- Impact crushing
When the Reaming Bit is working at the bottom of the hole, the impact crushing effect of the gear teeth on the rock is the main method of the reamer bit to break the rock. When the drill bit is rotated, the teeth are impacted and pressed into the rock at a certain speed. This crushing method is similar to the characteristics of the static pressure crushing test. The tooth is pressed into the rock and requires sufficient specific pressure and contact time. Therefore, the axial load of the reamer bit on the rock includes static pressure and impact load. The drilling weight applied to the drill bit is the static pressure part; the impact load is caused by the longitudinal vibration of the drill bit when it rotates at the bottom of the well, which causes the drill bit-drill string system to continuously compress and expand, and the lower drill string transmits this periodic elastic deformation energy to Generated by the roller cone, this is the source of the impact pressure of the tooth when the drill bit breaks the rock. Increasing the impact pressure of the drill bit teeth on the formation can improve the efficiency of breaking rock.
- Sliding shear
In the rock with high plasticity, in addition to the impact crushing effect of the tooth on the rock at the bottom of the well, the tooth is also required to have a certain sliding effect on the formation, so that the tooth shears the rock to expand the rock crushing effect. This point It is very important when drilling in soft formations. The measures to make the roller wheel slip when rolling at the bottom of the well include over-top, compound cone and shift shaft.
(1) Super top. Overtop means that the cone tip of the cone exceeds the centerline of the drill bit. The distance that the top of the cone exceeds the center line is called the over-top distance. The greater the over-top distance, the greater the amount of sliding. The over-top generates slip in the tangential direction, cutting off the rock between the teeth on each ring gear of the cone.
(2) Compound cone. The compound cone causes the roller to slide in the tangential direction, and like the super-top, it also cuts the rock between the teeth on each ring gear of the roller.
(3) Shift axis. The shift axis means that the axis of the cone is translated by a distance relative to the axis of the bit. This distance is called the shift wheelbase. If the shift axis distance is larger, the sliding amount of the cone increases, and the shearing effect increases. The shift axis causes the teeth to slide axially and cut the rocks between the ring gears on the cone.
- Shearing effect of teeth
When the tooth is eaten into the rock under the action of axial pressure (drill pressure), the wedge-shaped surface of the tooth produces a horizontal shear force on the rock in contact with it. The rock is sheared and broken along the shear surface. Remove the broken rock by moving, which is the shearing effect of the tooth on the rock.