Stories from the Field,Fundamental Questions and Solutions - Measurement While Drilling Signal Analysis, Optimization and Design - page 11

usually offered without detailed basis or description, e.g., the types of mud used
and the corresponding hole depths are rarely quoted.
From a business perspective, there is little incentive for existing oil service
companies to improve the technology. They monopolize the logging industry,
maintain millions of dollars in tool inventory, and understandably prefer the
status quo. Then again, high data rates are not easily achieved. Quadrupling a 3
bits/sec signal under a 12 Hz carrier wave, as we will find, involves much more
than running a 48 Hz carrier with all else unchanged. Moreover, there exist
valid theoretical considerations (via Joukowski's classic formula) that limit the
ultimate signal possible from sirens. Very clever mechanical designs for
positive pulsers have been proposed and tested in the past. Some offer
extremely strong signals, although they are not agile enough for high data rates.
But unfortunately, the lack of complementary telemetry schemes and surface
signal processing methods renders them hostage to strong reverberations and
signal distortions at desurgers.
Figure 1.1a. Prototype single-siren tool (assembled).
Figure 1.1b. Prototype single-siren tool (disassembled).
One would surmise that good “back of the envelope” planning, from a
systems engineering perspective underscoring the importance of both downhole
and surface components, is all that is needed, at least in a first pass. Acoustic
modeling in itself, while not trivial, is after all a well-developed science in many