Rotary control of rotary steerables using servo-accelerometers
AssigneeSchlumberger Technology Corporation
InventorsStewart Blake Brazil, Mark Kuchenbecker, Ronggang Zhang
Life of this patent
Estimating the term…
Abstract
A system and method for steering a rotating downhole drilling tool is provided. The downhole tool includes an inclinometer having directional accelerometers capable of measuring drilling parameters, such as angular position and centripetal acceleration, of the downhole tool. An offset accelerometer is further included for determining centripetal acceleration of the downhole tool. Collar rotation rate and the toolface may be determined from the drilling parameters. Filters, analog to digital converters and processor devices may be used to process the signals and send commands in response thereto for steering the tool.
Claims30
A system for determining rotation rate and position information of a rotating downhole drilling tool, comprising:
- an inclinometer mounted to a collar in the drilling tool, the inclinometer comprising multiple accelerometers positioned so that their respective measurement points are centered on the axis of rotation and aligned with a corresponding x, y and z Cartesian coordinate axis of the collar, the inclinometer generating output signals representing position of the collar with respect to gravity;
- an offset accelerometer mounted to said collar and positioned offset from the axis of rotation of the collar by an offset distance and aligned with one of the accelerometers in the inclinometer, the offset accelerometer generating a signal representing centripetal acceleration of the collar as a function of the offset distance;
- an analog to digital converter coupled to the inclinometer and to the offset accelerometer to convert the output signals thereof into digital signals;
- and
- a processor device coupled to the analog to digital converter to process the digital signals and generate therefrom one or both of collar rotation rate and position of a toolface of a bit shaft coupled to the collar through a geostationary offset mandrel.
A method for steering a rotating downhole drilling tool having a drill collar, comprising steps of:
- detecting acceleration of the collar using at least one directional accelerometer mounted to said collar;
- detecting acceleration of the collar using an offset accelerometer mounted to said collar the offset accelerometer positioned parallel to at least one directional accelerometer a distance therefrom;
- measuring the resolver angle of the collar;
- generating collar rotation rate of a bit shaft and a toolface position;
- and
- adjusting the counter rotation speed of the offset mandrel whereby the tool is steered in the desired direction;
- wherein the step of generating toolface comprises translating directional accelerometer output to a rotating coordinate system according to the equation [ G y_m G z_m ] = [ cos ( Θ res ) sin ( Θ res ) - sin ( Θ res ) cos ( Θ res ) ] · [ G y_c G z_c ] ,
- where Θres is the resolver angle, and Gy—c and Gz —c, are values of directional accelerometers mounted in alignment with respect to the y axis and z axis, respectively, of the collar and Gy—m and Gz—m are the translated values.
A method for generating rotation rate and/or toolface position information of a rotating downhole drilling tool, comprising steps of:
- detecting an inclination of a rotating collar in a downhole drilling tool that drives a bit shaft to form a borehole in an earth formation using accelerometers mounted to said collar;
- and
- detecting centripetal acceleration of the collar using an offset accelerometer mounted to said collar offset by a distance from the axis of rotation of the collar;
- and
- generating one or both of collar rotation rate and toolface position of a bit shaft coupled to the collar through geostationary offset mandrel from the detected inclination of the collar and the centripetal acceleration of the collar;
- wherein the step of detecting the inclination of the collar comprises detecting output from each of three accelerometers that are mounted to said collar to measure gravity components of the collar with respect to each of a respective one of the x, y and z Cartesian coordinate axes of the collar, wherein the axis of rotation of the collar is the x-axis;
- and
- wherein the step of generating toolface position information comprises translating accelerometer output to a rotating coordinate system according to the equation [ G y_m G z_m ] = [ cos ( Θ res ) sin ( Θ res ) - sin ( Θ res ) cos ( Θ res ) ] · [ G y_c G z_c ] ,
- where Θres is an angle measurement between the collar and a bit-shaft coupled to the collar through an geostationary offset mandrel, and Gy_c and Gz_c, are values of accelerometers mounted in alignment with the y axis and z axis, respectively, of the collar and Gy_m and Gz_m are the translated values.
The method claim, and further comprising the step of low pass filtering Gy_m and Gz_m prior to computing (Φgtf), such that Φgtf=arctan(−gz,gy), where gz and gy are filtered versions of Gy_m and Gz_m respectively.
A system for determining rotation rate and/or toolface position information of a rotating downhole drilling tool, comprising:
- first, second and third accelerometers mounted to a collar that is controlled to rotate in the downhole drilling tool, each of the first, second and third accelerometers being positioned so that their respective measurement points are centered on an axis of rotation and aligned with respect to a corresponding x, y and z Cartesian coordinate axis of the collar, wherein the x-axis is the axis of rotation of the collar, each of the first, second and third accelerometer generating an output signal;
- a fourth accelerometer mounted to said collar and positioned offset from the axis of rotation of the collar by an offset distance and aligned with the second accelerometer, the fourth accelerometer generating a signal representing centripetal acceleration of the collar as a function of the offset distance;
- an analog to digital converter coupled to the first, second, third and fourth accelerometers to convert the output signals thereof into digital signals;
- and a processor device coupled to the analog to digital converter to process the digital signals and generate therefrom one or both of collar rotation rate and toolface position of a bit shaft coupled to the collar through a geostationary offset mandrel.
Dependencies are inferred from the claim text.