STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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946 Drilling and Well Completions
Example 8: Mud Pulse Telemetry-Negatlve
Pulse Calculations
The negative mud pulse system works with a nozzle which periodically opens
in the wall of the drill collar to lower the pressure in the pipe string. The
following data will be used:
Bit nozzles: 3 x $j or 3 x $ or 3 x 4$ in.
Pulse nozzle sizes: 0.3 or 0.4 or 0.5 in. diameter
Mud flowrates: 400 or 500 or 600 gal/min
Mud weight: 12 lb/gal
1. Compute the pressure change inside the drillpipe at bottom when the pulse
nozzle opens in each case. Give the optimal combinations for getting 200
to 250 psi pulses.
2. A 10-bit digital system uses the sequence 180, 90, 45, 22.5, etc., to transmit
the azimuth value. What is the accuracy of the transmission? Give the
binary numbers for S-23-E by excess, default and nearest.
3. 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
pulse nozzle diameter: 0.5 in.
mud flowrate: 400, 500, 600 gal/min
mud motor efficiency: 80%
4. Same question taking into account the pressure drop in the bit nozzles with
3 X $j in. nozzles. Solving for AP in Equation 4-186 gives
Q' y 144
AP =
2 g, C2 A2
where Q = flowrate in fts/s
A = nozzle area in in.2
C = nozzle factor (C = 1.0)
AP = pressure drop across the nozzles in psi
y = mud specific weight in lb/ft3
g, = 32.2 ft/s2
HP = eff x AP x Q/1714
Solution
1.
Table 4-125
Optimum Nozzles Combination for Generating
200 to 250 psi Pulses
Bit Nozzles
Pulse Nozzles
400 gal/min 15/32 in.
400 galimin 16/32 in.
500 gallmin 15/32 in.
500 gallmin 16/32 in.
600 gal/rnin 16/32 in.
0.4 in.
0.5 in.
0.3 in.
0.4 in.
0.3 in.