TACHOMETER FOR A ROTATING CONTROL DEVICE

1 . A rotating control device (RCD) for use with an offshore drilling unit, comprising:

a tubular housing having a flange formed at each end thereof;

a stripper seal for receiving and sealing against a tubular;

a bearing for supporting rotation of the stripper seal relative to the housing;

a retainer for connecting the stripper seal to the bearing; and

a tachometer, comprising:

a probe connected to the retainer and comprising:

a tilt sensor;

an angular speed sensor;

an angular acceleration sensor;

a first wireless data coupling; and

a microcontroller operable to receive measurements from the sensors and to transmit the measurements to a base using the first wireless data coupling;

the base connected to the housing and comprising:

a second wireless data coupling operable to receive the measurements; and

an electronics package in communication with the second wireless data coupling and operable to relay the measurements to the offshore drilling unit.

2 . The RCD of claim 1 , wherein:

the stripper seal is an upper stripper seal,

the retainer is an upper retainer, and

the RCD further comprises a lower stripper seal and a lower retainer for connecting the lower stripper seal to the bearing.

3 . The RCD of claim 2 , wherein the tachometer further comprises a pressure sensor in communication with a pathway for measuring pressure between the stripper seals.

4 . The RCD of claim 1 , wherein the probe further comprises a battery.

5 . The RCD of claim 1 , wherein the sensors are accelerometers.

6 . The RCD of claim 1 , wherein the angular speed sensor is a gyroscope, comprising:

an outer frame;

an inner frame;

a dither driver operable to dither the inner frame relative to the outer frame; and

a Coriolis sensor for tracking movement of the outer frame.

7 . The RCD of claim 1 , wherein:

the stripper seal, bearing, and retainer are part of a bearing assembly,

the bearing is part of a bearing pack having a self contained lubricant system,

the bearing assembly further comprises a catch sleeve,

the housing is part of a docking station, and

the docking station further comprises a latch operable to engage the catch sleeve, thereby fastening the bearing assembly to the docking station.

8 . The RCD of claim 7 , further comprising a data sub, comprising:

a second probe connected to the catch sleeve and comprising:

a second tilt sensor;

a temperature sensor in fluid communication with the lubricant system;

a third wireless data coupling; and

a second microcontroller operable to receive measurements from the second tilt and temperature sensors and to transmit the measurements to a second base using the third wireless data coupling;

the second base connected to the housing and comprising:

a fourth wireless data coupling operable to receive the measurements; and

an electronics package in communication with the fourth wireless data coupling and operable to relay the measurements to the offshore drilling unit.

9 . The RCD of claim 8 , wherein:

the second tilt sensor is a first accelerometer,

the second probe further comprises second and third accelerometers, and

the accelerometers are triaxially oriented.

10 . A method for drilling a subsea wellbore using the RCD of claim 1 , comprising:

injecting drilling fluid down a drill string while rotating the drill string having a drill bit located at a bottom of the subsea wellbore,

wherein the RCD is engaged with the drill string, thereby diverting returns from the wellbore to an outlet of the RCD; and

monitoring the measurements while drilling the wellbore.

11 . The method of claim 10 , wherein the measurements are monitored by forecasting a remaining lifespan of the stripper seal.

12 . The method of claim 11 , wherein the lifespan is forecast using the tilt measurement.

13 . The method of claim 11 , further comprising adjusting a drilling parameter to optimize the remaining lifespan.

14 . The method of claim 10 , wherein the measurements are monitored by comparing the angular speed of the RCD to the angular speed of the drill string.

15 . The method of claim 10 , wherein the measurements are monitored by determining vibration of the drill string.

16 . The method of claim 15 , wherein the determined vibration includes stick-slip, bit-bounce, and whirl.

17 . The method of claim 10 , further comprising exerting backpressure on the returns.

18 . The method of claim 10 , further comprising, while drilling the wellbore:

measuring a flow rate of the drilling fluid;

measuring a flow rate of the returns; and

comparing the returns flow rate to the drilling fluid flow rate to ensure control of an exposed formation adjacent to the wellbore.