Drill String Design | Drill String Overview
Exercises
1. Explain briefly how the drill string transmits energy to the drill bit.
Solution
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?
- Formation characteristics
- Circulating pressure
- Desired bit weight
- Crooked hole tendencies
- (a), (c) and (d) only
- a), (b), (c) and (d)
Solution
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
Solution
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.
Assessment
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
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