2. ๏ The tool used to crush/ scrap/ scratch the
rock
๏ Most bits work by scraping or crushing
the rock, or both, usually as part of a
rotational motion
๏ The bit is on the bottom of the drillstring
(part of BHA) and it must be changed
when it becomes excessively dull or
stops making progress due to wear and
3. DRILLING BIT CLASSIFICATION
1. Roller Cone Bit
๏ Steel Milled Tooth Bit
๏ Inserted Tooth Bit
2. Fixed Cutter Bit
๏ Blade Bits
๏ Natural Diamond Bit (ND)
๏ Polycrystalline Diamond Compact (PDC) Bits
๏ Impregnated Bit
3. Hybrid Bit
4. Core Bit
4. ROLLER CONE BIT
๏ Roller cone bits are comprised of two or three
cones having teeth sticking out of them
๏ Nowadays three cone bits are being used in the
Petroleum industry
๏ These teeth apply a force exceeding the
compressive strength of the rock
๏ Hydraulic cleaning action is achieved by using
nozzles present in the bit body
8. ADVANTAGES
1. Can handle rough drilling conditions
2. Used in both hard and soft formations
3. High penetration rate
4. Less expensive than PDC bits
5. They are more sensitive to the amount of
pressure overbalance and thus better
indicator of overpressured formations
9. LIMITATIONS
๏ Wear and tear is more as compared to
PDC bits
๏ Bit Hours (Bit rotation time) are less as
compared to PDC bits
11. JOURNAL ANGLE
The journal angle is defined as the angle
formed by a line perpendicular to the axis
of the journal and the axis of the bit
๏ The Journal Angle translates the angle the
cones make with the rock and in effect
determines the amount of cutting action
applied to the rock
12. ๏ The Lower the journal angle means the
teeth come into a more forceful contact
with the rock and provides a higher
cutting action
๏ Thus, a lower journal angle is used for
soft formations to provide a higher
cutting action, and a higher journal angle
is used for hard formations
13. OFFSET ANGLE
๏ Offset of the bit shows how much the axis
of the cones are out of center
๏ Cone axis do not intersect at a common
point
๏ This offset causes the cones to stop
rotating periodically as the bit turns and
scraps the borehole similar to the cutting
action of a drag bit
๏ Offset angle varies from 0 - 4 degrees
14.
15.
16. ๏ The amount of offset is directly related to
the strength of rock being drilled
๏ Soft rocks require a higher offset to
produce greater scraping and gouging
actions
๏ As the rock type gets harder, the tooth
length and cone offset must be reduced
to prevent premature tooth breakage
17. GAUGE
๏ The gauge of the hole drilled by roller
cone bits is maintained by the outside
cutters which are also known as โgauge
cuttersโ
๏ Cones are commonly heat treaded and
made of NiMo โ steel, teeth are
sometimes made of NiCrMo โ steel or
Tungsten Carbide
18.
19.
20.
21.
22.
23. MILLED TOOTH BIT
๏ Teeth are milled out of the same body the
cones consist of
๏ These bits are very robust and tolerate
severe drilling conditions but wear out
relatively quickly
24.
25.
26. INSERTED TOOTH BIT
๏ These are also called Tungsten Carbide
bits, have teeth made of Tungsten Carbide
which are fitted on the cone bodies
๏ These bits can drill long sections before
being worn out
๏ More expensive than Milled Tooth Bits
๏ Also called โButton Bitsโ
27.
28.
29.
30.
31. ๏ A new technology of insert bits coats the
teeth with a layer of diamond
๏ These bits, also known as Tungsten
Carbide Inserts (TCIs) bits, exhibit a
significantly improved bit life in abrasive
formations
32. FIXED CUTTER BIT
๏ Fixed cutter or drag bits have no moving
parts (e.g. rolling cones)
33.
34. POLYCRYSTALLINE DIAMOND COMPACT (PDC) BIT
๏ PDC bits have industrially manufactured
diamond disk which is mounted on a
tungsten carbide stud
๏ Very expensive
๏ PDC bits are manufactured in many
different shapes that determine their
behavior to use them in different
formations and to drill directional or
straight trajectories
38. ๏ Good results have been reported in
Carbonates, Sandstone, Siltstone and
Shale
๏ Hydraulic cleaning action is achieved by
using nozzles
๏ Other design features are: Size, shape
and number of cutters and the angle of
attack
39. ADVANTAGES
1. Can drill very long hole sections when
the proper drilling conditions are given
2. They exhibit higher Bit Hours in hard,
abrasive formations
3. As a rule of thumb, the advantages of
diamond bits over roller bits increase as
the depth increases and the borehole
diameter decreases
47. IMPORTANCE OF BIT SELECTION
๏ Bit is the most important part of the drill
string
๏ Proper bit selection means good
penetration rate (ROP) โ Time saving
๏ So, the most appropriate bit is selected
on the basis of technical and economical
view point - knowledge and experience
factors
48. SELECTION CRITERIA
๏ Unfortunately, most of the time the selection
of best available bit for the job can only be
determined by hit and trial method or by
using the offset well data
๏ Prognosed lithology column with detailed
description of each formation
๏ Well profile
๏ Cost per foot
49. FACTORS AFFECTING ROP
1. Rig Efficiency
2. Personnel Efficiency
3. Formation Characteristics
4. Drilling Fluid Properties
5. Operating Conditions
6. Bit Type
7. Bit Wear
8. Bit Hydraulics
51. An eight point dull grading system that has
been established by the IADC to enable
drilling engineers and bit manufacturers
to evaluate the performance of a used drill
bit
52. ๏ During the planning stage, the Drilling
Engineer makes a thorough review of the
offset well data and records bit
performance and bit grading
characteristics in formations comparable
to the well being designed (Prospect Well)
๏ All occurrences of gauge wear, tooth
dulling characteristics and premature bit
failures must be noted
