Mud Acoustics in Modern Drilling - Wave Propagation in Drilling, Well Logging and Reservoir Applications - page 291

waves originating from any direction in a completely transient three-
dimensional field. These authors then expressed their findings in terms of finite
difference operators in space and time; the resulting difference molecule
clusters, of course, translate directly into requirements for pressure transducer
spacing and data acquisition sampling time in the MWD context. In the late
1970s, this author applied the new ideas to computational unsteady transonic
flows at Boeing. In particular, special filtering schemes were used to eliminate
inward reflections at the boundaries of finite size solution domains, so that
smaller computational boxes requiring less computing resources could be used.
This specialized subject and its application to MWD signal processing is
discussed in the new topic Measurement While Drilling Signal Analysis,
Optimization and Design (Chin et al , 2014).

Mud pump

Desurger

Transducer #1

Transducer #3

Transducer #2

Collar

Annulus

Bi t

MWD

Mud motor/drill

Figure 5.8. Drillpipe system as an acoustical waveguide.

5.5.3.8 Telemetry design objectives.
The downhole and surface acoustic problems described above, plus
additional attenuation issues associated with viscous drilling muds, limit the
functionality of existing MWD mud pulse systems to extremely low data rates
by comparison to transmission rates achievable by satellite systems or simple
systems on computer networks. At the present time, MWD bit rates at best
approach ten bits per second, but in this author' s opinion, commercial claims are
questionable and somewhat exaggerated since the environmental conditions
under which these are achieved (e.g., depth, temperature, mud type) are never
stated. In any event, the end objective in telemetry design is high data rate with
low probability of bit error in the presence of noise. One quantitative measure
of transmission error is achieved by a dimensionless plot relating the
“probability of bit error” on the vertical axis to the “signal-to-noise (S/N) ratio”
on the horizontal, for different host telemetry schemes.