Abstract:
Positional control of downhole actuators. A method for positional control of an actuator includes the steps of: applying pressure to both an input line and an output line connected to the actuator; and then releasing a predetermined volume of fluid from the output line, thereby displacing a piston of the actuator a corresponding predetermined distance. A system for positional control of an actuator includes the actuator included in a well tool positioned in a well; the input line connected to the actuator and extending to a remote location; the output line connected to the actuator and extending to the remote location; and a fluid volume measurement device connected to the output line at the remote location, the fluid volume measurement device being operative to meter the predetermined volume of fluid from the output line.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit under 35 USC §119 of the filing date of International Application No. PCT/US06/02304, filed Jan. 24, 2006, the entire disclosure of which is incorporated herein by this reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to equipment utilized and operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides positional control for downhole actuators. 
         [0003]    A pressure actuated downhole actuator is typically operated by applying pressure to a line in order to displace a piston of the actuator. However, some well tools, such as downhole chokes and other types of flow control devices, are operated using a type of actuator in which the piston is not just required to displace, but is also required to displace a certain distance or to a certain position in order to produce a desired change in the well tool. For example, a certain displacement of the piston may produce a corresponding change in flow rate through a downhole choke. 
         [0004]    Unfortunately, pressure is generally applied to an input line of the actuator from a remote location, such as a surface location, which may be thousands of meters from the actuator. Fluid compressibility, friction, expansion of the input line due to applied pressure, thermal expansion of the input line and fluid, etc. cause it to be very difficult to determine how the piston displaces in response to pressure applied to the input line. 
         [0005]    Various methods have been devised for overcoming this problem, but each of these methods has its own shortcomings. One method is to use a displacement sensor in the actuator to directly sense the movement of the piston. However, this method requires that the sensor be accommodated in the well tool, and that a communication system be provided for transmitting signals from the sensor to the surface. In addition, the sensor must be capable of withstanding the downhole environment (high temperatures/pressures, vibration, etc.). 
         [0006]    Another method is to use a certain number or pattern of pressure applications to the input line to produce a corresponding displacement of the piston. However, this method requires that the well tool be designed with a control system capable of decoding the pressure applications, and that an operator at the surface be capable of determining when the appropriate pressure applications have been received and decoded at the control system. The more complex the control system, the less likely that it will survive long term in the downhole environment. 
         [0007]    Therefore, it may be seen that improvements are needed in the art of positional control of downhole actuators. Preferably, systems and methods for controlling the position of a piston in a downhole actuator should be reliable and relatively inexpensive, but should provide for very accurate control of position. 
       SUMMARY 
       [0008]    In carrying out the principles of the present invention, a system and associated method are provided which solve at least one problem in the art. One example is described below in which input and output lines of downhole actuators are pressurized simultaneously, and then fluid is released from an output line to displace a piston of a selected actuator. Another example is described below in which a volume of fluid released from the output line is measured using various techniques. 
         [0009]    In one aspect of the invention, a method for positional control of at least one downhole actuator is provided. The method includes the steps of: applying pressure to both an input line and an output line connected to the actuator; and then releasing a predetermined volume of fluid from the output line, thereby displacing a piston of the downhole actuator a corresponding predetermined distance. 
         [0010]    In another aspect of the invention, a method for positional control of a downhole actuator includes the steps of: applying pressure to an input line connected to the actuator; transmitting the pressure from the input line, through the actuator and to an output line connected to the actuator, the pressure being prevented from escaping from the output line by a valve; and then opening the valve, thereby releasing a predetermined volume of fluid from the output line, and displacing a piston of the actuator a corresponding predetermined distance. 
         [0011]    In yet another aspect of the invention, a system for positional control of a downhole actuator is provided. The system includes the downhole actuator as part of a well tool positioned in a well. An input line is connected to the downhole actuator and extends to a remote location. An output line is connected to the downhole actuator and extends to the remote location. A fluid volume measurement device is connected to the output line at the remote location. The fluid volume measurement device is operative to meter a predetermined volume of fluid from the output line to thereby displace a piston of the downhole actuator a corresponding predetermined distance. 
         [0012]    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, in which similar elements are indicated in the various figures using the same reference numbers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic partially cross-sectional view of a system and associated method embodying principles of the present invention; 
           [0014]      FIG. 2  is a schematic hydraulic circuit diagram for the system of  FIG. 1 ; and 
           [0015]      FIGS. 3-6  are alternate configurations of the hydraulic circuit of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Representatively illustrated in  FIG. 1  is a system  10  and associated method which embody principles of the present invention. In the following description of the system  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used 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 embodiments are described merely as examples of useful applications of the principles of the invention, which is not limited to any specific details of these embodiments. 
         [0017]    As depicted in  FIG. 1 , a tubular string  12  (such as a production tubing string) has been conveyed into a wellbore  14 . The tubular string  12  includes two well tools  16 ,  18  and a packer  20  positioned between the well tools. The packer  20  isolates two annuli  22 ,  24  formed between the tubular string  12  and the wellbore  14 . 
         [0018]    The upper annulus  22  is in communication with an upper zone  26  intersected by the wellbore  14 . The lower annulus  24  is in communication with a lower zone intersected by the wellbore  14 . The well tools  16 ,  18  each include a flow control device  30 ,  32  (such as a choke, valve, flow regulator, etc.) for controlling flow between the interior of the tubular string  12  and the respective annuli  22 ,  24 . 
         [0019]    To operate the flow control devices  30 ,  32 , each of the well tools  16 ,  18  further includes a pressure operated actuator  34 ,  36 . Lines  38  are connected to the actuators  34 ,  36  to conduct fluid and pressure between the actuators and a remote location, such as the earth&#39;s surface or another surface location (e.g., a subsea wellhead, floating or stationary rig, etc.), or a remote location in the wellbore  14 . 
         [0020]    It should be clearly understood that the principles of the invention are not limited to the details of the system  10  described herein. For example, the well tools  16 ,  18  could include devices other than flow control devices, it is not necessary for multiple well tools to be used, it is not necessary for the well tools to be interconnected in the tubular string  12 , any number of well tools and/or actuators may be used, etc. The system  10  is described merely as one example of how the invention could be utilized. 
         [0021]    Referring additionally now to  FIG. 2 , a schematic hydraulic circuit diagram of the system  10  is representatively illustrated. The actuators  34 ,  36  are depicted apart from the remainder of the well tools  16 ,  18  for simplicity and clarity of description. 
         [0022]    Note that the lines  38  illustrated in  FIG. 1  are represented in  FIG. 2  by an input line  40  connected to each of the actuators  34 ,  36 , and output lines  42 ,  44  connected to respective ones of the actuators. A separate input line could be connected to each of the actuators  34 ,  36  if desired, but only the single input line  40  is used in the representative system  10  for enhanced reliability and reduced expense. Similarly, a single output line could be connected to both of the actuators  34 ,  36  if desired, with a downhole manifold for selective communication between the actuators and the remote location via the output line. 
         [0023]    A valve  46  is connected between the input line  40  and a pressure source  48  at the remote location. As depicted in  FIG. 2 , the pressure source  48  is a pump, but other pressure sources (such as an accumulator, compressed gas, etc.) could be used in keeping with the principles of the invention. 
         [0024]    Another valve  50  is connected between the output line  42  and a fluid volume measurement device  52 . The volume measurement device  52  is used to measure a volume of fluid discharged from the output line  42  (or the output line  44 ) as described in further detail below. 
         [0025]    Yet another valve  54  is connected between the output line  44  and the volume measurement device  52 . It will be appreciated that, by opening either the valve  50  or the valve  54 , a respective one of the output lines  42 ,  44  may be placed in communication with the volume measurement device  52 . 
         [0026]    When one of the valves  50 ,  54  is opened, fluid flows from the respective output line  42 ,  44  into the volume measurement device  52 , thereby displacing a piston  56 . The displacement of the piston  56  can be directly measured (such as via a graduated indicator  58 ) to thereby directly measure the volume of fluid discharged from the output line  42  or  44 . 
         [0027]    After discharge of a predetermined volume of fluid from the output line  42  or  44 , the respective valve  50 ,  54  is closed. The fluid in the volume measurement device  52  can then be discharged to a reservoir  60  via another valve  64 , for example, using a biasing force exerted on the piston  56  by a spring  62 . 
         [0028]    Many different fluid volume measurement devices may be used in place of the device  52  depicted in  FIG. 2 . A few alternate volume measurement devices are representatively illustrated in  FIGS. 3-6 , but it should be clearly understood that any type of volume measurement device may be used in keeping with the principles of the invention. 
         [0029]    Each of the actuators  34 ,  36  includes a respective piston  66 ,  68 . Displacement of each of the pistons  66 ,  68  is used to operate the respective well tools  16 ,  18 . For example, displacement of the piston  66  could be used to displace a closure member or choke member of the flow control device  30 . Note that displacement of the pistons  66 ,  68  could be used to operate the respective well tools  16 ,  18 , or to cause a change in operation of the respective well tools, in any manner in keeping with the principles of the invention. 
         [0030]    In operation, pressure is applied to the input line  40  and both of the output lines  42 ,  44  by opening the valve  46  and applying pressure to the input line from the pressure source  48 . The pressure is transmitted through the input line  40 , and through the actuators  34 ,  36  to the output lines  42 ,  44 . The valves  50 ,  54  are closed at this point to prevent the pressure from escaping from the output lines  42 ,  44 . 
         [0031]    When the applied pressure has stabilized in the input line  40  and output lines  42 ,  44 , one of the valves  50 ,  54  is opened. A predetermined volume of fluid is thus permitted to flow from the respective output line  42  or  44  into the volume measurement device  52 . 
         [0032]    This discharge of a predetermined volume of fluid into the volume measurement device  52  causes a predetermined displacement of the respective piston  66  or  68 . The displacement of the respective piston  66  or  68  causes a desired operation, or change in operation, of the respective well tool  16  or  18 . 
         [0033]    The valve  50  or  54  is then closed, and the valve  64  is opened to discharge the fluid from the volume measurement device  52  into the reservoir  60 . The other one of the valves  50 ,  54  could then be opened to produce a desired displacement of the other one of the pistons  66 ,  68 , or the same one of the valves could again be opened to produce another displacement of the same one of the pistons. 
         [0034]    If no further displacement of either of the pistons  66 ,  68  is desired, then the valve  46  can be closed. The pressure applied to the input line  40  and the output lines  42 ,  44  can remain in these lines, or the pressure can be bled off. Bleeding off the pressure can produce some minimal displacement of the pistons  66 ,  68 , but this can be predicted and accounted for when the respective pistons are displaced by opening the valves  50 ,  54  as described above. 
         [0035]    It is an important feature of the system  10  that the pressure is applied to both the input line  40  and each of the output lines  42 ,  44  prior to opening one of the valves  50 ,  54 . In this manner, the lines  40 ,  42 ,  44  are pressurized to a known reference pressure at which the lines have expanded to a certain extent, the fluid in the lines has been compressed to a certain extent, the lines and fluid are at an approximate equilibrium temperature in the well, etc. 
         [0036]    To compensate for temperature in the well, expansion of the lines  40 ,  42 ,  44 , compressibility of the fluid in the lines, etc., the reference pressure may be applied to the lines and allowed to stabilize. The valve  50  may then be opened and the piston  66  displaced its full stroke in the actuator  34 . 
         [0037]    The volume of fluid discharged into the volume measurement device  52  will then represent the full stroke of the piston  66 . It will then be known what proportion of this fluid volume is required to produce a corresponding proportional displacement of the piston  66 . 
         [0038]    For example, to displace the piston  66  only half of its stroke in the actuator  34 , fifty percent of the full stroke fluid volume should be discharged into the volume measurement device  52 . The same procedure may be used to compensate for temperature, expansion, compressibility, etc. in operation of the other actuator  36 . 
         [0039]    It will be appreciated that the system  10  produces many benefits over prior methods of operating downhole actuators. One benefit is that complex calculations do not have to be used to compensate for temperature, expansion, compressibility, etc. in determining what volume of fluid should be pumped into an input line to produce a desired displacement of a piston in a downhole actuator. Another benefit is that the system  10  is relatively uncomplicated and does not rely on complex downhole mechanisms or sensors and their associated communication systems to determine displacement of a downhole piston. Yet another benefit is that these advantages are obtained economically, with only the lines  40 ,  42 ,  44  being installed downhole to operate the well tools  16 ,  18 . Preferably, the valves  46 ,  50 ,  54 ,  64 , pressure source  48  and volume measurement device  52  are installed at a surface location where they are conveniently operated and maintained. 
         [0040]    Referring additionally now to  FIGS. 3-6 , alternate forms of fluid volume measurement devices are representatively illustrated for the system  10 . Only a portion of the hydraulic circuit diagram of  FIG. 2  is shown in each of  FIGS. 3-6 , but it will be appreciated that the remainder of the hydraulic circuit diagram is preferably the same as depicted in  FIG. 2 . 
         [0041]    In  FIG. 3  a fluid volume measurement device  70  includes a sensor interconnected between the valves  50 ,  54  and the reservoir  60 . The sensor could be a volume meter which directly measures the volume of fluid flowing though the sensor. The sensor could instead be a flowmeter which measures a flow rate of fluid through the sensor. In that case, the fluid flow rate may be integrated over time to determine the volume of fluid which flows through the sensor. Other types of sensors may be used in keeping with the principles of the invention. 
         [0042]    In  FIG. 4  a fluid volume measurement device  72  includes a flow rate regulator which preferably maintains a relatively constant flow rate of fluid over a wide range of pressure differentials. If the flow rate is known (for example, using a flowmeter), then a duration of the flow can be determined which will produce a desired volume of fluid flow. Thus, the device  72  can include a timer for setting a duration of the flow through the device. 
         [0043]    In  FIG. 5  a fluid volume measurement device  74  includes a valve for controlling flow discharge into the reservoir  60 . When calibrating the system  10  (compensating for temperature, expansion, compressibility, etc.) as described above, after the reference pressure has been applied to the lines  40 ,  42 ,  44  and a selected one of the valves  50 ,  54  has been opened, the valve of the device  74  may be opened and the time it takes to displace the respective one of the pistons  66 ,  68  its full stroke can be measured. Thereafter, when it is desired to displace the respective one of the pistons  66 ,  68  a certain proportion of its full stroke, the valve of the device  74  can be opened a corresponding proportion of the measured full stroke time. Thus, the device  74  can also include a timer for setting a duration of the flow through the device. 
         [0044]    In  FIG. 6  a fluid volume measurement device  76  includes a flow restrictor. The flow restrictor is preferably calibrated, so that for a certain fluid, temperature, pressure differential, etc., a flow rate of fluid through the restrictor is known. In this manner, a predetermined volume of fluid can be flowed through the restrictor, for example, by integrating the flow rate over time, or limiting a duration of a constant flow rate, etc. For these purposes, the device  76  may also include a timer for setting a duration of the flow through the device. 
         [0045]    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 the 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.