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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 steelyields low cost drilling

� straight hole drilling yields safe and low cost D&B operations

The most common drilling methods in use

Top Hammer(hydraulic or pneumatic)

Down-the -Hole(pneumatic)

Rotary(roller bits)

Rotary(drag bits)

- 120,000

- 100,000

- 80,000

- 60,000

- 40,000

- 20,000

50,000 -

40,000 -

30,000 -

20,000 -

10,000 -Uni

axia

l com

pres

sive

str

engt

h, U

CS

(ps

i)

Rot

ary

pulld

own

(lbs)

I I I I I I I I I I I I I I I1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 "25 51 76 102 127 152 178 203 229 254 279 305 330 356 381 mm

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)

Case study – Singrauli Coal Mine, India

■ Rock Overburden sandstone■ Drill rig P1524 / HL1560 / chain feed■ Tubes ST68 threads / Ø96mm / 2 x 12’ SP■ Bits 6” Retrac

■ 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’

Shoulder strike

Bottom strike

Guide plate for tubes

Mechanics of percussive drilling

Percussive drilling

Down-the-hole, DTHStress waves transmitted directly through bit into rock

TophammerStress wave energy transmitted through shank, rods, bit, and then into rock

Basic functions

percussion - reciprocating piston used to producestress waves to power rock indentation

feed - provide bit-rock contact at impact

rotation - provide bit impact indexing

flushing - cuttings removal from hole bottom

foam flushing - drill-hole wall stabilisation

FEED

PERCUSSION

CUTTINGS

FLUSHING

ROTATION

How rock breaks by indentation

ubutton

Fbutton

ubit

Vcuttings

Abutton footprint

Fbutton

ubutton

Volume of cuttings

Energy used for rock breakage

1

ubit

k1Energy lost as elastisc rock deformation

Chip formation by bit indentation and

button indexing

Spray paint applied between bit impacts

Chipping around button footprint

Button footprint

Ø76mm / 3”

Direction of bit rotation

How flushing works along the drill string

Lift force F lift = 1/2 · ρair · vair 2 · Aparticle · cv

vair = Q / A

cv = 0.3 for spheres

Gravity G = ρparticle · Vparticle · g

Flift

G

Return air velocity profile:- highest along hole wall- lowest along drill string

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 tomud up hole walls)

� high altitude(low density air)

���� large chips

Flift

G

Flift

G

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

Foam flushing – an aid for drilling in caving

material

Burst of inhole water

Time consumption for 2 holes

15

30

45

60

75

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)

Hol

e de

pth

(ft)

tough holenormal hole

drilling uncoupling

tube #2 back to carousel

rock found with tube #5

hole ready - 22 minhole ready -1h 46min

uncoupling

Indentation with multiple chipping

Drop in button force indicates elastically

stored energy in rock released by chipping

chipping while on-loading

chipping after off-loading

k1 = 30 kN/mm for on-loading

k2 = 112.5 kN/mm for off-loading

γ = k1 / k2 = 0.27

Energy transfer efficiency η related to

rock chipping

η = Wrock / Wincident

= ηimpedance · ( 1 – γ )

ηimpedance-max ≈ 0.90

No energy retained in rock after off-loading for γ = 1.0(all elastic energy in rock returned to drill strin g)

106 4020 10060

Button resistance, k 1 / N (kN/mm)

0.10

0.20

0.06

0.40

0.60

1.00

γ=

k1

/ k2

8

0.80

static bit testspercussive drilling

How does this apply to practical drilling?

“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

106 4020 10060

Button resistance, k 1 / N (kN/mm)

0.10

0.20

0.06

0.40

0.60

1.00

γ=

k1

/ k2

8

0.80

static bit testspercussive drilling

“Hopeless” drilling situation- no bit advance rate for γ = 1.0

Energy transfer efficiency η related to impedance matching between bit and drill steel forces

ubutton

Fbit

1

k1 = indentation resistance of bit (kN/mm)

ηηηη impedance

k1

Feed

2 · LpistonLpiston

How do we study energy transfer issues?

� strain gauge measurements on rods/tubes while drill ing

� on-line stress waves measurements by lasers

� numerical modelling

=> the tell-tale items we are looking for:

Time, t (ms)

Str

ess

in r

ods,

σ

(MP

a)

inci

dent

wav

e

bit m

ass

… etc.

1stte

nsile

1stco

mpr

essi

ve

1stγ

refle

ctio

n

Energy transfer chain

- video clip cases

cavity

bit face bottoming – caused by:

■ drilling with too high impact energy■ drilling with worn bits i.e. buttons with too low p rotrusion

bit / rock gap – i.e. underfeed

“perfect” bit / rock match

Energy transmission efficiencies are

divided into:

←←←← Tensile wave

Compressive wave →→→→���� 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

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 throughthe bottom or shoulder contact as in the case for c ompressive waves.

High surface stresses combined with micro-sliding r esult in high coupling temperaturesand heavy wear of threads.

Feed force requirements

From a drilling point of view From a mechanical poin t of view

- to provide bit-rock contact - compensate piston motion

- to provide rotation resistance - compensate linear momentumso as to keep threads tight of stress waves in rods

14.99 15 15.01 15.02 15.03 15.04 15.05 15.06 15.07 15.08-150

-100

-50

0

50

100

150

200

250

300

MP

a | m

m

time [s]

Feed forceRod force

Stress waves in rod (MPa)

Piston movement (mm)

Ranger DX700 and 800 / Pantera DP1500

vgauge (ft/s)

2nd

coup

ling

tem

pera

ture

, °F

1.0 1.2 1.4 1.5 1.7 1.9 2.1

100

140

180

210

250

285

UF

Drilling with disabled stabilizer

Baseline for stabilizer drills = ?

79 92 105 118 132 145 1586667 79 90 101 112 125 13556

RPM for Ø76mm – 3”

47 55 63 71 79 87 953939 46 53 59 66 72 7933

RPM for Ø89mm – 3½”

RPM for Ø127mm – 5”RPM for Ø152mm – 6”

0.85

HL700 + OMR50 HL700 +

Poclain MS 05

59 69 78 88 98 108 11849 RPM for Ø102mm – 4”

vgauge = ππππ d · RPM / ( 60·1000 )

R7002 / Poclain / Ø76 mm / MF-T45 / Otava

R700 / Ø76 mm / MF-T45 / Toijala

R700 / Ø70-89 mm / MF-T45 / Croatia

R8002 / HL800T / Ø76 mm / MF-T45 / Savonlinna

P1500 / Ø152 mm / MF-GT65 / Myllypuro

P1500 / Ø127 mm / MF-GT60 / Baxter-Calif.

70

HL800T + Calzone MR450

Summary of drill settings - TH

� higher percussion pressure => penetration rates inc rease proportionally with percussion power=> more drill steel breakage if …=> deviation increases with percussion energy

� feed ratio ( P feed / Ppercussion )=> ratio controls average feed levels=> UF reduces drill steel life (heats up threads)=> OF increases deviation (especially bending)

� higher rotation pressure => tightens threads (open threads reduce drill steel life)=> increases with OF=> increases with drill string bending

� higher bit RPM => increases gauge button wear (espe cially in abrasive rocks)=> increases indexing of button footprints on dril l hole bottom=> straighter holes=> higher thread temperatures

� bits => select bits with regard to penetration rates, h ole straightness,stabile drilling (percussion dynamics), price, …

=> bit condition / regrind intervals / damage to r ock drill

Summary of TH percussion dynamics

0 2 4 6 8 10 12 14 16 18 20-100

-50

0

50

100

150

200

(ms)

σ(M

Pa)

Percussive energy transfer

Bit indentation work

Energy transfer efficiency

Contact 1 Contact 4 - gap

Ffeed

Rotation

ubutton

Fbit

Contact 3 - m bit

ηηηη / / / / ( 1 1 1 1 −−−− γ )

k1

Wrock = ∫∫∫∫ F du

Drilling control range

Piston strike energy

Contact 2

Selecting drilling tools

� bit face and skirt design

� button shape, size and carbide grade

� shanks, rods, tubes, …

� grinding equipment and its location

Guidelines for selecting cemented carbide

grades

� avoid excessive button wear (rapid wearflat develop ment)=> select a more wear resistant carbide grade or d rop 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

PCD ?48 DP65

Selecting button shapes and cemented

carbide grades

R48

Robust ballistic buttons48

S65

Spherical buttonsDP65

Optimum bit / rod diameter

relationship for TH

Thread Diameter Diameter Optimumcoupling bit size

R32 ∅∅∅∅44mm ∅∅∅∅32mm ∅∅∅∅51-2”T35 ∅∅∅∅48 ∅∅∅∅39 ∅∅∅∅57-2¼”T38 ∅∅∅∅55 ∅∅∅∅39 ∅∅∅∅64-2½”T45 ∅∅∅∅63 ∅∅∅∅46 ∅∅∅∅76-3”T51 ∅∅∅∅71 ∅∅∅∅52 ∅∅∅∅89-3½”GT60 ∅∅∅∅82 ∅∅∅∅60 ∅∅∅∅92-3.62”GT60 ∅∅∅∅85 ∅∅∅∅60/64 ∅∅∅∅102-4”

Optimum bit / guide or pilot (lead) tube

relationship for TH

Thread Diameter Diameter Optimumcoupling bit size

T38 ∅∅∅∅55mm ∅∅∅∅56mm ∅∅∅∅64-2½”T45 ∅∅∅∅63 ∅∅∅∅65 ∅∅∅∅76-3”T51 ∅∅∅∅71 ∅∅∅∅76 ∅∅∅∅89-3½”GT60 ∅∅∅∅85 ∅∅∅∅87 ∅∅∅∅102-4”GT60 ∅∅∅∅85 ∅∅∅∅102 ∅∅∅∅115-4½”

Trendlines for bit service life

102 4 61 2004020 10060

3,000

6,000

1,800

1,200

600

300

12,000

18,000

30,000

60,000

Siever’s J Value, SJ

Bit

Ser

vice

Life

(ft/

bit)

Rotary Drilling - Ø12½” / Std.

DTH *

Tophammer *

* Bit service life highly dependenton regrind intervals – regardcurve as toplimit

Limestone

Dolomite

Granite

Quartzite

Relationship between SJ and VHNR

� rock surface hardness, VHNR

� rock surface hardness, SJ

Vickers Hardness Number Rock, VHNR

700500400300200100 1000 1500

Non-weatheredrock

Weathered rock

Rock with "zero"grain bonding

Sie

vers

J V

alue

, SJ

100

2

3

5

4

6

87

910

20

30

40

50

60

8070

90

200

300

400

500600

800900

1000

700

0.5

0.4

0.6

0.80.7

0.91

chuck

guidetungsten carbide bit

guide

200 revs

8.5mm 110g

20 kg

Bit regind intervals, bit service life

and over-drilling

33,0003,30033065 130 200

Bit service life (ft)

Bit

regr

ind

inte

rval

s (f

t)

6,600

3,300

7

33

330

13

26

20

660

1,320

130

65

660 1,320 6,600 13,200O

ver-

drill

ed

Premature button failures

d d

d/3 d/3

1,970

200

Example of drill steel followup for MF-T51

Shanks

MF-T51 rods

330

Bit service life (ft)

Rod

and

sha

nk s

ervi

ce li

fe (

ft)

165 3,3001,320 33,000660 6,600

3,300

330

33,000

Short holes

Long holes

6,600

13,200

66,000

13,2001,980

19,800

1,320

1,980

660

52,800

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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