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Drilling Bit Introduction and bit Selection (Part 3)

(PART 1,2 & 3)
1. Drilling mechanisms
2. Bit classifications (fixed cutter and roller cone bits)
3. IADC code descriptions
4. Tri-cone bits life time
5. Geometrical analysis of roller cone bits
• Fundamentals of bit design
• Basics of cone geometry design
• Oversize angle
• Offset
• Teeth and inserts
• Additional design criteria: tooth to tooth and groove clearances and etc.
• Cone-shell thickness
• Bearings factors
• Rock bit metallurgy
• Heat treatment
• Legs and cones material
• Tungsten carbide materials
• Legs and cones hard facing
• Tungsten carbide grade selection for inserts
• Bearings, seals and lubrication
• Bearing shape
• Bearing precisions and geometry
• Seal systems and seal details
• Dull grading system
6. Geometrical analysis of PDC bits
• PDC materials and constructions
• Matrix materials testing
• Differs between matrix & steel body
• Matrix body bits manufacturing
• Steel body bits manufacturing
• PDC bit design parameters: mechanical, hydraulic, rock properties
• Weld strength of PDC bits and cutters
• PDC cutter manufacturing process
• Tsp cutter properties vs PDC
• The influences of bit profile and profile elements
• PDC forces
• PDC bit stability
• PDC bit steer-ability
• Back rake
• Side rake
• Depth of cut
• Cutter exposure
• Cutter density
• Thermal damage and degradation of cutters
• Cutting mechanics
• PDC cutter substrate and its thickness
• Cutting structure elements
• Single set bladed cutting structures
• Plural set bladed cutting structures
• Dull grading system
7. ROP management based on drilling parameters
• WOB
• Rpm
• Sold content of mud
• Mud weight
• Cutter shape
• Cutters geometry
• Depth
• Abnormal pressure
• Drilling formation properties

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Drilling Bit Introduction and bit Selection (Part 3)

  1. 1. PDC BIT COURSE
  2. 2. PDC
  3. 3. PDC BIT BASICS • STEEL PDC BITS • Are milled (machined) from steel stock. PDC cutters are attached and silver brazed in place in appropriately located drilled pockets. Surfaces that are subject to abrasion and erosion must be protected by hard-facing and coating. • MATRIX PDC BITS • Are castings made of matrix material. PDC cutters are attached and silver brazed in place in appropriately located pockets. Because of the natural hardness of matrix, it is unnecessary to provide additional protection against abrasion or erosion.
  4. 4. MATERIALS Differs Between Matrix & Steel • Matrix bits have a cast body, steel bits are milled from forgings or wrought materials. Matrix material is too hard to be machined. • Matrix bits are far more abrasion and erosion resistant than steel. Steel bit must be protected against abrasion and erosion with hard-facing. • Steel bits are structurally stronger and tougher than matrix bits. Matrix bits require the support of an internal steel structural member (a blank).
  5. 5. MATERIALS Differs Between Matrix & Steel • Steel bits are relatively easy to manufacture and can be delivered relatively quickly. Cast, matrix require cores, patterns and / or milled molds that can be difficult and time consuming to produce. • Milled, steel bits are dimensionally more accurate and are more repeatable than cast, matrix bits. • Because of the difference in structural capabilities of steel and matrix, bit geometries are dissimilar. For example, steel blades can often be taller and less think than matrix bit blades. • Impregnated bits can only be constructed of matrix materials.
  6. 6. MATERIALS Differs Between Matrix & Steel • Because of the weld-ability of steel, steel body bits can be easily refurbished. Cutters and hard-facing can be replaced, minor erosion damage can be repaired, and threads can be restored. GeoDiamond developmental now makes certain rebuild activities possible with matrix bits, too. • Matrix-body PDC bits are commonly preferred over steel bits in cases in which erosion of the body is likely to cause the bit to fail. • For example, in smaller diameter wells in which drilling mud flow rate is high or in which the mud contains a high proportion of abrasive solid material.
  7. 7. Matrix Materials Testing
  8. 8. PDC: POLYCRYSTALLINE DIAMOND COMPACT • A PDC is a composite comprised of synthetic (man- made) diamond grit and tungsten carbide. • “Compact” is a term given to materials formed by the compression of powders. • The diamond is sintered, with a metallic binder, onto a sintered tungsten carbide substrate for use as a cutter. • Diamond crystals in PCD are oriented in diverse directions.
  9. 9. TSP: THERMALLY STABLE PCD • diamond. As PCD is heated, the contained catalyst will expands at a greater rate than the surrounding Diamond particles. At about 750°C, the expanded catalyst begins to break diamond-to-diamond bonds and thermal degradation of the PDC will begin. • PDC thermal stability can be improved by removing catalyst content from the PDC by an acid leaching process. After catalyst removal, the modified PDC is called TSP and is thermally stable to a temperature of1,150°C (similar but slightly below diamond). • TSP is manufactured in wafers that can be cut into required shapes and sizes suitable for an intended application. Like diamond, TSP it is not “wettable,” however, and cannot, as a result, be bonded to a supporting substrate.
  10. 10. Matrix Manufacturing
  11. 11. Matrix Manufacturing
  12. 12. Matrix Manufacturing
  13. 13. Matrix Manufacturing
  14. 14. MANUFACTURING STEEL BODY BITS • Are manufactured from forged, alloy steel that is heat treated to the proper mechanical properties. • The bit profile, hydraulic design, and API pin connection are all machined. Cutter attachment is achieved by brazing PDC cutters into the machined cutter pockets. The pockets are drilled into the bit body face with a CNC.
  15. 15. MANUFACTURING STEEL BODY BITS • tungsten carbide hard-facing is then applied to the blade faces and top using thermal spray techniques. • Field experience has shown that steel body bits are more susceptible to erosion and abrasion than matrix bits. • This generally occurs in conjunction with high bit pressure drops, extended bit runs, and / or high solids content drilling fluids. • This becomes the limiting factor when cutters cannot be replaced or the nozzle retention system is hampered, due to erosion or abrasion.
  16. 16. PDC CUTTER MANUFACTURING PROCESS • The diamond layer in PDC, is called wafer. • Wafer is produced by mixing fine grained, man-made, diamond grit (100 microns or less in diameter) with a catalyst, typically cobalt or nickel. • mixture is subjected to pressure, over million psi., temperature, 1350ºC • The final product is a thin piece of random oriented, interconnected diamonds with the pore space filled with residual catalyst.
  17. 17. PDC CUTTER MANUFACTURING • hybrid bits are named because more than one diamond type is employed in their construction • All PDC wafer is made in two steps: – manufacture diamond grit from graphite – a growth of mono-crystalline grit crystals • The shape of the container determines the final shape of the product.
  18. 18. PDC BIT DESIGN • Mechanical design parameters, • Hydraulic conditions, and, • The properties of the rock being drilled.
  19. 19. Weld Strength • All PDC bits are manufactured in two parts, the body section and the pin section. • These two sections are integrated by a weld that joins the steel, structural bit blank in the body with the steel pin section. • • This joint must be capable of transferring full torque loads between the body and pin and must withstand all impact loading the bit sustains.
  20. 20. Weld Strength Braze strength is principally governed by four factors: • Joint design, • Joint integrity, • Materials capabilities, and, • Manufacturing methods.
  21. 21. PDC BIT PROFILE • Bit stability, • Bit steer-ability, • Bit cutter density, • Bit durability, • Bit ROP, • Bit cleaning efficiency, and, • Prevention of thermal damage to cutters by cooling efficiency.
  22. 22. THE INFLUENCES OF BIT PROFILE • Balance two cross purposes: – bit ROP – bit stability • When a bit is capable of generating cuttings faster than they can be removed, however, penetration is restricted by the cuttings and the achievement of optimal ROP is impeded.
  23. 23. PDC FORCES
  24. 24. PDC FORCES
  25. 25. PROFILE ELEMENTS • The apex • The cone • The nose • The shoulder or taper • The outside diameter radius • The gage
  26. 26. Cone Area Deep Cone Angle 90 Deg, Shallow Cone Angle, 150 Deg, Profile
  27. 27. Deep Cones • provide a high degree of bit stability. • The cone shaped portion of the borehole bottom projects upward into the bit’s cone and counteract forces encouraging lateral bit movement • makes bits difficult to steer & the large central area renders less aggressive. • The large central area of deep cone bits makes high central area cutter densities possible. • This is an advantage for diamond bits in highly abrasive formations. • For PDC bits, large cutter density at the bit center is not an advantage, however. • Because cuttings must travel over a relatively longer, (compared to shallow cones), and curved distance to escape the cone area, bits with deep cones are relatively more difficult to clean.
  28. 28. Shallow Cone • Shallow cone bits: – more steerable – easier to clean – more aggressive than deep cone bits. • Flatness of the profile provides cutters in nearly the same plane, allowing more cutters to take impact loads as hard stringers are encountered. • The shallow cone and absence of a nose characteristic of this profile provide little stabilization for radial loads. The profile requires a long gage to maintain directional stability. • Any eccentric rotation of these motors during the rotary mode will produce excessive wear on the gage cutters because of the low number of cutters available to support gage Loading.
  29. 29. Bit Nose • The location of a bit nose and the sharpness of nose radius curvature influence bit aggressiveness and durability of the design. • More generous nose radii increase bit durability; the closer the centerline of a bit is to the bit’s nose, the more aggressive the design will be.
  30. 30. Bit Nose • Potential for cutter density in a bit design is a function of the bit’s nose shape and length. • Longer profile lengths have more surface area available for the placement of cutters, hydraulic layouts, and nozzles. Surface area requiring cleaning increases with longer profile lengths. • Shorter profile lengths are less stable but reduce the distance cuttings must travel to reach the annulus. • Shorter profiles provide more uniform loading, when drilling across transitions, than do longer profiles.
  31. 31. Nose Radii • A large nose radius provides higher surface area for better load distribution in hard and transitional drilling. • A small or sharp radius provides higher point loading on cutters and is best suited for soft, homogeneous formations.
  32. 32. Nose location • closer to the centerline of the bit provides a larger bit surface area and makes it possible to increase cutter density on the bit shoulders and suitable for soft, abrasive formations. • Nose locations closer to the bit gage provide more surface area on the bit face for better load distribution. This type of profile is best suited for harder formations.
  33. 33. Gage • Gage helps to stabilize the bit and maintain an in- gage wellbore. • Bit gage features can also provide stabilization to the bit and help to prevent undesirable operating properties such as bit whirl.
  34. 34. PROFILE TYPES • Flat profile, • Short parabolic profile, • Medium parabolic profile, • Long parabolic profile.
  35. 35. Flat profiles • Flat profiles with relatively sharper noses are used for drilling relatively softer, less abrasive formations. • Flat profiles are less aggressive than parabolic profiles.
  36. 36. Short Parabolic Profile • it provides an effective compromise between ROP, wear, and cleaning. • Surface area is not significantly increased, relative to cleaning and cooling. • Cutter density can be increased due to the increase in surface area, thus the ability to evenly distribute workloads and wear. • Note: generally as cutter density is increased, ROP will be reduced. • This reduction is offset by the more aggressive profile. • This bit profile does offer good resistance to impact loading of the cutters due to the blunt nose.
  37. 37. Short Parabolic Profile • The characteristic provides a large surface area on the nose to accommodate a higher cutter density. • As with the flat shallow cone profile, a greater number of cutters are available to take up impact loading as harder formations are encountered. • The short parabolic profile does not accomplish this task as well as the shallow cone profile, but becomes a good compromise if greater wear resistance is needed by increasing cutter density. • Typically this profile is used both for rotary and down-hole motor applications. • Have the sharpest noses of the three types of parabolic profiles. • This profile is not aggressive and is used for drilling softer, less abrasive formations.
  38. 38. Medium & Long Profile • Medium Parabolic Profile • Medium parabolic profiles with relatively wide noses are rather aggressive and are used to drill harder and more abrasive formations. • Medium parabolic profiles clean better than short parabolic profiles. • Long Profile • Long parabolic profiles with wide noses are used to drill harder and more abrasive formations,
  39. 39. CUTTER DENSITY • Redundancy of cutters will generally increase from the center to the outer radius of the bit, due to work of greater radial positions. • Increased cutter density lowers ROP but increases bit life. • Cleaning of a bit can be expected to fall as cutter density increases. • Decreasing number of cutters results with same WOB the unit load per cutter is increased & cutters are pushed deeper into the formation (greater depth of cut) finally ROP increases and higher torque results.
  40. 40. When cutter density is increased • Design engineers increase cutter density on a bit face with increased radial distance from bit centerline. • This is because, as a cutter’s radial position increases, it must travel farther and faster. For an equal depth of cut, a cutter on the outer radius travels farther at a higher linear velocity and must remove more rock per revolution than an inner cutter. • It is evident that outer cutters are required to do more work. • Outer cutters are subject to a greater wear rates than those near the centerline.
  41. 41. When cutter density is increased • In order to equalize work and the associated wear, the WOB supported by each cutter must be reduced as radial position increases. • To achieve uniform wear, cutters are shifted outward, radially to provide higher regional density in areas of higher wear and lower density in areas of lower wear. • Regional cutter density can be examined by rotating the cutter placement, through 360º onto a single plane, • Note: The graphic shows that cutter density as been increased, for the depicted bit, in the “outward” radial direction from bit centerline. • Note also that the planer cutter strike pattern inscribes an image of bit profile.
  42. 42. CUTTER EXPOSURE • The manner in which exposure is achieved depends on: – The depth to which a cutter is mounted in the bit body, – Cutter size, and / or, – Structures designed onto the bit to elevate the cutters above the face. • From the hydraulic aspect: – exposure and thus chip clearance should be small in order to maintain high fluid velocities that quickly remove cuttings and effectively cool the cutters. – exposure must be sufficiently large so that it does not impede chip generation and removal.
  43. 43. CUTTER EXPOSURE • In soft formations & larger chips, insufficient exposure cause the cuttings compact under the bit This impedance results in bit balling. • The use of fluid courses fed by a nozzle along the cutting edge, as in blade bits, has proven to be an effective arrangement. • Fluid along the cutting edge is maintained at a sufficient velocity through a constant area watercourse along the cutting edge or blade. • Junk slots, placed at the end of the watercourse or gage, allow fluids to be channeled from a high pressure area directly to a low-pressure area.
  44. 44. CUTTER EXPOSURE • Weight on bit can produce a significant effect on cleaning with regard to cutter exposure. • As WOB is increased, average differential pressure applied to the formation below the bit increase. • Thus, the use of maximum practical cutter exposure should be employed. Maximum cutter exposure: – Provides and maintains space for chip clearance, – Enables unimpeded fluid flow and velocity, and, – Assures best possible cleaning efficiency.
  45. 45. Cutter Exposure • Partial Cutter Exposure • When a portion of the cutter face is mounted within the bit body, it is said to be partially exposed. • This design exhibits excellent cutter impact and retention strength, but limits chip clearance in a way that can interfere with cuttings generation. Partially exposed cutters are best suited for applications in harder formations because generated cuttings volume is small. • Full Cutter Exposure • Full exposure requires that the entire cutter face be exposed to the formation. This provides a larger chip clearance that minimizes interference.
  46. 46. CUTTER ORIENTATION back rake & side rake • BACK RAKE ANGLE: • Back rake defines the aggressiveness of the cutter • Rake angles would be closer to zero in the bit center • As back rake angle is increased, the tendency of cuttings to stick to the bit face is reduced • greater back rake angles is suitable for Harder formations require to give durability to the cutting structure and reduce “chatter” or vibration but it reduces ROP
  47. 47. BACK RAKE ANGLE • TSP cutters generally have lower back rake than PDC cutters, in the order of 0º - 5º. This aggressiveness is possible because TSP cutters are thermally stable and are not, for the most part, subject to thermal degradation wear as are PDC cutters.
  48. 48. SIDE RAKE ANGLE • he angle between the cutter face and the radial plane of the bit • A mechanical cleaning action is the benefit of side rake • Cutters that incorporates side rake are • forced forward in both a radial and a tangential direction when the bit rotates • Typical side rake is in the 15º order of magnitude although the range is between 0º and 45º or even more.
  49. 49. PDC CUTTER DEVELOPMENT • manufactured layer of diamond, normally 0.5 to 1.2 millimeter thick. • The diamond layer is characterized by a randomly oriented, interconnected diamond crystal network with residual cobalt at the crystal interfaces. • PDC WEARING • PDC and TSP cutting elements are subject to three types of wear mechanisms: – Abrasive (including erosion) wear, – Impact wear, and, – Thermal Damage. • Each of these mechanisms is intensified at elevated temperatures because of reduced mechanical strength and increased thermal stresses.
  50. 50. ABRASIVE WEAR • volumetric wear from abrasion is proportional to the load and sliding distance at a particular speed. • • Abrasive wear occurs, through a process of impact shock and fatigue on the individual diamond grains. • In this case, the rate at which abrasion occurs is dependent upon the hardness differential between cutter and formation. • • In soft formations, this wear rate is very low; as formation hardness increases, wear rate also increases. • Thermal conditions in a cutter directly affect the abrasion resistance. • PDC cutters are considered thermally stable to 750°C and TSP cutters are thermally stable to 1200°C.
  51. 51. Thermal Damage • This results in a mismatch of the thermal expansion coefficient between the diamond / tungsten carbide interface, producing large compressive and tensile stresses. (350 to 700 Deg) • abrasive wear is the only wear mechanism occurring if cutter contact point temperature is maintained below 350°C • The effect of cutter velocity is seen on dull bits, in which outer radii cutters are significantly more worn than the inner cutters. This is due to the higher linear velocity of the cutters as radial position increases.
  52. 52. The depth of cut per revolution • F = ROP / RPM • if greater penetration rate is required, it is better to achieve it by increasing WOB rather than rotary speed. • Thermal degradation is the actual wear mechanism in PDC cutters.
  53. 53. THERMAL DEGRADATION • Constant contact with abrasive rock rapidly heats the cutting tip of the PDC cutters. The cobalt that fills the pore space within the diamond lattice has a much higher coefficient of thermal expansion than diamond. • In very hard, abrasive rocks the temperatures achieved at the diamond cutting edge /point can exceed 2350ºF; thereby, spontaneously reverting the diamond to graphite and immediate wear of the newly formed graphite. • At temperatures mentioned above, diamond, being carbon, combines chemically with various media being drilled, iron bearing minerals and silicates, for example.
  54. 54. CUTTING MECHANICS • Rock types: – Brittle – Semi-Brittle – Ductile • rock strength, is a function of rock composition and down-hole conditions: – Temperature – Pressure – Depth • Stresses Can be: – Tensile – Torsional – Compression • Strain (Deforming) Can be: – very little for Brittle – Elastic plastic for Ductile
  55. 55. CUTTING MECHANICS • PDC bits are primarily designed to drill by shearing. • The resultant force defines a plane of thrust for the cutter. • In shear stress the energy required to reach the plastic limit for rupture is significantly less than for compressive stress. • This result can be seen in the lower PDC bit weight required in comparison to milled tooth bits.
  56. 56. Substrate • Substrates are a tungsten carbide material • Generally, geometries that increase interface surface area improve bonding. Geometries also attempt to hold stresses at the bond to the lowest possible level.
  57. 57. The maximum thickness of a diamond layer is limited in two ways • Diamond to diamond bonding requires that cobalt be thoroughly diffused in the diamond grit. This diffusion becomes more difficult as diamond table thickness increases and diamond to diamond bonding becomes erratic. • • Chipping or flaking of the diamond table at the edges and corners. Cracking in diamond layer that can lead catastrophic failure of the diamond table and eventually even the substrate.
  58. 58. Diamond Table Thickness Ratio (DTTR) • DTTR =CTT / PTT
  59. 59. PDC Cutting Structures • Cutting structures must provide adequate bottom hole coverage to address formation hardness, abrasiveness, potential vibrations, and satisfy customer productive and economic needs.
  60. 60. PDC Cutting Structures 1. Single set cutting structures: A random spiral distribution of individual PDC cutters over the full face of a bit with one cutter in each radial position on the face. 2. Single set ribbed or bladed cutting structures: A multiplicity of ribs or blades with one PDC cutter in each radial position. 3. Plural set ribbed or bladed cutting structures: A multiplicity of ribs or blades more than one PDC cutter in each radial position on the bit face
  61. 61. SINGLE SET BLADED CUTTING STRUCTURES • This evolutionary stage of cutting structure design focused on visible change through its addition of blades and also through innovation in cutter placement • the design continues to be focused on bottom hole coverage rather than cutter performance and longevity. • Clockwise cutter distribution is called a forward spiral; counterclockwise distribution is a reverse spiral,
  62. 62. PLURAL SET BLADED CUTTING STRUCTURES • the current standard of cutting structure evolution. • In plural set designs, invisible features (such as force balancing) have the biggest influence on bit stability and cutter layout and distribution. • Plural set structures employ sets of cutters comprised of two or more cutters per set having identical radial positions.
  63. 63. OTHER CUTTING STRUCTURE ELEMENTS • Visible features include: – blade and cutter – Layout – gage geometry – low friction pad, etc. • Non-visible features: – force balancing – cutter distribution and layout, etc.
  64. 64. Nomenclatures
  65. 65. Nomenclatures
  66. 66. Nomenclatures Junk Slot Area
  67. 67. Nomenclatures Total face volume
  68. 68. Nomenclatures PDC BACKREAMING BACK-UP FACE CUTTERS
  69. 69. Nomenclatures Gage Protection Lo-Vibe or Anti Shock
  70. 70. DULL GRADING SYSTEM
  71. 71. DULL GRADING SYSTEM NO.1, NO.2
  72. 72. DULL GRADING SYSTEM NO.1, NO.2
  73. 73. Dull Characteristics
  74. 74. Location
  75. 75. Bearings/Seals & Amount Under-gage • Bearings/Seals: It will always be marked “X” for fixed cutter bits. • the amount the bit is under-gage is recorded to the nearest 1/16th of an inch
  76. 76. Reason Pulled

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(PART 1,2 & 3) 1. Drilling mechanisms 2. Bit classifications (fixed cutter and roller cone bits) 3. IADC code descriptions 4. Tri-cone bits life time 5. Geometrical analysis of roller cone bits • Fundamentals of bit design • Basics of cone geometry design • Oversize angle • Offset • Teeth and inserts • Additional design criteria: tooth to tooth and groove clearances and etc. • Cone-shell thickness • Bearings factors • Rock bit metallurgy • Heat treatment • Legs and cones material • Tungsten carbide materials • Legs and cones hard facing • Tungsten carbide grade selection for inserts • Bearings, seals and lubrication • Bearing shape • Bearing precisions and geometry • Seal systems and seal details • Dull grading system 6. Geometrical analysis of PDC bits • PDC materials and constructions • Matrix materials testing • Differs between matrix & steel body • Matrix body bits manufacturing • Steel body bits manufacturing • PDC bit design parameters: mechanical, hydraulic, rock properties • Weld strength of PDC bits and cutters • PDC cutter manufacturing process • Tsp cutter properties vs PDC • The influences of bit profile and profile elements • PDC forces • PDC bit stability • PDC bit steer-ability • Back rake • Side rake • Depth of cut • Cutter exposure • Cutter density • Thermal damage and degradation of cutters • Cutting mechanics • PDC cutter substrate and its thickness • Cutting structure elements • Single set bladed cutting structures • Plural set bladed cutting structures • Dull grading system 7. ROP management based on drilling parameters • WOB • Rpm • Sold content of mud • Mud weight • Cutter shape • Cutters geometry • Depth • Abnormal pressure • Drilling formation properties

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