Work string controller

{
  "publication_number": "US7841414B1",
  "country": "US",
  "kind": "B1",
  "title": "Work string controller",
  "abstract": "Well bore servicing equipment is provided. The well bore servicing equipment comprises a first manipulator to grip a well bore work string, to raise the work string, and to lower the work string. The well bore servicing equipment further comprises a controller to receive a work string trajectory input and to automatically control the first manipulator to raise and lower the work string substantially in conformance with the work string trajectory input.",
  "claims": [
    "1. A pressure observer, comprising: a first proportional-integral (PI) controller portion operable to determine a first pressure error and to generate a first corrective signal based on the first pressure error; a first feed-forward portion operable to determine a first flow rate based on a first velocity and a first gain; a first integrator operable to integrate the sum of the first corrective signal and the first flow rate; and a second gain operable to amplify an output of the first integrator by a first model gain and to produce a first pressure estimate.",
    "2. The pressure observer of claim 1, wherein the first proportional-integral controller portion is further operable to determine a first flow disturbance signal based on the first pressure error.",
    "3. The pressure observer of claim 1, wherein the first pressure error is determined as the difference of a first sensed pressure and the first pressure estimate.",
    "4. The pressure observer of claim 1, wherein the first gain is proportional to the difference of an area of a piston of a hydraulic actuator and an cross-section area of a rod of the hydraulic actuator.",
    "5. The pressure observer of claim 1, wherein the first model gain is proportional to a bulk modulus of a hydraulic fluid and is inversely proportional to a volume comprising a rod side chamber of a hydraulic actuator, wherein the volume of the rod side chamber changes as a rod of the hydraulic actuator moves.",
    "6. The pressure observer of claim 1, further comprising: a second proportional-integral (PI) controller portion operable to determine a second pressure error and to generate a second corrective signal based on the second pressure error; a second feed-forward portion operable to determine a second flow rate based on a second velocity and a second gain; a second integrator operable to integrate the sum of the second corrective signal and the second flow rate; and a second gain operable to amplify an output of the second integrator by a second model gain and to produce a second pressure estimate.",
    "7. A control system for controlling movement of a work string in a well bore, comprising: a controller comprising a processor, a memory, and a pressure observer component, the pressure observer component comprising a first proportional-integral (PI) controller portion operable to determine a first pressure error and to generate a first corrective signal based on the first pressure error; a first feed-forward portion operable to determine a first flow rate based on a velocity of a first hydraulic actuator and a first gain; a first integrator operable to integrate the sum of the first corrective signal and the first flow rate; and a second gain operable to amplify an output of the first integrator by a first model gain and to produce a first pressure estimate, wherein the controller commands the first hydraulic actuator to move the work string based at least in part on the first pressure estimate.",
    "8. The control system of claim 7, wherein the first proportional-integral controller portion is further operable to determine a first flow disturbance signal based on the first pressure error, and wherein the controller commands the first hydraulic actuator to move the work string further based on the first flow disturbance signal.",
    "9. The control system of claim 7, wherein the first pressure error is determined as the difference of a first sensed pressure and the first pressure estimate.",
    "10. The control system of claim 7, wherein the first gain is proportional to the difference of an area of a piston of the first hydraulic actuator and a cross-section area of a rod of the first hydraulic actuator.",
    "11. The control system of claim 7, wherein the first model gain is proportional to a bulk modulus of a hydraulic fluid and is inversely proportional to a volume comprising a rod side chamber of the first hydraulic actuator, wherein the volume of the rod side chamber changes as a rod of the first hydraulic actuator moves.",
    "12. The control system of claim 7, wherein the pressure observer component further comprises: a second proportional-integral (PI) controller portion operable to determine a second pressure error and to generate a second corrective signal based on the second pressure error; a second feed-forward portion operable to determine a second flow rate based on a velocity of a second hydraulic actuator and a second gain; a second integrator operable to integrate the sum of the second corrective signal and the second flow rate; and a second gain operable to amplify an output of the second integrator by a second model gain and to produce a second pressure estimate, wherein the controller further commands the second hydraulic actuator to move the work string based at least in part on the second pressure estimate.",
    "13. A method of servicing a wellbore with a work string, comprising: receiving a work string trajectory input from a user interface, wherein the work string trajectory comprises at least a first work string target position and a first work string target velocity; determining a first pressure error and generating a first corrective signal based on the first pressure error; determining a first flow rate based on a velocity of a first hydraulic actuator and a first gain; integrating the sum of the first corrective signal and the first flow rate to determine a first integrated value; determining a first pressure estimate based on amplifying the first integrated value by a first model gain; determining a first hydraulic actuator control command based on the first pressure estimate and the work string trajectory input moving the workstring within the wellbore responsive to the first hydraulic actuator control command.",
    "14. The method of claim 13, further comprising determining a first flow disturbance signal based on the first pressure error, wherein determining the first hydraulic actuator control command is further based on the first flow disturbance signal.",
    "15. The method of claim 13, wherein the first pressure error is determined as the difference of a first sensed pressure and the first pressure estimate.",
    "16. The method of claim 13, wherein the first gain is proportional to the difference of an area of a piston of the first hydraulic actuator and a cross-section area of a rod of the first hydraulic actuator.",
    "17. The method of claim 13, wherein the first model gain is proportional to a bulk modulus of a hydraulic fluid and is inversely proportional to a volume comprising a rod side chamber of the first hydraulic actuator, wherein the volume of the rod side chamber changes as a rod of the first hydraulic actuator moves.",
    "18. The method of claim 13, further comprising: determining a second pressure error and to generate a second corrective signal based on the second pressure error; determining a second flow rate based on a velocity of a second hydraulic actuator and a second gain; integrating the sum of the second corrective signal and the second flow rate to determine a second integrated value; determining a second pressure estimate based on amplifying the second integrated value by a second model gain and to produce a second pressure estimate; and determining a second hydraulic actuator control command based on the second pressure estimate and the work string trajectory input.",
    "19. The method of claim 18, further comprising determining a second flow disturbance signal based on the second pressure error, wherein determining the second hydraulic control command is further based on the second flow disturbance signal.",
    "20. The method of claim 18, wherein the second pressure error is determined as the difference of a second sensed pressure and a second pressure estimate."
  ],
  "description_excerpt": "Not applicable.\n\nAutomated control systems attempt to drive physical characteristics of a system, for example a process or object, to achieve system objectives. Automated control systems may be able to improve on the control provided manually by a human operator, for example by providing a higher frequency response, by taking account of a greater number of system parameters, and/or by providing a higher accuracy of control. Automated control systems may take many forms and may be designed to use continuous time controllers and/or discrete time controllers. Control systems may be both designed and described with control diagrams representing processing blocks. Generally, a control system may be built and implemented from the control system diagram. A well bore may be serviced using a work string. A work string may include continuous coiled tubing which is fed continuously into the well bore from large spools. The longer the continuous tubing, the greater the tensile strength of the tubing may be to support the weight of the longer tubing. On the other hand, the greater the tensile strength of the tubing, the less flexible the tubing may be and the greater stress that may be produced in the tubing as it flexes going into the well bore and coming back out of the well bore. An advantage of coiled tubing is that it can be fed relatively rapidly and continuously into a well bore. A work string may also be composed of interconnected pieces or joints of pipe, for example joints of pipe about 10 meters long with a male threaded end and an opposite female threaded end.",
  "cpc": [
    "E21B 19/086",
    "B25J 9/1664",
    "G05B 2219/39219",
    "G05B 2219/39554"
  ],
  "ipc": [
    "E21B 23/00"
  ],
  "assignees": [
    "HALLIBURTON ENERGY SERV INC"
  ],
  "inventors": [
    "BORGSTADT JUSTIN"
  ],
  "filing_date": "2010-09-02",
  "publication_date": "2010-11-30",
  "grant_date": "2010-11-30",
  "priority_date": "2008-06-16",
  "application_number": "US-87500110-A",
  "family_id": "41100783",
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}