Marking and sensing a borehole wall
A downhole drilling apparatus, passing through a subterranean borehole, may mark an inner wall of the borehole with a marking element. A sensor, spaced axially from the marking element on the drilling apparatus, may subsequently sense the marking as it passes. A rate of penetration of the drilling apparatus may be calculated by dividing an axial distance, between the marking element and the sensor, by a time interval, between when the marking element marks the inner wall and when the marking is sensed by the sensor. Alternately, a second sensor, spaced axially from the first, may also sense the marking. A rate of penetration may then be calculated by dividing an axial distance, between the two sensors, by a time interval, between when the two sensors sense the marking.
1. A downhole drilling assembly, comprising:
a drilling apparatus comprising:
a marking element capable of marking an inner wall of a borehole, wherein the marking element comprises a radially extendable cutting element capable of degrading the inner wall of the borehole, and marking the inner wall of the borehole comprises: degrading the inner wall and varying a radius of the borehole by repeatedly extending and retracting the radially extendable cutting element;
a sensor, spaced axially from the marking element, capable of sensing the marking of the inner wall, wherein sensing the marking comprises: identifying changes in standoff from the inner wall, a measuring a distance to the inner wall, or any combination thereof; and
a trimming cutter spaced axially from the sensor, wherein the trimming cutter is fixed to an exterior of the drilling apparatus and extends radially farther than the radially extendable cutting element when the radially extendable cutting element is fully extended.
2. The downhole drilling assembly of claim 1 , further comprising a processor capable of calculating a rate of penetration.
3. The downhole drilling assembly of claim 1 , the drilling apparatus further comprising two radially extendable cutting elements spaced axially from each other and extendable together.
4. The downhole drilling assembly of claim 3 , wherein the sensor is disposed axially between the two radially extendable cutting elements.
5. The downhole drilling assembly of claim 1 , further comprising a second sensor spaced axially from the sensor, the second sensor capable of sensing the marking of the inner wall.
6. The downhole drilling assembly of claim 1 , wherein the sensor comprises at least one of an ultrasonic sensor, a resistivity sensor or a physical caliper.
7. The downhole drilling assembly of claim 1 , wherein the sensor is spaced circumferentially from the marking element.
8. A method for downhole drilling, comprising:
forming a borehole by engaging cutting elements of an assembly to degrade a formation, wherein the borehole comprises a cylindrical shape;
marking an inner wall of the borehole with a marking element, wherein marking the inner wall comprises varying a radius of the borehole from the cylindrical shape to form a pattern, wherein the marking element comprises a radially extendable cutting element, and the varying radii of the pattern corresponding to extending and retracting the radially extendable cutting element from the assembly to degrade the inner wall of the borehole, wherein extending and retracting the radially extendable cutting element is timed with rotation of the assembly to form the pattern; and
sensing the marking of the inner wall with a sensor spaced axially from the marking element, wherein sensing the marking comprises measuring a distance to the inner wall.
9. The method for downhole drilling of claim 8 , further comprising calculating a rate of penetration by: dividing an axial distance, between the radially extendable cutting element and the sensor, by a time interval, between when the radially extendable cutting element marks the inner wall and when the marking is sensed by the sensor.
10. The method for downhole drilling of claim 9 , wherein when the radially extendable cutting element marks the inner wall is determined by detecting extension of the radially extendable cutting element.
11. The method for downhole drilling of claim 8 , further comprising reaming degradation from the inner wall with a second radially extendable cutting element spaced axially from the radially extendable cutting element.
12. The method for downhole drilling of claim 8 , further comprising calculating a rate of penetration by: dividing an axial distance, between the marking element and the sensor, by a time interval, between when the marking element marks the inner wall and when the marking is sensed by the sensor.
13. The method for downhole drilling of claim 8 , further comprising:
sensing the marking of the inner wall with a second sensor spaced axially from the sensor; and
dividing an axial distance by a time interval, wherein the axial distance is a distance between the sensor and the second sensor, and the time interval is an interval between when the marking is sensed by the sensor and when the marking is sensed by the second sensor.
14. A method for downhole drilling, comprising:
forming a borehole by engaging cutting elements of an assembly to degrade a formation, wherein the borehole comprises a cylindrical shape;
marking an inner wall of the borehole with a marking element, wherein marking the inner wall comprises varying a radius of the borehole from the cylindrical shape to form a pattern by extending a cutting element radially from the assembly to degrade the inner wall of the borehole and retracting the cutting element toward the assembly during a rotation of the assembly, wherein the pattern varies the radius on a portion of a circumference of the inner wall; and
sensing the marking of the inner wall with a sensor spaced axially from the marking element, wherein sensing the marking comprises identifying changes in standoff from the cylindrical shape of the inner wall.
15. The method for downhole drilling of claim 14 , further comprising calculating a rate of penetration by: dividing an axial distance, between the marking element and the sensor, by a time interval, between when the marking element marks the inner wall and when the marking is sensed by the sensor.
16. The method for downhole drilling of claim 14 , wherein the method further comprises calculating a rate of penetration by: dividing an axial distance by a time interval, wherein the axial distance is a distance between the cutting element and the sensor, and the time interval is an interval between when the cutting element marks the inner wall and when the marking is sensed by the sensor.
17. The method for downhole drilling of claim 16 , wherein when the cutting element marks the inner wall is determined by detecting extension of the cutting element.
18. The method for downhole drilling of claim 14 , wherein sensing the marking of the inner wall comprises sensing the pattern.
19. The downhole drilling assembly of claim 1 , wherein the drilling apparatus comprises a drill bit.