Structure and Rock Breaking Mechanism of PDC Bit

PDC bit is made of polycrystalline diamond cutting blocks, and then a certain number of cutting blocks are mounted (or sintered) on the bit body.

The cutting block is sintered into a whole by a thin layer of synthetic polycrystalline diamond (about 0.6-2.5mm) and a bottom layer of tungsten carbide. It has a flat cylindrical shape. It is called polycrystalline diamond composite sheet (composite sheet for short). The composite sheet and the cylindrical body are welded together to form a cutting element.

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1. The structure of PDC bit

According to different materials and manufacturing processes, the structure of PDC drill bits can be divided into two series: steel body PDC bit and matrix body PDC bit.

(1) Parabolic type: with a larger drill surface, more cutting blocks can be mounted to improve the wear resistance and footage of the drill.

(2) Double cone type: there are inner cone and outer cone to keep the bit stable. The outer cone surface is longer and can be inlaid with more cutting blocks. When drilling hard interlayers or hard formations, the top cutting block is easily damaged by impact.

(3) Short cone: it is good for drilling through hard interlayer. The surface area of the drill bit is small, so the hydraulic power is more concentrated and the cleaning is better.

2. Rock breaking mechanism of PDC bit

The cutting block of PDC drill bit is used to crush the rock by scraping and squeezing. The self-sharpening cutting block cuts into the formation under the action of weight on bit, and then moves forward to shear the rock under the action of torque. It makes full use of the low shear strength of rocks. When the PDC bit breaks the rock, there is no repeated cutting caused by the "holding effect" caused by the pressure difference when the cone bit teeth break the rock.