Diamond Bit Hydraulics
The horizontal fluid velocity is the key element in diamond bit life and bit performance. It can be determined using:
The fluid courses assist this by directing the drilling fluid across the bit to cool the diamonds and to remove the cuttings.
The diamond bit “Total Flow Area” consists of two components:
1. Fluid Course Area - is the area of all fluid courses on the bit. They are cast into the bit body.
2. Diamond Exposure Area - is the area between the bit face and formation, produced by the diamond exposure.
The desired TFA is calculated and designed into the bit by varying the diamond exposure, and the width and depth of the fluid courses. Another phenomenon which occurs with natural diamond bits is called hydraulic pump-off. The hydrodynamic pressure of the mud at the bit acts over the bit face area (between the cutting face of the bit and the formation) and tends to lift the bit off the bottom of the hole. For example, the pumpoff force on a 8-1/2 inch radial flow diamond bit (having a pressure drop of 900 psi) would be approximately 8600 pounds. It will require at least this much bit weight to keep the face of the bit in contact with the bottom of the hole.
