H - Electricity – 04 – B
Patent
H - Electricity
04
B
329/11, 349/5
H04B 11/00 (2006.01) E21B 47/12 (2006.01) E21B 47/18 (2006.01) H03L 7/10 (2006.01) H04L 27/22 (2006.01)
Patent
CA 1126848
The disclosure is applicable for use in a logging- while-drilling apparatus for obtaining subsurface measure- ments during drilling in a fluid-filled borehole. Acoustic carrier waves are generated downhole in the borehole fluid and are PSK modulated in accordance with digital data representative of downhole measurements. The PSK modulation is obtained by momentarily unidirectionally either decreasing or increasing frequency of the acoustic carrier signal until either a desired phase lag (for a decrease in frequency) or phase lead (for an increase in frequency) is imparted to the acoustic carrier signal. An uphole receiving subsystem includes transducers for converting the modulated acoustic carrier waves to electronic signals and circuitry for de- modulating the electronic signals to recover the measurement information taken downhole. In accordance with an important feature of the invention, a filter is provided for selectively filtering the electronic signals before the demodulation thereof The filter is provided with a bandpass characteristic having a center frequency which is displaced from the nominal frequency in the direction of the unidirectional decrease or increase of frequency applied when originally modulating the acoustic carrier waves. The center frequency is preferably offset from the nominal carrier frequency by an amount which is a function of the bit rate of the digital information, preferably an amount equal to one-half the bit rate of the digital information. In the preferred embodiment of the invention, the bandpass characteristic of the filter means is skewed in the same direction as the offset.
322257
Schlumberger Technology Corporation
Smart & Biggar
LandOfFree
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