STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

768 Drilling and Well Completions
From offset wells, it is known that six joints of heavy-weight drill pipe are
desirable
Assume vertical hole.
Solution
Selection drill collar size, Table 4-73, 7q x 2% in., unit weight = 139 lb/ft.
Such drill collars can be caught with overshot or washed over with washpipe.
(60,000)(1’15) = 608ft
Length of drill collars = (139)( 0.816)
Note: Buoyant factor = 0.816.
Select 21 joints of 2 x 2# in. drill collars that give the length of 630 ft.
Section modulus of drill collars calculate to be 89.6 in.3.
Determine size of heavy-weight drill pipe.
To maintain BSR of less than 5.5, selection 5-in. heavy-weight drill pipe with
unit weight of 49.3 lb/ft (see Table 491) and section modulus of 21.4 in3.
Length of heavy-weight drill pipe hw = (5)(30) = 180 ft.
Selection 5 in. IEU new drill pipe with unit nominal weight 19.5 lb/ft (see
Table 4-79), steel grade X-95, with NC 50 tool joint (see Table 4-89).
Unit weight of drill pipe corrected for tool joint is 21.34 lb/ft. Section
modulus of this pipe can be calculated to be 5.7 in3.
From Table 4-80, the minimum tensile load capacity of selected drill pipe
PI = 501,090 lb.
From Table 4-89, the recommended makeup torque T = 26,000 ft/lb.
The tensile load capacity of drill pipe corrected for the effect of the maximum
allowable torque, according to Equation 458 is
Determine the maximum allowable length of the selected drill pipe from
Equation 4-72:
L, = 403,271 - (630)(139) - (180)(49.3) = 12,022ft
(1.4)(0.816)(21.34) 21.34 21.34
Required length of drill pipe L,.p = 10000 - (630+180) = 9,190 ft.
Since the required length of drill pipe (9,190 ft) is less than the maximum
allowable length (12,022 ft), it is apparent that the selected drill pipe satisfies
tensile load requirements.
Obtained margin of overpull:
MOP = (0.9)(501090) - [(630)( 139) + (180)(49.3) + (9190)(21.34)](0.816)
= 212,253 lb (greater than required 100,000 lb).
In the above example, the cost of drill string is not considered. From a practical
standpoint, the calculations outlined above should be performed for various drill