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NGWA (National Ground Water Association) Air Rotary
Drilling Exam 2025 | Featuring Principles of Air Rotary
Drilling, Equipment Operation, Borehole Stability, and
Air Pressure | Just Released
Explain how drill subs are used in the drill string. ---------CORRECT ANSWER---------- -------connect components in the drill string, facilitate transitions in diameter and thread type, add weight for penetration, and enable the incorporation of specialized tools for optimized drilling operations. Explain how pH can be affected by certain unconsolidated formations. --------- CORRECT ANSWER-----------------mineral content What are some measures to keep wear down on the kelly bar? ---------CORRECT ANSWER-----------------maintain alignment, use lubricants, inspect regularly, apply optimal weight on the bit, and select suitable drilling fluids. How can storage co-efficients be measured in unconsolidated formations? --------- CORRECT ANSWER-----------------using aquifer tests, where water levels are monitored in observation wells during pumping, allowing for the calculation of storage based on changes in water levels over time.
Assuming you have drilled down to rock and set the casing, what viscosity mud should you have for continuing the drilling? Explain. ---------CORRECT ANSWER----- ------------30 to 50 centipoise What can change rates of penetration in rock formations? ---------CORRECT ANSWER-----------------rock hardness, bit design, weight on bit, rotary speed, fluid properties, and the presence of fractures or faults After continuing into rock formations the centrifugal mud pump starts cavitating. What should you do? ---------CORRECT ANSWER-----------------reduce the pump speed, check for any blockages in the suction line, ensure proper mud levels in the pit, and verify that the mud viscosity is appropriate What causes differential sticking? How can you best control against it happening? ---------CORRECT ANSWER-----------------Differential sticking occurs when a drill pipe gets stuck against the walls of the borehole. Maintain proper mud weight, ensure good hole cleaning to prevent cuttings buildup, monitor for pressure changes, and use drilling techniques that minimize contact between the pipe and the borehole wall What are bentonite materials? ---------CORRECT ANSWER-----------------Bentonite materials are clay minerals rich in montmorillonite, known for their absorbency and swelling properties, commonly used in drilling fluids and various industrial applications.
What materials could be used to properly grout a mud rotary well? --------- CORRECT ANSWER-----------------Bentonite, cement, or a bentonite-cement mix. How does weight (density) of the drilling fluid affect the down hole conditions during drilling? ---------CORRECT ANSWER-----------------controls downhole pressure, stabilizes the borehole, prevents formation collapse, and helps control fluid loss or blowouts. How is mud weight controlled? What factors enter into the viscosity of mud? ------ ---CORRECT ANSWER-----------------Mud weight is controlled by adding materials like barite or bentonite Viscosity factors: Type of additives, fluid composition, and solids content. What causes cavitations in pumping drilling method? ---------CORRECT ANSWER---- -------------Cavitation is caused by low fluid levels, high pump speed, air entrainment, or improper pump suction, leading to vapor bubbles that collapse and damage equipment. Explain why soft formations require low annular velocities. ---------CORRECT ANSWER-----------------to prevent erosion, collapse, or destabilization of the borehole due to excessive cuttings removal or formation washout.
What can cause lost circulation in mud rotary drilling? ---------CORRECT ANSWER--- --------------Fractured formations, porous zones, or over-pressurized drilling fluids forcing fluid into the formation. What are the most common types of mud pumps? ---------CORRECT ANSWER------- ----------Duplex, triplex, and centrifugal pumps. Polyphosphates are used for what purpose? ---------CORRECT ANSWER----------------
- used to prevent mineral scaling and to disperse clays in drilling fluids Explain percentage retention in designing a screen for a gravel well. --------- CORRECT ANSWER-----------------the proportion of gravel or formation particles that the screen is designed to retain, ensuring proper filtration while allowing water flow without clogging. How are screen lengths determined? ---------CORRECT ANSWER-----------------by the thickness of the water-bearing formation and the desired water yield. What information should you have available when determining well screen design ---------CORRECT ANSWER-----------------Formation particle size, water flow rate, well depth, and aquifer characteristics.
Why is it important to identify the boundaries of an aquifer? ---------CORRECT ANSWER-----------------is important to estimate water supply, manage sustainable extraction, and prevent over-pumping or contamination from adjacent formations. What techniques are used to obtain good samples in mud rotary drilling in unconsolidated formations? ---------CORRECT ANSWER-----------------Split-spoon sampling, core sampling, and continuous cuttings collection. What are hydrating clays? How does a mud rotary driller handle these formations? ---------CORRECT ANSWER-----------------Hydrating clays swell when exposed to water, causing drilling challenges. To handle these, a mud rotary driller uses additives like polymers to inhibit swelling and adjusts mud properties to reduce sticking. In mud rotary drilling what are some indications that you have encountered a permeable formation? ---------CORRECT ANSWER-----------------Increased fluid loss, reduced mud returns, and faster drilling rates. Explain bit design for different unconsolidated formations. ---------CORRECT ANSWER-----------------Soft: Drag or modified PDC bits. Loose: Tricone bits, wide gauge. Clayey: Sharp-toothed bits, lower weight.
Fractured: Reinforced bits, tricone/PDC combo. Mixed: Adjustable/hybrid bits. Where should you use drag bits? What formations are best to use the roller cone type bits? ---------CORRECT ANSWER-----------------Drag Bits: Use in soft formations (e.g., clay, silt). Roller Cone Bits: Best for loose, gravelly, and mixed formations. What precautions must be used when sand seams are encountered in air rotary drilling in unconsolidated formation? ---------CORRECT ANSWER-----------------1. Reduce Air Pressure
- Use of Foam or Polymers
- Monitor Cuttings
- Casing Advancement
- Slow Drilling Rate How are samples obtained in air rotary drilling in unconsolidated formations? ----- ----CORRECT ANSWER-----------------Continuous Sampling of Cuttings: Split-Spoon Sampling Drilling Fluids/Polymers
What functions must a drill pipe perform to drill unconsolidated formations? ------ ---CORRECT ANSWER-----------------Transmit torque circulate drilling fluid/air support drill string weight maintain borehole integrity When would you use heavy drill collars? ---------CORRECT ANSWER-----------------to add weight on the bit, stabilize the drill string, and prevent buckling in deep or hard formations. Explain how chip catchers can aid in formation logging? ---------CORRECT ANSWER- ----------------help collect cuttings for accurate formation logging by preventing loss of samples during drilling, ensuring representative data. How does bit design vary with geology? ---------CORRECT ANSWER----------------- varies by formation hardness, with softer formations needing wider teeth and harder formations requiring tougher, more durable materials. Heavy steel casing would best be used in what rotary process? ---------CORRECT ANSWER-----------------best used in the air rotary process for stabilizing unconsolidated or collapsing formations.
What air compressor checks must be made daily? ---------CORRECT ANSWER-------- ---------Oil level filters belts air pressure leaks What type of drill bit maintenance can be done in the field? ---------CORRECT ANSWER-----------------Cleaning inspecting for wear sharpening teeth replacing damaged parts Differential sticking of drill pipe can be prevented by what methods? --------- CORRECT ANSWER-----------------Use higher mud flow reduce drill string contact maintain proper mud weight. What common fishing tool are used in rotary drilling? ---------CORRECT ANSWER--- --------------Overshot spear
How does cost per foot air rotary compare with mud rotary in unconsolidated formations? ---------CORRECT ANSWER-----------------air rotary is generally lower due to faster drilling, but mud rotary may be more efficient in maintaining borehole stability in unconsolidated formations. Uphole annular velocity for most air rotary drilling would be? ---------CORRECT ANSWER-----------------3,000 to 5,000 feet per minute. What methods are used to set screens in air rotary drilling? ---------CORRECT ANSWER-----------------Gravity placement, tremie pipe, and surge block. How do you develop wells that are air rotary drilled? - --------CORRECT ANSWER---- -------------Air surging, backwashing, and pumping. How can you control caving problems with air rotary drilling? ---------CORRECT ANSWER-----------------Use foam or polymers, reduce air pressure, and advance casing. What fluids are used in air rotary drilling in unconsolidated formations? --------- CORRECT ANSWER-----------------Water, foam, polymers.
When is gravel packing usually necessary in air rotary wells? ---------CORRECT ANSWER-----------------to prevent sand intrusion. Mud rings can be controlled by what methods? ---------CORRECT ANSWER----------- ------Increase air pressure, use foam or polymers, and adjust drilling fluid properties. Crooked holes can cause other problems. How can you control drift in air rotary drilling? ---------CORRECT ANSWER-----------------Use stabilizers, adjust bit weight, and maintain proper drilling alignment. Water pressure and air pressure can work against each other. Explain. --------- CORRECT ANSWER-----------------Water pressure can resist air pressure, causing inefficient cuttings removal or formation blowouts if not properly balanced. Uphole velocity in soft formations can cause caving. How can you handle this problem? ---------CORRECT ANSWER-----------------Reduce up hole velocity, use foam or polymers, and advance casing. What advantages does air rotary drilling have over mud rotary? Disadvantages? -- -------CORRECT ANSWER-----------------Advantages: Faster drilling, cleaner samples, less fluid handling.
Explain how down pressure may vary due to formation changes. ---------CORRECT ANSWER-----------------Down pressure increases in harder formations for better penetration and decreases in softer formations to avoid over drilling or hole collapse. After a water bearing formation is located what is necessary to clean up the formation? ---------CORRECT ANSWER-----------------Air surging, backwashing, and pumping to remove fines and improve water flow. After the bore hole has been cased to the rock formation, how can drilling rates be increased using air rotary? ---------CORRECT ANSWER-----------------Increase drilling rates by using a smaller bit, higher air pressure, and optimizing down pressure in the rock formation. What are some advantages and disadvantages of down hole hammer drilling? ----- ----CORRECT ANSWER-----------------Advantages: Fast penetration, effective in hard rock, minimal cuttings clogging. Disadvantages: High air requirements, noise, wear on equipment in abrasive formations.
What methods are used to speed up hole cleaning with air rotary? --------- CORRECT ANSWER-----------------Increase air pressure, use foam or polymers, and adjust up hole velocity. What affect does injecting water into the air stream cause in rock formations? ---- -----CORRECT ANSWER-----------------cools the bit, reduces dust, and helps remove cuttings in rock formations. How much pressure and volume is needed to operate down hole hammer drills? - --------CORRECT ANSWER-----------------Pressure: 150-500 psi Volume: 250-1000 CFM How much down pressure is needed on the drill string to operate the DHH drill in hard rock? ---------CORRECT ANSWER-----------------500 to 1,500 pounds per inch of bit diameter. Mud seams in rock formations could cause mud rings on the drill string. What indicators tell the driller this is occurring? ---------CORRECT ANSWER----------------- Slower penetration rate, increased torque, and erratic pressure readings.
efficient drilling, while small or powdery cuttings suggest bit wear or improper function. How do roller cone bits differ for different formations? ---------CORRECT ANSWER- ----------------Soft formations: Larger, wider teeth for faster cutting. Hard formations: Smaller, tougher teeth with more durability. After cutting several hundred feet of hard rock the rate has slowed down. What is the probably cause? ---------CORRECT ANSWER-----------------Bit wear or dulling, reducing cutting efficiency. What purpose does a Kelly saver sub serve? ---------CORRECT ANSWER----------------
- A Kelly saver sub protects the Kelly from excessive wear by absorbing the torque and stress during drilling operations. What type of lubrication system is used for DHH drilling? ---------CORRECT ANSWER-----------------a mist or oil injection lubrication system to reduce wear and cool the hammer mechanism.
Explain these terms: misting. dusting. ---------CORRECT ANSWER----------------- Misting: Injecting water or fluid into the air stream to control dust and cool the bit. Dusting: Drilling without sufficient fluid, resulting in excessive dust and potential bit overheating. What is a surfactant? When is it needed? ---------CORRECT ANSWER----------------- Reduces surface tension; needed to create foam in drilling fluids for effective cuttings removal. Explain the difference between high and low pressure air rotaries. --------- CORRECT ANSWER-----------------High-pressure air rotary: Faster drilling, better cuttings removal, used in hard formations. Low-pressure air rotary: Slower drilling, more controlled, used in softer or unstable formations. Explain the difference between high and low volume air rotaries. ---------CORRECT ANSWER-----------------High-volume air rotary: Moves more air, better for deep holes or large cuttings removal. Low-volume air rotary: Moves less air, suited for shallow holes or smaller cuttings.
