Measurement-while-drilling assembly using gyroscopic devices and methods of bias removal

A method of making measurements using a sensor assembly including a two-axis gyroscope rotatably mounted in a measurement-while-drilling ("MWD") tool in a bottomhole assembly having a drillbit thereon during the drilling of a borehole, the method comprising: (a) locating the MWD tool in the borehole at a first predetermined depth; (b) taking a measurement from the two-axis gyroscope and at least one additional sensor on the sensor assembly at a first rotational position of the sensor at the first predetermined depth; (c) rotating the sensor assembly a predetermined angle relative to the first position about a known axis of the sensor to at least one additional rotational position at the predetermined depth and taking a measurement from the two-axis gyroscope and the at least one additional sensor at the at least one additional position; (d) using a processor on the tool for combining measurements made by the two-axis gyroscope and the at least one additional sensor at the first and at least one additional rotational position to determine a bias in the measurements in at least one of (i) the two-axis gyroscope, and, (ii) the at least one additional sensor, and obtaining corrected measurements therefrom; and (e) determining from said corrected measurements a parameter of interest selected from the group consisting of (i) an azimuth with respect to the true north, (ii) toolface orientation with respect to the true north, iii) amplitude of measurements of the earth's rate vector for a two-axis gyroscope, (iv) amplitude of measurements of the earth's rate vector for a three-axis gyroscope, and (v) local apparent latitude for a three-axis gyroscope.

A measurement-while-drilling (MWD) downhole assembly for use in drilling boreholes, comprising: (a) a housing; (b) sensor assembly including a two-axis gyroscope and at least one additional sensor rotatably mounted in the housing for providing signals relating to the motion of the tool; (c) a device in the tool for rotating the sensor assembly about an axis of the sensor assembly; and (d) a processor in the tool, said processor combining signals from the sensor assembly taken at positions corresponding to a plurality of rotational positions at a predetermined depth in the borehole to determine a bias present in the measurements made by the sensor assembly during drilling of the borehole and determining therefrom corrected measurements, the processor further using said corrected measurements to determine a parameter of interest selected from the group consisting of (i) an azimuth with respect to the true north, (ii) toolface orientation with respect to the true north, iii) amplitude of measurements of the earth's rate vector for a two-axis gyroscope, (iv) amplitude of measurements of the earth's rate vector for a three-axis gyroscope, and (v) local apparent latitude for a three-axis gyroscope.

A method of making measurements using a sensor assembly including a gyroscope rotatably mounted in a measurement-while-drilling ("MWD") tool in a bottomhole assembly having a drillbit thereon during the drilling of a borehole, the method comprising: (a) locating the MWD tool in the borehole at a first predetermined depth; (b) taking a measurement from the gyroscope and at least one additional sensor on the sensor assembly at a first rotational position of the sensor at the first predetermined depth; (c) rotating the sensor assembly a predetermined angle relative to the first position about a known axis of the sensor to at least a one additional rotational position at the predetermined depth and taking a measurement from the gyroscope and the at least one additional sensor at the at least one additional position; and (d) using a processor on the tool for combining measurements made by the gyroscope and the at least one additional sensor at the first and the at least one additional rotational position to determine a bias in the measurements in at least one of (i) the gyroscope, and, (ii) the at least one additional sensor, and obtaining corrected measurements therefrom.

A method of making measurements made by at least one sensor rotatably mounted in a measurement-while-drilling ("MWD") tool in a bottomhole assembly having a drillbit thereon during the drilling of a borehole, the method comprising: (a) locating the MWD tool in the borehole at an arbitrary depth; (b) taking a measurement from the at least one sensor at a first rotational position of the sensor at the predetermined depth; (c) using a stepper motor to rotate the at least one sensor a predetermined angle relative to the first rotational position about a known axis of the sensor to at least one additional rotational position at the predetermined depth and taking a measurement from the at least one sensor at the at least one additional rotational position; and (d) using a processor on the tool for combining the first measurement and the at least second measurement to determine a bias in the measurements made by the at least one sensor.