Systems and methods for controlling a drilling path based on drift estimates

1. A method for controlling a drilling operation, comprising:

(a) determining, by a computer system coupled to a drilling rig, a present position of a bottom hole assembly (BHA) in a borehole;

(b) calculating, by the computer system, a toolface vector needed for the borehole to converge with a desired target path;

(c) determining, by the computer system, a compensated toolface vector that is responsive to the toolface vector and a geological formation drift estimate vector corresponding to a trajectory bias for the BHA within a geological formation observed while drilling along a straight path;

(d) orienting the BHA and drilling the borehole responsive to the compensated toolface vector; and

(e) repeating steps (a)-(d) until the borehole converges with the desired target path.

2. The method of claim 1 , wherein the toolface vector is calculated using information comprising build rate, present error vector, and well plan information.

3. The method of claim 2 , wherein the calculating the toolface vector step further comprises the steps of:

determining, by the computer system, a look ahead point that is a fixed distance ahead of the BHA; and

calculating, by the computer system, a direction of drilling toward the look ahead point.

4. The method of claim 3 , wherein the compensated toolface vector is determined responsive to a formation drift associated with a geological formation in which the BHA is located.

5. The method of claim 3 , further comprising the steps of:

performing a slide operation and a rotate operation to move the BHA along the compensated toolface vector.

6. The method of claim 1 , wherein the geological formation drift estimate vector is responsive to a geological formation drift calculation from a recent drilling operation.

7. The method of claim 1 , wherein the orienting the BHA step is performed according to a plan for sliding activity.

8. The method of claim 7 , wherein the plan for sliding activity is responsive to BHA wear.

9. The method of claim 7 , wherein the plan for sliding activity is responsive to when a next drill string pipe connection will occur.

10. The method of claim 1 , wherein the calculating the toolface vector step further comprises the steps of:

determining a plurality of potential toolface vectors corresponding to a plurality of potential drill paths; and

selecting the toolface vector from the plurality of potential toolface vectors according to which of the plurality of potential drill paths satisfies a drilling need.

11. The method of claim 10 , wherein the drilling need comprises a cost factor.

12. The method of claim 10 , wherein the drilling need comprises a total vertical depth error.

13. A drilling system, comprising:

a control system for generating steering control signals to control a bottom hole assembly (BHA), wherein the control system further comprises executable instructions to:

(a) determine a present position of the BHA within a borehole being drilled;

(b) calculate a toolface vector needed for the borehole to converge with a desired target path;

(c) determine a compensated toolface vector that is responsive to the toolface vector and a geological formation drift estimate vector corresponding to a trajectory bias for the BHA within a geological formation observed while drilling along a straight path;

(d) cause at least one control parameter to be modified in order to alter a drilling direction of the BHA in accordance with the compensated toolface vector;

(e) transmit the at least one control parameter to a drilling rig to drill the borehole in accordance with the compensated toolface vector; and

(f) repeat steps (a)-(e) until the borehole converges with the desired target path.

14. The drilling system of claim 13 , wherein the toolface vector is calculated using information comprising build rate, present error vector, and well plan information.

15. The drilling system of claim 14 , wherein the control system calculates the toolface vector by

determining a look ahead point that is a fixed distance ahead of the BHA; and

calculating a direction of drilling toward the look ahead point.

16. The drilling system of claim 15 , wherein the compensated toolface vector is determined responsive to a formation drift associated with a geological formation in which the BHA is located.

17. The drilling system of claim 13 , wherein the geological formation drift estimate vector takes into account a geological formation drift calculation from a recent drilling operation.

18. The drilling system of claim 13 , wherein the executable instructions to calculate the toolface vector step further comprise instructions to:

determine a plurality of potential toolface vectors corresponding to a plurality of potential drill paths; and

select the toolface vector from the plurality of potential toolface vectors according to which of the plurality of potential drill paths comprises a lowest cost alternative.

19. The drilling system of claim 13 , wherein the executable instructions to calculate the toolface vector step further comprise instructions to:

determine a plurality of potential toolface vectors corresponding to a plurality of potential drill paths; and

select the toolface vector from the plurality of potential toolface vectors according to which of the plurality of potential drill paths comprises a total vertical depth error correction.

20. The drilling system of claim 13 , wherein the at least one control parameter further comprises parameters associated with a slide operation and a rotate operation to move the BHA along the compensated toolface vector.