Automatic mud pulse telemetry band selection
A method for automatically selecting a frequency band for transmission of a mud pulse telemetry signal includes transforming acquired transducer measurements from a time domain to a frequency domain to obtain a spectrum of measurements. The spectrum of measurements is processed to compute a total energy in band and a standard deviation of the power spectral density in band for a plurality of frequency bands. A ratio of the total energy in band to the standard deviation acquiring a plurality of transducer measurements of transmitted mud pulse telemetry pressure pulses and of the power spectral density in band is computed for at least two of the plurality of frequency bands. The frequency band having the highest computed ratio is selected and automatically downlinked to a downhole mud pulse telemetry transmitter.
1. A method for automatically selecting a frequency band for transmission of a mud pulse telemetry signal, the method comprising:
(a) acquiring a plurality of transducer measurements of transmitted mud pulse telemetry pressure pulses;
(b) transforming the transducer measurements acquired in (a) from a time domain to a frequency domain to obtain a spectrum of measurements;
(c) processing the spectrum of measurements to compute a total energy in band and a standard deviation of the power spectral density in band for a plurality of frequency bands;
(d) computing a ratio of the total energy in band to the standard deviation of the power spectral density in band for at least two of the plurality of frequency bands;
(e) selecting the frequency band having the highest ratio computed in (d); and
(f) automatically downlinking the frequency band selected in (e) to a downhole mud pulse telemetry transmitter.
2. The method of claim 1 wherein the transducer measurements are transformed in (b) using a fast Fourier transform.
3. The method of claim 1 , wherein the total energy in band and the standard deviation of the power spectral density in band are computed using the following mathematical equations:
E
(
fc
,
BW
)
=
∑
k
=
fc
-
BW
2
fc
+
BW
2
S
(
k
)
2
Sdev
(
fc
,
BW
)
=
1
BW
∑
k
=
fc
-
BW
2
fc
+
BW
2
(
PSD
(
k
)
-
PSD
(
k
)
_
)
2
wherein E(fc, BW) represents the total energy in band, Sdev(fc, BW) represents the standard deviation of the power spectral density in band, fc represents a center frequency of the frequency band, BW represents a bandwidth of the frequency band, S(k) represents a magnitude of the spectrum at each incremental frequency, and PSD(k) represents a magnitude squared at each incremental frequency.
4. The method of claim 1 , wherein (c) and (d) in combination comprise:
(i) processing the spectrum of measurements to compute the total energy in band and the standard deviation of the power spectral density in band for the plurality of frequency bands;
(ii) discarding frequency bands in which the total energy in band is less than a threshold; and
(iii) computing a ratio of the total energy in band to the standard deviation of the power spectral density in band for the frequency bands not discarded in (ii).
5. The method of claim 4 , wherein the threshold is ten times a smallest energy in band computed (i).
6. The method of claim 1 , wherein (c) and (d) in combination comprise:
(i) processing the spectrum of measurements to compute the total energy in band and the standard deviation of the power spectral density in band for the plurality of frequency bands;
(ii) processing the total energy in band and a center frequency of the frequency band to compute a weighted energy in band; and
(iii) computing a ratio of the weighted energy in band to the standard deviation of the power spectral density in band for the frequency bands not discarded in (ii).
7. The method of claim 6 , wherein the processing in (ii) assigns more weight to the total energy in band in higher frequency bands.
8. The method of claim 6 , wherein the total energy in band is weighted by a factor equal to: √{square root over (1+fc 2 )}, where fc represents the center frequency.
9. The method of claim 1 , wherein (c) and (d) in combination comprise:
(i) processing the spectrum of measurements to compute the total energy in band and the standard deviation of the power spectral density in band for the plurality of frequency bands;
(ii) discarding frequency bands in which the total energy in band is less than a threshold;
(iii) processing the total energy in band and a center frequency of the frequency band to compute a weighted energy in band; and
(iv) computing a ratio of the weighted energy in band to the standard deviation of the power spectral density in band for the frequency bands not discarded in (ii).