Reducing error contributions to gyroscopic measurements

Abstract

A method and system for reducing error contributions to gyroscopic measurements is provided. The method includes receiving a plurality of signals indicative of at least one component of the Earth's rotation substantially perpendicular to a portion of a wellbore and a component of the Earth's rotation substantially parallel to the portion of the wellbore. The plurality of signals is generated by one or more gyroscopic sensors within the portion of the wellbore. The method further includes calculating, using the plurality of signals and using one or more signals indicative of the Earth's rotation rate and one or more signals indicative of the latitude of the one or more gyroscopic sensors within the portion of the wellbore, a mass unbalance offset for the one or more gyroscopic sensors.

1 - 23 . (canceled) 
     
     
         24 . A method, comprising:
 receiving a plurality of angular rotation rate measurements about a first axis of a survey tool disposed in a wellbore from one or more first gyroscopic sensors of the survey tool, wherein the one or more first gyroscopic sensors are positioned in a first plurality of index positions;   receiving a plurality of angular rotation rate measurements about a second axis of the survey tool from the one or more first gyroscopic sensors positioned in the first plurality of index positions;   receiving a plurality of angular rotation rate measurements about a third axis of the survey tool from a second gyroscopic sensor of the survey tool, wherein the second gyroscopic sensor is positioned in a second plurality of index positions; and   determining one or more bias values based on the plurality of angular rotation rate measurements about the first axis, the plurality of angular rotation rate measurements about the second axis, the plurality of angular rotation rate measurements about the third axis, or combinations thereof.   
     
     
         15 . The method of  claim 24 , wherein the one or more first gyroscopic sensors comprise one or more Coriolis vibratory gyroscopic sensors, one or more microelectromechanical system (MEMS) gyroscopic sensors, or combinations thereof. 
     
     
         26 . The method of  claim 24 , wherein the second gyroscopic sensor comprises a Coriolis vibratory gyroscopic sensor or a microelectromechanical system (MEMS) gyroscopic sensor. 
     
     
         27 . The method of  claim 24 , wherein the third axis is substantially parallel to a longitudinal axis of the survey tool. 
     
     
         28 . The method of  claim 24 , wherein the first axis and the second axis are substantially perpendicular to the third axis, and wherein the first axis and the second axis are substantially perpendicular to each other. 
     
     
         29 . The method of  claim 24 , wherein the first axis corresponds to an x-axis of the survey tool, the second axis corresponds to a y-axis of the survey tool, and the third axis corresponds to a z-axis of the survey tool. 
     
     
         30 . The method of  claim 24 , wherein the plurality of angular rotation rate measurements about the first axis correspond to a plurality of measurements of a component of the Earth's rotation along the first axis. 
     
     
         31 . The method of  claim 24 , wherein the plurality of angular rotation rate measurements about the second axis correspond to a plurality of measurements of a component of the Earth's rotation along the second axis. 
     
     
         32 . The method of  claim 24 , wherein the plurality of angular rotation rate measurements about the third axis correspond to a plurality of measurements of a component of the Earth's rotation along the third axis. 
     
     
         33 . The method of  claim 24 , wherein the one or more first gyroscopic sensors comprises a dual-axis gyroscopic sensor, one or more single-axis gyroscopic sensors, or combinations thereof. 
     
     
         34 . The method of  claim 24 , wherein the second gyroscopic sensor comprises a dual-axis gyroscopic sensor or a single-axis gyroscopic sensor. 
     
     
         35 . The method of  claim 24 , further comprising:
 receiving one or more measurements from one or more accelerometers of the survey tool; and   determining an inclination, a tool face angle, or both based on the one or more measurements from the one or more accelerometers, the plurality of angular rotation rate measurements about the first axis, the plurality of angular rotation rate measurements about the second axis, and the plurality of angular rotation rate measurements about the third axis.   
     
     
         36 . The method of  claim 24 , wherein receiving the plurality of angular rotation rate measurements about the first axis comprises:
 receiving a measurement about the first axis of the survey tool at a first index position of the first plurality of index positions; and   receiving a measurement about the first axis of the survey tool at a second index position of the first plurality of index positions, wherein the first index position and the second index position are positioned 180 degrees from one another, and wherein the one or more first gyroscopic sensors are configured to rotate about the third axis between the first index position and the second index position.   
     
     
         37 . The method of  claim 24 , wherein receiving the plurality of angular rotation rate measurements about the second axis comprises:
 receiving a measurement about the second axis of the survey tool at a first index position of the first plurality of index positions; and   receiving a measurement about the second axis of the survey tool at a second index position of the first plurality of index positions, wherein the first index position and the second index position are positioned 180 degrees from one another, and wherein the one or more first gyroscopic sensors are configured to rotate about the third axis between the first index position and the second index position.   
     
     
         38 . The method of  claim 24 , wherein receiving the plurality of angular rotation rate measurements about the third axis comprises:
 receiving a measurement about the third axis of the survey tool at a first index position of the second plurality of index positions; and   receiving a measurement about the third axis of the survey tool at a second index position of the second plurality of index positions, wherein the first index position and the second index position are positioned 180 degrees from one another, and wherein the second gyroscopic sensor is configured to rotate about the first axis or the second axis between the first index position and the second index position.   
     
     
         39 . The method of  claim 24 , wherein a single drive motor is configured to rotate the one or more first gyroscopic sensors and the second gyroscopic sensor simultaneously among the first and second plurality of index positions. 
     
     
         40 . The method of  claim 24 , wherein the one or more first gyroscopic sensors are positioned on a first side of a drive motor of the survey tool, and wherein the second gyroscopic sensor is positioned on a second side of the drive motor. 
     
     
         41 . A system, comprising:
 a survey tool disposed in a wellbore, comprising:   
       one or more first gyroscopic sensors configured to provide a plurality of angular rotation rate measurements about a first axis of a survey tool, and to provide a plurality of angular rotation rate measurements about a second axis of the survey tool, wherein the one or more first gyroscopic sensors are positioned in a first plurality of index positions; 
       a second gyroscopic sensor configured to provide a plurality of angular rotation rate measurements about a third axis of the survey tool, wherein the second gyroscopic sensor is positioned in a second plurality of index positions; 
       a processor; and
 a memory comprising program instructions which, when executed by the processor, cause the processor to determine one or more bias values based on the plurality of angular rotation rate measurements about the first axis, the plurality of angular rotation rate measurements about the second axis, the plurality of angular rotation rate measurements about the third axis, or combinations thereof. 
 
     
     
         42 . The system of  claim 41 , wherein the one or more first gyroscopic sensors comprise one or more Coriolis vibratory gyroscopic sensors, one or more microelectromechanical system (MEMS) gyroscopic sensors, or combinations thereof. 
     
     
         43 . The system of  claim 41 , wherein the second gyroscopic sensor comprises a Coriolis vibratory gyroscopic sensor or a microelectromechanical system (MEMS) gyroscopic sensor.