Siren Design and Evaluation in Mud Flow Loops and Wind Tunnels - Measurement While Drilling Signal Analysis, Optimization and Design - page 265

9.5.1 Real-world flow loops.
A number of long mud flow loops have been built by various organizations
for MWD telemetry testing. Many are proprietary, but perhaps the best known
is the 9,460 feet loop at Louisiana State University. This facility is described in
“MWD Mud Pulse Telemetry System,” by W.R. Gardner, Gas Research
Institute Report GRI-02/0019, April 2002, and also, “MWD Transmission Data
Rates Can be Optimized,” by Desbrandes, R., Bourgoyne, A.T., and Carter, J.A.,
Petroleum Engineer International, June 1987, pp. 46-50. The information
quoted here is publicly available.
Figure 9.18. Lousiana State University 9,460 feet flow loop.
As shown in Figure 9.18, the buried loop overlaps twice, with each side of
the square layout measuring about 1,400 ft. Despite the apparent simplicity,
time domain results needed to understand downhole and surface reflection
physics can be difficult to interpret. For example, the PEI paper states that
drillpipe used for the main loop has an ID of 3.64 inch. Discharge from the
pulser, however, is arranged through a return line consisting of 300 feet of 2
inch pipe, so that a large area mismatch factor of 3.3 is found - the flowloop, in
this sense, resembles a telescoping waveguide that may amplify or reduce
incident signals depending on wavelength. A downstream valve is also used to
control pressure. In addition, fluid is discharged into a open reservoir, as
opposed to a semi-infinite annulus that supports wave propagation. Thus, the
reflections and time domain waveforms obtained bear no resemblance to those
encountered downhole and cannot be used to study echo cancellation and wave
interference methods. The six-segment acoustic waveguide model derived and