Exercise
Determine the number of 8″, 150 lb/ft, 31-ft drill collars needed for the following well conditions:
- Well trajectory: vertical
- Required weight-on-bit = 58,000 lb
- Mud weight = 13.0 lb/gal
- Buoyancy factor = .801
- Safety factor = 1.15
Solution
Required weight of collars in air = 
Weight of one 8′′ collar = 
Number of collars required = 
⇒ pick up 18 drill collars
Assessment What is a Drill Collar?
1. Which of these statements about bottomhole assembly design is TRUE?
A .The neutral point of tension and compression (NPT&C) is an important parameter in drill collar selection and BHA design.
B .In a vertical well, the drill collars should be selected such that their buoyed weight corresponds to the desired weight-on-bit.
C .In an inclined wellbore, some of the weight of the drill pipe can be transmitted to the bit with minimal risk of helical buckling.
D .A and B
E .A and C
F .B and C
2. The Neutral Point of Bending (NPB)_____.
A .is equivalent to the neutral point of tension and compression (NPT&C)
B .should always be located within the bottomhole assembly
C .is not a consideration in bottomhole assembly design
3. What is the primary reson for running a tapered drill collar string?
A .To minimize the load on the rig’s hoisting system.
B .To reduce the potential for connection failures and fatigue damage.
C .To make pipe recovery easier if fishing becomes necessary.
4. Which of these drill collar features is designed to help prevent differential sticking of the bottomhole assembly?
A .Spiral grooves
B .Stepped bores
C .Fishing necks
D .Slip and elevator recesses
5. Which of these drill collar features is NOT suitable for highly corrosive environments?
A .Slip and elevator recesses
B .Spiral grooves
C .Non-magnetic alloys
6. Design of the best rotary-shouldered connection for a drill collar calls for the box and pin to be balanced in bending fatigue. What range of section modulus ratios (box:pin)is best suited for maintaining this balance?
A .1 to 1.5
B .2.25 to 2.75
C .3.5 to 4.0
D .4.5 to 5.5
7. Cold rolling of thread roots is made in order to:
A .Decrease the possibility of swelled boxes
B .Make the connection more resistant for bending fatigue
C .Increase torsional strength
D .Eliminate leaking joints
Recommended for You
Drill String and Bit Considerations in Deviated Wells
Underbalanced Drilling in Directional Wells
