*PETE 411Well Drilling

Lesson 7Drilling 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

*The purpose of Chapter 5 (ADE) is to introduce the student to the:Rotary Drill bits selection and operation of 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 Drag bits (fixed cutter blades)Fishtail bitNatural diamond bitsPDC Bits (Polycrystalline Diamond Compact)

Rolling cutter bits (rock bits - with cones)Mill tooth bitsTungsten carbide bits

*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 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

*Drag BitsDrag bits drill by physically plowing or machining cuttings from the bottom of the hole.

*Drag BitsCutter 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.

*Fishtail type drag bit

*

Natural Diamond Bits PDC Bits

*Natural Diamond bit

junk slotcuttingsradial flow

high Dp across face

*Soft Formation Diamond bit Larger diamonds Fewer diamonds Pointed nose

*Hard Formation Diamond bit Smaller diamonds More diamonds Flatter nose

*Natural DiamondsThe size and spacing of diamonds on a bit determine its use. NOTE: One carat = 200 mg precious stones

What is 14 carat gold?

*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? 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

* Top view of diamond bit

*Side view of diamond bit

*PDC bitsCourtesy Smith Bits

*PDC Cutter

*

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

*The Rise in Diamond Bit Market Share

*Coring bitPDC + natural diamond

*Bi-Center bitCourtesy Smith 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.

*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 Parameters for effective use include

weight on bit mud pressure flow rate rotational speed

*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 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 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, contd

*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

*PDC Bits Bit Design, contd 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 Bits Factors that limit operating range and economics: Lower life from cutter fractures Slower ROP from bad cleaning Bit design, contd

*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

*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, contd

*PDC Bits Various Sizes Experimental dome shape Round with a buttress edge for high impact loads Polished with lower coefficient of friction Cutters, contd

*PDC Bits Bit Whirl (bit instability) Bit whirl = any deviation of bit rotation from the bits geometric center

Caused by cutter/rock interaction forces

PBC bit technology sometimes reinforces whirl Can cause PDC cutters to chip and break

*PDC Bits Preventing Bit Whirl

Cutter force balancing Bit asymmetry Gauge design Bit profile Cutter configuration Cutter layout

*PDC Bits Applications

PDC bits are used primarily in

Deep and/or expensive wells

Soft-medium hard formations

*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, contd

*PDC Bits Application, contd 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 BitsCT - 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 contdLT - Lost CutterBit is missing one or more cuttersLN - Lost NozzleBit is missing one or more nozzles

*Table 7.7 - Commonly Used Bit Sizes For Running API CasingCasing Size Coupling Size Common Bit (OD in.) (OD in.) Sizes Used (in.) 4 1/2 5.06, 6 1/8, 6 1/45 5.5636 1/2, 6 3/45 1/2 6.0507 7/8, 8 3/86 6.6257 7/8, 8 3/8, 8 1/26 5/8 7.3908 1/2, 8 5/8, 8 3/47 7.6568 5/8, 8 3/4, 9 1/27 5/8 8.5009 7/8, 10 5/8, 118 5/8 9.62511, 12 1/49 5/8 10.62512 1/4, 14 3/410 3/4 11.7501513 3/8 14.37517 1/216 17 2020 21 24, 26

*ENDofLesson 7 - Drag Bits -