Bit nozzle

Rheological Classification of Drilling Fluids 829. Flow Regimes 830. Principle of Additive Pressures 834. Friction Pressure Loss Calculations 836. Pressure Loss Through Bit Nozzles 839. 

Roller rock bit nozzle sizes are given in Table 4-98. The total pressure drop across a roller rock bit, Pj (psi), is [47]... 

Figure 4-143. Bit nozzle selection nomogram [47]. (Courtesy Harcourt Brace Co.)...

Bit Nozzle Sizes. The pressure loss through the bit must be 500 psi with a circulation flowrate of 348 gal/min with 11.6-lb/gal mud weight. The pressure loss through a roller rock bit with three nozzles is (see the section titled Drilling Bits and Downholes Tools )... 

Formula 4-180 will apply to the bit nozzle pressure loss. 

Equation 4-180 can be used to calculate the pressure change inside the drill collars by changing the cross-sectional area from bit nozzles only to bit nozzles plus the pulser nozzle. 

We are using a mud motor which rotates at 500 rpm and develops a useful power of 100 hp. Assuming a constant flowrate of 500 gal/min, no pressure loss in the bit nozzles and 80% motor efficiency, compute the total bottomhole assembly AP at 0.2- and 0.5-in. valve opening. 

A positive displacement mud motor is included in the downhole assembly between the bit and the MWD system. It develops a true power of 100 hp when the pulse nozzle is closed. What is the true power obtained when a 200-psi pulse is created The bit nozzle pressure loss will be neglected. Use... 

Same question taking into account the pressure drop in the bit nozzles with 3 X in. nozzles. Solving for AP in Equation 4-186 gives... 

On determining the optimal flowrate q (gal/min) and pressure drop across the bit nozzles p, the total flow area is calculated from... 

Annulus. From the drill pipe, the drilling fluid is jetted out of the bit nozzles and into the annulus. The jets are designed to remove drilled cuttings away from the drill bit. The pressure drop across the nozzles accounts for about 60% of the total frictional pressures losses during the circulation of the drilling fluid. About 90% of the pressure drop across the nozzles is due to the turbulence at the outlet, with only about 10% due to the flow through the nozzles. 

---