Drill String Design | Drill String Overview


1. Explain briefly how the drill string transmits energy to the drill bit.


The drill string supplies mechanical energy to the bit from the weight and rotation of the drill string, and hydraulic energy from the mud pumps and circulating drilling fluid.

2. Which of the following considerations are important in drill string design?

  1. Formation characteristics
  2. Circulating pressure
  3. Desired bit weight
  4. Crooked hole tendencies
  5. (a), (c) and (d) only
  6. a), (b), (c) and (d)


6. all of these considerations are important in drill string design

3. In one or two sentences, describe the main functions of these drill string components:

  • Kelly
  • Drill pipe
  • Drill collars
  • Heavy wall drill pipe
  • Stabilizers
  • Vibration dampeners
  • Jars
  • Reamers
  • Crossover subs
  • MWD
  • LWD
  • Shock subs
  • Float subs
  • Mud motors


Kelly: turns the drill string by transferring energy from the rotary table

Drill pipe: provides length to the drill string, rotational motion to the bottomhole assembly and bit, and serves as a pathway for drilling fluid

Drill collars: provide weight and stability to the drill bit and maintain tension on drill pipe

Heavy wall drill pipe: provides added drill string stability and reduces pipe fatigue

Stabilizers: centralize drill collars, aid in directional control and maintain hole gauge

Vibration dampeners: absorb vibration and shock loads

Jars: provide hammer-like blows to free stuck pipe

Reamers: maintain a full-gauge hole diameter

Crossover subs: join tools with different types of connections

MWD: include devices for measuring wellbore inclination and azimuth, downhole pressure, and monitors drilling dynamics measurements such as shock and vibration.

LWD: provides real-time formation evaluation data similar to that obtained from wireline logging devices.

Shock sub: minimizes the effect of shock loads on the bit to enhance bit performance and bit life.

Float sub: prevents drilling fluid from backflowing into the drill string and reduces the potential for swabbing.

Mud Motor: Converts the hydraulic energy of the circulating drilling fluid into mechanical energy to rotate the bit.


1. Which of these statements is FALSE?

A .Within certain operating limits, increasing weight-on-bit results in an increase in penetration rate.
B .Controlling wellbore deviation is a minor drill string design consideration in non-directional wells.
C .Certain drill string tools are designed to prevent undergauge hole problems.
D .A drill string’s internal diameter can have a significant effect on drilling hydraulics.

2. Which of these components performs the same function as a kelly-rotary table assembly?

A .Rotary hose
B .Top drive unit with power swivel
C .Drill collar
D .Rotary reamer

3. Which of these bottomhole assembly components is used to centralize the drill string and maintain a full-gauge hole diameter?

A .Heavy wall drill pipe
B .Stabilizers
C .Drilling jars

Recommended for You

Drill Pipe

Directional Drilling Overview

Drill String and Bit Considerations in Deviated Wells

What is a Kelly in drilling?

What is a Drill Collar?

Underbalanced Drilling in Directional Wells

Previous page 1 2 3

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button