NGWA (EF) MUD ROTARY DRILLING EXAM QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES
2026 QUESTIONS AND ANSWERS GRADED A+ LATEST UPDATE.
1. The primary purpose of drilling mud is to
A. lubricate the drill bit
B. remove cuttings from the borehole
C. maintain wellbore stability
D. all of the above
D. all of the above
Drilling mud serves multiple functions including lubrication,
cuttings removal, and stabilizing the wellbore.
2. The typical density range for freshwater drilling mud is
A. 5–7 lb./gal
B. 8–12 lb./gal
C. 14–16 lb./gal
D. 18–20 lb./gal
B. 8–12 lb./gal
Freshwater-based muds typically fall in this density range to
balance formation pressures without fracturing the formation.
3. Which drilling fluid property is most critical for carrying cuttings to
the surface?
A. Viscosity
B. pH
, C. Electrical conductivity
D. Temperature
A. Viscosity
Viscosity affects the carrying capacity of the mud, allowing
efficient removal of cuttings from the hole.
4. The term “gel strength” in drilling mud refers to
A. the ability to resist flow after circulation stops
B. the mud’s chemical composition
C. the density of the mud
D. the mud’s filtration rate
A. the ability to resist flow after circulation stops
Gel strength indicates the mud’s capacity to suspend cuttings and
weighting materials when circulation is paused.
5. Which type of drilling bit is most commonly used for soft
formations?
A. PDC bit
B. Tricone roller cone bit
C. Diamond bit
D. Drag bit
D. Drag bit
Drag bits are ideal for soft formations as they scrape the
formation instead of crushing it.
6. Lost circulation in a well is typically caused by
A. high mud density
B. permeable formations
C. low mud pH
D. low pump pressure
, B. permeable formations
When drilling into highly permeable zones, the drilling fluid can be
lost into the formation.
7. Which additive is commonly used to increase the viscosity of
water-based drilling mud?
A. Barite
B. Bentonite
C. Sodium chloride
D. Lime
B. Bentonite
Bentonite clay swells in water, thickening the mud and improving
it carrying capacity.
8. What is the primary role of barite in drilling mud?
A. Increase fluid viscosity
B. Provide weight to control formation pressure
C. Lubricate the drill string
D. Reduce mud pH
B. Provide weight to control formation pressure
Barite is a high-density mineral added to mud to help balance
formation pressures.
9. The annular space is
A. the space inside the drill pipe
B. the space between the drill pipe and the borehole wall
C. the area around the drilling rig
D. the drilling mud storage tank
B. the space between the drill pipe and the borehole wall
, The annular space allows circulation of drilling fluid and removal
of cuttings.
10. Which measurement indicates the frictional resistance of
drilling mud?
A. Yield point
B. Gel strength
C. Plastic viscosity
D. pH
C. Plastic viscosity
Plastic viscosity measures the internal resistance of the fluid to
flow under shear.
11. A mud motor is used primarily for
A. circulating mud
B. rotating the drill bit without turning the drill string
C. increasing mud density
D. measuring formation pressure
B. rotating the drill bit without turning the drill string
Mud motors convert hydraulic energy of the drilling fluid into
rotational energy at the bit.
12. When should a mud engineer test for mud weight?
A. Only at the start of drilling
B. Every 24 hours
C. Regularly during drilling operations
D. Only after encountering a formation fracture
C. Regularly during drilling operations
Frequent mud weight checks ensure wellbore stability and prevent
formation influx or blowouts.
CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES
2026 QUESTIONS AND ANSWERS GRADED A+ LATEST UPDATE.
1. The primary purpose of drilling mud is to
A. lubricate the drill bit
B. remove cuttings from the borehole
C. maintain wellbore stability
D. all of the above
D. all of the above
Drilling mud serves multiple functions including lubrication,
cuttings removal, and stabilizing the wellbore.
2. The typical density range for freshwater drilling mud is
A. 5–7 lb./gal
B. 8–12 lb./gal
C. 14–16 lb./gal
D. 18–20 lb./gal
B. 8–12 lb./gal
Freshwater-based muds typically fall in this density range to
balance formation pressures without fracturing the formation.
3. Which drilling fluid property is most critical for carrying cuttings to
the surface?
A. Viscosity
B. pH
, C. Electrical conductivity
D. Temperature
A. Viscosity
Viscosity affects the carrying capacity of the mud, allowing
efficient removal of cuttings from the hole.
4. The term “gel strength” in drilling mud refers to
A. the ability to resist flow after circulation stops
B. the mud’s chemical composition
C. the density of the mud
D. the mud’s filtration rate
A. the ability to resist flow after circulation stops
Gel strength indicates the mud’s capacity to suspend cuttings and
weighting materials when circulation is paused.
5. Which type of drilling bit is most commonly used for soft
formations?
A. PDC bit
B. Tricone roller cone bit
C. Diamond bit
D. Drag bit
D. Drag bit
Drag bits are ideal for soft formations as they scrape the
formation instead of crushing it.
6. Lost circulation in a well is typically caused by
A. high mud density
B. permeable formations
C. low mud pH
D. low pump pressure
, B. permeable formations
When drilling into highly permeable zones, the drilling fluid can be
lost into the formation.
7. Which additive is commonly used to increase the viscosity of
water-based drilling mud?
A. Barite
B. Bentonite
C. Sodium chloride
D. Lime
B. Bentonite
Bentonite clay swells in water, thickening the mud and improving
it carrying capacity.
8. What is the primary role of barite in drilling mud?
A. Increase fluid viscosity
B. Provide weight to control formation pressure
C. Lubricate the drill string
D. Reduce mud pH
B. Provide weight to control formation pressure
Barite is a high-density mineral added to mud to help balance
formation pressures.
9. The annular space is
A. the space inside the drill pipe
B. the space between the drill pipe and the borehole wall
C. the area around the drilling rig
D. the drilling mud storage tank
B. the space between the drill pipe and the borehole wall
, The annular space allows circulation of drilling fluid and removal
of cuttings.
10. Which measurement indicates the frictional resistance of
drilling mud?
A. Yield point
B. Gel strength
C. Plastic viscosity
D. pH
C. Plastic viscosity
Plastic viscosity measures the internal resistance of the fluid to
flow under shear.
11. A mud motor is used primarily for
A. circulating mud
B. rotating the drill bit without turning the drill string
C. increasing mud density
D. measuring formation pressure
B. rotating the drill bit without turning the drill string
Mud motors convert hydraulic energy of the drilling fluid into
rotational energy at the bit.
12. When should a mud engineer test for mud weight?
A. Only at the start of drilling
B. Every 24 hours
C. Regularly during drilling operations
D. Only after encountering a formation fracture
C. Regularly during drilling operations
Frequent mud weight checks ensure wellbore stability and prevent
formation influx or blowouts.
