Several Design Options for PDC Rock Bits

PDC rock bit crown profile design

The crown profile design of PDC rock bits is based on three basic profiles: single cone, shallow cone and double cone. The single cone profile is mainly used in soft formations with large cutting teeth, which is easy to use hydraulic power and can provide high mechanical drilling speed in soft formations. It is suitable for low to medium density distribution and is suitable for drilling into extremely soft to medium soft formations. The shallow cone profile drill bit strengthens the load-bearing capacity of cutting teeth and has a longer life. It is suitable for low to high density distribution and is suitable for drilling into soft to medium hard formations. The double cone profile drill bit has a pointed nose and deep inner cone, suitable for medium to high density distribution and is suitable for drilling into medium to medium hard formations.

In response to the characteristics of the multi-layer formations in the Shengli Oilfield, the crown profile design is based on the principle of equal wear and equal cutting using PDC cutters, and is based on the fitting of three basic profile theoretical curves equations. Combining with the experience of drill bit design and analog use of drill bits, the shape of the crown profile suitable for drilling into multi-layer formations is determined, which is a shallow cone and double arc crown profile with a moderate length of the outer cone. The double arc profile section has the characteristics of effectively arranging cutting teeth on the drill bit surface and smoothly transitioning from the cutting teeth of the nose to the uniform diameter cutting teeth.

PDC rock bit cutting structure design

The design of the cutting structure of the drill bit includes factors such as the size and size of the cutting teeth, the cutting angle, the density of the teeth, and the method of tooth distribution. Considering that the main characteristics of conventional PDC rock bit damage are: chip shedding, fragmentation, erosion peeling and excessive wear, etc. In response to the main characteristics of conventional PDC rock bit damage and the characteristics of the applied formation, a cutting structure and composite cutting structure aimed at preventing early damage to the PDC composite sheet are designed. This structure uses the composite sheet as the main cutting element, and uses artificial thermally stable polycrystalline diamond blocks as the auxiliary cutting element, and adopts a certain tooth distribution method and density to achieve the purpose of crushing multi-layer formations.

PDC rock bit hydraulic structure design

The hydraulic structure of PDC rock bit is related to the working performance of the drill bit and the length of service life. During use, it is found that in addition to the impact of instantaneous load on PDC cutting teeth due to formation hardness, abrasiveness, and instantaneous load, another main factor is that the PDC rock bit is affected by hydraulic erosion of the matrix and cutting teeth, which affects the service life of the drill bit. Therefore, the design of the hydraulic structure of the drill bit is an important link in the design of the composite PDC rock bit. Based on the previous hydraulic structure and drill bit erosion characteristics of PDC rock bits.

PDC rock bit stability design

For the stability design of the new PDC rock bit, it mainly involves the following aspects:

• Force balance design. The PDC drill bits for sale are designed according to the principle of force balance, and the lateral unbalanced force is generally controlled within 5% of the drilling pressure. The force balance design can significantly reduce downhole vibration generated by the cutting action of the drill bit, increase the stability of the drill bit during operation, and thereby improve the service life of the drill bit. The design of the composite PDC rock bit continues to use the principle of force balance design, and the calculated lateral unbalanced force is only 2.1%.

• Design of spiral blade. The helical blade can reduce the rotary action of the drill bit. The use of a spiral blade structure disperses the cutting force of the cutting teeth generated when cutting the formation, reducing the contact stress between the spiral blade of the drill bit and the well wall, thereby reducing the number of times the drill bit rotates during use. The spiral blade can naturally present a certain lateral inclination angle, which is helpful for drilling fluid to carry rock fragments and clean the well bottom. In addition, the spiral patterned uniform diameter block can also increase the contact surface with the well wall and improve the stability of the drill bit.