METHOD AND APPARATUS FOR SIGNAL BANDPASS SAMPLING IN MEASUREMENT-WHILE-DRILLING APPLICATIONS

摘要

A logging apparatus is provided for use in a wellbore for measuring an attribute of at least one of the wellbore and a surrounding formation, when coupled to a wellbore tubular expended in the wellbore. The logging apparatus includes a housing, at least one transmitter and at least one receiver. The transmitter is carried by the housing and is individually and selectively operable for producing electromagnetic interrogating signal at selected interrogation frequency for passage to the wellbore and surrounding formation. The receiver is carried by the housing in a selected position relative to the transmitter, and is tuned to receive electromagnetic signals at the interrogation frequency to the exclusion of other frequencies. A portion of at least one of the wellbore and surrounding formation has an attribute value which can be derived from at least one of amplitude attenuation of electromagnetic interrogating signal as determined from measurements of the electromagnetic interrogating signals taken through the receiver, and phase shift of electromagnetic interrogating signal as determined from measurements of electromagnetic signal taken through the receiver. The apparatus further includes means for sampling signals from the receiver or receivers at a sampling frequency which is less than the interrogation frequency. A controller member is provided for selectively energizing the transmitters and for selectively obtaining measurements of the electromagnetic interrogating signal with the receivers, and determining an accurate measure of the attribute value.