drill bits Flashcards
What is the primary mode of failure for roller cone bits?
Bearing failure
PDC bits drill with what parameter?
PDC bits drill with RPM. The higher the rpm, the more shearing action imparted by the bit on the rock and hence more cuttings generated.
What kind of RPM is required for impreg bits to drill?
1000 RPM or more
What bit is the most widely used in the industry?
Roller cone bits (Tri-cone)
What does PDC stand for?
Polycrystalline diamond bits
What 2 designs do PDC bits have?
Matrix and steel
What does IADC stand for?
International association of drilling contractors
What are the 7 drilling parameters?
ROP, mud weight, horse power, pump power, torque, WOB, flow rate
Name 8 criteria for bit selection in order of importance
Economics, geological prognosis, bit dull characteristics, well prognosis, agressiveness, specific energy, well post prognosis, environmental impact.
What are the three rock cutting mechanisms and which bit performs them?
- Roller cone bits- crushing
- PDC bits- shearing
- Diamond bits- grinding/ ploughing
Which bit is most effective in a hard formation?
PDC or natural diamond
In drill bit market classification, what do the 1st, 2nd and 3rd numbers stand for?
- Bit type
- Formation type
- Bearing type
What kind of formation would be best suited for a long toothed bit?
Soft formation
What are the two major types of drill bits?
Roller cone bits and fixed cutter bits
What are the sub categories of roller cone bits?
Mill tooth
Tungsten carbide inserts (two cone, 3 cone, 4 cone)
What are the sub categories of fixed cutter bits?
PCD
Natural diamond
Diamond impregnated
What are the 3 bearing types?
Unsealed
Sealed
Journal
What is an unsealed bearing? What are its characteristics?
Ball bearings
Drilling fluid from wellbore lubricates
Least expensive
What is a sealed bearing?
Internal grease system and rubber seal
Ball bearings
What is a journal bearing?
Sealed, ball bearing
Floating bushing instead of rollers
List the applications for milled tooth bits
Surface holes/top holes
Good for softer formations
List the applications for tungsten carbide insert bits
Can drill in soft to very hard
Longer run available than with milled tooth bit
Good For formations that PDC’s cannot be used
List applications for PDC bits
Soft to medium hard formations
Multi well economics
Best in homogeneous formation
Good for coil tubing and horizontal drillinf
List applications for natural and impregnated diamond bits
Natural- medium to hard formations
Impreg- med to hard formation, best used with a turbine
What do the following dull grading acronyms stand for? BT WT TR OC LT LC ER CR CD
Broken teeth Worn teeth Tracking Off center wear Lost teeth Lost cone Erosion Cored Cone dragged
Give 4 examples of what would cause worn teeth?
Formation
Improper bit selection
Excessive RPM
Excessive hours
Give 3 examples of what would cause tracking?
Plastic formation
Change bit type
Change operating parameters
What is an example of a plastic formation?
Shale
Give examples of what could cause Off Center wear dull grading?
Bent collars
Increase stabilization
What would cause Lost teeth dull grading?
Over loading
Name 2 things that would cause a Lost cone dull grading?
Exceeding hours
Bearing seal failure
What is the one thing that Would cause erosion dull grading?
Nozzle velocity to high
What causes cored dull grading?
Excessive WOB
Improper break in
What causes cone dragged dull grading?
Bearing or seal failure
When grading PDC bit, what would you indicate in the box for bearings?
An x, since PDC’s do not have bearings
What does DHF stand for in reason pulled?
Downhole tool failure
When the BHA experiences vibration, this is known as?
Bit whirl and stick slip
Define stick slip
When forward moment of the drill string is hampered and results in a momentary stop-rotate-stop motion of the drill string.
What is the best method to reduce whirl?
Increase weight on bit
Rotary bits drill the formation using what two primary principles?
- Rock removal by exceeding it’s shear strength
2. Removal by exceeding the compressive strength
What is the ultimate objectives in selecting a drill string with an appropriate bit?
Drill Faster and Drill furthur
Define shear failure
involves the use of a bit to shear or cut the rock into small pieces.
Define Compressive failure
a rock segment requires that the load be placed on the rock that will exceed the compressive strength of that given rock type. The load must remain on the rock surface long enough for rock failure to occur.
What is the one major difference between PDC bits and Roller cone bits that give PDC bits a competitive advantage?
No moving parts
What effect will a plugged nozzle have on the bit?
It would results in the bit not being able to clean and cool cutters at the same time, With high RPM`s, this could result in local heating of the bit structure and cause the cutters to be dislodged from the structure.
What happens to the bit drilling pattern as a whirl is generated?
The instantaneous centre of rotation moves around the face of the bit, and the bit whirls backwards around the hole while rotation of the string is still in clockwise direction.
