Methods and systems for performing automated drilling of a wellbore

1. A method of performing automated drilling of a wellbore using a drill bit, comprising:

drilling the wellbore according to one or more drilling parameter targets associated with one or more corresponding drilling parameters;

using a drilling controller communicating with: a rotational drive unit controller; a rotation rate sensor; a height control apparatus; a height sensor; a depth sensor; and a hookload sensor, to:

determine, during the drilling of the wellbore, that the drill bit has entered or exited a stringer, comprising determining that a controlling drilling parameter of the one or more drilling parameters is outside a threshold window; and

in response to determining that the drill bit has entered or exited the stringer, and during the drilling of the wellbore, update one or more controlled drilling parameter targets of the one or more drilling parameter targets, wherein updating the one or more controlled drilling parameter targets comprises updating at least one of a revolutions per minute (RPM) target and a weight-on-bit (WOB) target; and

after updating the one or more controlled drilling parameter targets, further drilling the wellbore according to the updated one or more controlled drilling parameter targets.

2. The method of claim 1 , further comprising:

further determining that the controlling drilling parameter is outside the threshold window; and

in response thereto, further updating the one or more controlled drilling parameter targets.

3. The method of claim 2 , wherein further updating the one or more controlled drilling parameter targets comprises further updating the one or more controlled drilling parameter targets a predetermined period of time after the further determining that the controlling drilling parameter is outside the threshold window.

4. The method of claim 1 , wherein the one or more drilling parameter targets further comprise one or more of a differential pressure target, a torque target, and a mechanical specific energy (MSE) target.

5. The method of claim 1 , wherein the controlling drilling parameter comprises at least one of ROP and MSE.

6. The method of claim 1 , wherein the threshold window is continuously determined.

7. The method of claim 1 , wherein the threshold window is determined using a moving average of the controlling drilling parameter.

8. The method of claim 4 , wherein the MSE target is determined according to one or more of: WOB, RPM, torque, differential pressure, mud flow rate, bit diameter, mud motor speed to flow ratio, a maximum mud motor torque, and a maximum differential pressure.

9. The method of claim 1 , wherein:

determining that the controlling drilling parameter is outside the threshold window comprises determining that ROP is less than a lower limit of the threshold window, or that MSE has exceeded an upper lower limit of the threshold window; and

updating the one or more controlled drilling parameter targets comprises at least one of reducing the RPM target and increasing the WOB target.

10. The method of claim 1 , wherein:

determining that the controlling drilling parameter is outside the threshold window comprises determining that ROP has exceeded an upper limit of the threshold window, or that MSE is less than a lower limit of the threshold window; and

updating the one or more controlled drilling parameter targets comprises at least one of increasing the RPM target and decreasing the WOB target.

11. The method of claim 1 , wherein updating the one or more controlled drilling parameter targets comprises:

determining the updated one or more controlled drilling parameter targets; and

adjusting over a period of time the one or more controlled drilling parameter targets until the one or more controlled drilling parameter targets are within a predetermined range of the updated one or more controlled drilling parameter targets.

12. The method of claim 1 , wherein updating the one or more controlled drilling parameter targets comprises adjusting the one or more controlled drilling parameter targets by a preset amount.

13. The method of claim 1 , wherein updating the one or more controlled drilling parameter targets comprises adjusting the one or more controlled drilling parameter targets using one or more historical controlled drilling parameter targets.

14. The method of claim 13 , wherein each historical controlled drilling parameter target is associated with a formation type, and wherein the method further comprises:

determining a type of formation through which drilling is proceeding; and

prior to adjusting the one or more controlled drilling parameter targets, filtering the one or more historical controlled drilling parameter targets based on the type of formation through which drilling is proceeding and based on the respective formation type associated with each historical controlled drilling parameter target.

15. The method of claim 14 , further comprising, after a predetermined period of time has elapsed since determining that the controlling drilling parameter is outside the threshold window, associating at least one historical controlled drilling parameter target with a normal formation.

16. The method of claim 1 , wherein drilling the wellbore according to the one or more drilling parameter targets comprises:

drilling the well bore according to a first drilling parameter target, wherein the first drilling parameter target comprises a first drilling parameter offset modified by a first drilling parameter perturbation signal;

measuring a first drilling performance metric to determine a measured first drilling performance metric, wherein the first drilling performance metric is indicative of a response of the drilling to the first drilling parameter target;

determining an output of a first objective function using the measured first drilling performance metric;

determining a first correlation between the output of the first objective function and the first drilling parameter perturbation signal;

determining an integral of the first correlation;

updating the first drilling parameter target using the integral of the first correlation modified by the first drilling parameter perturbation signal; and

after the first drilling parameter target has been updated, drilling the wellbore according to the first drilling parameter target.

17. The method of claim 16 , wherein the drilling of the well bore according to the first drilling parameter target occurs in response to determining that one or more controlled drilling parameters are within a predetermined range of their corresponding one or more controlled drilling parameter targets.

18. The method of claim 1 , wherein drilling the wellbore according to the updated one or more controlled drilling parameter targets comprises:

drilling the well bore according to a first drilling parameter target, wherein the first drilling parameter target comprises a first drilling parameter offset modified by a first drilling parameter perturbation signal;

measuring a first drilling performance metric to determine a measured first drilling performance metric, wherein the first drilling performance metric is indicative of a response of the drilling to the first drilling parameter target;

determining an output of a first objective function using the measured first drilling performance metric;

determining a first correlation between the output of the first objective function and the first drilling parameter perturbation signal;

determining an integral of the first correlation;

updating the first drilling parameter target using the integral of the first correlation modified by the first drilling parameter perturbation signal; and

after the first drilling parameter target has been updated, drilling the wellbore according to the first drilling parameter target.

19. The method of claim 18 , wherein the drilling of the well bore according to the first drilling parameter target occurs in response to determining that one or more controlled drilling parameters are within a predetermined range of their corresponding one or more controlled drilling parameter targets.

20. A system for performing automated drilling of a well bore, the system comprising:

a height control apparatus configured to adjust a height of a drill string comprising a drill bit used to drill the wellbore;

a height sensor;

a rotational drive unit comprising a rotational drive unit controller and a rotation rate sensor;

a depth sensor;

a hookload sensor;

a drilling controller communicatively coupled to the rotational drive unit controller, the rotation rate sensor, the height control apparatus, the height sensor, the depth sensor, and the hookload sensor, the drilling controller configured to perform a method comprising:

drilling the wellbore according to one or more drilling parameter targets associated with one or more corresponding drilling parameters;

determining, during the drilling of the wellbore, that the drill bit has entered or exited a stringer, comprising determining that a controlling drilling parameter of the one or more drilling parameters is outside a threshold window;

in response to determining that the drill bit has entered or exited the stringer, and during the drilling of the wellbore, updating one or more controlled drilling parameter targets of the one or more drilling parameter targets, wherein updating the one or more controlled drilling parameter targets comprises updating at least one of a revolutions per minute (RPM) target and a weight-on-bit (WOB) target; and

after updating the one or more controlled drilling parameter targets, further drilling the wellbore according to the updated one or more controlled drilling parameter targets.

21. A non-transitory computer-readable medium having stored thereon program code executable by a processor and configured, when executed, to cause the processor to communicate with a rotational drive unit controller, a rotation rate sensor, a height control apparatus, a height sensor, a depth sensor and a hookload sensor to perform a method of performing automated drilling of a well bore using a drill bit, comprising:

drilling the wellbore according to one or more drilling parameter targets associated with one or more corresponding drilling parameters;

determining, during the drilling of the wellbore, that the drill bit has entered or exited a stringer, comprising determining that a controlling drilling parameter of the one or more drilling parameters is outside a threshold window;

in response to determining that the drill bit has entered or exited the stringer, and during the drilling of the wellbore, updating one or more controlled drilling parameter targets of the one or more drilling parameter targets, wherein updating the one or more controlled drilling parameter targets comprises updating at least one of a revolutions per minute (RPM) target and a weight-on-bit (WOB) target; and

after updating the one or more controlled drilling parameter targets, further drilling the wellbore according to the updated one or more controlled drilling parameter targets.