Method and apparatus for signal bandpass sampling in measurement-while-drilling applications

A logging apparatus for use in interrogating a borehole and surrounding formation, comprising:

• a housing;
• at least one transmitter antenna carried by said housing;
• at least one receiver antenna carried by said housing;
• at least one oscillator circuit, which is electrically coupled to said at least one transmitter antenna for selectively energizing said at least one transmitter antenna, which has at least one digital input and an analog output, and which provides an analog output at a particular interrogation frequency in response to a digital command at said at least one digital input;
• at least one controller which is electrically coupled to said at least one oscillator circuit through said at least one digital input and which is electrically coupled to said at least one receiver antenna;
• a reception circuit including at least one digital output for utilizing said at least one receiver antenna in measuring at least one attribute of at least one of (a) said borehole and (b) said surrounding formation and providing digital data to said at least one controller through said at least one digital output;
• said at least one controller being operable in a plurality of modes of operation, including:
• (1) a transmission mode of operation, wherein said at least one controller provides a particular digital command signal to said at least one digital input in response to program instructions, to produce an analog signal from said analog output of said at least one oscillator having a particular frequency which is associated with said particular command signal, for energizing said at least one transmitter to initiate propagation of an interrogating electromagnetic field, having an interrogation frequency, through said borehole and surrounding formation;
• and
• (2) a reception mode of operation, wherein said at least one controller samples measurements of at least one attribute of said interrogating electromagnetic field, made utilizing said at least one receiver antenna, at a sampling frequency which is less than said interrogation frequency.

A logging apparatus for use in a wellbore for determining an attribute of at least one of (a) said wellbore, and (b) a surrounding formation, when coupled to a wellbore tubular and suspended in said wellbore, comprising:

• a housing, including means for coupling said housing to said wellbore tubular;
• at least one transmitter carried by said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through said wellbore and said surrounding formation;
• at least one receiver, carried by said housing in a selected position relative to said at least one transmitter, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said at least one of (a) said wellbore, and (b) said surrounding formation has an attribute value which can be derived from at least one of (a) amplitude attenuation of said electromagnetic interrogating signal as determined from measurements of said electromagnetic interrogating signal taken through said at least one receiver, and (b) phase shift of said electromagnetic interrogating signal as determined from measurements of said electromagnetic interrogating signal taken through said at least one receiver;
• a sampling circuit for sampling signals from said at least one receiver by directly digitizing a signal detected by said at least one receiver at a sampling frequency which is less than said interrogation frequency;
• a controller member for (a) selectively energizing said at least one transmitter causing said electromagnetic interrogating signal to pass through said wellbore and said surrounding formation in a particular direction relative to said at least one receiver, (b) for selectively obtaining measurements of said electromagnetic interrogating signal from said at least one receiver with said means for sampling circuit, and (c) determining an accurate measure of said attribute value.

A logging apparatus for use in interrogating a borehole and surrounding formation, comprising:

• a housing;
• at least one transmitter antenna carried by said housing;
• at least one receiver antenna carried by said housing;
• at least one oscillator circuit, which is electrically coupled to said at least one transmitter antenna for selectively energizing said at least one transmitter antenna, which has at least one digital input and an analog output, and which provides an analog output at a particular interrogation frequency in response to a digital command at said at least one digital input;
• at least one controller which is electrically coupled to said at least one oscillator circuit through said at least one digital input and which is electrically coupled to said at least one receiver antenna;
• a reception circuit including at least one digital output for utilizing said at least one receiver antenna in measuring at least one attribute of at least one of (a) said borehole and (b) said surrounding formation and providing digital data to said at least one controller through said at least one digital output;
• said at least one controller being operable in a plurality of modes of operation, including:
• (1) a transmission mode of operation, wherein said at least one controller provides a particular digital command signal to said at least one digital input in response to program instructions, to produce an analog signal from said analog output of said at least one oscillator having a particular frequency which is associated with said particular command signal, for energizing said at least one transmitter to initiate propagation of an interrogating electromagnetic field, having an interrogation frequency, through said borehole and surrounding formation;
• and
• (2) a reception mode of operation, wherein said at least one controller samples measurements of at least one attribute of said interrogating electromagnetic field, made utilizing said at least one receiver antenna, by directly digitizing a signal detected by said at least one receiver antenna at a sampling frequency which is less than said interrogation frequency.

A logging apparatus for use in a wellbore for determining an attribute of at least one of (a) said wellbore, and (b) a surrounding formation, when said logging apparatus is conveyed into said wellbore, comprising:

• a housing;
• at least one transmitter carried by said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through said wellbore and said surrounding formation;
• at least one receiver, carried by said housing in a selected position relative to said at least one transmitter, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said at least one of (a) said wellbore, and (b) said surrounding formation has an attribute value which can be derived from at least one of (a) amplitude attenuation of said electromagnetic interrogating signal as determined from measurements of said electromagnetic interrogating signal taken through said at least one receiver, and (b) phase shift of said electromagnetic interrogating signal as determined from measurements of said electromagnetic interrogating signal taken through said at least one receiver;
• a sampling circuit for directly sampling signals from said at least one receiver without altering the frequency of the signals from said at least one receiver;
• a controller member for (a) selectively energizing said at least one transmitter causing said electromagnetic interrogating signal to pass through said wellbore and said surrounding formation in a particular direction relative to said at least one receiver, (b) for selectively obtaining measurements of said electromagnetic interrogating signal from said at least one receiver with said sampling circuit, and (c) determining a measure of said attribute value.

A method of logging a wellbore and determining an attribute of at least one of (a) said wellbore, and (b) a surrounding formation, when coupled to a wellbore tubular and suspended in said wellbore, comprising the method steps of:

• locating at least one transmitter in said wellbore, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through said wellbore and said surrounding formation;
• locating at least one receiver in said wellbore in a selected position relative to said at least one transmitter, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• selectively energizing said at least one transmitter causing said electromagnetic interrogating signal to pass through said wellbore and said surrounding formation in a particular direction relative to said at least one receiver,
• selectively obtaining measurements of said electromagnetic interrogating signal from said at least one receiver by sampling at a sampling frequency which is less than said interrogation frequency;
• and
• determining an accurate measure of said attribute value.

A logging apparatus for use in a wellbore for measuring an attribute of at least one of (a) said wellbore, and (b) a surrounding formation, when coupled to a wellbore tubular and suspended in said wellbore, comprising:

• a housing, including means for coupling said housing to said wellbore tubular;
• at least one transmitter carried by said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through said wellbore and said surrounding formation;
• at least one receiver, carried by said housing in a selected position relative to said at least one transmitter, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said at least one of (a) said wellbore, and (b) said surrounding formation has an attribute value which can be derived from at least one electrical signal attribute resulting from measurements of said electromagnetic interrogating signal taken through said at least one receiver, and (b) mapping of said electrical signal attribute to said attribute of at least one of (a) said wellbone, and (b) a surrounding formation;
• a sampling circuit for sampling signals from said at least one receiver at a frequency which is less than the selected interrogation frequency;
• a controller member for (a) selectively energizing said at least one transmitter causing said electromagnetic interrogating signal to pass through said wellbore and said surrounding formation in a particular direction relative to said at least one receiver, (b) for selectively obtaining measurements of said electromagnetic interrogating signal from said at least one receiver with said means for sampling, and (c) determining an accurate measure of said attribute value.

A logging apparatus for use in a wellbore for determining an attribute downhole, when the logging apparatus is conveyed in the wellbore, comprising:

• a tool body;
• a transmitter carried by the tool body for transmitting an electromagnetic interrogating signal at a selected interrogating frequency for passage into a formation surrounding the tool body;
• a receiver carried by the tool body for (a) receiving electromagnetic signals at the interrogating frequency from the formation which are responsive to the transmitted signals, and (b) providing signals corresponding to the signals received by the receiver from which the attribute can be derived;
• a sampling circuit for sampling the signals from the receiver at a sampling rate which is less than the Nyquist rate for the interrogating frequency;
• and
• a controller for determining the attribute from the sampled signals.

A logging apparatus for use in a wellbore for determining an attribute downhole, when the logging apparatus is conveyed in the wellbore, comprising:

• a tool body;
• at least one transmitter carried by the tool body, each transmitter adapted to produce an electromagnetic interrogating signal at a selected interrogating frequency for passage into a formation surrounding the tool body;
• a plurality of receivers, said receivers carried by the tool body at positions relative to the at least one transmitter;
• a circuit for sampling the signals from each of the receivers at a sampling rate which is less than the Nyquist rate for the interrogating frequency;
• and,
• a controller member for determining the attribute from the sampled signals.

A logging apparatus for use in a wellbore for determining an attribute downhole, when the logging apparatus is conveyed in the wellbore, comprising:

• a tool body;
• a transmitter carried by the tool body for transmitting an electromagnetic interrogating signal at a selected interrogating frequency for passage into a formation surrounding the tool body;
• a receiver carried by the tool body for receiving electromagnetic signals at the interrogating frequency from the formation which are responsive to the transmitted signals and providing signals corresponding to the received signals from which the attribute can be derived;
• a sampling circuit in the tool body, the sampling circuit receiving signals directly from the receiver and digitizing the received signals without altering the frequency of the received signals;
• and
• a controller circuit carried by the tool body, the controller circuit receiving the digitized signals from the sampling circuit, measuring a characteristic of the received signal from the receiver, which characteristic is selected from a group comprising phase, amplitude and attenuation, and determining therefrom the selected attribute.

A method of determining an attribute downhole by a logging tool when said downhole tool is conveyed into a wellbore, the logging tool having at least one transmitter for transmitting electromagnetic signals into a formation surrounding the wellbore and at least one receiver for receiving signals from the formation that are responsive to the transmitted signals, comprising:

• energizing the at least one transmitter to transmit the electromagnetic signals at a selected interrogating frequency into the formation;
• receiving signals from the formation by the at least one receiver;
• sampling the received signals at a sampling rate which is less than the Nyquist frequency associated with the interrogating frequency;
• and
• processing the sampled signals to determine a measure of the attribute.