Grade | Protodyakonov Coefficient (f) | Representative Formations/Rocks | Recommended Drill Bits |
Grade 1 (Loose Soil) | 0.3~1.0 | Secondary loess, secondary red rock, soft sand without gravel/breccia, diatomite | PDC drag bit、 PDC reaming bit、 PDC combined guide bit |
Grade 2 (Loose Rock) | 1~2 | Yellow rock, red soil, peaty clay, sand soil, kaolin-type formations | PDC drag bit、 PDC reaming bit、 PDC combined guide bit |
Grade 3 (Lightly Soft Rock) | 2~4 | Strongly weathered shale/slate/grazing rock/schist/micro-cemented sand layer | PDC drag bit、 PDC reaming bit、 PDC combined guide bit |
Grade 4 (Slightly Soft Rock) | 4~6 | Shale, sandy shale, oil shale, carbonaceous shale, calcareous shale, sandy shale interlayer, argillaceous limestone | PDC drag bit、 PDC concave drill bit、PDC arc angle drill bit、PDC reaming bit、 PDC combined guide bit |
Grade 5 (Slightly Hard Rock) | 6~8 | Gravel layer, crushed stone layer, collapsed argillaceous slate, sericite-chlorite greenstone slate, schist, limestone, marble | PDC drag bit、 PDC concave drill bit、PDC arc angle drill bit、PDC reaming bit、 PDC combined guide bit |
Grades 6–7 (Medium-Hard Rock) | 8~12 | Chlorite, mica, slate, dry wood rock, schist, silicified limestone, calcite | PDC concave drill bit、PDC arc angle drill bit、PDC reaming bit、 PDC combined guide bit |
Grades 8–9 (Hard Rock) | 12~16 | Silicified mica rock, gneiss, basalt, diorite, pyroxenite, quartz Anshan porphyry | PDC concave drill bit、PDC arc angle drill bit、PDC reaming bit、 PDC combined guide bit、Tricone Drill Bit |
Grades 10–11 (Extremely Hard Rock) | 16~18 | Granite, granodiorite, gneiss, rhyolite, quartzite | PDC concave drill bit、PDC arc angle drill bit、PDC reaming bit、 Flat Matrix、 Tricone Drill Bit |
Grade 12 (Extremely Hard Rock) | 18~20+ | Quartzite, jasper, hornfels, corundum rock, quartz, flint, jasper | PDC reaming bit、 Flat Matrix、 Tricone Drill Bit |
