Dual actuator control for automated directional drilling

Abstract

A drilling system having a drill string and bottom-hole assembly (24) is used to drill a wellbore into a formation. The BHA includes an optional mud motor (30), a rotary steerable system (28), and a drill bit (26). The drill bit (26) is steered, either from actions applied at surface or actions applied at the drill bit, so that the wellbore location and shape approximate a path of a planned wellbore (23). A dual actuated control structure (36) controls drilling system operation and includes a decision logic (44), which assigns control of drill bit steering to be actions applied at the drill bit if in there is a proposed directional change that exceeds a designated angle and that also results in a change between a current steering force and a proposed steering force that exceeds a designated amount.

Description

Attorney Docket No.: 0005355.000235 (65ATM-510694) PCT PATENT APPLICATION DUAL ACTUATOR CONTROL FOR AUTOMATED DIRECTIONAL DRILLING Inventors: Felix Häusser Kai Karvinen Clemens Vanja Rene Klemme Christian Hansen Rolf Findeisen CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. Provisional Application Serial No. 63 / 554,811, filed February 16, 2024, the full disclosure of which is incorporated by reference herein in its entirety and for all purposes. BACKGROUND OF THE INVENTION 1. Field of Invention

[0002] The present disclosure relates to steering a drill bit with an action applied at surface or an action applied downhole at the drill bit depending on proposed changes in path direction or force applied to the bit. 2. Description of Prior Art

[0003] Directional drilling in a subterranean formation generally involves drilling boreholes that adhere to a specified reference well plan as closely as possible while ensuring safe operation. This process is typically controlled by repeatedly adjusting the steering inputs of an underground bottom-hole assembly (“BHA”). In contrast, the surface inputs, such as the mud flow rate, the drill string rotation speed, or the hook load, are only occasionally adjusted, requiring the expert knowledge of a directional driller. -1- IM-#10601610.8

[0004] Controlling the steering of a BHA while underground usually requires sending communication signals downhole (e.g., downlinks) to the BHA, which is typically performed using telemetry, such as, mud pulses, electromagnetic signals, or wired pipe. Wireless communication in a wellbore has drawbacks due to wellbore depth, downhole noise, and bandwidth limitations that constrict communication downhole and introduce time lags.

[0005] A problem with surface input control is the complexity with which the surface inputs affect the drilling operation, which is a complex interaction that cannot be easily modelled, often resulting in an inadequate control of the drilling process using the surface inputs. This is the case for both traditional model-based approaches (due to the lack of precise mathematical process models) as well as for data-based approaches (due to the amount of required high-quality data).SUMMARY OF THE INVENTION

[0006] Disclosed herein is an example method of drilling that includes forming a wellbore in a formation with a drilling system with a drill string and a bottom-hole assembly having a drill bit and a rotary steerable system. The example method further includes configuring the wellbore based on a planned wellbore, and steering the drill bit by applying an action downhole at the drill bit when a difference between a current steering parameter and a proposed steering parameter exceeds a designated threshold. In embodiments, the steering parameter is a steering direction and the designated threshold is an angle that is at least 2 degrees, and the change in direction is a change of steer direction related to gravity / high side of the toolface. In examples in which the steering parameter is a steering force, the designated threshold is a steer force that is at least 5% of a maximum steer force of the rotary steerable system. In an alternative, the drill bit is steered with an action applied at surface when not being steered with an action applied downhole at the drill bit. A downlink signal is optionally transmitted into the wellbore when the threshold angle or threshold steer force are detected, and where the downlink signal provides a command to the rotary steerable system to change steering of the drill bit, further optionally, the downlink signal is a first downlink signal, the example method further including delaying transmission of a second downlink signal for a set period of time and after drilling for a particular distance. The method further optionally includes transmitting periodic surface control signals for adjusting surface inputs. Examples of the steering parameter include steering direction, steering force, steering mode, and combinations.

[0007] Another example method of drilling includes forming a wellbore in a formation with a drilling system made up of a drill string and a bottom-hole assembly having a drill bit and a rotary steerable system, configuring the wellbore to approximate a configuration of a planned wellbore, and steering the drill bit using the rotary steerable system when a proposed change in direction exceeds a threshold angle or when a difference between a proposed steer force and a current steer force exceeds a threshold steer force. The drill bit of this example is alternatively steered with an action applied at surface, and where an action applied at surface includes weight on bit, rotational speed of the drill string, and combinations. In an embodiment the threshold angle is 2° and the threshold steer force is 5% of a maximum steer force.

[0008] An example of a drilling system for forming a wellbore is disclosed, which includes a drill string, bottom-hole assembly (“BHA”) mounted onto an end of the drill string and that includes a drill bit and a rotary steerable system (“RSS”), and a controller configured to steer the BHA with the RSS when a change in direction of the drill bit exceeds a threshold angle or a proposed change of force in the drill bit exceeds a threshold amount. In an alternative of the drilling system, the change in direction results in the wellbore configuration being approximate to a planned wellbore. The drilling system optionally further includes a means for controlling a weight on bit of the drilling bit, a means for controlling a rotational speed of the drilling string, a means for directing drilling fluid into the drilling string and for controlling a flow rate of the drilling fluid, a means for controlling a pressure of the drilling fluid, and combinations.BRIEF DESCRIPTION OF DRAWINGS

[0009] Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

[0010] FIG. 1 is a side partial sectional view of an example of forming a wellbore in accordance with the present disclosure.

[0011] FIGS. 2 and 2A are schematic examples of a control structure for controlling drilling a wellbore in accordance with the present disclosure.

[0012] FIG. 3 is a flowchart of a portion of the control structure of FIG. 2.

[0013] FIG. 4 is a chart with plots that represent prophetic build rates over time for different control schemes when forming a well.

[0014] FIGS. 5A-5F are charts with a plot representing prophetic drilling parameters over time.

[0015] While subject matter is described in connection with embodiments disclosed herein, it will be understood that the scope of the present disclosure is not limited to any particular embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents thereof.DETAILED DESCRIPTION OF INVENTION

[0016] The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes + / - 5% of a cited magnitude. In an embodiment, the term “substantially” includes + / - 5% of a cited magnitude, comparison, or description. In an embodiment, usage of the term “generally” includes + / - 10% of a cited magnitude.

[0017] It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

[0018] Disclosed is an example of a dual actuator control concept able to simultaneously adjust the steering and surface inputs of a directional drilling process in an automatic fashion. This control concept combines conventional automated steering input control with a surface input control approach. A logic-based module determines when each of the two input types is used. An objective of the dual actuator controller is to follow a reference signal as closely as possible while ensuring a safe and efficient operation. Reference tracking refers to a system being able to follow a reference setpoint. In many cases, open-loop systems struggle to track the reference signal due to disturbances. For these cases, a feedback controller can be developed to reject the disturbance (e.g. unmodeled dynamics in the drilling environment, such as a formation push on the bit). By reacting to the disturbance, the controller is able to improve the reference tracking.

[0019] The dual actuator controller (“DUAC”) provides a structure and function that implements a strategy to coordinate surface input control and downhole steering control and it provides an event-based "decision logic" for determining if and when the surface or steering input controller is to be used. Overall, the automation of the directional drilling operation is a general task that canbe tackled in different ways. However, the automation of surface input control always faces the problem of complex interaction mechanisms between the surface inputs and the directional drilling process downhole. These interaction mechanisms are not easily modelled, neither by model-based approaches nor by data-based approaches. In an example of the proposed method, a simplified data-based surrogate model of the directional drilling process is combined with an adaptive two degree of freedom control structure. The control concept disclosed herein offers a possible control structure to solve the problem of integrating surface and conventional steering input control. A decision-making process is needed to decide when either the steering or surface inputs are updated.

[0020] Automated directional drilling services do not yet consider surface controllable parameters such as weight on bit (“WOB”), the drill string rotational speed (“RPM”) or the rate of penetration (“ROP”). Instead, these parameters are currently still set manually by human experts and only adjusted from time to time. While surface controllable parameters have less of an influence on the directional drilling process than downhole steering control, situations exist in which surface control provides an acceptable form of controlling directional drilling, which is faster and less expensive as they can be adjusted without the need to downlink new steering parameters to a rotary steerable system (RSS). Thus, even limited use of the surface controllable parameters to control the drilling process, instead of the downhole steering parameters, could lead to a reduction of necessary downlinks, thus potentially reducing the non-productive time and lowering the overall cost of drilling a wellbore.

[0021] In embodiments, the DUAC is a data-driven and optimization-based control concept that by considering the special properties of the drilling process circumvents the above-mentioned problems. In an example, a surrogate model of the drilling process is developed, which uses process-based assumptions to decrease the complexity of the trained model. Further in this example, the surrogate model is used to apply an optimization-based controller to automatically control the surface inputs of the drilling process. Including the surface input control is an important step towards a fully automated control of the directional drilling process.

[0022] Shown in a side partial sectional view in FIG. 1 is an example of forming a wellbore 10 through a formation with a drilling system 14. Included with drilling system 14 is a drilling rig 16 having a derrick 18 on surface. A surface input means 20 is included for selectively applying surface inputs to a drill string 22 shown extending into the formation 12. A surface input means20 includes all devices or systems on surface for regulating or controlling drilling. Examples of surface input means 20 include draw works (not shown) with traveling and crown blocks for adjusting a hook load to the drill string 22 for obtaining a designated WOB, mud pumps, and drilling mud in tanks on surface. An example of a reference wellbore 23 is shown in dashed outline, which as described below represents a projected path of a wellbore. An embodiment of a bottom-hole assembly 24 (“BHA”) is shown on a lower end of drill string 22, which includes a drill bit 26 for excavating through the formation 12, a rotary steerable system 28 (“RSS”) for steering the drill bit 26 through the formation 12, and an optional motor 30 for rotating the drill bit 26. An example of an RSS 28 selectively exerts a lateral force onto an inner sidewall of the wellbore 10 to alter a direction of the drill bit 26 to a designated path in the formation 12. The wellbore 10 includes a build section (I), a drop section (II), and another build section (III). Examples of the RSS 28 include a push-the-bit system, a point-the-bit-system, and a continuous- proportional-steering system. An example of a controller 32 is shown on surface in selective communication with the BHA 24 via communication means 34, examples of communication means 34 include mud pulse telemetry, fiber optics, conductive wire (e.g., wired pipe), and electromagnetic waves. In a non-limiting example, command signals are generated in controller 32 and transmitted to BHA 24 via communication means 34. The types of command signals include steering input(s) that is(are) transmitted to the RSS 28 for steering drill bit 26, where the commands are generated in accordance with the dual actuator controller (“DUAC”) disclosed herein and alternatives, examples of these commands include changing the steer force, changing the steering angle, changing the steering mode, changing the target azimuth, changing the target inclination, changing the build-rate, changing the turn rate, and combinations thereof.

[0023] An example control concept for the automated control of the surface inputs for the purpose of directional drilling is found in F. Häusser, A. Himmel, K. S. Karvinen and R. Findeisen, "Data- driven Adaptive Surface Control for Automated Directional Drilling”, 2023 IEEE Conference on Control Technology and Applications (CCTA), Bridgetown, Barbados, 2023, pp. 520-525, DOI: 10.1109 / CCTA54093.2023.10252434.; which is incorporated by reference herein in its entirety and for all purposes. In an example, the surrogate model is generated using a variety of methods from machine learning, such as neural networks or Gaussian processes, up to simpler methods such as look-up interpolation tables. In a subsequent step, the surrogate model is used in combination with an optimization-based feedforward and feedback control scheme toautomatically adjust the surface controllable parameters based on the control objective. While the feedforward component allows to quickly react to changes of the control objective, e.g., a changed reference build or turn rate, the feedback component enables the controller to counteract model- plant mismatches.

[0024] An objective in directional drilling is to follow a pre-defined well plan, usually starting vertically at the drilling rig and ending at a specified position and orientation underground. Some current automated directional drilling services utilizing an RSS use an intermediate path planner, as opposed to directly applying the well plan to control the steering inputs. Based on the well plan as reference and the BHA position and orientation, the path planner computes an optimized path, for minimizing control setpoint changes, reducing the need for steering downlinks and other changes to improve efficiency of the drilling process. This optimized path consists of sections with constant curvature, denoted in terms of build rate and turn rate, such as the rates of inclination and azimuth change over a specified drilled distance, respectively. By separating the path planner from the steering input controller, the former can be designed independently of the specific BHA configuration, enhancing the modularity of the control approach. The proposed dual actuator controller aims to integrate the surface input controller in the existing automated steering input controller while maintaining a modular structure that uses the path planner’s optimized path as reference.

[0025] The distinctive characteristics of the two types of system inputs, i.e., steering and surface, in the controller design require consideration. The steering inputs allow precise adjustments of the drilling direction and resulting path curvature at the BHA 24. However, communication bandwidth via mud-pulse telemetry is limited. The surface inputs are not bandwidth constricted, but have a weaker effect on steering than steering inputs. Changes to surface inputs result in smaller alterations of path curvature and only affect curvature extent but not direction. Additionally, predicting necessary changes to surface inputs is challenging. Consequently, a control framework is implemented to address the adjusted control by manipulating both steering and surface inputs while considering the distinct characteristics of each input type. In examples disclosed herein, steering and surface inputs are integrated, and in a specific embodiment combines conventional steering input control with surface input control into a cohesive and coordinated control strategy. An example of conventional steering input control is found in Hansen et al., U.S. Patent No. 12,129,751, which is assigned to the same assignee of the present application, and is incorporatedby reference herein in its entirety and for all purposes. An example of surface input control is found in F. Häusser, A. Himmel, K. S. Karvinen, and R. Findeisen, “Data-driven adaptive surface control for automated directional drilling”, in 2023 IEEE Conference on Control Technology and Applications (CCTA), 2023, pp.520–525, which is incorporated by reference herein in its entirety and for all purposes. A logic-based module determines the appropriate use of each input type.

[0026] The dual actuator control concept disclosed herein leverages the strengths of each of the steering and surface input types to mitigate their respective drawbacks. In a non-limiting example, the steering inputs are adjusted on a limited basis and with low-bandwidth control, which lowers the frequency and quantity of downlinks sent. The steering inputs are used to get the build and turn rate to approximately those of the reference curvature, e.g., after a significant reference change where the sole application of the surface inputs would be insufficient. The surface inputs are used subsequently to keep the path curvature of the wellbore 10 at the reference curvature and to counteract noise and minor disturbances (high-bandwidth control). Implementing the dual actuator controller increases intervals between requested downlinks with new steering inputs, which improves the reference following capabilities as compared to conventional steering input control.

[0027] Schematically illustrated in FIG. 2 is an example of the DUAC control structure 36 designed for a directional drilling process with the drilling system 14 of FIG. 1. As shown, in the DUAC control structure 36 of FIG. 2, information in a well plan 38 is input to a path planner 40, which compares the well plan 38 to a current location and orientation of the BHA 24 (FIG. 1) in the formation 12. Based on this comparison, the path planner 40 calculates an optimized path (such as by an optimization scheme), the controller 32 generates and transmits steering commands to the BHA 24 intended to follow the optimized path. In a non-limiting example, the well plan 38 represents a reference path that is followed as closely as possible. The path planner 40 runs in real- time and calculates an optimized path designed to follow the well plan 38 but by minimizing steering input setpoints. Deviations from the well plan can occur so that a corrective path is deemed necessary to return to the well plan, a function optionally performed by the path planner 40. The optimized path can be denoted using sections of constant curvature. In alternatives, this signal is used as the reference curvature rcurv for the DUAC control structure 36 (whether or not there are deviations from the original well plan or not). Referring to FIG. 2A, the DUAC control structure 36 includes a steering input controller 42, decision logic 44, and surface input controller 46. Output from the DUAC control structure 36 is sent to a directional drilling process 48 (FIG.2), including the surface inputs uSFfor the drilling rig 16 and the steering inputs uDHfor the RSS 28. In this example, most system states are not accessible using the measurements y directly, instead estimated states wDH are used, which are provided to a path planner, such as that disclosed in K. S. Karvinen, “Constrained path optimization for automated directional drilling,” 2023 IEEE 19th International Conference on Automation Science and Engineering (CASE), 2023; which is incorporated by reference herein in its entirety. Based on these estimates and the well plan, the path planner calculates a piecewise constant path reference curvature signal rcurvused in the dual actuator controller, from the reference curvature rcurv and the estimated states wDH, the steering input controller computes a steering input proposal sent to the decision logic of FIG. 3. The decision logic uses event-based logic to determine whether to downlink the steering input proposal, to trigger a surface input update, or maintain the current system inputs. If triggered, the surface input controller computes updates surface inputs uSF, using an adaptive two degree of freedom control approach. The controller 32 with the DUAC control structure 36 is configured to steer the bit 26 for constructing the wellbore 10 so that it has a shape, contour, and location in the formation 12 that approximates the reference wellbore 23. In one example of constructing the wellbore 10 to approximate the reference wellbore 23, the axes of the reference wellbore 23 and wellbore 10 are largely coaxial or parallel.

[0028] In a non-limiting example of operation, the steering input controller 42 determines a setpoint uDH for the steer force and direction of the RSS 28, considering the current reference signal rcurvand the estimated states wDH. The steering input controller 42 optionally utilizes a proportional-integral (PI) controller with a feed-forward component and is activated whenever new state estimates wDH are available, and in alternatives employs different PI and feed-forward controllers based on the current steer mode of the RSS, determined by the estimated orientation and the reference curvature of the current path section. In this example, the steer force is the force exerted by the RSS 28 onto the formation 12 (FIG.1), which in an example is from a hydraulic rib (not shown) mounted on the string 22 or BHA 24 near the bit 26.

[0029] In an embodiment, the surface input controller 46 uses an adaptive data-driven two degree of freedom control approach and tracks the reference curvature rcurv by adjusting the surface inputs uSF, which influence the drilling direction indirectly through the drill string 22. Due to this and the absence of a precise system model, the surface input controller 46 (FIG. 2A) instead operates on input from a simplified data-driven surrogate model of the drilling process. To handle theresulting model-plant mismatch, an adaptive two degree of freedom control structure, comprising two cascaded feedback controllers, is employed. Both feedback controllers are based on the surrogate model, which is constantly updated using the latest state estimates wDH. The primary controller focuses on reference tracking employing a model predictive control scheme the surrogate model. The secondary controller, addressing model-plant mismatch and disturbances, relies on the error between the reference and estimated path curvature. It utilizes an MPC scheme based on a linear approximation of the surrogate model around the primary input, incorporating an integrative part to counteract set-point mismatches.

[0030] Referring now to FIG. 3, shown is a flowchart 49 illustrating an example of the decision logic 44 of FIG. 2. Depicted in the flowchart 49 is the use of the steering and surface input controllers 42, 46 for determining when to adjust the steering inputs via a downlink, trigger a surface input update, or maintain the current inputs. In the first stage, the decision logic checks whether a downlink with updated steering inputs uDH is necessary. In an example, this is prompted by when there is a difference between current steering parameter input uDHand a proposed steering input ûDH that exceeds a designated threshold. Examples of steering inputs include steer direction, steering force, and steering mode, and examples of the designated threshold include a difference between the current and proposed steer directions of at least about 2° and a difference between the current and proposed steer forces that exceeds a threshold value of 5% of the maximum steer force, dependent on the configuration of the BHA 24. In this example, a value of the proposed steer force is estimated on surface based on information known about the formation 12 and drilling system 14, and optionally from data obtained during drilling, such as encoded in a signal transmitted from the BHA 25. In a non-limiting example of operation, the change in direction and / or change in proposed steer force occurs substantially instantaneously, in alternatives, these changes occur over a set distance or a range of distances. In this example, the maximum steer force is the maximum force the RSS 28 is capable of exerting against the formation 12, which in some examples varies depending on the design or characteristics of the particular RSS. If either of these conditions are met, a determination is made to transmit a downlink, such as by commands stored in controller 32 (FIG. 1) in accordance with the DUAC control structure 36 of FIG. 2 and flowchart 49 of FIG. 3. After a downlink is triggered, there is a delay of 300 seconds and an additional 2 meters are drilled before allowing subsequent downlinks or surface input updates. This accounts for the time needed for the downlink process and its delayed impact on the estimatedpath curvature, respectively. In the second stage, the decision logic evaluates the need for a surface input update. Unless blocked by a downlink, a surface input update is triggered every 2 meters drilled. This delay accommodates the delayed impact on the estimated path curvature, preventing unnecessary wear on the drilling system caused by too frequent surface input updates. Given that the time for surface inputs to influence the downhole drilling process is in the order of seconds, there is no need to incorporate an additional time delay. In alternatives, the first condition referenced above is satisfied if the difference between the current and proposed steer directions exceeds a threshold value within one of the following ranges: a range of about 0.5° to about 5°, about 1° to about 4°, about 1.5° to about 3.5°, about 1.75° to about 3°, any value within these ranges, and combinations of these ranges, further in this alternative, the second condition referenced above is satisfied if the proposed difference between the current and proposed steer forces exceeds one of the following threshold values: a threshold value of about 1% of the maximum steer force, a threshold value of about 2% of the maximum steer force, a threshold value of about 3% of the maximum steer force, or a threshold value of about 4% of the maximum steer force, and further in this alternative, downlinks are triggered by different combinations of the alternative first and second conditions.

[0031] Examples of the disclosed dual actuator control concept automates directional drilling operations, while minimizing the required communication with the downhole steering controller. This improves product quality while simultaneously lowering drilling operation costs by reducing non-productive time. Automation of the directional drilling process provides further advantages of remote operation and role amalgamation, improving the reliability of the drilling operation while reducing personal exposure to health, safety, and environmental risks. Advantages of the control concept include using the surface parameters to control the drilling process reduces the number of necessary downlinks to the BHA. While the surface parameters cannot be solely used to control the automatic trajectory drilling, their usage prolongs the time until a new set of steering parameters must be sent to the BHA, thus reducing non-productive time. Additionally, a controller that automatically sets the surface parameters relieves the drilling personal from the otherwise required repeated decision making. The surface parameter controller could be run either in fully automated or only in advisory mode.

[0032] The novelty of the dual actuator control concept disclosed herein has multiple facets, such as the event-based control structure that combines a conventional steering input control with asurface input controller for simultaneous automatic control of both the steering and surface inputs for the purpose of directional drilling. Another contribution is the proposition of the "decision logic", an event-based decision logic module disclosed above and shown in FIG. 3, which determines when either the steering input controller or the surface input controller is used.

[0033] Advantages of applying the proposed dual actuator control concept include the integration of surface input control in conventional steering input control can reduce the number of necessary downlinks to the BHA. In turn, this reduces communication with the BHA and potentially also the non-productive time during this communication. This can increase the drilling speed and thereby reduces the cost of the drilling operation. The automated control of the steering and surface inputs further facilitates the automation of the directional drilling process. As such, the drilling personal could be relieved from the repeated decision making. The dual actuator controller can be run either in fully automated or in advisory mode. The proposed dual actuator control concept allows flexibility in its design. While it is currently designed with the purpose of accurate reference tracking, it is also possible to consider other control objectives in its design. Possible secondary objectives are drill speed optimization, mitigation of drill string vibrations, or the reduction of material wear. The further automation of the directional drilling process facilitates remote operations and role amalgamation, improving the reliability of the drilling operation while reducing personal exposure to health, safety, and environmental risks.

[0034] In a non-limiting example of use, wellbore 10 (FIG. 1) is drilled based on a reference well plan 38 (FIG. 2). To form the wellbore 10 so its configuration and position approximates that of the reference wellbore 23, adjustments are made to the surface inputs and / or steering inputs. Surface inputs include WOB and drill string RPM, and steering inputs include steer force and steer direction. In this example, operation of drilling system 14 is controlled by commands stored in controller 32, which include the DUAC control structure 36 (FIG.2) and provide for simultaneous and automatic control of both surface and downhole operations by generation and transmission of surface and steering inputs via the decision logic 46 (FIG. 2) found in flowchart 49 (FIG. 3). An advantage of the decision logic 46 is the minimization of downlinks and deviation from the well plan. In this example the decision logic 46 generates and transmits a downlink from surface to the steering system if the path planner 40 (FIG. 2) proposes a 2° or more change of steer direction related to gravity / high side of the toolface or a proposed steer force change that is more than 5%of a maximum steer force. The drill string 22 and BHA 24 are removed from the wellbore 10 after drilling is completed.

[0035] In a prophetic non-limiting example of use, the dual actuator control concept disclosed herein is investigated in a virtual directional drilling test environment to achieve a desired trajectory curvature. More specifically, a computer plant model of the drilling process was used for testing the dual actuator control algorithms and drill wellbore trajectories virtually using a model-in-the-loop simulation. The test results are evaluated and compared with the application results of conventional and wired pipe steering input control as well as surface input control. This comparison is graphically illustrated in the chart 50 of FIG.4 having an abscissa representing time (seconds) and an ordinate representing build rate (degrees every 30 meters). In the chart 50 are plots 52, 54, 56, 58, and 60; where plot 52 represents test data of build rate versus time for a steering control scenario, plot 54 represents test data of build rate versus time for a wired pipe steering input control scenario, plot 56 represents test data of build rate versus time for a surface input control scenario, plot 52 represents test data of build rate versus time for a DUAC scenario, and plot 60 represents a reference. The disclosed DUAC 32 was shown to offer the best reference tracking capabilities of the tested control concepts, and enhance the conventional steering input control by improving the reference tracking accuracy while simultaneously reducing the number of necessary downlinks.

[0036] In another prophetic non-limiting example of use, the dual actuator control concept is tested in a virtual directional drilling test environment to achieve a desired trajectory curvature, and included a closed-loop test environment in a simplified drilling process model covering both the drilling rig and the BHA downhole, as depicted in FIG. 2. The drill string 22 is not modeled in detail, leading the surface input controller 46 to directly adjust drill string RPM and WOB rather than hook load adjustments. The surrogate model in the surface input controller 46 is constructed from a data set of 89900 points representing various combinations of surface inputs, steering inputs, and BHA orientations. For each combination, a simplified open loop simulation is run to calculate the expected wellbore curvature. Cubic spline interpolation is used to construct the surrogate model. New measurements become available every 30 seconds and are used with Kalman filters to estimate the build and turn rates. These downhole measurements are taken at the RSS and not at the drill bit, which allows drilling of approximately 1 meter before input changes have a measurable effect on the path curvature. A control objective is to track the reference signalprovided by a simulated path planner, with an additional goal of minimizing the speed of surface input adjustments over time. In directional drilling, different drill sections are classified based on how the wellbore orientation changes. The objective is to follow a piecewise constant reference signal for the build rate, while the turn rate reference remains zero. The application of dual actuator control for this scenario is depicted in the charts 62, 64, 66, 68, 70, 72 of FIGS. 5A-5F, showing build rate (chart 62) and a turn rate (chart 64) including their reference signals, surface input of WOB (chart 66) and surface input of RPM (chart 68) and steering inputs of steer force (chart 70) and steer direction (chart 72). The controller starts at 4000 seconds, with the initial time needed for cold starting the virtual test environment. The dual actuator controller exhibits precise reference tracking with deviations below 0.1° every 30 meters, and responds as intended, downlinking new steering inputs only after reference changes at 6600 seconds and 10200 seconds when the trigger conditions in the decision logic are met. Surface inputs are employed for subsequent reference tracking and disturbance rejection, notably between 8000 seconds and 10000 seconds, where adjustments counteract the evolving BHA dynamics. The adjustment of WOB, with a stronger impact on the build rate than RPM, is prioritized to minimize overall surface input changes. A model-plant mismatch of the surrogate model is observed at 4000 seconds setting the WOB incorrectly to 95,000 N leading to an overshoot in build rate. The secondary component of the surface input controller counteracts this, increasing WOB until the build rate reference is matched showcases the two degree of freedom control structure’s ability to address model-plant mismatch. The test results are investigated and compared with the application results of conventional and wired pipe steering input control as well as surface input control. The proposed dual actuator control is shown to offer the best reference tracking capabilities of the tested control concepts. It proves to be an enhancement of the conventional steering input control by improving the reference tracking accuracy while simultaneously reducing the number of required downlinks.

[0037] The present invention described herein, therefore, is well adapted to carry out the objectives and attain the ends and advantages mentioned, as well as others inherent therein. While one or more embodiments have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Claims

CLAIMS What is claimed is.

1. A method of drilling comprising: forming a wellbore in a formation with a drilling system comprising a drill string and a bottom-hole assembly having a drill bit and a rotary steerable system; configuring the wellbore based on a planned wellbore; and steering the drill bit by applying an action downhole at the drill bit when a difference between a current steering parameter and a proposed steering parameter exceeds a designated threshold.

2. The method of Claim 1, wherein the steering parameter comprises a steering direction and the designated threshold comprises an angle that is at least 2 degrees.

3. The method of Claim 2, wherein the change in direction is a change of steer direction related to gravity / high side of the toolface.

4. The method of Claim 1, wherein the steering parameter comprises a steering force and the designated threshold is a steer force that is at least 5% of a maximum steer force of the rotary steerable system.

5. The method of Claim 1, wherein the drill bit is steered with an action applied at surface when not being steered with an action applied downhole at the drill bit.

6. The method of Claim 1, wherein a downlink signal is transmitted into the wellbore when the threshold angle or threshold steer force are detected, and wherein the downlink signal provides a command to the rotary steerable system to change steering of the drill bit.

7. The method of Claim 6, wherein the downlink signal comprises a first downlink signal, the method further comprising delaying transmission of a second downlink signal for a set period of time and after drilling for a particular distance.

8. The method of Claim 1, further comprising transmitting periodic surface control signals for adjusting surface inputs.

9. The method of Claim 1, wherein the steering parameter is selected from the group consisting of steering direction, steering force, steering mode, and combinations.

10. A method of drilling comprising: forming a wellbore in a formation with a drilling system comprising a drill string and a bottom-hole assembly having a drill bit and a rotary steerable system; configuring the wellbore to approximate a configuration of a planned wellbore; and steering the drill bit using the rotary steerable system when a proposed change in direction exceeds a threshold angle or when a difference between a proposed steer force and a current steer force exceeds a threshold steer force.

11. The method of Claim 10, wherein the drill bit is selectively steered with an action applied at surface, and wherein an action applied at surface comprises weight on bit, rotational speed of the drill string, and combinations.

12. The method of Claim 10, wherein the threshold angle is 2° and the threshold steer force is 5% of a maximum steer force.

13. A drilling system for forming a wellbore comprising: a drill string; bottom-hole assembly (“BHA”) mounted onto an end of the drill string and that includes a drill bit and a rotary steerable system (“RSS”); and a controller configured to steer the BHA with the RSS when a change in direction of the drill bit exceeds a threshold angle or a proposed change of force in the drill bit exceeds a threshold amount.

14. The drilling system of Claim 13, wherein the change in direction results in the wellbore configuration being approximate to a planned wellbore.

15. The drilling system of Claim 13, further comprising a means for controlling a weight on bit of the drilling bit.

16. The drilling system of Claim 13, further comprising a means for controlling a rotational speed of the drilling string.

17. The drilling system of Claim 13, further comprising a means for directing drilling fluid into the drilling string and for controlling a flow rate of the drilling fluid.

18. The drilling system of Claim 13, further comprising a means for controlling a pressure of the drilling fluid.

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