received by the International Bureau on 20 December 2018 (20.12.2018)

WHAT IS CLAIMED IS:

1. A method for generating an output of a downhole inertial measurement unit (IMU) comprising:

generating a trajectory between a plurality of survey points of a planned well data as a function of time, the planned well data comprising a plurality of three- dimensional coordinates corresponding to the survey points of an underground planned well, the trajectory comprising a plurality of trajectory coordinates between consecutive ones of the survey points;

generating sensor data for each of the trajectory coordinates as a function of time based on geodetic reference parameters, the generated sensor data comprising: generated accelerometer output; generated gyroscopic output; and generated magnetometer output;

receiving sensor noise parameters;

adding sensor noise to the generated accelerometer output, the generated gyroscopic output, and the generated magnetometer output and

outputting the generated accelerometer output; the generated gyroscopic output; and the generated magnetometer output as a function of time as a generated output of the downhole IMU.

2. The method of claim 1 , wherein the generating the trajectory between survey points is performed at a time step of 1 per second to 1000 per second.

3. The method of claim 1 , wherein each of the generated trajectory coordinates comprises a three-dimensional position, a three-dimensional orientation, and a timestamp.

4. The method of claim 3, wherein each three-dimensional orientation comprises an azimuthal angle, an inclination angle, and a toolface angle of a drill bit.

5. The method of claim 3, further comprising:

generating the accelerometer output in accordance with the three-dimensional positions and the timestamps of the trajectory coordinates;

generating the gyroscopic output in accordance with the three-dimensional orientation and the timestamps of the trajectory coordinates; and

generating the magnetometer output in accordance with:

the geodetic reference parameters; and

the three-dimensional positions and the timestamps of the trajectory coordinates.

6. The method of claim 5, wherein the computing the generated accelerometer output comprises converting generated accelerometer data from a navigation frame to a body frame of a drill bit,

wherein the computing the generated gyroscopic output comprises converting generated gyroscopic data from the navigation frame to the body frame of the drill bit, and

wherein the computing the generated magnetometer output comprises converting generated magnetometer output from the navigation frame to the body frame of the drill bit.

7. (Cancelled)

8. The method of claim 1 , wherein the sensor noise comprises at least one of:

quantization noise;

white noise;

bias instability;

bias random walk; and

bias ramp.

9. The method of claim 1 , further comprising, between each consecutive pair of survey points: determining whether the trajectory between the consecutive pair of survey points is a rotational mode trajectory or a sliding mode trajectory;

in response to determining the rotational mode trajectory, adding rotational mode drilling noise to the generated accelerometer output, the generated gyroscopic output, and the generated magnetometer output; and

in response to determining the sliding mode trajectory, adding sliding mode drilling noise to the generated accelerometer output, the generated gyroscopic output, and the generated magnetometer output.

10. The method of claim 1 , further comprising verifying the generated output of the IMU by:

supplying the generated accelerometer output, the generated gyroscopic output, and generated magnetometer output to an inertial navigation system (INS) to generate an INS system trajectory; and

verifying the generated output of the IMU when a difference between the INS system trajectory and the trajectory computed from the planned well data is below a threshold value.

1 1. The method of claim 1 , wherein the sensor data further comprises pressure data.

12. A system for generating the data output of a downhole inertial measurement unit (IMU) comprising:

a processor; and

a memory storing instructions that, when executed by the processor, cause the processor to:

generate a trajectory between the survey points of planned well data as a function of time, the planned well data comprising a plurality of three- dimensional coordinates corresponding to the survey points of an underground planned well, the trajectory comprising a plurality of trajectory coordinates between consecutive ones of the survey points;

31 generate sensor data for each of the trajectory coordinates as a function of time based on the geodetic reference parameters, the generated sensor data comprising: generated accelerometer output; generated gyroscopic output; and generated magnetometer output;

receive sensor noise parameters; and

add sensor noise to the generated accelerometer output, the generated gyroscopic output, and the generated magnetometer output.

13. The system of claim 12, wherein the system is implemented on a realtime target machine and used as hardware-in-the-loop.

14. The system of claim 13, wherein the real-time target machine is configured to send commands to a motion controller to control a nonmagnetic motion simulator apparatus.

15. The system of claim 1 1 , wherein each of the generated trajectory coordinates comprises a three-dimensional position, a three-dimensional orientation, and a timestamp.

16. The system of claim 15, wherein each three-dimensional orientation comprises an azimuthal angle, an inclination angle, and a toolface angle of a drill bit.

17. The system of claim 12, wherein the memory further stores instructions that, when executed by the processor, cause the processor to:

compute the generated accelerometer output in accordance with the three- dimensional positions and the timestamps of the trajectory coordinates,

compute the generated gyroscopic output in accordance with the three- dimensional orientation and the timestamps of the trajectory coordinates; and

compute the generated magnetometer output in accordance with:

the geodetic reference parameters; and

the three-dimensional positions and the timestamps of the trajectory coordinates.

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18. The system of claim 17, wherein the instructions for computing the generated accelerometer output comprise instructions that, when executed by the processor, cause the processor to convert generated accelerometer data from a navigation frame to a body frame of a drill bit,

wherein the instructions for computing the generated gyroscopic output comprise instructions that, when executed by the processor, cause the processor to convert generated gyroscopic data from the navigation frame to the body frame of the drill bit, and

wherein the instructions for computing the generated magnetometer output comprise instructions that, when executed by the processor, cause the processor to convert generated magnetometer output from the navigation frame to the body frame of the drill bit.

19. (Cancelled)

20. The system of claim 12, wherein the sensor noise comprises at least one of:

quantization noise;

white noise;

bias instability;

bias random walk; and

bias ramp.

21. The system of claim 12, wherein the memory further stores instructions that, when executed by the processor, cause the processor to, between each consecutive pair of survey points:

determine whether the trajectory between the consecutive pair of survey points is a rotational mode trajectory or a sliding mode trajectory;

in response to determining the rotational mode trajectory, add rotational mode drilling noise to the generated accelerometer output, the generated gyroscopic output, and the generated magnetometer output; and

33 in response to determining the sliding mode trajectory, add sliding mode drilling noise to the generated accelerometer output, the generated gyroscopic output, and the generated magnetometer output.

22. The system of claim 12, wherein the memory further stores instructions that, when executed by the processor, cause the processor to verify the generated output of the IMU by:

supplying the generated accelerometer output, the generated gyroscopic output, and generated magnetometer output to an inertial navigation system (INS) to generate an INS system trajectory; and

verifying the generated output of the IMU when a difference between the INS system trajectory and the trajectory computed from the planned well data is below a threshold value.

23. A non-transitory computer readable medium having instructions stored thereon that, when executed by a processor, cause the processor to:

generate a trajectory between the survey points of planned well data as a function of time, the planned well data comprising a plurality of three-dimensional coordinates corresponding to the survey points of an underground planned well, the trajectory comprising a plurality of trajectory coordinates between consecutive ones of the survey points;

generate sensor data for each of the trajectory coordinates as a function of time based on the geodetic reference parameters, the generated sensor data comprising: generated accelerometer output; generated gyroscopic output; and generated magnetometer output;

receive sensor noise parameters; and

add sensor noise to the generated accelerometer output, the generated gyroscopic output, and the generated magnetometer output.

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