Mud Acoustics in Modern Drilling - Wave Propagation in Drilling, Well Logging and Reservoir Applications - page 294

5.6 Recent MWD Developments
Research programs expanding on our ideas have been introduced in several
leading organizations, among them China National Petroleum Corporation
(CNPC), China Oilfield Services Ltd (COSL), GE Oil & Gas, Sinopec and
others. Many subtle aspects of high-data-rate mud pulse telemetry have been
defined and solved. Developments are discussed in Measurement While
Drilling (MWD) Signal Analysis, Optimization and Design (Chin et al , 2014). It
turns out that poppet valves provide large signals but cannot be reciprocated
quickly to allow fast transmissions, while mud sirens, as shown in Figure 5.6,
allow rapid rotational speed changes to telemeter digital 0' s and 1' s, although
signal strengths are typically much lower than those of poppet valves for the
same flow rate. Figure 5.10 shows typical sirens designed for prototype testing.
Figure 5.10. Actual siren prototype sources.