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1 aêáääáåö=ó råçéêëí~åçáåö=cìåç~ãéåí~äë ^êåé=iáëäéêìç

2 Agenda for drilling operations well planned operations and correctly selected rigs yield low cost drilling technically good drilling (good drill settings) and correctly selected drill steel yields low cost drilling straight hole drilling yields safe and low cost D&B operations

3 The most common drilling methods in use Uniaxial compressive strength, UCS (psi) 50,000-40,000-30,000-20,000-10,000 - Rotary (drag bits) Top Hammer (hydraulic or pneumatic) Down-the-Hole (pneumatic) Rotary (roller bits) - 120, ,000-80,000-60,000-40,000-20,000 Rotary pulldown (lbs) I I I I I I I I I I I I I I I " mm

4 Drilling consists of a working system of: bit drill string boom or mast mounted feed TH or DTH - hammer Rotary - thrust drill string rotation and stabilising systems powerpack automation package drilling control system(s) collaring position and feed alignment systems flushing (air, water or foam) dedusting equipment sampling device(s)

5 Case study Singrauli Coal Mine, India Rock Drill rig Tubes Bits Overburden sandstone P1524 / HL1560 / chain feed ST68 threads / Ø96mm / 2 x 12 SP 6 Retrac Bottom strike Shoulder strike Bit penetration rate 367 ft/ph = 6.13 ft/min Feed ratio 90 bar / 150 bar = 0.60 bit service life 18,620 shank service life 11,770 / 62,745 / 84,720 tube shank service life 4,465 / 16,585 / 36,680 Guide plate for tubes

6 Mechanics of percussive drilling PERCUSSION ROTATION FEED Percussive drilling Down-the-hole, DTH Stress waves transmitted directly through bit into rock Tophammer Stress wave energy transmitted through shank, rods, bit, and then into rock FLUSHING Basic functions CUTTINGS percussion feed rotation flushing foam flushing - reciprocating piston used to produce stress waves to power rock indentation - provide bit-rock contact at impact - provide bit impact indexing - cuttings removal from hole bottom - drill-hole wall stabilisation

7 How rock breaks by indentation F button F button 1 k 1 Energy used for rock breakage Energy lost as elastisc rock deformation u button u bit u button V cuttings Volume of cuttings u bit A button footprint

8 Chip formation by bit indentation and button indexing Direction of bit rotation Spray paint applied between bit impacts Button footprint Ø76mm / 3 Chipping around button footprint

9 How flushing works along the drill string Lift force F lift = 1/2 ρ air v air 2 A particle c v v air c v = Q / A = 0.3 for spheres Gravity G = ρ particle V particle g F lift G Return air velocity profile: - highest along hole wall - lowest along drill string

10 Flushing of drill-cuttings Insufficient air < 50 ft/s low bit penetration rates poor percussion dynamics interupt drilling to clean holes plugged bit flushing holes stuck drill steel circulating big chip wear Too much air > 100 ft/s excessive drill steel wear erosion of hole collar extra dust emissions increased fuel consumption Correction factors high density rock badly fractured rock (air lost in fractures - use water or foam to mud up hole walls) high altitude (low density air) large chips F lift G F lift G

11 Collar erosion stabilisation With water injection (or foam) cleaner collars no loose stones holes easy to charge No water injection loose stones can make holes unchargeable requiring redrilling problems increase with water saturation and thickness of prior sub-drill zone drill-hole deviation starts with poor collaring

12 Foam flushing an aid for drilling in caving material Time consumption for 2 holes tough hole normal hole Burst of inhole water Hole depth (ft) drilling uncoupling rock found with tube #5 tube #2 back to carousel hole ready - 22 min uncoupling hole ready - 1h 46min 0:00:00 0:14:24 0:28:48 0:43:12 0:57:36 1:12:00 1:26:24 1:40:48 1:55:12 Time (h:min:s)

13 Indentation with multiple chipping k 1 = 30 kn/mm for on-loading k 2 = kn/mm for off-loading γ = k 1 / k 2 = 0.27 chipping while on-loading chipping after off-loading Drop in button force indicates elastically stored energy in rock released by chipping

14 Energy transfer efficiency η related to rock chipping γ = k 1 / k No energy retained in rock after off-loading for γ = 1.0 (all elastic energy in rock returned to drill string) η = W rock / W incident = η impedance ( 1 γ) η impedance-max static bit tests percussive drilling Button resistance, k 1 / N (kn/mm)

15 How does this apply to practical drilling? γ = k 1 / k Hopeless drilling situation - no bit advance rate for γ = 1.0 Poor drilling situation - chipping after off-loading - potential for severely reduced drill steel life - correct choice of bit design and size? - sufficient bit regrinding (resharpening)? Good drilling situation - chipping during on-loading - potential to achieve max drill steel service life 0.06 static bit tests percussive drilling Button resistance, k 1 / N (kn/mm)

16 Energy transfer efficiency η related to impedance matching between bit and drill steel forces L piston 2 L piston Feed η impedance F bit k 1 1 k1 = indentation resistance of bit (kn/mm) u button

17 How do we study energy transfer issues? strain gauge measurements on rods/tubes while drilling on-line stress waves measurements by lasers numerical modelling => the tell-tale items we are looking for: incident wave Stress in rods, σ (MPa) bit mass 1 st tensile 1 st compressive 1 st γ reflection etc. Time, t (ms)

18 Energy transfer chain -video clip cases cavity perfect bit / rock match bit / rock gap i.e. underfeed bit face bottoming caused by: drilling with too high impact energy drilling with worn bits i.e. buttons with too low protrusion

19 Energy transmission efficiencies are divided into: energy transmission through the drill string - optimum when the cross section throughout the drill string is constant - length of stress wave - weight of bit energy transmission to rock - bit indentation resistance k 1 - bit-rock contact Compressive wave Tensile wave The most critical issue in controlling stress waves is to avoid high tensile reflection waves. Tensile stresses are transmitted through couplings by the thread surfaces - not through the bottom or shoulder contact as in the case for compressive waves. High surface stresses combined with micro-sliding result in high coupling temperatures and heavy wear of threads.

20 Feed force requirements From a drilling point of view From a mechanical point of view - to provide bit-rock contact - compensate piston motion - to provide rotation resistance - compensate linear momentum so as to keep threads tight of stress waves in rods Rod force Feed force MPa mm Stress waves in rod (MPa) Piston movement (mm) time [s]

21 Ranger DX700 and 800 / Pantera DP1500 2nd coupling temperature, F Drilling with disabled stabilizer 140 HL700 + OMR50 HL Poclain MS HL800T + Calzone MR450 Baseline for stabilizer drills =? UF v gauge R700 2 / Poclain / Ø76 mm / MF-T45 / Otava R700 / Ø76 mm / MF-T45 / Toijala R700 / Ø70-89 mm / MF-T45 / Croatia R800 2 / HL800T / Ø76 mm / MF-T45 / Savonlinna P1500 / Ø152 mm / MF-GT65 / Myllypuro P1500 / Ø127 mm / MF-GT60 / Baxter-Calif. v gauge = π d RPM / ( ) (ft/s) RPM for Ø76mm 3 RPM for Ø89mm 3½ RPM for Ø102mm RPM for Ø127mm 5 RPM for Ø152mm 6

22 Summary of drill settings -TH higher percussion pressure feed ratio ( Pfeed / Ppercussion ) higher rotation pressure higher bit RPM bits => penetration rates increase proportionally with percussion power => more drill steel breakage if => deviation increases with percussion energy => ratio controls average feed levels => UF reduces drill steel life (heats up threads) => OF increases deviation (especially bending) => tightens threads (open threads reduce drill steel life) => increases with OF => increases with drill string bending => increases gauge button wear (especially in abrasive rocks) => increases indexing of button footprints on drill hole bottom => straighter holes => higher thread temperatures => select bits with regard to penetration rates, hole straightness, stabile drilling (percussion dynamics), price, => bit condition / regrind intervals / damage to rock drill

23 Summary of TH percussion dynamics Piston strike energy Contact 2 Rotation Contact 3 - m bit F feed Contact 1 Contact 4 - gap Drilling control range σ (MPa) η / ( 1 γ) F bit 0-50 W rock = F du (ms) k 1 u button Percussive energy transfer Energy transfer efficiency Bit indentation work

24 Selecting drilling tools bit face and skirt design button shape, size and carbide grade shanks, rods, tubes, grinding equipment and its location

25 Guidelines for selecting cemented carbide grades avoid excessive button wear (rapid wearflat development) => select a more wear resistant carbide grade or drop RPM avoid button failures (due to snakeskin development or too aggressive button shapes) => select a less wear resistant or tougher carbide grade or spherical buttons => use shorter regrind intervals 48 DP65 PCD?

26 Selecting button shapes and cemented carbide grades S65 Spherical buttons DP65 R48 Robust ballistic buttons 48

27 Optimum bit / rod diameter relationship for TH Thread Diameter Diameter Optimum coupling bit size R32 44mm 32mm 51-2 T ¼ T ½ T T ½ GT GT /

28 Optimum bit / guide or pilot (lead) tube relationship for TH Thread Diameter Diameter Optimum coupling bit size T38 55mm 56mm 64-2½ T T ½ GT GT ½

29 Trendlines for bit service life 60,000 Rotary Drilling - Ø12½ / Std. 30,000 DTH * 18,000 Tophammer * 12,000 6,000 * Bit service life highly dependent on regrind intervals regard curve as toplimit 3,000 Bit Service Life (ft/bit) 1,800 1, Siever s J Value, SJ Limestone Dolomite Granite Quartzite

30 Relationship between SJ and VHNR rock surface hardness, VHNR rock surface hardness, SJ Rock with "zero" grain bonding 8.5mm 110 g 20 kg Weathered rock guide 200 revs chuck guide tungsten carbide bit Non-weathered rock 3 Sievers J Value, SJ Vickers Hardness Number Rock, VHNR

31 Bit regind intervals, bit service life and over-drilling 6,600 3,300 1,970 1, Over-drilled Premature button failures Bit regrind intervals (ft) d d d/3 d/ ,320 3,300 6,600 13,200 33,000 Bit service life (ft)

32 Example of drill steel followup for MF-T51 66,000 52,800 Rod and shank service life (ft) 33,000 19,800 13,200 6,600 3,300 1,980 1, Shanks MF-T51 rods ,3201,980 3,300 6,600 13,200 33,000 Bit service life (ft) Short holes Long holes

33 Jobsite KPI s for drill steel drill steel component life bit regrind intervals bit replacement diameters component discard analysis cost in $ per dr-ft or yd 3

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