Geology Reference
In-Depth Information
6
Signal Processor Design
and Additional Noise Models
The MWD signal processor must accommodate numerous noise sources,
where both type and relative contribution may vary with bottomhole assembly,
bit design, drilling mud, rock type, drilling rig, surface piping arrangement,
transmission frequency, and so on. It is important for MWD designers to
accurately characterize the noise environment through field and laboratory tests.
This chapter is not intended to provide an exhaustive treatment on noise and
filtering. Quite the opposite, we only introduce the reader to basic ideas,
directing him to detailed literature elsewhere. Only physical mechanisms
related to fluid and wave processes, the author's areas of specialty, are
developed from first principles. While we discuss noise components separately,
for the purposes of presentation, we emphasize that in the design of the signal
processor, filter operations are not commutative, that is, the process of applying
“A, then B” may not yield results identical to “B, then A.” Some
experimentation is therefore necessary, especially in determining the best
sequencing for our reflection filters and others.
Contents
1.
Desurger Distortion
2.
Downhole Drilling Noise (Positive Displacement Motors,
Turbodrills, Drillstring Vibrations)
3.
Attenuation Mechanisms
4.
Drillpipe Attenuation and Mudpump Reflection
5.
Applications to Negative Pulser Design in Fluid Flows and to
Elastic Wave Telemetry Analysis in Drillpipe Systems
6.
LMS Adaptive and Savitzky-Golay Smoothing Filters
7.
Low Pass Butterworth, Low Pass FFT and Notch Filters
8.
Typical Frequency Spectra and MWD Source Properties
153
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