| Table of classification of formation hardness and bit selection |
| Roller cone bit |
IADC code of diamond bit |
Formation description |
Rock type |
Compressive strength(Mpa) |
ROP(m/h) |
| IADC code |
| 111/124 |
M/S112~M/S223 |
Very soft:sticky soft formation with low compressive strength. |
Clay |
<25 |
>20 |
| Siltstone |
| sandstone |
| 116/137 |
M/S222~M/S323 |
Soft:soft formation with low compressive strength and high drillability. |
Clay rock |
25~50 |
10~20 |
| Marl |
| Lignite |
| sandstone |
| 417/527 |
M/S323~M/S433 |
Medium soft:soft to medium formation with low compressive strength and steak. |
Clay rock |
50~75 |
5~15 |
| Marl |
| Lignite |
| Sandstone |
| Siltstone |
| Anhydrite |
| Tuff |
| 517/537 |
M322~M443 |
Medium:medium to hard formation with high compressive strength and thin abrasive streak. |
Mudstone |
75~100 |
2~6 |
| Dark rock |
| shale |
| 537/617 |
M422~M444 |
Medium hard:hard and dense formation with high compressive strength and medium abrasiveness. |
Dark rock |
100~200 |
1.5~3 |
| Hard shale |
| Anhydrite |
| Sandstone |
| Dolomite |
| |
| 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 |
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