NGWA (EF) Mud Rotary Drilling
Certification Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. What is the primary purpose of drilling mud in mud rotary drilling?
A. To cool the drill bit
B. To lubricate the drill string
C. To remove cuttings from the borehole
D. To seal the aquifer
Rationale: Drilling mud carries cuttings to the surface, maintains
hydrostatic pressure, and stabilizes the borehole.
2. Which type of drilling fluid is most commonly used in water well mud
rotary drilling?
, A. Oil-based mud
B. Foam mud
C. Water-based bentonite mud
D. Synthetic polymer mud
Rationale: Water-based bentonite mud is standard in water well drilling
because it stabilizes the hole and is cost-effective.
3. What is the main function of bentonite in drilling mud?
A. To dissolve rock formations
B. To act as a lubricant only
C. To accelerate drilling speed
D. To increase viscosity and form a filter cake
Rationale: Bentonite increases viscosity and forms a thin filter cake that
stabilizes the borehole walls.
4. What is the term for the mixture of water and cuttings returned to the
surface in mud rotary drilling?
A. Slurry
B. Core
C. Drilling mud or return mud
D. Grout
,Rationale: Return mud carries cuttings to the surface and allows
monitoring of drilling progress.
5. What could cause a sudden loss of drilling mud into the formation?
A. High bit weight
B. Excessive rotation speed
C. Permeable formation or fractures
D. Low pump pressure
Rationale: Drilling mud can be lost into permeable formations, fractures,
or cavings in the borehole.
6. How can lost circulation be minimized during mud rotary drilling?
A. Increase bit RPM
B. Add lost circulation materials to the mud
C. Reduce mud viscosity
D. Increase air injection
Rationale: Materials such as calcium carbonate, cellulose, or other agents
can seal fractures to reduce mud loss.
7. What does “annular velocity” refer to in mud rotary drilling?
A. Rotation speed of the bit
B. Rate of penetration
, C. Velocity of drilling fluid in the annular space between the drill
string and borehole wall
D. Pump output rate
Rationale: Annular velocity affects cuttings transport and borehole
cleaning.
8. Which type of drill bit is most commonly used in soft to medium
unconsolidated formations?
A. Tricone bit
B. PDC bit
C. Roller-cone bit
D. Diamond core bit
Rationale: Roller-cone bits are versatile and suitable for many
unconsolidated and semi-consolidated formations.
9. What is the function of the shale shaker in a mud rotary system?
A. To cool the drill bit
B. To add chemicals to the mud
C. To remove cuttings from returning drilling fluid
D. To measure mud density
Rationale: Shale shakers separate cuttings from the mud, maintaining fluid
properties and preventing blockages.
Certification Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of drilling mud in mud rotary drilling?
A. To cool the drill bit
B. To lubricate the drill string
C. To remove cuttings from the borehole
D. To seal the aquifer
Rationale: Drilling mud carries cuttings to the surface, maintains
hydrostatic pressure, and stabilizes the borehole.
2. Which type of drilling fluid is most commonly used in water well mud
rotary drilling?
, A. Oil-based mud
B. Foam mud
C. Water-based bentonite mud
D. Synthetic polymer mud
Rationale: Water-based bentonite mud is standard in water well drilling
because it stabilizes the hole and is cost-effective.
3. What is the main function of bentonite in drilling mud?
A. To dissolve rock formations
B. To act as a lubricant only
C. To accelerate drilling speed
D. To increase viscosity and form a filter cake
Rationale: Bentonite increases viscosity and forms a thin filter cake that
stabilizes the borehole walls.
4. What is the term for the mixture of water and cuttings returned to the
surface in mud rotary drilling?
A. Slurry
B. Core
C. Drilling mud or return mud
D. Grout
,Rationale: Return mud carries cuttings to the surface and allows
monitoring of drilling progress.
5. What could cause a sudden loss of drilling mud into the formation?
A. High bit weight
B. Excessive rotation speed
C. Permeable formation or fractures
D. Low pump pressure
Rationale: Drilling mud can be lost into permeable formations, fractures,
or cavings in the borehole.
6. How can lost circulation be minimized during mud rotary drilling?
A. Increase bit RPM
B. Add lost circulation materials to the mud
C. Reduce mud viscosity
D. Increase air injection
Rationale: Materials such as calcium carbonate, cellulose, or other agents
can seal fractures to reduce mud loss.
7. What does “annular velocity” refer to in mud rotary drilling?
A. Rotation speed of the bit
B. Rate of penetration
, C. Velocity of drilling fluid in the annular space between the drill
string and borehole wall
D. Pump output rate
Rationale: Annular velocity affects cuttings transport and borehole
cleaning.
8. Which type of drill bit is most commonly used in soft to medium
unconsolidated formations?
A. Tricone bit
B. PDC bit
C. Roller-cone bit
D. Diamond core bit
Rationale: Roller-cone bits are versatile and suitable for many
unconsolidated and semi-consolidated formations.
9. What is the function of the shale shaker in a mud rotary system?
A. To cool the drill bit
B. To add chemicals to the mud
C. To remove cuttings from returning drilling fluid
D. To measure mud density
Rationale: Shale shakers separate cuttings from the mud, maintaining fluid
properties and preventing blockages.
