Carrier tracking apparatus and method for a logging-while-drilling system
A logging-while-drilling apparatus for obtaining subsurface measurements during drilling in a fluid-filled borehole and for communicating the measurements to the surface of the earth comprises: a downhole sensing and transmitting subsystem including means mountable on a drill string for obtaining measurement information; means for generating acoustic carrier waves at a nominal frequency in the borehole fluid; means for psk modulating the generated acoustic carrier waves in accordance with digital data representative of said measurements by momentarily unidirectionally either decreasing or increasing the frequency of said acoustic carrier signal; and an uphole receiving subsystem including transducer means for converting the modulated acoustic carrier waves to an input electronic signal; and a carrier tracking loop circuit which includes a controlled oscillator having a control terminal, the frequency of said oscillator being determined by a signal applied to said control terminal; comparator means for generating a control signal by comparing the phase of a signal derived from said input signal to the phase of a signal derived from the output of said controlled oscillator; means for applying said control signal to the control terminal of said oscillator; and means responsive to transitions in said input signal for compensating the signal applied to said control terminal to account for the difference between the nominal frequency of said carrier and the average frequency of the input signal which results from the unidirectional nature of the carrier modulation; and means for recovering the digital data by demodulating said input signal with a signal derived from the output of said controlled oscillator.
- Assignee:
- Sangamo Weston Inc
- Patent Number(s):
- US 4215427
- OSTI ID:
- 7090612
- Resource Relation:
- Patent File Date: Filed date 27 Feb 1978
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
03 NATURAL GAS
15 GEOTHERMAL ENERGY
MWD SYSTEMS
DIGITAL SYSTEMS
WELL LOGGING
BOREHOLES
COMPARATOR CIRCUITS
ELECTRIC POTENTIAL
FREQUENCY CONTROL
MODULATION
OSCILLATORS
PULSE GENERATORS
REMOTE SENSING
SIGNALS
SOUND WAVES
TRANSDUCERS
CAVITIES
ELECTRONIC CIRCUITS
ELECTRONIC EQUIPMENT
EQUIPMENT
FUNCTION GENERATORS
020300* - Petroleum- Drilling & Production
030300 - Natural Gas- Drilling
Production
& Processing
150900 - Geothermal Engineering