What Is Rock Drillability

How to choose suitable tricone bit,PDC bit or rock hole opener during your drilling?Rock drilliability is a very important factor.

Rock drillability refers to the ability of rock to resist pressure and breakage during drilling; it also indicates the efficiency of penetration. Therefore, rock drillability is a combination of various rock characteristics and is the main indicator for measuring the difficulty of rock drilling. Generally, the number of penetrations per unit time is used to indicate the level of drillability. According to this classification method, rock drillability is often divided into twelve levels.

Due to the different physical and mechanical properties of various rocks, they have different effects on drilling speed. In the actual drilling process, under certain technical conditions, the drilling speed of various rocks measured is generally referred to as rock drillability, that is, the difficulty of rock being broken by the drill bit.

The rock drillability classification during core drilling is as follows:

Level 1: Loose soil

Soft and loose---representative rocks are: secondary loess, secondary red soil, soft sandy soil without gravel and breccia, diatomaceous earth, and peat humus layer without plant roots. (Drillability: 7.50m/h, one-time drilling length: 2.80m/time).

Level 2: Softer and loose rock

Softer and looser---representative rocks are: loess layer, laterite layer, soft peat layer, clay and sandy soil containing 10%-20% gravel and crushed stone, soft kaolin, humus layer containing plant roots. (Drillability: 4.00m/h, one-time drilling length: 2.40m/time).

Level 3: Soft rock

Soft---representative rocks are: strongly weathered shale, slate, phyllite and schist, slightly cemented sand layer, sandy soil containing 20% ​​gravel and crushed stone, loess layer containing 20% ​​calcite, gypsum soil layer, marl, talc schist, shell limestone, lignite, bituminous coal. (Drillability: 2.45 m/h, one-time drill length: 2.00 m/time).

Level 4: Slightly soft rock

Slightly soft---representative rocks are: shale, sandy shale, oil shale, carbonaceous shale, calcareous shale, sandstone shale interlayer, denser marl, muddy sandstone. Massive limestone, dolomite, strongly weathered peridotite, pure peridotite, serpentinite and apatite, medium-hard coal seam, rock salt, crystalline gypsum, kaolin layer, volcanic marl, frozen water-bearing sand layer. (Drillability: 1.60 m/h, one-time drill length: 1.70 m/time).

Level 5: Slightly Hard Rock

Slightly Hard - Representative rocks are: pebbles, gravel and gravel layers, collapse layers, mudstone slate, sericite chlorite slate, phyllite and schist, fine-grained crystalline limestone, marble, softer sandstone, serpentinite, dunite, weathered amphibole porphyry and trachyte, hard bituminous coal, anthracite, frozen coarse-grained sand, gravel layers, frozen soil layers. (Drillability: 1.15 m/h, one-time drill length: 1.50 m/time).

Level 6-7: Medium Hard Rock

Medium Hard - Representative rocks are: chlorite, mica, sericite slate, phyllite, schist, slightly silicified limestone, calcite, epidote, calcareous cemented conglomerate, feldspar sandstone, quartz sandstone, quartz trachyte, amphibole porphyry. Diopside rock, gabbro, frozen gravel layer. (Drillability: 0.82 m/h, drilling length per drill: 1.30 m/time) Quartz, hornblende, mica, hematite slate, phyllite, schist, micro-silicified slate, phyllite, schist, feldspar quartz sandstone, quartz monzonite, micro-schistified albite porphyry, trachyte, hornblende porphyry, gravel, crushed stone layer, slightly weathered coarse-grained granite, syenite, porphyry, gabbro and other igneous rocks, siliceous limestone, flint limestone, etc. (Drillability: 0.57 m/h, drilling length per drill: 1.10 m/time).

Level 8-9: Hard rock

Hard rock---Representative rocks are: silicified sericite slate, phyllite, schist, gneiss, epidote rock, carbonate rock containing quartz, quartz barite rock, quartzite containing magnetite and hematite, calcareous cemented conglomerate, basalt, diabase, andesite, pyroxenite, quartz andesite porphyry, medium-grained crystalline sodium porphyry and amphibole porphyry, fine-grained siliceous cemented quartz sandstone and feldspar sandstone, containing large flint limestone, slightly weathered granite, granite gneiss, pegmatite, diorite, gabbro, etc. (Drillability: 0.38 m/h, one-time drilling length: 0.85 m/time).

Highly silicified slate, phyllite, limestone, sandstone; coarse-grained granite, granodiorite, granite gneiss, syenite, gabbro, trachyte; slightly weathered: quartz trachyte, pegmatite granite, limestone, silicified tuff, hornblende tuff, fine-grained quartzite, quartz apatite, pegmatite. (Drillability: 0.25 m/h, one-time drilling length: 0.65 m/time).

Level 10--Level 11: Hard rock

Hard rock---representative rocks are: fine-grained granite, granodiorite, granite gneiss, rhyolite, microcrystalline granite, quartz trachyte, quartz sodium porphyry, hard quartz pegmatite, flint rock. (Drillability: 0.15 m/h, one-time drilling length: 0.50 m/time).

Corundum, quartzite, jasper, massive quartz, the hardest iron hornfels, jasper-like silicified slate, flint. (Drillability: 0.09 m/h, one-time drill length: 0.32 m/time).

Level 12: Hardest Rock

Hardest Rock---Representative rocks are: unweathered extremely dense quartzite, jasper, hornfels, pure sodium pyroxene corundum, quartz, flint, jasper. (Drillability: 0.045 m/h, one-time drill length: 0.16 m/time).