Download - Tech Drilling Drilling DragBits
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PETE 411Well Drilling
Lesson 7Drilling Bits - Drag Bits
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Contents
The Ideal Bit Drag Bits
Fishtail Type Natural Diamond Polycrystalline Diamond Compact
(PDC)
Relative Costs of Bits
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Read: ADE, Ch.5 (bits)
HW # 3: due 9 -18- 2002
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The purpose of Chapter 5 (ADE) is to introduce the student
to the:
Rotary Drill bits
selection and operation
of rotary drilling bits.
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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
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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
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The Ideal Bit *
1. High drilling rate
2. Long life
3. Drill full-gauge, straight hole
4. Moderate cost
* (Low cost per ft drilled)
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The Ideal Bit
Hardness (soft, medium, hard) abrasiveness cuttings stickiness other considerations … e.g. cost
“The Ideal Bit” will depend on the type of formation to be drilled
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Drag Bits
Drag bits drill by physically “plowing”
or “machining” cuttings from the
bottom of the hole.
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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.
11Fishtail type drag bit
12Natural Diamond Bits PDC Bits
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Natural Diamond
bit
junk slotcuttings
radial flow
high p 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
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Natural Diamonds
The size and spacing of diamonds on a bit determine its use.
NOTE: One carat = 200 mg precious stones
What is 14 carat gold?
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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.
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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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24At about $10,000-150,000 apiece, PDC bits cost five to 15 times more than roller cone bits
PDC Bits
25The 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
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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.
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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
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PDC Bits
Parameters for effective use include
weight on bit mud pressure flow rate rotational speed
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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
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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
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PDC Bits
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
Bit Demand, cont’d
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PDC Bits
Improvements are a result of the following: Research Good Engineering Practices Competition with other PDC bit manufacturers/rock bit industries
Bit Design General Electric introduced PDC in 1973
Product Life = 2 years
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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
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PDC Bits
Factors that limit operating range and economics:
Lower life from cutter fractures
Slower ROP from bad cleaning
Bit design, cont’d
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PDC Bits
Cutters• Consist of thin layer of bonded diamond
particles + a thicker layer of tungsten carbide
• Diamond• 10x harder than steel• 2x harder than tungsten carbide• Most wear resistant material
but is brittle and susceptible to damage
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PDC Bits
• 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
Cutters, cont’d
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PDC Bits
• Various Sizes
• Experimental dome shape
• Round with a buttress edge for high impact loads
• Polished with lower coefficient of friction
Cutters, cont’d
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PDC Bits
Bit Whirl (bit instability)• Bit whirl = “any deviation of bit rotation
from the bit’s geometric center”• Caused by cutter/rock interaction forces
• PBC bit technology sometimes reinforces whirl
• Can cause PDC cutters to chip and break
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PDC Bits
Preventing Bit Whirl
• Cutter force balancing
• Bit asymmetry
• Gauge design
• Bit profile
• Cutter configuration
• Cutter layout
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PDC Bits
Applications
• PDC bits are used primarily in
• Deep and/or expensive wells
• Soft-medium hard formations
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PDC Bits
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
Application, cont’d
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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
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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
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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
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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
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ENDof
Lesson 7 - Drag Bits -