Evaluating a condition of a downhole component of a drillstring

1. A method for evaluating a condition of a downhole component of a drilling assembly in a borehole, the method comprising:

estimating a bending moment on the component at a selected depth along the borehole;

determining a number rotations of the component at the selected depth;

associating the number of rotations of the component at the selected depth with the bending moment on the component at the selected depth; and

estimating the condition of the component using the number of rotations at the bending moment;

wherein a spectrum of bending moment values is divided into a number of mutually exclusive moment windows, and wherein estimating the condition comprises tracking a total estimated number of rotations wherein the component is subjected to bending moment values in a corresponding moment window;

wherein the condition is at least one of: i) accumulated fatigue of the component; and ii) estimated remaining useful life of the component.

2. The method of claim 1 further comprising deriving the estimated bending moment using an estimated deviation on a selected length of the borehole about the selected depth.

3. The method of claim 2 further comprising deriving the estimated deviation from a borehole model.

4. The method of claim 1 , wherein the method further comprises deriving an estimated location of the component in the borehole using an axial offset of the component from a distal end of the drilling assembly.

5. The method of claim 1 , wherein at least one selected window is greater than a predetermined threshold bending moment.

6. The method of claim 1 , further comprising:

associating a weight factor with at least one moment window; and

using at least the weight factor and the total estimated number of rotations wherein the component is subjected to the bending moment values in the corresponding moment window to estimate the condition of the component.

7. The method of claim 1 , further comprising estimating the condition of the component while conducting drilling operations in the borehole.

8. The method of claim 1 further comprising:

deriving the estimated bending moment from a borehole model using an estimated deviation on a selected length of the borehole about the selected depth and dimensions of the component; and

deriving an estimated location of the component in the borehole using an axial offset of the component from a distal end of the drilling assembly;

wherein a spectrum of bending moment values is divided into a number of mutually exclusive moment windows, and estimating the condition comprises tracking a total estimated number of rotations wherein the component is subjected to bending moment values in a corresponding moment window and wherein at least one selected window is greater than a predetermined threshold bending moment; and

wherein the component is at the bottom hole assembly and the condition is at least one of: i) accumulated fatigue of the component; and ii) estimated remaining useful life of the component.

9. A system for conducting drilling operations, the system comprising:

a drilling assembly configured to be conveyed into a borehole, the drilling assembly comprising at least one component;

a first sensor associated with the drilling assembly and responsive to a depth of the component along the borehole;

a second sensor associated with the drilling assembly and responsive to rotation of the component; and

at least one processor configured to:

determine a depth of the component along the borehole using information from the first sensor;

estimate a bending moment on the component at the depth;

determine a number of rotations of the component at the selected depth using information from the second sensor;

associate the number of rotations of the component at the selected depth with the bending moment on the component at the selected depth; and

estimate the condition of the component using the number of rotations at the bending moment;

wherein the processor is further configured to separate a spectrum of bending moment values into a number of mutually exclusive moment windows, and track a total estimated number of rotations wherein the component is subjected to bending moment values in at least one selected moment window;

wherein the condition is at least one of: i) accumulated fatigue of the component; and ii) estimated remaining useful life of the component.

10. The system of claim 9 , wherein the processor is further configured to derive an estimated location of the component using an axial offset of the component from a distal end of the drilling assembly.

11. The system of claim 9 , wherein the processor is further configured to derive the estimated bending moment using an estimated deviation on a selected length of the borehole about the depth.

12. The system of claim 11 , wherein the processor is further configured to derive the estimated deviation from a borehole model.

13. The method of claim 9 , wherein the at least one selected window is greater than a predetermined threshold bending moment.

14. The method of claim 9 , wherein the processor is further configured to:

associate a weight factor with the at least one selected moment window; and

use at least the weight factor and the total estimated number of rotations wherein the component is subjected to the bending moment values in the corresponding moment window to estimate the condition of the component.

15. The system of claim 9 , wherein the processor is further configured to estimate the condition of the component before the component is removed from the borehole.