Table of classification of formation hardness and bit selection

Roller cone bit

IADC code

IADC code of diamond bit

Formation description

Rock type

Compressive strength(Mpa)

ROP(m/h)

111/124

M/S112~M/S223

Very soft:sticky soft formation with low compressive strength.

Clay

Siltstone

sandstone

<25

>20

116/137

M/S222~M/S323

Soft:soft formation with low compressive strength and high drillability.

Clay rock

Marl

Lignite

sandstone

25~50

10~20

417/527

M/S323~M/S433

Medium soft:soft to medium formation with low compressive strength and steak.

Clay rock

Marl

Lignite

Sandstone

Siltstone

Anhydrite

Tuff

50~75

5~15

517/537

M322~M443

Medium:medium to hard formation with high compressive strength and thin abrasive streak.

Mudstone

Dark rock

shale

75~100

2~6

537/617

M422~M444

Medium hard:hard and dense formation with high compressive strength and medium abrasiveness.

Dark rock

Hard shale

Anhydrite

Sandstone

Dolomite

100~200

1.5~3

IADC CODE SELECTION

IADC  

WOB

RPM

Application

(KN/mm)

(r/min)

111/114/115

0.3-0.75

200-80

very soft formations with low compressive strength and high drill ability, like clay, mudstone, chalk

116/117

0.35-0.8

150-80

very soft formations with low compressive strength and high drill ability, like clay, mudstone, chalk

121

0.3-0.85

200-80

soft formations with low compressive strength and high drill ability, like mudstone, gypsum, salt, soft limestone

124/125

180-60

131

0.3-0.95

180-80

soft to medium formations with low compressive strength, like medium, soft shake, medium soft limestone, medium soft sandstone, medium formation with harder and abrasive interbeds

136/137

0.35-1.0

120-60

211/241

0.3-0.95

180-80

medium formations with high compressive strength, like medium, soft shake, hard gypsum, medium soft limestone, medium soft sandstone, soft formation with harder interbeds.

216/217

0.4-1.0

100-60

246/247

0.4-1.0

80-50

medium hard formation with high compressive strength, like hard shale, limestone, sandstone, dolomite

321

0.4-1.0

150-70

medium abrasive formations, like abrasive shale, limestone, sandstone, dolomite, hard gypsum, marble

324

0.4-1.0

120-50

437/447/435

0.35-0.9

240-70

very soft formations with low compressive strength and high drill ability, like clay, mudstone, chalk, gypsum, salt, soft limestone

517/527/515

0.35-1.0

220-60

soft formations with low compressive strength and high drill ability, like mudstone, gypsum, salt, soft limestone

537/547/535

0.45-1.0

220-50

soft to medium formations with low compressive strength, like medium, soft shake, medium soft limestone, medium soft sandstone, medium formation with harder and abrasive interbeds

617/615

0.45-1.1

200-50

medium hard formation with high compressive strength, like hard shale, limestone, sandstone, dolomite

637/635

0.5-1.1

180-40

hard formation with high compressive strength, like limestone, sandstone, dolomite, hard gypsum, marble

Note: Above limits of WOB and RRPM should not be used simultaneously