Modelling electromagnetic telemetry signals in deviated wells

1. A method for modeling an electromagnetic (EM) telemetry signal, comprising:

straightening a well in a model;

dividing the well into a plurality of segments;

determining an electrical current in one or more of the plurality of segments when the well is straightened;

replacing the well with equivalent electrical sources based at least partially upon the electrical current in the one or more of the plurality of segments;

bending the well back into its original shape in the model;

determining an electrical current in the one or more of the plurality of segments by projection when the well is back in its original shape; and

summing EM fields for each of the one or more of the plurality of segments, based at least partially upon the electrical current in the one or more of the plurality of segments when the well is back in its original shape, to estimate the EM telemetry signal.

2. The method of claim 1 , wherein the well is substantially vertical when straightened.

3. The method of claim 1 , further comprising simulating the EM telemetry signal from a transmitter in the well, which generates the electrical current in the one or more of the plurality of segments when the well is straightened.

4. The method of claim 1 , wherein the equivalent electrical sources comprise electric dipoles.

5. The method of claim 1 , wherein the electrical current in the one or more of the plurality of segments when the well is back in its original shape is determined based at least partially upon an azimuthal angle, an inclination angle, or both for the one or more of the plurality of segments when the well is back in its original shape.

6. The method of claim 1 , further comprising performing an EM telemetry measurement-while-drilling (MWD) job in response to the estimated EM telemetry signal.

7. A method for modeling an electromagnetic (EM) telemetry signal, comprising:

replacing a first well with equivalent electrical sources in a model;

determining an electrical current in one or more segments in the first well based at least partially upon the equivalent electrical sources;

generating a simulated electrical current in a second well;

determining a normalized voltage in the one or more segments in the first well in response to the simulated electrical current in the second well;

determining a segment voltage in the one or more segments in the first well based at least partially upon the electrical current of the one or more segments in the first well and the normalized voltage of the one or more segments in the first well; and

estimating the EM telemetry signal from a transmitter in the first well based at least partially upon the segment voltages of the one or more segments in the first well.

8. The method of claim 7 , wherein replacing the first well with the equivalent electrical sources in the model comprises:

straightening the first well in the model;

dividing the first well into the one or more segments; and

determining the electrical current in the one or more of the segments in the first well when the first well is straightened.

9. The method of claim 8 , wherein electrical currents in the equivalent electrical sources are determined in the one or more of the segments in the first well when the first well is straightened.

10. The method of claim 8 , wherein replacing the first well with the equivalent electrical sources in the model further comprises:

bending the first well back into its original shape in the model; and

determining an electrical current in the one or more of the segments in the first well by projection when the first well is back in its original shape.

11. The method of claim 7 , wherein determining the segment voltage in the one or more segments in the first well comprises multiplying the electrical current in the one or more segments in the first well by the normalized voltage in the one or more segments in the first well.

12. The method of claim 7 , wherein estimating the EM telemetry signal comprises summing the segment voltages for the one or more segments in the first well.

13. The method of claim 7 , wherein the EM telemetry signal is estimated at a sensor in the second well.

14. The method of claim 7 , wherein the second well comprises a metallic casing.

15. The method of claim 7 , wherein the equivalent electrical sources comprise electric dipoles.

16. The method of claim 7 , further comprising drilling the first well in response to the estimated EM telemetry signal.

17. A computing system comprising:

one or more processors; and

a memory system comprising one or more non-transitory computer-readable media storing instructions that, when executed by at least one of the one or more processors, cause the computing system to perform operations, the operations comprising:

replacing a first well with equivalent electrical sources in a model;

determining an electrical current in one or more segments in the first well based at least partially upon the equivalent electrical sources;

generating a simulated electrical current in a second well;

determining a normalized voltage in the one or more segments in the first well in response to the simulated electrical current in the second well;

determining a segment voltage in the one or more segments in the first well based at least partially upon the electrical current of the one or more segments in the first well and the normalized voltage of the one or more segments in the first well; and

estimating an electromagnetic (EM) telemetry signal from a transmitter in the first well based at least partially upon the segment voltages of the one or more segments in the first well.

18. The computing system of claim 17 , wherein replacing the first well with the equivalent electrical sources in the model comprises:

straightening the first well in the model;

dividing the first well into the one or more segments;

determining the electrical current in the one or more of the segments in the first well when the first well is straightened;

bending the first well back into its original shape in the model; and

determining an electrical current in the one or more of the segments in the first well by projection when the first well is back in its original shape.

19. The computing system of claim 17 , wherein determining the segment voltage in the one or more segments in the first well comprises multiplying the electrical current in the one or more segments in the first well by the normalized voltage in the one or more segments in the first well.

20. The computing system of claim 17 , wherein the operations further comprise performing an EM telemetry measurement-while-drilling (MWD) job in response to the estimated EM telemetry signal.