Why tricone drill bit are most widely used
Due to impact, crushing and shearing rock breaking when roller cone rotates, the contact area between cone and bottom hole is small, the specific pressure is high, the working torque is small, and the working blade has a large total length and can be suitable for rock of various kinds.
Tricone bits rely on the impact of the cone on the formation, crushing and sliding shear to crush the rock.
|Table of classification of formation hardness and bit selection|
|Roller cone bit IADC code||Formation description||Rock type||compresssive strength (Mpa)||ROP m/h||Recommended type of diamond bit|
|111/124||Very soft:sticky soft formation with low compressive strength||
|116/137||Soft:soft formation with low compressive strength and high drillability||
S/M1642 1652 1952
|417 / 527||Medium soft: soft to medium formation with low compressive strength and streak||
Clay rock Maril Lignite
S 1963 ,1652 1362
M 1953 1662 1375
|517/537||Medium: medium to hard formation with high compressive strength and thin abrassive streak||
M 1662 1363 1375
|537/617||Medium : hard and dense formation with high compressive strength and medium abrasiveness||