During the drilling process of conventional PDC bit, based on the affection of the shearing action of PDC cutting teeth, most of rock debris obtained is mostly fine sand with very small size, which cannot be accurately geologically seized and evaluated.
The design concept of the core-while-drilling bit is to remove 1-2 teeth in the center of the normal PDC bit. During the normal drilling process, the core is continuously formed in the center area of the bit without affecting the cutting structure of the bit.
When the length of the small-sized core is continuously increased to the nominal length, it will contact a core destruction device and cut off the core using lateral force. There is a larger and deeper groove in the middle of the two front blades, and the small-sized core will move into the annulus through this hollow area. This hollow area is always kept open to prevent the risk of blockage of a drill bit.
Compared with the traditional PDC bits, the advantages of core-while-drilling bits are:
1. It can increase the mechanical drilling speed. The cutting surface of the common drill bit has the lowest drilling speed in the center position. The new drill bit avoids it.
2. It can improve the quality of cuttings and form micro-cores for geological analysis and evaluation without having to repeatedly drill, which saving costs.
3. The stability of the drill bit can be strengthened, and the central core column can effectively prevent the eddy and lateral vibration of the drill bit, so that the outer cone cutting teeth are prevented from being subjected to a large impact load, thereby improving the drill bit service life.