Drilling bit classification

Transcription

1 Drilling Bits

2 Drilling bit classification 1.Roller Cone Bit Milled Tooth Bit Inserted Tooth Bit 2. Fixed Cutter Bit (Drag Bit)

3 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 industry Teeth apply a force exceeding the compressive strength of the rock Hydraulic cleaning action is achieved by using nozzles

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5 As the rock type gets harder, the tooth length and cone offset must be reduced to prevent tooth breakage

6 advantages 1. Can handle rough drilling conditions 2. Used in both hard and soft formations 3. Fastest penetration rate 4. Less expensive than fixed cutter bits 5. Are more sensitive to the amount of pressure overbalance and thus better indicator of overpressure formations,

7 disadvantages Wear and tear is more as compared to PCD bits Bit Hours (Bit rotation time) are less

8 Borehole diameter (gauge) The gauge of the hole drilled by roller cone bits is maintained by the outside cutters which are also known as gauge cutters Cones are commonly heat treaded and made Cones are commonly heat treaded and made of NiMo-steel, teeth are sometimes made of NiCrMo-steel.

9 offset Offset of the bit shows how much the axis of theconesareoutofcenter Coneaxisdonotintersectatacommonpoint This offset causes the cones to stop rotating periodically as the bit is turned and scraps the hole similar to the cutting action of a drag bit Offset angle varies from O-4 degree

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11 Mill Tooth Bit Teeth are milled out of the same body the cones consist of Thesebitsareveryrobustandtoleratesevere drilling conditions but wear out relatively quickly

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14 Inserted Tooth Bit These are also called tungsten carbide bits, have teeth made of tungsten carbide which arefittedontheconebodies. These bits do not tolerate shock loadings but they can drill long sections before being worn out More expensive than milled Tooth Bits Also called Button Bits

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17 A new technology of insert bits coats the teeth with a layer of diamond. These bits, also known as tungsten carbide insert bits (TCI), exhibit a significantly improved bit life in abrasive formations.

18 Fixed Cutter Bit Fixed cutter or drag bits have no moving parts(e.g. bearings)

19 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. They allow higher bit rotations which are given when down hole motors are applied 4. Asaruleofthumb,theadvantagesofdiamond bits over roller bits increase as the depth increases and the borehole diameter decreases.

20 disadvantages 1. Sensitive to steel at bottom of borehole (lost junk), 2. Have to be run in carefully, borehole has to be washed clean. 3. Fail to drill very soft and gummy formations (Bit balling effect) 4. Higherprice.

21 Polycrystalline diamond bit (PCD) Polycrystalline diamond compact (PCD) bits have an industrially manufactured diamond disk mounted on a tungsten carbide stud Very expensive Under the proper drilling conditions, they can drill very fast for long distances PDC bits are manufactured in many different shapes that determine their behavior to rather drill directional or straight trajectories.

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24 Diamond disc on tungsten carbide stud

25 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 numberofcuttersandtheangleofattack

26 Importance of bit selection Bit is the most important part of the drill string Proper bit selection means good penetration rate(rop). Sowehavetoselectthemosteconomicalbit.

27 Selection criteria Unfortunately, the selection of best available bit for the job can only be determined by hit and trial method. The most valid criteria for comparing the The most valid criteria for comparing the performance of various bits and selection of most appropriate bit type for particular formation are:

28 1. Cost per foot. 2. Geological formations. 3. Off set wells bits records or Dull grading

29 Cost per foot The criterion for bit selection is normally based on cost per foot by the equation. Where C = B+(T+t)R/F ($/ft) B = Bit cost ($) T = Trip time (h) t = Rotating time(h) R = Rig cost per hour ($/h) F = Length drilled (ft)

30 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