Calibration of drillstring weight with drag for friction factor estimation

1 . A method comprising:

determining a value of at least one oppositional force for a drillstring at multiple depths in a wellbore, wherein the at least one oppositional force includes a centralizer friction force based on the presence of one or more centralizers positioned within the wellbore;

determining a value of hook load for the drillstring at the multiple depths in the wellbore based at least in part on the value of the at least one oppositional force;

determining a calibrated drillstring weight based on a change of the value of hook load for the drillstring over the multiple depths in the wellbore;

determining a friction factor based on the calibrated drillstring weight; and

controlling one or more drilling operations performed on the wellbore based at least in part on the friction factor.

2 . The method of claim 1 ,

wherein determining the value of hook load for the drillstring comprises determining a value of a measured hook load for the drillstring at the multiple depths based on the value of the at least one oppositional force, and determining a value of an estimated hook load for the drillstring at the multiple depths based on the value of the at least one oppositional force, and

wherein determining the calibrated drillstring weight comprises determining the calibrated drillstring weight based on a change in the measured hook load and a change in the estimated hook load.

3 . The method of claim 2 , wherein determining the value of the estimated hook load further comprises determining an adjusted drillstring weight at the multiple depths in the wellbore based on the value of the at least one oppositional force, and the value of the estimated hook load, and wherein determining the calibrated drillstring weight comprises determining the calibrated drillstring weight based on the change in the measured hook load and a change in the adjusted drillstring weight.

4 . The method of claim 1 , further comprising:

determining a value of an adjusted estimated hook load for the drillstring at the multiple depths in the wellbore based on the calibrated drillstring weight,

wherein determining the value of the adjusted estimated hook load comprises determining the value of the adjusted estimated hook load based on the calibrated drillstring weight, and the value of the at least one oppositional force at the multiple depths in the wellbore.

5 . The method of claim 1 , wherein determining the calibrated drillstring weight based on a change in the value of hook load for the drillstring over the multiple depths in the wellbore comprises determining a rate of change of the value of hook load over at least two of the multiple depths in the wellbore.

6 . The method of claim 5 , wherein the at least two of the multiple depths in the wellbore comprise a first depth in the wellbore before addition of a first centralizer of the one or more centralizers to the wellbore and a second depth in the wellbore after addition of the first centralizer to the wellbore.

7 . The method of claim 1 , wherein

the at least one oppositional force includes a centralizer running drag based on a number of the one or more centralizers positioned within the wellbore and a set of drag per centralizer values.

8 . The method of claim 7 , wherein the set of drag per centralizer values is approximated from one or more manufacturer specifications.

9 . The method of claim 1 , wherein determining the friction factor further comprises:

determining a first friction factor for the drillstring for a first depth in the wellbore based on a first calibrated drillstring weight, and the value of hook load, the value of the at least one oppositional force,

wherein determining the first calibrated drillstring weight comprises determining the calibrated drillstring weight for the first depth in the wellbore.

10 . The method of claim 9 , further comprising:

determining a second friction factor for the drillstring for a second depth in the wellbore based on a second calibrated drillstring weight, the value of hook load, and the value of the at least one oppositional force,

wherein determining the second calibrated drillstring weight comprises determining the calibrated drillstring weight for the second depth in the wellbore.

11 . The method of claim 10 , wherein the wellbore is substantially vertical at the first depth and the second depth.

12 . The method of claim 10 , further comprising:

determining whether the friction factor increases as a function of a number of the one or more centralizers positioned in the wellbore at the first depth and a number of the one or more centralizers positioned in the wellbore at the second depth and on the first friction factor and the second friction factor; and

based on a determination that the friction factor increases as a function of the number of centralizers in the wellbore, increasing a value of drag per centralizer.

13 . The method of claim 10 , further comprising:

determining whether the friction factor decreases as a function of a number of the one or more centralizers positioned in the wellbore based on a number of centralizers in the wellbore at the first depth and a number of centralizers in the wellbore at the second depth and on the first friction factor and the second friction factor; and

based on a determination that the friction factor decreases as a function of the number of centralizers in the wellbore, decreasing a value of drag per centralizer.

14 . One or more non-transitory machine-readable media comprising program code for drillstring weight calibration, the program code to:

determine a value of at least one oppositional force for a drillstring at multiple depths in a wellbore, wherein the at least one oppositional force includes a centralizer friction force based on the presence of one or more centralizers positioned within the wellbore;

determine a value of hook load for the drillstring at the multiple depths in the wellbore based at least in part on the value of the at least one oppositional force;

determine a calibrated drillstring weight based on a change of the value of hook load for the drillstring over the multiple depths in the wellbore;

determine a friction factor based on the calibrated drillstring weight; and

control one or more drilling operations performed on the wellbore based at least in part on the friction factor.

15 . The one or more non-transitory machine-readable media of claim 14 , wherein program code to determine the calibrated drillstring weight comprises program code to:

determine a rate of change of the value of hook load over at least two of the multiple depths in the wellbore.

16 . The one or more non-transitory machine-readable media of claim 15 , the at least two of the multiple depths in the wellbore comprise a first depth in the wellbore before addition of a first centralizer to the wellbore and a second depth in the wellbore after addition of the first centralizer to the wellbore.

17 . The one or more non-transitory machine-readable media of claim 14 , further comprising program code to:

determine a first friction factor for the drillstring for a first depth in the wellbore based on a first calibrated drillstring weight, the value of hook load, and the value of the at least one oppositional force,

wherein determining the first calibrated drillstring weight comprises determining the calibrated drillstring weight for the first depth in the wellbore;

determine a second friction factor for the drillstring for a second depth in the wellbore based on a second calibrated drillstring weight, the value of hook load, the value of the at least one oppositional force,

wherein determining the second calibrated drillstring weight comprises determining the calibrated drillstring weight for the second depth in the wellbore; and

determine whether the friction factor increases as a function of a number of centralizers in the wellbore based on a number of centralizers in the wellbore at the first depth and a number of centralizers in the wellbore at the second depth and on the first friction factor and the second friction factor.

18 . The one or more non-transitory machine-readable media of claim 17 , further comprising program code to:

based on a determination that the friction factor increases as a function of the number of centralizers in the wellbore, increase a value of drag per centralizer.

19 . An apparatus comprising:

a processor; and

a non-transitory machine-readable medium having program code executable by the processor to cause the apparatus to,

determine a first value of at least one oppositional force for a drillstring at a first depth in a wellbore, wherein the at least one oppositional force includes a centralizer friction force based on the presence of one or more centralizers positioned within the wellbore at the first depth;

determine a first value of hook load for the drillstring at the first depth in the wellbore based on the first value of the at least one oppositional force at the first depth

determine a second value of the at least one oppositional force for the drillstring at a second depth in the wellbore, wherein the at least one oppositional force includes a centralizer friction force based on the presence of one or more centralizers positioned within the wellbore at the second depth;

determine a second value of hook load for the drillstring at the second depth in the wellbore based on the second value of the at least one oppositional force at the second depth;

determine a first calibrated drillstring weight based on a difference between the first value of hook load and the second value of hook load;

determine a friction factor based on the first calibrated drillstring weight; and

control one or more drilling operations performed on the wellbore based at least in part on the friction factor.

20 . The apparatus of claim 19 , wherein the program code further comprises program code executable by the processor to cause the apparatus to:

determine a third value of the at least one oppositional force for the drillstring at a third depth in the wellbore;

determine a third value of hook load for the drillstring at the third depth in the wellbore based on the third value of the at least one oppositional force at the third depth; and

determine a second calibrated drillstring weight based on the first calibrated drillstring weight and on a difference between the second value of hook load and the third value of hook load.