drilling bit
TRANSCRIPT
PETE 203
DRILLING ENGINEERING
Chapter 5Chapter 5
Drilling BitsDrilling Bits
Contents:
• Various bit types available (classification).
• Criteria for selecting the best bit for a given situation.
• Standard methods for evaluating dull bite
• Factors affecting bit wear and drilling speed.
• Different Rock Failure mechanisms
• Optimization of bit weight and rotary speed
• Relative Costs of Bits
Ideal Bit (Lowest Cost $/ft)
• High drilling rate
• Long life
• Drill full-gauge, straight hole
• Moderate cost
Selecting Ideal Bit
• Drilling Cost per foot
• Drillability
• Abrasiveness
• Type of Reservoir
• Cost of the Bit
• Depth
Improving Bit Performance
• Stabilize the Bit
• Maintain minimum mud weight, sand & solids
• Maintain adequate bottom hole cleaning
• Protect the seals - avoid pressure surges
• Thoroughly inspect bit before re-running
• Keep oil from the mud, and from the seals
• Follow manufacturers recommendations (e.g.
6,000 lb/in of diameter and 40-60 RPM)
Common Types of Drilling Bits
Types of Bits1. Drag Bits: Fixed cutter blades
Consist of fixed cutter blades that are
integral with the body of the bit and rotate
as a unit with the drill string (19th century).
2. Rolling Cutter Bits: Rock bits - with cones
(1909) have two or more cones containing
the cutting elements which rotate about
the axis of the cone as the bit is rotated at
the bottom of the hole.
Drag Bits
• Design Features
– Number & shape of cutting blades/stones
– Size and location of the water courses
– Metallurgy of the bit and cutting elements
Drag Bits– Drilling is achieved by physically blowing
cuttings from the bottom of the bore-hole
AdvantagesAdvantages
– No rolling parts which require strong clean
bearing surfaces
– Because it is made from one solid piece of steel
there is less chance of bit breakage, which
would leave junk in the bottom of the hole
Drag Bits
Fishtail Drag Bit
Drag Bits
• Cutter may be made from:
– Steel
– Tungsten carbide
– Natural diamonds
– Polycrystalline diamonds
(PDC)
Drag Bits
• Types of Drag BitsTypes of Drag Bits
– Steel cutter bits (Steel cutter bits (Fishtail Type)
– Diamond bitsDiamond bits
– Polycrystalline diamond bitsPolycrystalline diamond bits
• Best for
– Soft formations
– Uniform formations
– unconsolidated formations
• Now, replaced by other types in all
area
Steel Cutter BitsSteel Cutter Bits
When Using Natural Diamond Bit?
• Penetration rate of rock bit < 10 ft/hr
• Hole diameter < 6 inches
• When it is important to keep the bit and pipe
in the hole
• When bad weather precludes making trips
• When starting a side-tracked hole
• When coring
• When a lower cost/ft would result
– Best for hard non-brittle formations
– The face or crown of the bit consists of many
diamonds set in a tungsten carbide matrix
– Fluid courses are provided in the matrix to
direct the flow of drilling fluid over the face of
the bit.
Diamond BitsDiamond Bits
• Shape of crown profit:
– Step type
– Long taper (straight hole, high wt.)
– Short taper (easier to clean)
– Non taper (directional drilling)
Diamond BitsDiamond Bits
• Size and number of diamonds, depend on
the hardness of the formation
– Hard formations:
• Many small stones
• 0.07-0.125 carrot
– Soft formations:
• Few large stones
• 0.75-2.0 carrot
Diamond BitsDiamond Bits
• Pressure drop across the face of the bit
• Pump pressure measured with the bit off
bottom-pump pressure with the bit drilling =
500 : 1000 psi
• Manufacturer usually provide estimate of
approximate circulating rate required establishing
the needed pressure drop across the bit.
Diamond BitsDiamond Bits
Top View of Diamond Bit
Side View of Diamond Bit
Natural Diamond Bits PDC Bits
Natural Diamond
bit
junk slotcuttings
radial flow
high p across face
Soft
Formation
Diamond bit
Larger diamonds Fewer diamonds Pointed nose
Hard
Formation
Diamond bit
Smaller diamonds More diamonds Flatter nose
PolyCrystalline Diamond (PCD) Bits
• Since mid 1970’s a PDC Bits has been made
possible by the introduction of a sintered
polycrystalline diamond drill blanks, as a bit cutter
element
• The drill blanks consist of a layer of a synthetic
polycrystalline diamond about 1/64 in. thick that is
bonded to a cemented tungsten carbide substrate in
a high-pressure high-temperature (HPHT) process
PDC bits
Courtesy Smith Bits
PolyCrystalline Diamond (PCD) Bits
• It contains many small diamond crystals bonded
together
• The PCD is bonded either to a tungsten carbide
bit-body matrix or to a tungsten carbide stud that
is mounted in a steel bit body
• They perform best in soft, firm, and medium-hard,
non-abrasion formations (not gummy)
PolyCrystalline Diamond (PCD) Bits
• Good results are obtained in carbonates or
evaporates that are not broken up with hard shale
stringers.
• Also good in a sandstone, siltstone, shale
• Design of crown profile is important, double-cone
and flat profile
• Size, shape, number of cutters and angle of attack
back rake, side rake and exposure
PolyCrystalline Diamond (PCD) Bits
• Advantages:
– Increase penetration rates in oil & gas wells
– Reduce drilling time and costs
– Cost 5-15 times more than roller cone bits
– 1.5 times faster than those 2 years earlier
– Work better in oil based muds; however, these
areas are strictly regulated
At about $10,000-150,000 a piece, PDC bits cost five to 15 times more than roller cone bits
PDC Bits
Relative Costs of Bits
Diamond WC Insert Milled Bits Bits Tooth Bits
$/Bit
• Diamond bits typically cost several times as much as tri-cone bits with tungsten carbide inserts (same bit diam.)• A TCI bit may cost several times as much as a
milled tooth bit.
Grading of Worn PDC Bits
CT - Chipped CutterLess than 1/3 of cutting element is gone
BT - Broken CutterMore than 1/3 of cutting element is broken to the
substrate
Grading of Worn PDC Bits – cont’d
LT - Lost CutterBit is missing one or more cutters
LN - Lost NozzleBit is missing one or more nozzles
Table 7.7 - Commonly Used Bit Sizes For Running API Casing
Casing Size Coupling Size Common Bit (OD in.) (OD in.) Sizes Used (in.)
4 1/2 5.0 6, 6 1/8, 6 1/4
5 5.563 6 1/2, 6 3/4
5 1/2 6.050 7 7/8, 8 3/8
6 6.625 7 7/8, 8 3/8, 8 1/2
6 5/8 7.390 8 1/2, 8 5/8, 8 3/4
7 7.656 8 5/8, 8 3/4, 9 1/2
7 5/8 8.500 9 7/8, 10 5/8, 118 5/8 9.625 11, 12 1/4
9 5/8 10.625 12 1/4, 14 3/4
10 3/4 11.750 1513 3/8 14.375 17 1/2
16 17 2020 21 24, 26