... for oil well drilling.Main structure features:1. This series adopts non-isometry teeth placement in combination with optimized teeth ... Very soft with low compressive strength, such as soft marl, clay, unconsolidated sandstorm, salt, etc. Recommended Bit type: GHJ437, Drilling ... m.2, Soft with low comprssive strength, such as shale, clay, sadstne, soft limestone, etc. Recommended Bit type: GHJ517, ...