Apparatus, System, and Method for Controlling the Flow of Drilling Fluid in a Wellbore
A drilling system includes a drill string extending through a BOP and a drilling fluid discharge coupling mounted to the BOP. In addition, the drilling system includes a drilling fluid control system configured to control a pressure or flow rate of a drilling fluid flowing through the discharge coupling. The drilling fluid control system includes a flow rate and pressure regulating device, a feedback controller system configured to operate the regulating device, and a first sensor configured to measure an actual pressure or flow rate of the drilling fluid flowing through the discharge coupling.
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This application claims benefit of U.S. provisional patent application Ser. No. 61/708,881 filed Oct. 2, 2012, and entitled “Apparatus, System, and Method for Controlling the Flow of Drilling Fluid in a Wellbore,” which is hereby incorporated herein by reference in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable.
BACKGROUNDThe present disclosure relates generally to apparatus, systems, and methods for controlling the flow of drilling fluid. More particularly, the disclosure relates to systems and methods for managing the pressure in a borehole by controlling the discharge of drilling fluid from the borehole as is performed, for example, during managed pressure drilling (MPD).
During the drilling of exploratory wells and the drilling and completing of oil and gas wells, drilling fluid, also called drilling mud, is pumped into the well to maintain a desired pressure within the borehole. Managing the pressure in the well is necessary to inhibit or reduce the influx of formation fluids into the wellbore, while ensuring excessive wellbore pressure does not fracture the formation and lead to significant drilling fluid loss into the formation. Managed Pressure Drilling (MPD) is a drilling process in which the annular pressure profile in the borehole is controlled. MPD helps manage and mitigate potential problems associated with drilling of fractured or karstic carbonate reservoirs, well bore instability, differentially stuck pipe, and drilling formations with a tight margin between formation fracturing pressure and pore pressure.
During conventional MPD operations, pressurized drilling fluid is pumped down the drill string that supports the drill bit and other downhole tools. The fluid discharges through nozzles in the drill bit. The drilling fluid then travels upward through the annulus located between the drill string and the borehole wall to the surface. The drilling mud in the annulus contacts the formation, thereby exerting pressure against the formation. The fluid exits the top of the borehole through a back-pressure device, which influences the pressure and flow rate of drilling fluid through the annulus. Within the borehole, fluid pressure is managed by the adjusting the density, and hence weight, of the drilling fluid to control the hydrostatic pressure, by adjusting the pressure supplied by the mud pump, and by regulating the restriction induced by the back-pressure device. When the pressure in the borehole moves outside a target pressure range, an adjustment is often made at the back-pressure device to steer the borehole pressure back into the target range. Reaching a value within the target pressure using conventional techniques typically requires repeated, iterative adjustments, which often result in an undesirable relatively slow response and/or undesirable over-shooting of the target range.
BRIEF SUMMARY OF THE DISCLOSUREThese and other needs in the art are addressed in one embodiment by a drilling system for forming a borehole in an earthen formation. In an embodiment, the drilling system includes a drill string extending through a blowout preventer, and a drilling fluid discharge coupling mounted to the blowout preventer. In addition; the drilling system includes a drilling fluid control system configured to control a pressure or flow rate of a drilling fluid flowing through the discharge coupling. Further, the drilling fluid control system includes a flow rate and pressure regulating device, a feedback controller system configured to operate the regulating device, and a first sensor configured to measure an actual pressure or flow rate of the drilling fluid flowing through the discharge coupling. The regulating device includes a drilling fluid inlet in fluid communication with the discharge coupling, a drilling fluid outlet, an annular cage positioned between the inlet and the outlet, a valve plug slidingly disposed within the cage, an actuator, and a second sensor. The actuator is configured to adjust an axial position of the valve plug relative to the cage to selectively control the flow of drilling fluid through the cage from the inlet to the outlet, and the second sensor is configured to measure an actual axial position of the valve plug relative to the cage. Still further, the feedback controller system is configured to receive a desired pressure or flow rate and includes a process control engine configured to adjust the axial position of the valve plug relative to the cage based on a comparison of the actual pressure or flow rate measured by the first sensor and the desired pressure or flow rate and based on a comparison of the actual change in the axial position of the valve plug relative to the cage measured by the second sensor and a desired change in the axial position.
These and other needs in the art are addressed in another embodiment by a method for controlling the pressure or flow rate of drilling fluid flowing from a borehole through a valve. In an embodiment, the method includes (a) measuring the pressure or flow rate of the drilling fluid. In addition, the method includes (b) obtaining a desired pressure or flow rate for the drilling fluid. Further, the method includes, comparing the measured pressure or flow rate with the desired pressure or flow rate. Still further, the method includes (d) determining a desired change in an axial position of a valve plug within the valve based on the comparison in (c). In addition, the method includes (e) adjusting the axial position of the valve plug based on the desired change in the axial position of the valve plug in (d). Continuing, the method includes (f) determining an actual change in the axial position of the valve plug during (e). The method also includes (g) comparing the actual change in the axial position of the valve plug with the desired change in the axial position of the valve plug during (e).
These and other needs in the art are addressed in another embodiment by a method for controlling the pressure or flow rate of drilling fluid flowing from a borehole through a flow rate and pressure regulating device. In an embodiment, the method includes utilizing a first control loop to determine a desired change in a position of a valve plug within the regulating device to achieve a desired pressure or flow rate of the drilling fluid. In addition, the method includes utilizing a second control loop to adjust the actual position of the valve plug within the regulating device based on the desired change in the position of the valve plug from the first control loop.
Embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a detailed description of the disclosed embodiments of the disclosure, reference will now be made to the accompanying drawings in which
The following description is exemplary of embodiments of the disclosure. These embodiments are not to be interpreted or otherwise used as limiting the scope of the disclosure, including the claims. One skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment.
The drawing figures are not necessarily to scale. Certain features and components disclosed herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. In some of the figures, one or more components or aspects of a component may be not displayed or may not have reference numerals identifying the features or components that are identified elsewhere in order to improve clarity and conciseness of the figure.
The terms “including” and “comprising” are used herein, including in the claims, in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first component couples or is coupled to a second component, the connection between the components may be through a direct engagement of the two components, or through an indirect connection that is accomplished via other intermediate components, devices and/or connections. In addition, if the connection transfers electrical power or signals, whether analog or digital for example, the coupling may comprise wires or a mode of wireless electromagnetic transmission such as radio frequency, microwave, optical, or another mode. So too, the coupling may comprise a magnetic coupling or any other mode of transfer known in the art, or the coupling may comprise a combination of any of these modes. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a given axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. Any reference to up or down in the description and the claims will be made for purpose of clarification, with “up,” “upper,” “upwardly,” or “upstream” meaning toward the surface of the well and with “down,” “lower,” “downwardly,” or “downstream” meaning toward the terminal end of the well, regardless of the well bore orientation. In some applications of the technology, the orientations of the components with respect to the surroundings may be different. For example, components described as facing “up,” may alternately face to the left, may face down, or may face in another direction in another instance or in one or more other embodiments. The recitation “based on” means “based at least in part on.” Therefore, if X is based on Y, X may be based on Y and any number of other factors.
Disclosed herein are embodiments of systems and methods for controlling the flow rate and pressure of drilling fluid within a wellbore. The systems and methods described herein are particularly suited for managed pressure drilling (MPD), but can be used in other types of drilling operations. It should be appreciated that the drilling fluid flowing through the annulus to the surface may include some formation fluids. In at least some embodiments, the equipment and control scheme are configured to achieve a mathematically linear or more-nearly mathematically linear relationship or response between the movement of an actuator in a valve (e.g. the movement of a control choke or the movement of valve plug relative to a valve seat) and the resulting change in pressure in the wellbore or the change in flow rate of the drilling fluid exiting the wellbore. However, depending on the design of the actuator in the valve, the movements of the actuator in the valve can be rectilinear in various embodiments. For example, in some embodiments, the valve actuator can rotate so that changes in pressure or flow rate are related to angular displacements of the actuator or are related to a combined angular and linear displacement of the actuator in the valve. Still further, the systems and methods described herein provide a means for quickly adjusting the drilling fluid exit flow path to compensate for changing well conditions or changing operational set-points, thereby offering the potential to achieve rapidly a targeted pressure or flow rate of drilling fluid in the borehole with minor likelihood of over-shooting or over-compensating.
Referring now to
An annular space or annulus 36 is formed between the sidewall of borehole 34 and drill string 15, and between casing 38 and drill string 15. In other words, annulus 36 extends through borehole 34 and casing 38. BOP 40 includes an annular flow path 41 in fluid communication with annulus 36.
Referring still to
During drilling operations, drilling fluid 52 from tank 54 is pressurized by pump 56 and sent through fluid supply line 58 and rotatable supply coupling 60 into drill string 15. The drilling fluid 52 flows down drill string 15 and is discharged at the borehole bottom through nozzles in drill bit 24. The drilling fluid 52 cools bit 24 and carries the formation cuttings to the surface through annulus 36, BOP flow path 41, and discharge coupling 72.
Referring still to
An inlet conduit 104 provides fluid communication between discharge coupling 72 and choke valve 110, and a discharge conduit 105 provides fluid communication between choke valve 110 and mud tank 54 via a solids control system (not shown). The solids control system substantially separates the cuttings from the drilling fluid 52 at the surface, and may include hardware such as shale shakers, centrifuges, and automated chemical additive systems.
Referring now to
Feedback controller system 200 also includes a process control engine 205 and a user interface 250 coupled to process control engine 205 with a communication link 270. In this embodiment, interface 250 includes one or more displays (e.g., monitors or single-line digital displays) with a data input capability or a data input device, and process control engine 205 includes a servo motor drive. Interface 250 is configured to display operational parameters and data, and to receive user input values for one or more of the operational parameters. Process control engine 205 is coupled to pressure sensor 102 with a cable 190 that transmits drilling fluid pressure measurements acquired by sensor 102 to control engine 205. In addition, process control engine 205 is coupled to actuator 150, rotary resolver 160, and linear position indicator 165 of choke valve 110 with cables 190 that transmit control signals and/or performance data between motor drive 205 and each of actuator 150, rotary resolver 160, and linear position indicator 165 to monitor and control the performance of choke valve 110.
In general, sensor 102 can be placed in a variety of locations within drilling system 10 and control system 100 to monitor and communicate the pressure (or, in some embodiments, flow rate) of the drilling fluid 52 disposed within discharge coupling 72. For example, in
Feedback controller system 200 is preferably electrically coupled to a larger drilling control system (not shown) configured to communicate with and to exchange data or control signals with system 200, as well as various other sensors, such as a downhole pressure sensor 22 on BHA 20, a weight-on-bit sensor, temperature sensors, a rotational speed senor, a motor torque sensor for a rotary table, or any of a number of sensors known in the art. The drilling control system is further configured to communicate with and to send commands to the actuators that influence the operation of drilling system 10, such as fluid pump 56, the downhole motor, top drive, or rotatory table that controls the rotational speed of drill string 15, etc.
Referring now to
Referring now to
As best shown in
Referring now to
Cage 132 has a first end 132A, a second end 132B opposite of end 132A and slidingly seated in guide sleeve 138, and a plurality of circumferentially-spaced holes or apertures 132C disposed between ends 132A, 132B. During drilling operations, drilling fluid flows into cage 132 through apertures 132C and flows out of cage 132 through end 132A. Accordingly, apertures 132C may also be referred to as inlets and end 132A may also be referred to as outlet end. Valve plug 133 can be moved axially through cage 132 to control the flow of drilling fluid through apertures 132C. For example, plug 133 can be positioned to block the apertures 132C (i.e., a fully-closed position), to open fully the apertures 132C, or to block partially apertures 132C. When valve 110 is fully-closed, first end 134A of plug 133 contacts interior shoulder 132E of cage 132, as shown in
Referring still to
Guide sleeve 138 includes a first or open end 138A, a second or closed end 138B opposite end 138A, a cylindrical inner chamber 138C extending axially from end 138A, and a through-bore 138D extending co-axially through closed end 138B to chamber 138C. A set of annular seals 148D are disposed about bore 138D at end 138B and sealingly engage stem 141 extending therethrough. Inner chamber 138C includes a first annular shoulder 138E axially positioned proximal end 138A, and a second annular shoulder 138F axially positioned between shoulder 138E and end 138B. An annular seal 148C is disposed within guide sleeve 138 between shoulders 138E, 138F.
Valve stem 140 extends through bore 138D, sealingly engages seals 148D, and has an end connected to end 135B of plug 133, which is disposed in chamber 138C and slidingly engages guide sleeve 138. Annular seal 148C forms a dynamic seal with plug 133 as it moves relative to guide sleeve 138. Second end 132B of cage 132 is seated in end 138A, and wave spring 144 is axially positioned between shoulder 138E and end 132B of cage 132. Through-bore 137 allows fluid communication between cylindrical inner chambers 135C, 138C and thereby serves to balance pressure between chambers 135C, 138C, which reduces the amount of force needed to move plug body 135 during operation.
As best shown in
Referring to
Referring still to
Rotary resolver 160 is axially disposed between housing 151 and motor 154 with driveshaft 155 passing therethrough. Accordingly, rotary resolver 160 may be considered to be a component of valve actuator 150. Resolver 160 is configured to detect the rotation of driveshaft 155 (direction of rotation, rotational speed, and rotational acceleration) and communicate that information to feedback controller system 200. In general, rotary resolver 160 may be any suitable rotary resolver known in the art.
Referring to
Actuator 150 is configured to move plug 133 axially relative to cage 132 and sleeve 138 by rotating shaft 155 to move sleeve 156, stem coupler 173, and valve stem 140 axially. The axial movement of plug 133 relative to cage 132 controls the flow through inlet apertures 132C of cage 132. In
Referring now to
The output signal of LVDT 165 may relate to linear movement of valve plug 133 in a more direct manner than the output of a rotary resolver such as rotary resolver 160. For example, rotary resolver 160 detects angular movement of driveshaft 155; however, it is driveshaft 155 that causes sleeve 156 to move in a linear path by means of their engaging threads. Thus ascertaining linear motion with resolver 160 involves sensing and calculating, e.g. numerically integrating, the rotation of driveshaft 155 as well as correlating the rotational and linear interaction of driveshaft 155 and sleeve 156. Whereas, for linear position indicator 165, the linear movement of plunger 167 and thus the linear movement of stem 140 may be directly measured as a change in resistance of element 168 without numerical integration. Thus, rotary resolver 160 and LVDT 165, which are both coupled to valve plug 133, both function as sensors that measure and communicate the actual axial position of the valve plug 133 relative to the cage 132.
Referring now to
With bonnet cap 146 threadingly attached to valve body 115, shaft 182 extends parallel to axis 118. With bonnet cap 146 unthreaded from valve body 115, trolley 183 may slide along shaft 182 while supporting the weight of bonnet 145, as well as any other components coupled thereto. With bonnet 146 unthreaded from body 115, bonnet 145 can be slide axially away from body 115, leaving flow and pressure control assembly 130 within body 115. Shaft 182 may then be pivoted about axis 181A to provide access to the inside of body 115.
Referring now to
In this embodiment, storage device 220 includes a process response module 222, a gain adjustment module 230, and a position control module 240, each of which comprises software executable by processor 210. Modules 222, 230, 240 are configured to cause the processor 210 to regulate the flow of fluid through control valve 110 based on data received from drilling fluid pressure sensor 102 to achieve a desired pressure or pressure profile in borehole 34. As previously described, in other embodiments, pressure sensor 102 is replaced by a flow rate sensor, thereby enabling controller system 200 to regulate the flow of fluid through control valve 110 based on data received from the flow rate sensor to achieve a desired flow rate of drilling fluid exiting borehole 34.
Continuing to reference
In this embodiment, user interface 250 includes an operational command module 256 and operational status module 258. Operational command module 256 is configured to receive instructions or parameter values from a user and provide instructions to process control engine 205. For the instructions or parameter values, operational command module 256 may include default values, which are usable individually or in multiplicity when one or more pieces of information is not entered by a user. The instructions processed by command module 256 may include, for example, mode selection to choose manual or automatic operation and jog, i.e. movement, commands.
As best shown in
Referring still to
Gain adjustment module 230, which may also be referred to as gain module 230, includes a comparison module 234 having a first input node “w,” a second input node “z,” a first result node “no,” and a second result node “yes.” Gain module 230 further includes an adjustment threshold module 232 coupled to the “w” input node, a lower gain value module 236 coupled to the “no” result node, and a higher gain value module 237 coupled the “yes” result node of the comparison module 234. Second input node “z” is coupled to PID module 226 with process adjustment signal path 280. In this embodiment, only one comparison module 234 coupled to two gain modules 236, 237 are provided. However, in other embodiments, more than one comparison module (e.g., module 234) and more than two gain modules (e.g., gain modules 236, 237) may be included to enable selection of a variety of different gain values.
Position control module 240 includes a servo motor drive that monitors rotary resolver 160 and adjusts the position of valve stem 140 and plug 133 relative to cage 132 in choke valve 110 based on information received from rotary resolver 160, process response module 222, and gain adjustment module 230.
Referring to
Perror=Pset-point−Pmeasured Equation 1
The result of Equation 1 may be positive, negative, zero valued. The Perror value is communicated to PID module 226, which produces an adjusted pressure error, Perror,adj, to achieve better stability for control system 100 using techniques known in the art. In some instances, adjusted pressure error, Perror,adj, will be equal to or nearly equal to pressure error, Perror. The adjusted pressure error is communicated from PID module 226 to displacement command module 228 and to comparison module 234 through path 280.
Using a Function 2, displacement command module 228 calculates a valve stem displacement command, ΔX, which is a value indicating or estimating the axial distance valve stem 140, and hence plug 133, should move from its the current position in an effort to achieve a desired change in drilling fluid pressure within inlet conduit 104, discharge coupling 72, and annulus 36. In other words, displacement command module 228 determines to what extent the valve 110 needs to be opened or closed to achieve the desired pressure. Function 2 for valve stem displacement command ΔX is shown here as Equation 2:
-
- Where: Lengthstroke,max=The full distance of travel of valve plug 133 between a fully-open and a fully-closed condition relative to apertures 132C of cage 132.
Module 228 communicates the valve stem displacement command, ΔX, to position control module 240 via path 282.
- Where: Lengthstroke,max=The full distance of travel of valve plug 133 between a fully-open and a fully-closed condition relative to apertures 132C of cage 132.
The process values, i.e. the pressure values, in Equations 1 and 2 may be associated with engineering units such as pounds-per-square-inch (PSI), kilopascal (KPa), or bar, for example, or may be associated with a digital value corresponding to a number between zero and the maximum value for the data bytes used by the processor or engine, such as processor 210 of process control engine 205. In at least one embodiment, process control engine 205 uses digital values in Equations 1 and 2 with each byte or piece of data comprising 16 bits or 16 digits; therefore, the maximum value handled by process control engine 205 in the embodiment is 32,767 when using a base-2 numbering system wherein the most-significant-bit is not utilized to indicate magnitude. In some such embodiments, the most-significant-bit may instead be assigned to represent the numeric sign (i.e., positive or negative) of the value, for example. This maximum value determines the maximum value of pressure error, Perror that can be calculated and recognized by process control engine 205. In the embodiment, the maximum result from Equation 1 is expressed as:
Perror,max=32,767 Equation 3
Process control engine 205 is configure so that in instances when the data that is input to the right-hand side of equation 1 would result in a value of Perror, having a magnitude (i.e. an absolute value) greater than Perror
In other embodiments, the maximum error may be more or less than the value shown in Equation 3. For example, in other various embodiments, a higher maximum error value and greater resolution is possible due to the processor or process control engine (e.g. process control engine 205) being configured to operate with larger data bytes comprising 32-bits or 64-bits, for example. Less operation resolution and a lesser value of maximum error value would be anticipated in an embodiment in which the processor or process control engine (e.g. process control engine 205) were configured to operate with only 16-bit or 8-bit data bytes, for example.
Referring still to
During operation, position control module 240 may receive a positive, a negative, or a zero value displacement command ΔX from response module 222 and a gain value from adjustment module 230, and evaluates a positive, a negative, or a zero value output signal. That output signal is sent to and magnified by current amplifier 245 to send an actuator control signal through path 278 to actuator 150. As commanded by the actuator control signal, actuator 150 moves valve stem 140 and valve plug 133 in one of two directions to increase or decrease the flow rate through cage 132 of choke valve 110 or keeps valve stem 140 and valve plug 133 in their current position to maintain the flow rate. On a continuous or periodic basis, feed-back from resolver 160 via path 276 indicates the position of actuator 150, or more specifically, the position of valve stem 140 and plug 133. Module 240 uses feed-back from path 276 to adjust the actuator control signal of path 278 to achieve improved position accuracy and stability for actuator 150 and plug 133 coupled thereto.
During operation, the remaining distance of travel for plug 133 to reach a fully-open or a full-closed condition for valve 110 depends on the current location of valve plug 133 relative to apertures 132C in cage 132. In some instances, for example due to a sudden rise or sudden drop in pressure in annulus 36, the evaluated value of the valve stem displacement command ΔX may be greater than the remaining distance of travel for plug 133 to reach a fully-open or a full-closed condition. In such instances, process control engine 205 may reduce the valve stem displacement command ΔX or may reduce the actuator control signal sent through path 278 to actuator 150 in order to cause plug 133 to reach a fully-open or a full-closed condition without attempting to overshoot, i.e. to go beyond a fully-open or a full-closed condition. In other embodiments, valve 110 may be designed to accept an actuator control signal that commands actuator 150 and plug 133 to go beyond a fully-open or a full-closed condition while valve 100 limits the movement of plug to the fully-open or the full-closed condition.
Referring still to
The second control loop assists the first loop in achieving the previously stated goal. The second control loop includes the components that were described as the aggregate actuator of the first control loop. Therefore, the second control loop includes the position control module 240, current amplifier 245, and choke valve 110 (including cage 132, plug 133, valve stem 140, actuator 150, and the valve position-indicating device, i.e. rotary resolver, 160). Position control module 240 may also be called a controller. The process controlled by the second control loop is the axial position of plug 133 relative to cage 132, which is adjustable by actuator 150. Rotary resolver 160 is a sensor to provide feed-back about the process to module 240. Thus, the second control loop includes a sensor, a controller, and an actuator.
During operation, the second control loop executes repeating cycles. The various cycles may have a similar duration in comparison to the other cycles or may vary in duration in some instances or embodiments. In a cycle, acting on a valve stem displacement command, ΔX, i.e. a set-point, module 240 commands actuator 150 to move valve stem 140 and plug 133 in one of two directions, while cage 132 remains at a fixed location within valve body 115. For example, in the embodiment of choke valve 110 of
Prior to or during the operation of the second control loop, the relative angular position or response of resolver 160 can be calibrated to the absolute position of plug 133 by methods known in the art. For example, an initial or “home” position of plug 133 may be established by moving valve stem 140 and plug 133 to a fully-extended position, causing plug end 134A to engage interior shoulder 132E of cage 132, which corresponds to the fully-closed condition. Module 240 registers this home position and uses subsequent readings from rotary resolver 160 to monitor, even to measure, the variable position of plug 133 while the second control loop operates. The fully-retracted position of valve stem 140 could alternatively be used as the initial position of plug 133. The output of LVDT 165 could also be used to calibrate the relative angular position or response of resolver 160.
In most conventional choke valves, the relationship between the valve stem position, i.e. the plug position, and the pressure measured by a sensor adjacent the valve inlet is non-linear. Thus, for example, changing the valve stem position by 1 cm does not cause a pressure change that is twice the magnitude of the pressure change resulting from a 0.5 cm change in valve stem position. However, in embodiments described herein, e.g.
In the embodiments previously described in reference to
In the embodiments previously described, controller system 200 controls and operates choke valve 110. However, other drilling fluid choke valves may also be used in connection with controller system 200. For example,
Choke valve 310 also includes a bonnet 345 extending from body 315 into yoke 370 and a removable bonnet cap 346 threadably coupled to bonnet 345. Valve body 315 includes an inlet 316 and an outlet 317, each being defined by a conduit having a connection flange at an end distal body 315. As best shown in
Referring now to
Referring now to
Referring again to
While user interface 250 was described as a display exemplified by a monitor or a single-line digital display, in some embodiments the user interface 250 comprises an analog indicator and an adjustable control dial, such as an analog face on a pressure gauge and a potentiometer, for example.
While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.
Claims
1. A drilling system for forming a borehole in an earthen formation, the drilling system comprising:
- a drill string extending through a blowout preventer;
- a drilling fluid discharge coupling mounted to the blowout preventer;
- a drilling fluid control system configured to control a pressure or flow rate of a drilling fluid flowing through the discharge coupling;
- wherein the drilling fluid control system includes a flow rate and pressure regulating device, a feedback controller system configured to operate the regulating device, and a first sensor configured to measure an actual pressure or flow rate of the drilling fluid flowing through the discharge coupling;
- wherein the regulating device includes a drilling fluid inlet in fluid communication with the discharge coupling, a drilling fluid outlet, an annular cage positioned between the inlet and the outlet, a valve plug slidingly disposed within the cage, an actuator, and a second sensor;
- wherein the actuator is configured to adjust an axial position of the valve plug relative to the cage to selectively control the flow of drilling fluid through the cage from the inlet to the outlet, and the second sensor is configured to measure an actual axial position of the valve plug relative to the cage,
- wherein the feedback controller system is configured to receive a desired pressure or flow rate and includes a process control engine configured to adjust the axial position of the valve plug relative to the cage based on a comparison of the actual pressure or flow rate measured by the first sensor and the desired pressure or flow rate and based on a comparison of the actual change in the axial position of the valve plug relative to the cage measured by the second sensor and a desired change in the axial position.
2. The drilling system of claim 1, wherein the process control engine is configured to:
- determine a desired change in the axial position of the valve plug relative to the cage based on a comparison of the desired pressure or flow rate and the measured pressure or flow rate from the first sensor;
- adjust the axial position of the valve plug relative to the cage with the actuator based on the desired change in the axial position of the valve plug;
- determine an actual change in the axial position of the valve plug relative to the cage based on the measured axial positions from the second sensor; and
- compare the desired change in the axial position of the valve plug relative to the cage to the actual change in the axial position valve plug relative to the cage while adjusting the axial position of the valve plug relative to the cage with the actuator.
3. The drilling system of claim 2, wherein the actuator includes a threaded shaft, a sleeve threaded onto the threaded shaft and coupled to the valve plug, and a motor configured to rotate the threaded shaft relative to the sleeve.
4. The drilling system of claim 3, wherein the second sensor is a rotary resolver.
5. The drilling system of claim 1, wherein the process control engine is configured to determine a gain based on the comparison of the desired pressure or flow rate and the measured pressure or flow rate, and adjust a speed of the change in the axial position of the valve plug relative to the cage based on the gain.
6. The drilling system of claim 2, wherein the feedback controller system further includes a user interface configured for inputting the desired pressure or flow rate and configured to display the actual pressure or flow rate of the drilling fluid disposed within the discharge coupling measured with the first sensor.
7. The drilling system of claim 2, wherein the cage includes a plurality of circumferentially spaced apertures in fluid communication with the drilling fluid inlet, wherein the valve plug is configured to control the flow of drilling fluid through the apertures.
8. A method for controlling the pressure or flow rate of drilling fluid flowing from a borehole through a valve, the method comprising:
- (a) measuring the pressure or flow rate of the drilling fluid;
- (b) obtaining a desired pressure or flow rate for the drilling fluid;
- (c) comparing the measured pressure or flow rate with the desired pressure or flow rate;
- (d) determining a desired change in an axial position of a valve plug within the valve based on the comparison in (c);
- (e) adjusting the axial position of the valve plug based on the desired change in the axial position of the valve plug in (d);
- (f) determining an actual change in the axial position of the valve plug during (e); and
- (g) comparing the actual change in the axial position of the valve plug with the desired change in the axial position of the valve plug during (e).
9. The method of claim 8, further comprising:
- (h) adjusting the axial position of the valve plug based on the comparison of the desire change in the axial position and the actual change in the axial position in (g).
10. The method of claim 8, wherein (a) comprises measuring the pressure or flow rate of the drilling fluid with a first sensor disposed upstream of the valve; and
- wherein (f) comprises measuring the axial position of the valve plug with a position sensor coupled to the valve plug.
11. The method of claim 8, further comprising:
- adjusting a speed of the change in the axial position in (e) based on the comparison the measured pressure or flow rate and the desired pressure or flow rate in (c).
12. The method of claim 11, wherein adjusting the speed of the change in the axial position comprises selecting a gain based on the comparison the measured pressure or flow rate and the desired pressure or flow rate in (c).
13. The method of claim 8, wherein (b) comprises inputting the desired pressure or flow rate at a user interface.
14. The method of claim 8, wherein (e) comprises:
- sending an actuator control signal to an actuator of the valve; and
- rotating a threaded shaft in the valve with the actuator.
15. The method of claim 8, wherein the desired change in the axial position of the valve plug is a function of the difference between the measured pressure or flow rate and the desired pressure or flow rate.
16. A method for controlling the pressure or flow rate of drilling fluid flowing from a borehole through a flow rate and pressure regulating device, the method comprising:
- utilizing a first control loop to determine a desired change in a position of a valve plug within the regulating device to achieve a desired pressure or flow rate of the drilling fluid; and
- utilizing a second control loop to adjust the actual position of the valve plug within the regulating device based on the desired change in the position of the valve plug from the first control loop.
17. The method of claim 16, further comprising:
- communicating the desire pressure or flow rate of the drilling fluid from a user interface to the first control loop.
18. The method of claim 16, further comprising utilizing the first control loop to determine a gain that influences a speed for the desired change in position of the valve plug.
19. The method of claim C3, wherein the second control loop adjusts the speed of the change in the actual position of the valve plug based on the gain determined by the first control loop.
20. The method of claim 16 wherein first control loop comprises a first sensor configured to provide feed-back about the pressure or flow rate of drilling fluid, a first controller, and a first actuator;
- wherein the second control loop comprises a second sensor, a second controller, and a second actuator.
- wherein the first actuator comprises the second control loop.
Type: Application
Filed: Oct 2, 2013
Publication Date: Apr 3, 2014
Applicant: National Oilwell Varco, L.P. (Houston, TX)
Inventors: Jerry E. Smith (Houston, TX), Philip A. Strassle (Spring, TX)
Application Number: 14/044,082
International Classification: E21B 21/08 (20060101);