In the drilling process, there is another link that needs attention but may often be ignored. The selection of drill bits for geothermal drilling is an important part of drilling construction. During the drilling process, the drill bit is the main tool for breaking rocks.The wellbore is formed by the drill bit breaking the rock. The quality of a wellbore and the time it takes to form a wellbore are not only related to the characteristics of the rock being drilled and the performance of the drill bit itself, but also to the degree of mutual matching between the drill bit and the formation. Reasonable selection of drill bits plays an important role in increasing drilling speed and reducing overall drilling costs.
As the main tool in drilling engineering, drill bits can be divided into drag bits, tricone bits and diamond drill bits according to different structures. The main indicators for measuring drill bits are drill bit footage and mechanical penetration rate. The main basis for selecting the drill bit type is the mechanical and physical properties of the rock. Depending on the formation conditions, the diameters of commonly used drill bits generally include Φ444.50mm (17 1/2″), Φ311.15mm (12 1/4″), Φ215.90mm (8 1/2″), etc.
- PDC bit
PDC bit with cutting edges are called diamond drill bits. This drill bit is an integrated drill bit with no moving parts and a relatively simple structure. It has high strength, high wear resistance and impact resistance. It was one of the three major drilling technologies in the world in the 1980s. Field use has proven that when drilling in soft-medium hard formations, diamond drill bits have the advantages of fast speed, more footage, long life, stable operation, fewer downhole accidents, and good well quality. Diamond drill bits are not only used for a long time,
but can also be reused. The diamond drill bits returned to the factory for repair have the same effect as the diamond drill bits shipped from the factory, which can save a lot of drilling costs. Although the price of drill bits is high, they have a long working life. If they are properly selected, they can achieve better economic results.
2. Tricone Bit
Tricone bit is the most widely used type of drilling bit. When the tricone bit is working, the cutting teeth alternately contact the bottom of the well. The rock breaking torque is small, the contact area between the cutting teeth and the bottom of the well is small, the specific pressure is high, and it is easy to eat into the formation. The total length of the working edge is large, so wear is relatively reduced. Tricone bits are capable of adapting to a variety of formations from soft to hard. Tricone bits are suitable for drilling various formations and are currently widely used.
3. Drag Bit
Drag bit is the earliest drill bit used in rotary drilling.The drag bit has a simple structure,on the elliptical cylindrical shell with internal threads, a lateral working blade is welded, a thin flake-shaped carbide cutting tool is welded on the blade, and a thin flake-shaped and cylindrical carbide cutting tools is welded on the diameter-preserving working surface of the blade, and overlaying granular carbide. The drag bit has a simple structure, is easy to manufacture, and can drill soft formations quickly, but has a large torque during drilling and can easily damage drilling
