Sensor equipped downhole motor assembly and method

1. A downhole motor for drilling a borehole, comprising:

a stator assembly comprising a helical-shaped stator;

a rotor assembly rotatably disposed in the stator assembly, wherein the rotor assembly comprises a helical-shaped rotor;

a sensor package received in the rotor assembly, wherein the sensor package comprises a first pressure sensor, a second pressure sensor, and a plurality of accelerometers; and

a processor configured to estimate a rotational speed of the rotor assembly based on a whirl rate of the helical-shaped rotor determined from measurements provided by the plurality of accelerometers, and wherein the processor is configured to estimate a rotational speed of the rotor assembly relative to a non-zero rotational speed of the stator assembly based on measurements provided by the plurality of accelerometers.

2. The downhole motor of claim 1 , wherein the rotor comprises a central passage extending between a first end of the rotor and a second end of the rotor.

3. The downhole motor of claim 2 , wherein:

a first passage is formed in a stator housing of the stator assembly adjacent a first end of the rotor of the rotor assembly;

a second passage is formed in the stator housing adjacent a second end of the rotor opposite the first end; and

the first pressure sensor is in fluid communication with the first passage and the second pressure sensor is in fluid communication with the second passage.

4. The downhole motor of claim 3 , wherein the sensor package comprises a gyroscope and a sensor housing that receives the first pressure sensor, second pressure sensor, the plurality of accelerometers, and the gyroscope.

5. The downhole motor of claim 4 , wherein the rotor assembly comprises a rotor catch coupled to an end of the rotor, and wherein the sensor package is received in a receptacle of the rotor catch.

6. The downhole motor of claim 5 , wherein the rotor catch comprises a central passage extending between opposite ends of the rotor catch, and wherein the central passage of the rotor catch is in fluid communication with the first passage of the stator assembly.

7. The downhole motor of claim 1 , wherein the plurality of accelerometers comprises a first accelerometer configured to measure acceleration along a first axis and a second accelerometer configured to measure acceleration along a second axis extending orthogonal from the first axis.

8. A drilling system for forming a borehole, comprising:

a downhole motor comprising:

a stator assembly comprising a helical-shaped stator;

a rotor assembly rotatably disposed in the stator assembly, wherein the rotor assembly comprises a helical-shaped rotor; and

a sensor package comprising a plurality of accelerometers, wherein the plurality of accelerometers are each disposed in a sensor housing of the sensor package and coupled to the rotor assembly such that relative rotation between the plurality of accelerometers and the helical-shaped rotor is restricted;

a processor configured to estimate a rotational speed of the rotor assembly relative to a non-zero rotational speed of the stator assembly based on measurements provided by the plurality of accelerometers.

9. The drilling system of claim 8 , wherein the sensor package comprises a first pressure sensor and a second pressure sensor.

10. The drilling system of claim 9 , wherein the processor is configured to estimate a power output of the downhole motor based on measurements provided by the first and second pressure sensors, the plurality of accelerometers, and a gyroscope of the sensor package.

11. The drilling system of claim 9 , wherein the rotor comprises a central passage extending between a first end of the rotor and a second end of the rotor.

12. The drilling system of claim 11 , wherein:

a stator housing of the stator assembly comprises a first passage adjacent a first end of the rotor of the rotor assembly and a second passage adjacent a second end of the rotor opposite the first end; and

the first pressure sensor is in fluid communication with the first passage and the second pressure sensor is in fluid communication with the second passage.

13. The drilling system of claim 12 , wherein the rotor assembly comprises a rotor catch coupled to an end of the rotor, and wherein the sensor package is received in a receptacle of the rotor catch.

14. The drilling system of claim 13 , wherein the rotor catch comprises a central passage extending between opposite ends of the rotor catch, and wherein the central passage of the rotor catch is in fluid communication with the first passage of the stator assembly.

15. The drilling system of claim 8 , wherein the processor is configured to estimate a whirl rate of the rotor assembly based on measurements provided by the plurality of accelerometers.

16. A method for forming a borehole, comprising:

(a) pumping fluid through a drillstring to a downhole motor coupled to the drillstring;

(b) rotating a rotor assembly of the downhole motor relative to a stator assembly of the downhole motor in response to (a); and

(c) measuring a rotational speed of the rotor assembly relative to a non-zero rotational speed of the stator assembly using a sensor package received in the rotor assembly such that relative rotation between accelerometers of the sensor package and a helical-shaped rotor of the rotor assembly is restricted.

17. The method of claim 16 , further comprising:

(d) measuring differential fluid pressure across opposite ends of the helical-shaped rotor of the rotor assembly using the sensor package; and

(e) measuring a power output of the downhole motor using the sensor package.

18. The method of claim 16 , further comprising:

(d) communicating fluid upstream of the rotor assembly to a first pressure sensor of the sensor package; and

(e) communicating fluid downstream of the rotor assembly through a central passage formed in the helical-shaped rotor of the rotor assembly to a second pressure sensor of the sensor package.

19. The method of claim 16 , further comprising:

(d) estimating a whirl rate of the rotor assembly based on measurements provided by a plurality of accelerometers and a gyroscope of the sensor package.