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Air Rotary Drilling Study Guide: Principles, Systems, and Safety, Exams of Agricultural engineering

Southern Polytechnic College of Engineering and Engineering TechnologyAgricultural engineering

This study guide provides a comprehensive overview of air rotary drilling, covering principles, air systems, drill rig components, bits and drilling tools, formation evaluation, troubleshooting, safety, and regulations. It includes key concepts such as up-hole velocity, compressor functions, drill string design, and drilling performance optimization. The guide also addresses advanced knowledge, casing and well construction, and air drilling variants, making it a valuable resource for students and professionals in the field. It features 77 questions and answers.

Typology: Exams

2024/2025

Available from 05/22/2025

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NGWA - STUDY GUIDE - AIR
ROTARY COMPREHENSIVE AIR
ROTARY DRILLING
Section 1: Drilling Principles
1. What is the primary purpose of using air in air rotary drilling?
Answer:
To remove cuttings from the borehole and cool the drill bit.
2. What is a key advantage of air rotary drilling over mud rotary drilling?
Answer:
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Partial preview of the text

Download Air Rotary Drilling Study Guide: Principles, Systems, and Safety and more Exams Agricultural engineering in PDF only on Docsity!

NGWA - STUDY GUIDE - AIR

ROTARY COMPREHENSIVE AIR

ROTARY DRILLING

Section 1: Drilling Principles

  1. What is the primary purpose of using air in air rotary drilling? Answer: To remove cuttings from the borehole and cool the drill bit.
  2. What is a key advantage of air rotary drilling over mud rotary drilling? Answer:

Faster drilling rates and cleaner boreholes in consolidated formations.

  1. What types of formations are best suited for air rotary drilling? Answer: Hard, consolidated rock formations like limestone, granite, and sandstone.
  2. What is "up-hole velocity," and why is it important? Answer: The speed at which air moves up the borehole. It must be sufficient to lift cuttings to the surface.
  3. What is the typical up-hole velocity needed to carry cuttings effectively? Answer: Generally 3,000–5,000 feet per minute (fpm). Section 2: Air Systems
  4. What is the function of a compressor in air rotary drilling? Answer: To supply high-pressure air to lift cuttings and cool the bit.
  5. What type of compressor is commonly used in air rotary drilling? Answer: Rotary screw compressors.
  6. What is the purpose of an air-oil separator? Answer: To remove oil from compressed air before it enters the drill string.
  7. What happens if oil is not adequately removed from compressed air? Answer: It may contaminate the formation or cause environmental issues.

Polycrystalline Diamond Compact bits; used in hard formations for high-speed drilling.

  1. What causes premature bit wear in air rotary drilling? Answer: Improper weight-on-bit (WOB), poor cooling, or abrasive formations.
  2. What is the purpose of stabilizers? Answer: To maintain borehole straightness and reduce vibration.
  3. What are down-the-hole (DTH) hammers used for? Answer: To drill extremely hard rock by combining percussion and rotary action. Section 5: Formation Evaluation & Sampling
  4. Why is it difficult to get accurate samples with air rotary drilling? Answer: High air velocity and bit disturbance may mix or destroy samples.
  5. What method is often used to improve formation sampling? Answer: Installing a cyclone separator or sample collector.
  6. What indicates a water-bearing zone while drilling with air? Answer: An increase in moisture in cuttings or mist/clouds in the discharge air.
  7. How is borehole deviation monitored? Answer: Using a borehole deviation tool or inclinometer.
  1. Why is drill log accuracy important? Answer: For legal records, well design, and future maintenance. Section 6: Troubleshooting & Maintenance
  2. What can cause loss of air circulation? Answer: Fractured formations, cave-ins, or blockages in the annulus.
  3. What does it mean when the drill pipe becomes excessively hot? Answer: Inadequate air flow or compressor malfunction.
  4. What is the solution for lost circulation? Answer: Use of foam or chemical additives to seal fractures.
  5. What indicates a plugged bit or drill string? Answer: Decreased airflow at the surface and lack of cutting returns.
  6. What maintenance is crucial for an air rotary rig? Answer: Regular checking of compressor oil levels, hose fittings, and air filters. Section 7: Foam and Additives
  7. What is the role of foam in air rotary drilling? Answer: To improve cuttings transport and seal minor loss zones.
  8. When is mist drilling used? Answer:
  1. What must be inspected daily before operation? Answer: Hoses, clamps, compressor oil, and pressure gauges. Section 9: Regulations and Best Practices
  2. What organization sets safety standards for well drilling? Answer: OSHA (Occupational Safety and Health Administration).
  3. What NGWA publication provides air rotary drilling guidance? Answer: NGWA Drilling Manual and ANSI/NGWA-01 standards.
  4. Why is proper casing installation important? Answer: To prevent contamination and maintain borehole integrity.
  5. What is the purpose of a sanitary seal? Answer: To protect the well from surface contaminants.
  6. How should used drill foam be disposed of? Answer: In accordance with local environmental regulations. Section 10: Advanced Knowledge
  7. What is reverse circulation air rotary? Answer: A method where air flows down the annulus and up the drill pipe, rarely used due to complexity.
  1. What type of air compressor is best for high-altitude drilling? Answer: Two-stage or high-pressure compressors with aftercoolers.
  2. What is "bit bounce" and how can it be reduced? Answer: Uncontrolled bouncing of the bit; reduced with proper WOB and collar use.
  3. How can you ensure borehole straightness? Answer: Use of stabilizers and consistent WOB and RPM.
  4. What parameter is most critical in determining correct bit selection? Answer: Formation type and expected wear conditions.Section 11: Drill String Design & Operations
  5. What is the main purpose of the drill string in air rotary drilling? Answer: To transmit rotation, weight, and compressed air from the surface to the drill bit.
  6. What material is commonly used for drill pipe? Answer: High-strength steel.
  7. What is meant by "stand" in drilling terminology? Answer: A set of two or three lengths of drill pipe that are connected and handled together.
  8. What causes drill string fatigue? Answer: Repeated bending, vibration, and pressure cycling.

Answer: Pounds per square inch – a measure of air pressure.

  1. What is a booster compressor used for? Answer: To increase air pressure in deep or high-resistance drilling.
  2. What is the function of an aftercooler on an air compressor? Answer: To cool the compressed air and remove moisture.
  3. Why is moisture in compressed air undesirable? Answer: It can cause corrosion and reduce drilling efficiency. Section 14: Downhole Conditions
  4. What is borehole collapse, and how is it prevented? Answer: When the hole walls fall in; prevented by proper air velocity and casing if necessary.
  5. How do you identify over-pressurized zones? Answer: Sudden changes in air pressure or water/air surges at surface.
  6. What are bridging cuttings? Answer: When cuttings build up and block the annulus, causing circulation loss.
  7. How can bridging be resolved? Answer: By increasing air velocity or adding foam to suspend and lift cuttings.
  1. What causes air hammer stalling? Answer: Low pressure, excessive backpressure, or water entry. Section 15: Casing and Well Construction
  2. When is temporary casing used during drilling? Answer: To support weak zones or prevent hole collapse during drilling.
  3. What is drive shoe and its purpose? Answer: A hardened bottom edge on casing to help advance it into the formation.
  4. What is centralizer used for? Answer: To center casing in the borehole for even grout/seal placement.
  5. Why is cement or bentonite grout used around casing? Answer: To seal off contamination pathways and stabilize the casing.
  6. What is the minimum recommended casing stick-up above ground? Answer: Typically 12 to 18 inches depending on code. Section 16: Air Drilling Variants
  7. What is aerated drilling? Answer: A mix of air and water (or drilling fluid) to balance formation pressure and improve cuttings lift.
  8. What is dust drilling?
  1. What agency provides certification standards for drillers? Answer: NGWA or applicable state licensing boards. Section 18: Safety & Emergency Procedures
  2. What is the risk of compressed air injection into the body? Answer: Air embolism – can be fatal even at low pressures.
  3. What safety devices must be installed on air lines? Answer: Whip checks, pressure relief valves, and shutoff valves.
  4. What is the primary danger when foam discharges to open air? Answer: Slip hazards and potential chemical exposure.
  5. What is a “hot bit” and how do you prevent injury from it? Answer: A bit overheated by friction—do not touch without cooling.
  6. Why should you avoid standing over pressurized pipe connections? Answer: To prevent injury from sudden failure or blowouts. Section 19: Troubleshooting
  7. What causes “dry hole” during air rotary drilling? Answer: No water encountered due to incorrect site selection or formation.
  8. How do you detect compressor failure during drilling? Answer:

Drop in pressure, oil carryover, or overheating alarms.

  1. What causes excessive bit wear in soft formations? Answer: Overdrilling and incorrect bit selection.
  2. What is surging, and how is it handled? Answer: Irregular flow or pressure changes—adjust air volume or install check valves.
  3. What could sudden increase in discharge temperature mean? Answer: Compressor overload or insufficient cooling. Section 20: Driller Best Practices
  4. Why is daily maintenance of air compressors critical? Answer: To ensure consistent performance and prevent downtime.
  5. What documentation should a driller maintain during a job? Answer: Drill log, equipment maintenance records, and safety checklists.
  6. How is total depth (TD) verified? Answer: By measuring the length of the drill string or using an electronic depth gauge.
  7. What is the benefit of logging formation return temperatures? Answer: Helps identify aquifer zones and geothermal gradients.
  8. What is the key to long-term rig reliability?