STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

~~~
MWD and LWD 945
2. What is the pulse amplitude (pressure surge) for the various flowrates when
the puppet valve travels from 0.2 to 0.5 in.? At what position will we have
a half-height pulse?
3. 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.
4. The pulses are used to transmit deviation data from 0' to 90' with a 45,
22.5, 11.25, etc., sequence binary code of 10 bits. What is the transmission
accuracy? Give the binary number for 27.4'.
5. Assuming the pressure pulse travels with the sound velocity of the mud,
how long will it take to reach the rig floor in a 12,000-ft borehole? The
sound velocity in the mud is given by
Solution
v = (g, x B x 144/~)'/~
where v = sound velocity in ft/s
B = mud bulk modulus (3.3 x lo5 psi)
y = mud specific weight in lb/ft3
1.
Table 4-123
Typical Positive Pulse Amplitude Generated at Bottomhole
0.2 in. 0.5 in. Amplitude
400 gal/min 187 psi 35 psi 152 psi
500 gal/min 290 psi 55 psi 235 psi
600 gal/min 420 psi 79 psi 341 psi
2.
Table 4-1 24
Half-Height Stroke of the Valve
Amplltude
Half Height
400 gal/min 152 0.264 in.
500 gal/min 235
0.264 in.
600 gal/min 341 0.264 in.
3. AP motor: 429 psi
Bottomhole AP: 0.2 in., 719 psi
0.5 in., 484 psi
4. 27.4": 0100110111
Accuracy: 0.08789'
Average error: 0.043945'
5. Sound velocity: 4510 ft/s
Travel time: 2.67 s