CWD Well Drilling Techniques & Equipment 3 — Questions and Answers
Question 1: What is the purpose of a mud rotary conductor casing installed before main drilling begins?
- To serve as the production casing for the finished well
- To prevent surface soils from caving into the borehole during drilling (Correct answer)
- To house the submersible pump permanently
- To provide a conduit for electrical cables
Correct answer: To prevent surface soils from caving into the borehole during drilling
Conductor casing is set near the surface to stabilize unconsolidated soils and prevent borehole collapse during the initial stages of drilling.
Question 2: In the context of well drilling, what does 'lost circulation' describe?
- Loss of drill string rotation due to motor failure
- Drilling fluid flowing into the formation rather than returning to the surface (Correct answer)
- Collapse of the borehole wall trapping the drill string
- Loss of pump pressure due to a worn impeller
Correct answer: Drilling fluid flowing into the formation rather than returning to the surface
Lost circulation occurs when drilling fluid migrates into highly permeable or fractured formations and fails to return to the surface.
Question 3: What is the main advantage of reverse-circulation (RC) rotary drilling over direct-circulation rotary?
- RC uses less horsepower for the same depth
- RC returns cuttings up the inside of the drill pipe, reducing cross-contamination (Correct answer)
- RC eliminates the need for drilling fluid entirely
- RC allows faster bit changes without tripping the string
Correct answer: RC returns cuttings up the inside of the drill pipe, reducing cross-contamination
In reverse circulation, fluid flows down the annulus and cuttings are returned inside the drill pipe, providing uncontaminated samples and high annular velocity.
Question 4: What is the purpose of adding bentonite to a water-based drilling fluid?
- To increase the pH above 12 for disinfection
- To add weight to the fluid to control formation pressure
- To improve viscosity and build a filter cake on borehole walls (Correct answer)
- To dissolve iron bacteria in the formation
Correct answer: To improve viscosity and build a filter cake on borehole walls
Bentonite swells when hydrated, increasing fluid viscosity for cutting transport and forming a filter cake that stabilizes permeable borehole walls.
Question 5: When a driller observes a sudden increase in penetration rate (drilling break) with no formation change, what hazard might this indicate?
- Bit wear requiring replacement
- Entry into a high-pressure zone or void that could cause a blowout (Correct answer)
- Optimal drilling parameters have been achieved
- The kelly has become disconnected from the drive bushing
Correct answer: Entry into a high-pressure zone or void that could cause a blowout
A sudden drilling break can indicate entry into an overpressured zone or cavernous void, which poses a risk of uncontrolled fluid flow or blowout.
Question 6: Which component of a cable tool rig is responsible for imparting the up-and-down motion to the drill string?
- Cathead
- Walking beam (Correct answer)
- Sand reel
- Bull reel
Correct answer: Walking beam
The walking beam is the pivoting arm on a cable tool rig that converts the crank's rotary motion into the up-and-down percussion needed to drill.
Question 7: What is the typical function of a 'spudder' in early cable tool drilling operations?
- To set the initial surface casing using impact (Correct answer)
- To remove accumulated cuttings from the bottom of the hole
- To circulate bailing fluid during the drilling process
- To measure total depth of the completed borehole
Correct answer: To set the initial surface casing using impact
A spudder attachment on a cable tool rig is used to drive and seat surface casing into the ground at the start of a well.
CWD Well Drilling Techniques & Equipment 3
What is the purpose of a mud rotary conductor casing installed before main drilling begins?