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BACKGROUND  
       [0001]     The present invention relates generally to operations performed and equipment utilized in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a hydraulically actuated control system.  
         [0002]     It is very desirable to be able to control operation of well tools from a remote location, such as the earth&#39;s surface or another location in a well. For example, it would be desirable to be able to control the flow rate of fluids through a downhole valve or choke. This would enable precise production (or injection) rate control without the need to intervene into the completion.  
         [0003]     Some control systems have been proposed for this purpose in the past. However, for the most part such control systems are inordinately complex and, therefore, unreliable, expensive and/or difficult to construct, maintain, calibrate, etc.  
         [0004]     What is needed is a control system which has reduced complexity and increased reliability, and which permits accurate control over actuation of well tools in a downhole environment.  
       SUMMARY  
       [0005]     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a control system is provided which utilizes a control module connected to an actuator for a well tool. Repeated applications of pressure to a fluid line causes the control module to repeatedly meter a known volume of fluid from the actuator to a second fluid line. As each metered volume of fluid is displaced from the actuator to the second fluid line, the actuator incrementally actuates the well tool.  
         [0006]     In one aspect of the invention, a control system for use in a subterranean well is provided. The system includes a well tool, an actuator for the well tool and a control module interconnected between the actuator and first and second fluid lines. The control module is operative to meter a predetermined volume of fluid from the actuator to the second line in response to pressure applied to the first line.  
         [0007]     In another aspect of the invention, another control system for use in a subterranean well is provided. The system includes a well tool, an actuator including an actuator piston which displaces to operate the well tool, and a control module interconnected between the actuator and first and second fluid lines. Pressure applied to the first line displaces the actuator piston and operates the well tool. The control module meters a predetermined volume of fluid from the actuator to the second line, to thereby limit displacement of the actuator piston in response to each of multiple applications of pressure to the first line.  
         [0008]     In yet another aspect of the invention, a method of controlling actuation of a well tool is provided. The method includes the steps of: interconnecting a control module between first and second fluid lines and an actuator of the well tool; applying pressure to the first line, the control module transmitting pressure applied to the first line to the actuator; metering a predetermined volume of fluid from the actuator to the second line via the control module in response to the pressure applying step, thereby incrementally actuating the well tool; and repeating the pressure applying and metering steps, thereby successively incrementally actuating the well tool.  
         [0009]     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic partially cross-sectional view of a hydraulically actuated control system as used in a subterranean well, the system embodying principles of the present invention;  
         [0011]      FIG. 2  is an enlarged scale hydraulic circuit diagram for the control system of  FIG. 1 , showing the control system in a first configuration;  
         [0012]      FIG. 3  is an enlarged scale hydraulic circuit diagram for the control system of  FIG. 1 , showing the control system in a second configuration;  
         [0013]      FIG. 4  is an enlarged scale hydraulic circuit diagram for the control system of  FIG. 1 , showing the control system in a third configuration; and  
         [0014]      FIG. 5  is an enlarged scale hydraulic circuit diagram for another control system embodying principles of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0015]     Representatively illustrated in  FIG. 1  is a control system  10  which embodies principles of the present invention. In the following description of the control system  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.  
         [0016]     As depicted in  FIG. 1 , the control system  10  is used to control actuation of a well tool  12  positioned in a wellbore  14 . The well tool  12  is representatively a choke used to regulate fluid flow between a formation  16  and the interior of a tubing string  18  in which the choke is interconnected. However, it should be clearly understood that the principles of the present invention may be used in conjunction with actuation of any type of well tool (including, but not limited to, valves, packers, test equipment, etc.).  
         [0017]     An actuator  20  is provided for the well tool  12 . The actuator  20  may be as simple as a piston in a bore, with the piston being connected to a closure member (or other operating member) of the well tool  12 , so that displacement of the piston causes actuation of the well tool. If the well tool  12  is a choke, such as the Interval Control Valve marketed by WellDynamics of Spring, Tex., then incremental displacements of the piston may be used to incrementally adjust a rate of fluid flow through the choke. However, other types of actuators may be used without departing from the principles of the invention.  
         [0018]     The control system  10  includes a control module  22  interconnected between the actuator  20  and fluid lines  24  extending to a remote location, such as the earth&#39;s surface or another location in the wellbore  14 . The lines  24  may transmit hydraulic fluid between the control module  22  and the remote location, although other types of fluid may be transmitted through the lines  24 , if desired.  
         [0019]     Referring additionally now to  FIG. 2 , the control module  22 , actuator  20  and well tool  12  are schematically and representatively illustrated. The lines  24  are separately illustrated as lines  26 ,  28  connected to ports  30  of the control module  22 . The actuator  20  is connected to the control module  22  via additional ports  32 .  
         [0020]     Note that the actuator  20  includes a piston  34  having opposite sides  36 ,  38 . The piston side  36  is in fluid communication with the line  26  via a fluid passage  40  extending through the control module  22 . The other piston side  38  is in fluid communication with the other line  28  via additional passages  42 ,  44  extending in the control module  22 .  
         [0021]     When pressure is applied to the line  26 , the control module  22  transmits this pressure to the piston  34  via the passage  40 . Preferably, the lines  26 ,  28  are initially balanced, that is, at substantially the same pressure. Pressure applied to the line  26  would, thus, cause an increase in pressure on the line  26  relative to that on the line  28 .  
         [0022]     The piston  34  is displaced to the left as viewed in  FIG. 2  and indicated by arrows  46 , due to the pressure differential between the piston sides  36 ,  38  (in fluid communication with the lines  26 ,  28 , respectively). Of course, as the piston  34  displaces to the left, it flows fluid from the actuator  20  into the passage  42  of the control module  22 .  
         [0023]     The control module  22  includes a piston  48  which is used to limit the volume of fluid transmitted from the actuator  20  into the control module  22  when the actuator piston  34  displaces to the left. The control module piston  48  has opposite sides  50 ,  52 , which are in fluid communication with the passages  42 ,  44 , respectively. As fluid flows from the actuator  20  into the passage  42  (due to displacement of the actuator piston  34  to the left), the corresponding fluid pressure is applied to the piston side  50 , thereby biasing the control module piston  48  downward, as indicated by arrows  54 .  
         [0024]     As the control module piston  48  displaces downward, it displaces fluid into the passage  44 , and thence to the line  28 . Note that the control module piston  48  is biased downward due to a differential between pressure on the piston side  50  and pressure on the piston side  52 . A biasing device  56  (representatively illustrated as concentric coiled compression springs) biases the control module piston  48  upwardly, so that the pressure differential between the piston sides  50 ,  52  must be sufficiently great to overcome the upwardly biasing force exerted on the piston by the biasing device, in order to displace the piston downwardly.  
         [0025]     The control module piston  48  can only displace downwardly a predetermined distance D, at which point the piston will come to the end of its stroke. When the piston  48  displaces the distance D, a corresponding predetermined volume of fluid is displaced by the piston into the passage  44  and thence into the line  28 . Since the control module piston  48  can only displace the distance D, it will be readily appreciated that the actuator piston  34  can only displace a certain corresponding distance. That is, the actuator piston  34  can only displace to the left a distance which will flow a volume of fluid through the passage  42  sufficient to displace the control module piston  48  downward the distance D.  
         [0026]     An adjustable stop  74  permits the distance D to be varied. This adjustment capability permits the system  10  to be used with different well tools for which corresponding different volumes of fluid may be desired to actuate the well tools in response to each displacement of the control module piston  48 . Representatively, the adjustable stop  74  is threaded a greater or lesser distance into the control module  22  to vary the distance D, although other types of adjustments may be used, if desired.  
         [0027]     Referring additionally now to  FIG. 3 , the system  10  is representatively illustrated after the control module piston  48  has been displaced to the end of its stroke. Note that the actuator piston  34  has displaced a corresponding distance to the left.  
         [0028]     If, at this point, further pressure is applied to the line  26 , the actuator piston  34  will not displace further, since flow from the actuator  20  through the passage  42  is prevented by the control module piston  48 , which is at the end of its stroke. This is very beneficial, in that a known incremental displacement of the actuator piston  34  may be obtained in response to an application of pressure to the line  26 . For example, if the well tool  12  is a choke, this known displacement of the actuator piston  34  may be used to produce a corresponding adjustment to the rate of fluid flow through the choke.  
         [0029]     Referring additionally now to  FIG. 4 , the control system  10  is representatively illustrated after the pressure applied to the line  26  has been reduced. As soon as the differential pressure applied across the sides  50 ,  52  of the control module piston  48  is reduced sufficiently, the biasing device  56  displaces the piston upward, as indicated by arrows  58 . However, note that the actuator piston  34  does not displace when the control module piston  48  displaces upward, because a valve  60  in the control module piston permits flow between the sides  50 ,  52  of the control module piston.  
         [0030]     When pressure in the line  26  is increased (as depicted in  FIG. 2 ), the valve  60  closes, preventing fluid flow from the side  50  to the side  52  of the control module piston  48 . The valve  60  is of the type known to those skilled in the art as a pilot-operated valve, in that pressure applied to a pilot port  70  closes the valve. Pressure is applied to the port  70  when pressure in the line  26  is increased, due to a passage  62  formed in the control module  22  between the passage  40  and the port  70 . Increased pressure in the passage  62  operates to force the valve  60  to its closed configuration, thereby preventing fluid from flowing from the passage  42  to the passage  44  through the control module piston  48 .  
         [0031]     For further assurance that fluid flowed from the actuator  20  into the passage  42  does not flow through the valve  60  when pressure in the line  26  is increased, a flow restrictor  64  is installed in the passage  42 . The flow restrictor  64  retards the increase in pressure on the side  50  of the control module piston  48  as compared to the increase in pressure at the port  70  via the passage  62 .  
         [0032]     It may now be fully appreciated that the control module  22  permits the actuator piston  34  to be incrementally displaced in response to repeated applications of pressure to the line  26 . When pressure in the line  26  is increased, the actuator piston  34  displaces a predetermined distance to the left, and the control module piston  48  displaces downward the distance D, thereby displacing the predetermined volume of fluid into the line  28 . When pressure in the line  26  is reduced, the control module piston  48  displaces upward the distance D (due to the force exerted by the biasing device  56 ), thereby “recocking” the control module  22 . When pressure in the line  26  is again increased, the actuator piston  34  will again displace incrementally to the left. This process may be repeated as many times as needed to displace the actuator piston  34  a desired distance, to thereby actuate the well tool  12  incrementally.  
         [0033]     When it is desired to actuate the well tool  12  by displacing the actuator piston  34  to the right (for example, to open a choke or valve, etc.), pressure in the line  28  may be increased. This increased pressure in the line  28  will cause fluid to flow through the passage  44 , through the control module piston  48  via the open valve  60 , through the passage  42 , and to the actuator  20 . A pressure differential from the side  38  to the side  36  of the actuator piston  34  will cause fluid to flow from the actuator  20  through the passage  40  and into the line  26 . Thus, the actuator piston  34  may be displaced all the way to the right in response to a single increase in pressure on the line  28 .  
         [0034]     Referring additionally now to  FIG. 5 , another embodiment of a control module  66  is representatively illustrated. The control module  66  may be used in place of the control module  22  in the system  10  described above. Since the control module  66  is similar in many respects to the control module  22 , the same reference numbers are used in  FIG. 5  to indicate similar elements. Of course, the control module  66  may be used in other systems, and may be differently configured, without departing from the principles of the invention.  
         [0035]     The control module  66  includes a pressure relief valve  68  installed in the passage  40 . Representatively, the relief valve  68  is designed to open when 1,000 psi has been applied to the line  26  (that is, a pressure differential of 1,000 psi across the relief valve). Of course, other relief pressures may be used, if desired.  
         [0036]     Note that the relief valve  68  is positioned in the passage  40  between its intersection with the passage  62  and the port  32  to the actuator  20 . Thus, pressure in the passage  62  will increase prior to the pressure being transmitted through the relief valve  68  to the actuator  20 , thereby ensuring that the valve  60  is closed before the actuator piston  34  displaces fluid from the actuator to the passage  42  of the control module  66 .  
         [0037]     However, since it is also desired to flow fluid from the actuator  20  to the line  26  via the passage  40  when pressure in the line  28  is increased (to displace the actuator piston  34  in an opposite direction, as described above), a check valve  72  is installed in parallel with the relief valve  68  in the passage  40 . The check valve  72  permits flow from the actuator  20  to the line  26  via the passage  40 , but prevents flow through the check valve in the opposite direction.  
         [0038]     Thus, when pressure in the line  26  is increased, the check valve  72  is closed and the relief valve  68  prevents the increased pressure from being transmitted to the actuator  20  until a predetermined pressure level is reached. When pressure in the other line  28  is increased, the check valve  72  opens, thereby permitting flow from the actuator  20  to the line  26 .  
         [0039]     Note that the relief valve  68  and check valve  72  are not necessary in keeping with the principles of the invention. For example, the relief valve  68  and check valve  72  could be replaced with a restrictor, such as the restrictor  64 .  
         [0040]     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.

Summary:
A control system for use in controlling actuation of tools in a subterranean well. In a described embodiment, a control system includes a well tool, an actuator for the well tool and a control module interconnected between the actuator and first and second fluid lines. The control module is operative to meter a predetermined volume of fluid from the actuator to the second line in response to pressure applied to the first line.