Pete 411 well drilling
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PETE 411 Well Drilling. Lesson 7 Drilling Bits - Drag Bits. Contents. The Ideal Bit Drag Bits Fishtail Type Natural Diamond Polycrystalline Diamond Compact (PDC). Relative Costs of Bits. Read: ADE, Ch.5 (bits). HW # 3: due 9 -18- 2002. Rotary Drill bits.

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PETE 411 Well Drilling

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Pete 411 well drilling

PETE 411Well Drilling

Lesson 7

Drilling Bits - Drag Bits



The Ideal Bit

Drag Bits

Fishtail Type

Natural Diamond

Polycrystalline Diamond Compact (PDC)

  • Relative Costs of Bits

Read ade ch 5 bits

Read: ADE, Ch.5 (bits)

HW # 3: due 9 -18- 2002

Rotary drill bits

Rotary Drill bits

The purpose of Chapter 5 (ADE) is to introduce the student to the:

  • selection and

  • operation

    of rotary drilling bits.

Rotary drilling bits

Rotary Drilling Bits

  • Bit types available

  • Criteria for selecting the best bit for a given situation

  • Standard methods for evaluating dull bits

  • Factors affecting bit wear and drilling speed

  • Optimization of bit weight and rotary speed

Bit types available

Bit types available

  • Drag bits (fixed cutter blades)

    • Fishtail bit

    • Natural diamond bits

    • PDC Bits (Polycrystalline Diamond Compact)

  • Rolling cutter bits (rock bits - with cones)

    • Mill tooth bits

    • Tungsten carbide bits

The ideal bit

The Ideal Bit *

1. High drilling rate

2. Long life

3. Drill full-gauge, straight hole

4. Moderate cost

* (Low cost per ft drilled)

The ideal bit1

The Ideal Bit

“The Ideal Bit” will depend on the type of formation to be drilled

Hardness (soft, medium, hard)


cuttings stickiness

other considerations … e.g. cost

Drag bits

Drag Bits

Drag bits drill by physically “plowing” or “machining” cuttings from the bottom of the hole.

Drag bits1

Drag Bits

  • Cutter may be made from:

    • Steel

    • Tungsten carbide

    • Natural diamonds

    • Polycrystalline diamonds (PDC)

Drag bits have no moving parts, so it is less likely that junk will be left in the hole.

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Fishtail type drag bit

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Natural Diamond Bits PDC Bits

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Natural Diamond bit

junk slot


radial flow

high Dp across face

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Soft Formation Diamond bit

  • Larger diamonds

  • Fewer diamonds

  • Pointed nose

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Hard Formation Diamond bit

  • Smaller diamonds

  • More diamonds

  • Flatter nose

Natural diamonds

Natural Diamonds

The size and spacing of diamonds on a

bit determine its use.

NOTE: One carat = 200 mgprecious stones

What is 14 carat gold?

Natural diamonds1

Natural Diamonds

2-5 carats - widely spaced diamonds are used for drilling soft formations such as soft sand and shale

1/4 - 1 carat - diamonds are used for drilling sand, shale and limestone formations of varying (intermediate) hardness.

1/8 - 1/4 carat -diamonds, closely spaced, are used in hard and abrasive formations.

When to consider using a natural diamond bit

When to Consider Using a Natural Diamond Bit?

1. Penetration rate of rock bit < 10 ft/hr.

2. Hole diameter < 6 inches.

3. When it is important to keep the bit and pipe in the hole.

4. When bad weather precludes making trips.

5. When starting a side-tracked hole.

6. When coring.

* 7. When a lower cost/ft would result

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Top view of diamond bit

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Side view of

diamond bit

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PDC bits

Courtesy Smith Bits

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PDC Cutter

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PDC Bits

At about $10,000-150,000 apiece, PDC bits cost five to 15 times more than roller cone bits

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The Rise in Diamond Bit Market Share

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Coring bit

PDC + natural diamond

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Bi-Center bit

Courtesy Smith Bits

Relative costs of bits

Relative Costs of Bits


Diamond WC Insert Milled

Bits Bits Tooth Bits

  • 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.

Pdc bits ref oil gas journal aug 14 1995 p 12

PDC BitsRef: Oil & Gas Journal, Aug. 14, 1995, p.12

Increase penetration rates in oil and 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

Pdc bits

PDC Bits

Parameters for effective use include

weight on bit

mud pressure

flow rate

rotational speed

Pdc bits1

PDC Bits

  • Economics

    • Cost per foot drilled measures Bit performance economics

    • Bit Cost varies from 2%-3% of total cost, but bit affects up to 75% of total cost

    • Advantage comes when

      - the No. of trips is reduced, and when

      - the penetration rate increases

Pdc bits2

PDC Bits

  • Bit Demand

    • U.S Companies sell > 4,000 diamond drill bits/year

    • Diamond bit Market is about $200 million/year

  • Market is large and difficult to reform

  • When bit design improves, bit drills longer

Pdc bits3

PDC Bits

  • Bit Demand, cont’d

Improvements in bit stability, hydraulics, and cutter design => increased footage per bit

Now, bits can drill both harder and softer formations

Formations in US are not as conducive to PDC bits as formations in some other areas

Pdc bits4

PDC Bits

  • Bit Design

    • General Electric introduced PDC in 1973

    • Product Life = 2 years

Improvements are a result of the following:


Good Engineering Practices

Competition with other PDC bit manufacturers/rock bit industries

Pdc bits5

PDC Bits

  • Bit Design, cont’d

  • Now, a speciality tool

  • PDC bit diameter varies from 3.5 in to 17.5 in

Goals of hydraulics:

clean bit without eroding it

clean cuttings from bottom of hole

Pdc bits6

PDC Bits

  • Bit design, cont’d

Factors that limit operating range and economics:

Lower life from cutter fractures

Slower ROP from bad cleaning

Pdc bits7

PDC Bits


Consist of thin layer of bonded diamond particles + a thicker layer of tungsten carbide


10x harder than steel

2xharder than tungsten carbide

Most wear resistant material

but is brittle and susceptible to damage

Pdc bits8

PDC Bits

  • Cutters, cont’d

Diamond/Tungsten Interface

Bond between two layers on cutter is critical

Consider difference in thermal expansion coefficients and avoid overheating

Made with various geometric shapes to reduce stress on diamond

Pdc bits9

PDC Bits

  • Cutters, cont’d

Various Sizes

Experimental dome shape

Round with a buttress edge for high impact loads

Polished with lower coefficient of friction

Pdc bits10

PDC Bits

  • Caused by cutter/rock interaction forces

  • PBC bit technology sometimes reinforces whirl

Bit Whirl (bit instability)

Bit whirl = “any deviation of bit rotation from the bit’s geometric center”

  • Can cause PDC cutters to chip and break

Pdc bits11

PDC Bits

  • Preventing Bit Whirl

    • Cutter force balancing

    • Bit asymmetry

    • Gauge design

  • Bit profile

  • Cutter configuration

  • Cutter layout

Pdc bits12

PDC Bits


PDC bits are used primarily in

Deep and/or expensive wells

Soft-medium hard formations

Pdc bits13

PDC Bits

  • Application, cont’d

  • Advances in metallurgy, hydraulics and cutter geometry

    • Have not cut cost of individual bits

    • Have allowed PDC bits to drill longer and more effectively

    • Allowed bits to withstand harder formations

Pdc bits14

PDC Bits

Application, cont’d

PDC bits advantageous for high rotational speed drilling and in deviated hole section drillings

Most effective: very weak, brittle formations (sands, silty claystone, siliceous shales)

Least effective: cemented abrasive sandstone, granites

Grading of worn pdc bits

Grading of Worn PDC Bits

CT - Chipped Cutter

Less than 1/3 of cutting element is gone

BT - Broken Cutter

More than 1/3 of cutting element is broken to the substrate

Grading of worn pdc bits cont d

Grading of Worn PDC Bits – cont’d

LT - Lost Cutter

Bit is missing one or more cutters

LN - Lost Nozzle

Bit is missing one or more nozzles

Table 7 7 commonly used bit sizes for running api casing

Table 7.7 - Commonly Used Bit Sizes For Running API Casing

4 1/2 5.06, 6 1/8, 6 1/4

5 5.5636 1/2, 6 3/4

5 1/2 6.0507 7/8, 8 3/8

6 6.6257 7/8, 8 3/8, 8 1/2

6 5/8 7.3908 1/2, 8 5/8, 8 3/4

7 7.6568 5/8, 8 3/4, 9 1/2

7 5/8 8.5009 7/8, 10 5/8, 11

8 5/8 9.62511, 12 1/4

9 5/8 10.62512 1/4, 14 3/4

10 3/4 11.75015

13 3/8 14.37517 1/2

16 17 20

20 21 24, 26

Casing Size Coupling Size Common Bit

(OD in.) (OD in.) Sizes Used (in.)

End of lesson 7 drag bits

ENDofLesson 7 - Drag Bits -

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