Method of operating a tubular string assembly within a wellbore

1. A method of positioning a string assembly within a wellbore comprising:

moving the string assembly at least axially within the wellbore;

obtaining surface data regarding at least one parameter associated with running the string assembly within the wellbore over a range of depths;

modeling the at least one parameter over the range of depths for a plurality of assumed friction factors to obtain modeled data for each assumed friction factor;

calculating a derivative of the surface data over the range of depths;

calculating a derivative of the modeled data over the range of depths;

comparing the derivative of the surface data to the derivative of the modeled data;

determining one or more local friction factors for the range of depths based on the comparison;

adjusting at least one string assembly operating parameter based on the one or more local friction factors; and

operating the string assembly within the wellbore by moving the string assembly at least axially within the wellbore using the adjusted operating parameter.

2. The method of claim 1 , wherein the at least one parameter is hook load or surface torque.

3. The method of claim 1 , wherein the string assembly comprises a drilling string or a casing string.

4. The method of claim 1 , wherein the modeling step is performed using a torque and drag computational model.

5. The method of claim 1 , wherein the plurality of assumed friction factors ranges between 0.05 and 0.5.

6. The method of claim 1 , further comprising plotting the surface data over the range of depths.

7. The method of claim 1 , further comprising plotting the modeled data over the range of depths.

8. The method of claim 1 , wherein determining one or more local friction factors for the range of depths comprises adopting, as the local friction factor for each depth of the range of depths, the friction factor corresponding to the modeled data with a derivative value that matches a derivative value of the surface data at that depth.

9. The method of claim 1 , wherein determining one or more local friction factors for the range of depths comprises adopting, as the local friction factor for each depth of the range of depths, a friction factor extrapolated from the modeled data with derivative values closest to a derivative value of the surface data at that depth.

10. The method of claim 1 , further comprising plotting the derivative of the surface data over the range of depths.

11. The method of claim 10 , further comprising plotting the derivative of the modeled data over the range of depths.

12. The method of claim 11 , wherein comparing the derivative of the surface data to the derivative of the modeled data comprises comparing the plot of the derivative of the surface data with the plot of the derivative of the modeled data.

13. The method of claim 12 , wherein determining one or more local friction factors for the range of depths comprises adopting, as the local friction factor for each depth of the range of depths, the friction factor corresponding to the modeled data with a derivative value that matches a derivative value of the surface data at that depth based on the comparison of the plot of the derivative of the surface data with the plot of the derivative of the modeled data.

14. The method of claim 12 , wherein determining one or more local friction factors for the range of depths comprises adopting, as the local friction factor for each depth of the range of depths, a friction factor extrapolated from the modeled data with derivative values closest to a derivative value of the surface data at that depth based on the comparison of the plot of the derivative of the surface data with the plot of the derivative of the modeled data.

15. The method of claim 1 , further comprising removing noise from the surface drilling data prior to calculating the derivative.

16. The method of claim 15 , wherein the step of removing noise is performed using at least one of the following methods: finite impulse response low pass filter, median filter, wavelet filter, and moving average.

17. The method of claim 1 , wherein adjusting at least one string assembly operating parameter comprises at least one of adjusting rotary speed, adjusting flow rate, adjusting drilling fluid circulation time, adjusting drilling fluid weight, adding lubricant fluid to drilling fluid, and adding beads to drilling fluid.

18. The method of claim 1 , wherein operating the string assembly within the wellbore by moving the string assembly at least axially within the wellbore using the adjusted operating parameter comprises conducting at least one drilling, moving casing, tripping a tubular string into or out of the wellbore, and positioning a downhole tool within the wellbore.

19. The method of claim 1 , wherein operating the string assembly within the wellbore by moving the string assembly at least axially within the wellbore using the adjusted operating parameter comprises at least one of (i) stretching a tubular string axially to determine a stuck point and (ii) moving tubular axially while circulating to prevent sticking of the tubular string.