Page 112 - Air and Gas Drilling Manual

3-40 Air and Gas Drilling Manual
Table 3-6 gives the axial tension force to produce yield in this dual wall pipe. This
tension force to yield is 206,900 lb. Equation 3-3 can be used to determine the
maximum allowable axial tension force for the drill pipe. Thus, Equation 3-3 is
F = 0 9. (206 900, )
a
F = 186 210, lb
a
The factor of safety is determined from Equation 3-4. Equation 3-4 gives
,
FS = 186 210
22 468
,
.
FS = 829
The MOP for this drilling example is obtained from Equation 3-5. Equation 3-5
gives
MOP = 30 000 − 22 468
,
,
MOP = 7 532 lb
,
This example demonstrates that the dual wall pipe has very high strength in
resisting structural failure. However, most shallow drilling rigs do not have the
hoisting capacity to lift these dual wall drill strings when deep drilling operations
are considered. This example shows that the Factor of Safety for the drill string is
quite high illustrating this structural strength. But this low MOP value illustrates
the inadequate capacity of most single rotary drill rigs that might be used for a
typical shallow drilling operation.

References
1. API Recommended Practices for Drill Stem Design and Operating Limits, API
RP7G, 16th Edition, August 1998.

2. Drilling Manual, International Association of Drilling Contractors (IADC),
Eleventh Edition, 1992.

3. Roscoe Moss Company, Handbook of Ground Water Development, Wiley, 1990.
4. Bourgoyne, A. T., Millheim, K. K., Chenevert, M. E., and Young, F. S.,
Applied Drilling Engineering, SPE, First Printing, 1986.

5. Durrett, E., “Rock Bit Identification Simplified by IADC Action,” Oil and Gas
Journal, Vol. 76, May 22, 1972.