Geology Reference
In-Depth Information
10.4.5 Design trade-offs.
Many engineers and managers have asked, “Is there one 'standard' design
we can recommend?” This innocuous question is not unreasonable. After all, in
the low-data-rate positive pulser world populated by 60-70 manufacturers
internationally, all designs (with minor exceptions) are generic “me too”
products. High-data-rate mud pulse telemetry, however, is different, because the
design options are numerous. And given that each set of options implies
significant engineering development, testing and manufacturing, and millions of
dollars in subsequent inventory, maintenance and repair costs, the choice is not
easily made. Here, we will summarize the options discussed in this topic - the
mechanical and electrical implications will be obvious. These are not given in
any particular order:
x Single siren, or multiple “sirens-in-series”?
x If multiple sirens, will all operate at one frequency from a single shaft, or at
different frequencies built on a more complicated design?
x Single-stage turbine, or multiple stages?
x Turbine versus batteries?
x Turbine, alternator, rechargeable battery option?
x Brushless DC or hydraulic motor drive for siren(s)?
x Self-spinning plus mechanical brake for modulation?
x Self-spinning plus magneto-rheological brake for modulation and motor
assist?
x FSK versus PSK?
x Top versus bottom mounted siren(s)?
x Collar versus probe-based design?
x Sensor types used, power demands, data density and logging speed?
x Surface signal process requirements?
x Downhole telemetry scheme, feedback and control requirements?
The above design options must be selected with care. Different companies
have different market needs, e.g., onshore versus offshore, number of sensors,
hole depth and attenuation constraints, power requirements and so on. Each
design represents a unique set of specifications. Development costs easily
exceed millions of dollars, and final designs are likely to remain in field use for
years. It is these practical but important objectives that our equations, wind
tunnels, test methods and advice address, and in the final analysis, the authors
hope that this topic has contributed meaningfully to solving these problems.
Search WWH ::
Custom Search