmitted via hydraulic line

173

to the right ends of the check valves

166

,

168

to disable their fluid flow blocking functions and thereby permit both leftward and rightward fluid flow therethrough while the check valves

164

,

170

continue to preclude rightward fluid flow therethrough.

During normal operation of the primary hydraulic pump

58

its electric motor

80

is cyclically reversed to cause reciprocation of the piston

70

within its cylinder

62

between left and right limit positions inwardly offset from the opposite ends

66

,

68

of the cylinder

62

. During this normal reciprocating operation of the primary hydraulic pump

58

, the piston

70

does not reach the right or distal end of the cylinder

62

. Accordingly, the pilot check valve

132

is not forcibly contacted by the right end portion

134

of the rod

72

and thus continues to block fluid flow leftwardly therethrough.

To move the choke drive piston

42

in a leftward opening direction, the switching pump piston

144

is driven rightwardly from its centered position within the cylinder

136

to pressurize line

172

and disable the fluid blocking functions of the pilot check valves

164

and

170

, and the main pump piston

70

is caused to reciprocably stroke in its normal pumping mode. On each rightward stroke of the main pump piston

70

, an incremental amount of pressurized hydraulic fluid is forced into the choke drive portion chamber

44

from the primary pump chamber

76

sequentially through the lines

95

and

174

, the pilot check valve

164

, and the line

98

. With the accumulator

108

being previously charged in a manner later described herein, pressurized hydraulic fluid in the accumulator chamber

114

is communicated (via line

128

) with the right end of the bore

64

to thereby prevent rightward flow of fluid through the pilot check valve

132

.

Entry of pressurized hydraulic fluid into the choke drive portion chamber

44

drives the piston

42

leftwardly a small distance within the body

38

and forcibly returns a corresponding incremental volume of hydraulic fluid from the choke drive portion chamber

46

into the left chamber

74

of the primary pump

58

sequentially through lines

99

and

177

, pilot check valve

170

, and lines

176

,

97

,

96

and

94

. The presence of the four check valves

100

,

102

,

104

,

106

in the hydraulic circuitry of the actuator

54

provides the primary pump

58

with a double pumping action such that when the primary pump piston

70

is subsequently stroked in a leftward direction within the cylinder

62

another incremental volume of pressurized hydraulic fluid is forced into the choke drive portion chamber

44

—this time from the left cylinder chamber

74

sequentially through lines

94

,

95

and

174

, pilot check valve

164

, and line

98

. The resulting leftward incremental movement of the choke drive portion piston

42

forcibly returns a corresponding volume of hydraulic fluid to the right main pump chamber

76

sequentially through lines

99

and

177

, the pilot check valve

170

, and the lines

176

,

97

and

95

.

To move the choke drive portion piston

42

in a rightward closing direction, the primary pump

58

is operated in its normal reciprocating pumping mode with the switching pump piston

144

leftwardly shifted from its center position to thereby pressurize line

173

and disable the fluid blocking function of the pilot check valves

166

and

168

. During a rightward stroke of the primary pump piston

70

, an incremental volume of pressurized hydraulic fluid is forced into the left choke drive portion chamber

46

from the primary pump chamber

76

sequentially through lines

95

and

174

, pilot check valve

166

and line

199

. The resulting rightward incremental movement of the choke drive portion piston

42

forcibly returns a corresponding volume of hydraulic fluid to the left primary pump chamber

74

sequentially via lines

98

and

175

, pilot check valve

168

, and lines

176

,

97

,

96

and

94

.

During the subsequent leftward stroke of the primary pump piston

70

, an incremental amount of pressurized hydraulic fluid is forced into the left choke drive portion chamber

46

from the left main pump chamber

74

sequentially through lines

94

,

95

and

174

, the pilot check valve

166

and the line

99

. The resulting rightward incremental movement of the piston

42

forcibly returns a corresponding incremental volume of hydraulic fluid from the right choke drive portion chamber

44

to the right primary pump chamber

76

sequentially through the lines

98

and

175

, the pilot check valve

168

, and lines

176

,

97

and

94

. As will be appreciated, the total opening or closing distance that the choke drive portion piston

42

is moved corresponds (for a given piston stroke distance) to the total number of pumping strokes imparted to the primary pump piston

70

by its associated reversible electrical drive motor

80

.

As just described, the choke drive portion piston

42

may be incrementally driven by the electrohydraulic actuator

54

leftwardly or rightwardly to progressively (and rather slowly) increase or decrease the inlet opening area

34

of its associated variable choke

32

a

(see FIG.

1

). Additionally, in a manner which will now be described with continuing reference to

FIG. 2

, the accumulator

108

may be selectively utilized to effect a rapid total opening or total closing of the variable choke

32

a

if conditions warrant.

To ready the accumulator

108

for its rapid choke opening and closing functions, it is first charged by reciprocating the main pump piston

70

in its normal pumping mode while the switching pump piston

144

is in its centered position in which all four of the pilot check valves

164

,

166

,

168

and

170

block rightward fluid flow therethrough. This reciprocation of the primary pump piston

70

pressurizes the chamber

114

of the accumulator

108

, via lines

94

,

95

and

95

a

, the pilot check valve

132

, and the line

128

, and correspondingly compresses the accumulator spring

118

. This pressurization of the accumulator chamber

114

also serves to pressurize the chamber

122

of the smaller auxiliary accumulator

110

and compress its spring

126

. The charged auxiliary accumulator

110

functions, via its connection to line

97

, to maintain a predetermined minimum pressure in the first fluid circuit portion of the actuator

54

.

When it is desired to relatively rapidly open the choke

32

a

, the switching pump piston

144

is moved rightwardly away from its centered position to thereby pressurize line

172

and disable the fluid blocking functions of pilot check valves

164

and

170

. The main pump piston

70

is then stroked to its distal or rightmost limit position which causes the right end portion

134

of the rod

72

to forcibly engage the pilot check valve

132

and disable its fluid blocking function. This causes pressurized hydraulic fluid in the accumulator chamber

114

to be flowed into the right choke drive portion chamber

44

(sequentially via line

128

, pilot check valve

132

, lines

95

a

,

95

and

174

, pilot check valve

164

and line

98

) to relatively rapidly drive the piston

42

leftwardly and fully open the choke

32

a.

When it is desired to relatively rapidly close the choke

32

a

, the switching pump piston

144

is moved leftwardly away from its centered position to thereby pressurize line

173

and disable the fluid blocking functions of pilot check valves

166

and

168

. The main pump piston

70

is then stroked to its distal or rightmost limit position which causes the right end portion

134

of the rod

72

to forcibly engage the pilot check valve

132

and disable its fluid blocking function. This causes pressurized hydraulic fluid in the accumulator chamber

114

to be flowed into the left choke drive portion chamber

46

(sequentially via lines

128

, pilot check valve

132

, lines

95

a

,

95

and

174

, pilot check valve

166

and line

99

) to relatively rapidly drive the piston

42

rightwardly and fully close the choke

32

a.

Turning now to

FIG. 3

, at each variable choke

32

(or other well tool assembly as the case may be), the actuator

54

with its source of fluid pressure

58

and its pressurized fluid routing system

178

(representatively the switching pump

60

and its associated pilot check valves and hydraulic circuitry) are powered by a source of electrical power such as via the electrical cable

90

connected to a surface electrical power source, and are incorporated in a control system

180

used to monitor and responsively control the operation of the variable choke

32

with which it is associated.

A suitable electronic controller

182

is incorporated into the control system

180

, and is utilized to control an operating parameter of its associated variable choke

32

, representatively the outside-to-inside fluid pressure drop (as sensed by the exterior and interior pressure sensors

50

,

52

shown in

FIG. 2

) at the production tubing

22

adjacent the choke. In this manner, with a control system

180

operatively associated with each of the chokes

32

a

-

32

c

, the fluid pressure drop at each choke may be controlled to provide a variety of production operational characteristics, such as assuring that a minimum positive exterior-to-interior pressure drop exists at each variable choke (to prevent unwanted zone-to-zone fluid transfer), maintaining essentially identical fluid pressure drops at each choke, etc.

As schematically indicated in

FIG. 3

, a desired choke operating parameter value signal

184

(such as a desired minimum fluid pressure drop across the choke) is appropriately input to the controller

182

which also respectively receives operational feedback signals

186

,

188

,

190

from the fluid pressure source

58

, the pressurized fluid routing system

178

and the choke

32

. Representatively, the feedback signal

186

can include one or more sensed operating parameters of the main pump

58

such as the position of its piston

70

, the feedback signal

188

can include one or more sensed operating parameters of the switching pump

60

such as the position of its piston

144

, and the feedback signal

190

can include one or more sensed operating parameters of the choke

32

such as the position of its drive piston

42

(as monitored by the choke's position sensing section

48

) and the adjacent production tubing fluid pressure drop (as transmitted from its pressure sensors

50

and

52

).

In response to the receipt of these feedback signals

186