Bài giảng Well drilling engineering - Chapter 4: Drilling Bits - Drag Bits (Part 1) - Đỗ Quang Khánh

1 Well Drilling Engineering Drilling Bits - Drag Bits Dr. DO QUANG KHANH 2 Contents The Ideal Bit Drag Bits Fishtail Type Natural Diamond Polycrystalline Diamond Compact (PDC) Relative Costs of Bits 3 Read: ADE, Ch.5 (bits) 4 The purpose of Chapter 5 (ADE) is to introduce the student to the: Rotary Drill bits selection and operation of rotary drilling bits. 5 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 6 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 7 The Ideal Bit * 1. High drilling rate 2. Long life 3. Drill full-gauge, straight hole 4. Moderate cost * (Low cost per ft drilled) 8 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 9 Drag Bits Drag bits drill by physically “plowing” or “machining” cuttings from the bottom of the hole. 10 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. 11 Fishtail type drag bit 12 Natural Diamond Bits PDC Bits 13 Soft Formation Diamond bit Larger diamonds Fewer diamonds Pointed nose 14 Hard Formation Diamond bit Smaller diamonds More diamonds Flatter nose 15 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? 16 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 . 17 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 18 Top view of diamond bit 19 Side view of diamond bit 20 PDC bits Courtesy Smith Bits 21 PDC Cutter 22 23 PDC Bits Ref: 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 24 PDC Bits Parameters for effective use include weight on bit mud pressure flow rate rotational speed 25 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 26 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 27 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 28 PDC Bits By year 2000: PDC bits had control of about 1/3 of the worldwide drilling market The total PDC bit market had risen to $400 million per year U.S. bit manufacturers had a 2/3 share of this market 29 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 30 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 31 PDC Bits Factors that limit operating range and economics : Lower life from cutter fractures Slower ROP from bad cleaning Bit design, cont’d 32 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 33 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 34 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 35 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 PDC bit technology sometimes reinforces whirl Can cause PDC cutters to chip and break 36 PDC Bits Preventing Bit Whirl Cutter force balancing Bit asymmetry Gauge design Bit profile Cutter configuration Cutter layout 37 PDC Bits Applications PDC bits are used primarily in Deep and/or expensive wells Soft - medium hard formations 38 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 39 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 40 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 41 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 42 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.