437/447/435

0.35~0.9

240~70

Very soft formations with low compressive strength and high drillability,such as clay,mudstone,chalk,gypsum,salt,soft limestone, etc.

517/527/515

0.35~1.0

220~60

Soft formations with low compressive strength and high drillability,such as mudstone,gypsum,salt,soft limestone, etc.

537/547/535

0.45~1.0

220~50

Soft to medium formations with low compressive strength, such as medium, soft shale, medium soft limestone, medium soft sandstone, medium formation with harder and abrasive interbeds, etc.

617/615

0.45~1.1

200~50

Medium hard formation with high compress strength, such as hard shale, limestone, sandstone, dolomite. etc

637/635

0.5~1.1

180~40

Hard formations with high compressive strength, such as sandstone, limestone, dolomite ,hard gypsum, marble, etc.

Note: The upper limits of WOB and RPM in above table should not be used simultaneously.