Method and apparatus for logging-while-drilling with improved performance through cancellation of systemic errors through combination of signals, utilization of dedicated transmitter drivers, and utilization of selected reference signals

A logging apparatus for use in a wellbore for determining resistivity of a 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;
• first and second transmitters, spaced apart a selected distance on said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through portions of said formation which surround said wellbore;
• first and second receivers, spaced apart a selected distance on said housing in a selected position relative to said first and second transmitters, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said formation which is disposed about said wellbore between said first and second receivers has a resistivity value which can be derived from at least one of (a) amplitude attenuation of said electromagnetic interrogating signal directed between said first and second receivers as determined from measurements of said electromagnetic interrogating signal taken by said first and second receivers and (b) phase shift of said electromagnetic interrogating signal directed between said first and second receivers as determined from measurements of said electromagnetic interrogating signal taken by said first and second receivers;
• a controller member for alternately energizing said first and second transmitters in (a) a first sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said first receiver to said second receiver and (b) a second sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said second receiver to said first receiver, for selectively obtaining measurements of said electromagnetic interrogating signal with said first and second receivers, and for combining said measurements to eliminate by cancellation error components;
• a first drive circuit which is responsive to said controller member for energizing said first transmitter;
• a second drive circuit which is responsive to said controller member for energizing said second transmitter;
• wherein said first drive circuit is dedicated to said first transmitter and is located proximate said first transmitter and remote from said first and second receivers;
• wherein said second drive circuit is dedicated to said second transmitter and is located proximate said second transmitter and remote from said first and second receivers.

A logging apparatus for use in a wellbore for determining resistivity of a 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;
• first and second transmitters, spaced apart a selected distance on said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through portions of said formation which surround said wellbore;
• first and second receivers, spaced apart a selected distance on said housing in a selected position relative to said first and second transmitters, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said formation which is disposed about said wellbore between said first and second receivers has a resistivity value which can be derived from at least one of (a) amplitude attenuation of said electromagnetic interrogating signal directed between said first and second receivers as determined from measurements of said electromagnetic interrogating signal taken by said first and second receivers and (b) phase shift of said electromagnetic interrogating signal directed between said first and second receivers as determined from measurements of said electromagnetic interrogating signal taken by said first and second receivers;
• a controller member for alternately energizing said first and second transmitters in (a) a first sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said first receiver to said second receiver and (b) a second sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said second receiver to said first receiver, for selectively obtaining measurements of said electromagnetic interrogating signal with said first and second receivers, and for combining said measurements to eliminate by cancellation said system error components;
• a first drive circuit which is responsive to said controller member for energizing said first transmitter;
• a second drive circuit which is responsive to said controller member for energizing said second transmitter;
• wherein said first drive circuit is dedicated to said first transmitter and is located proximate said first transmitter and remote from said first and second receivers;
• wherein said second drive circuit is dedicated to said second transmitter and is located proximate said second transmitter and remote from said first and second receivers;
• and
• wherein a plurality of conductors extend through said housing for coupling said controller member, said first and second transmitters, said first and second drive circuits, and said first and second receivers, which carry at least one reference signal which at least in-part synchronizes operation of said controller member, said first and second transmitters, said first and second drive circuits, and said first and second receivers, said at least one reference signal having a frequency which is substantially different from said interrogation frequency of said electromagnetic interrogating signal.

A logging apparatus for use in a wellbore to measure an electrical parameter of a formation surrounding a wellbore, the logging apparatus comprising:

• a housing;
• first and second transmitting antenna means, each arranged around said housing means and spaced from each other;
• transmitter circuit means for alternately supplying an oscillating drive signal to said first and second transmitting antenna means, said oscillating electrical drive signal causing said first and second transmitting antenna means to radiate an electromagnetic wave signal that propagates through said formation;
• first and second series resonant receiving antenna means for producing first and second pick-up signals, the resonant frequency of said first and second receiving antenna means being in a region embracing the frequency of said oscillating drive signal;
• said logging apparatus includes a plurality of system error components which are manifest as (a) amplitude-effecting error components including transmitter amplitude output variation and receiver amplitude sensitivity variation, and (b) phase-effecting error components including transmitter phase variation and receiver phase variation;
• and
• sampled-data signal processing means responsive to the pick-up signals for producing a signal that is a function of said electrical parameter of said formation and which eliminates said system error components by combining selected pickup signals.

A measurement-while-drilling apparatus for measuring an electrical parameter of a formation surrounding a borehole, the measurement-while-drilling apparatus comprising:

• a tubular steel drill collar section;
• first and second transmitting antenna means, each arranged around said tubular steel drill collar section and axially spaced from each other;
• transmitter circuit means for alternately supplying an oscillating drive signal to said first and second transmitting antenna means, said oscillating drive signal causing said first and second transmitting antenna means to radiate an electromagnetic wave signal that propagates through said formation;
• first and second series resonant receiving antenna means for producing first and second pick-up signals, each of said first and second series resonant receiving antenna means being arranged around said tubular steel drill collar section at an axially spaced position between said first and second transmitting antenna means and each including antenna circuit means in which an induced alternating current is produced while said electromagnetic wave signal propagates through said formation, the resonant frequency of said antenna circuit means being in a region embracing the frequency of said oscillating drive signal, and means responsive to said induced alternating current for producing a respective one of said pick-up signals;
• said measurement-while-drilling apparatus includes a plurality of system error components which are manifest as (a) amplitude-effecting error components including transmitter amplitude output variation and receiver sensitivity variation, and (b) phase-effecting error components including transmitter phase variation and receiver phase variation;
• and
• sampled-data signals processing means responsive to said pick-up signals for combining pickup signals to eliminate said system error components for producing a signal that is representative of said electrical parameter of said formation but which is substantially unaffected by said system error components.

A method for measuring an electrical parameter of the formation surrounding a borehole, which comprises the method steps of:

• positioning in said borehole first and second series resonant single turn receiving antennae that are each tuned with a series connected capacitor to increase reception sensitivity at a predetermined frequency, each of said first and second series resonant single turn receiving antennae being coupled by a receiver cable to a receiver circuit;
• generating an oscillating electrical drive signal at said predetermined frequency;
• alternately coupling said oscillating electrical drive signal to one and then another of a pair of transmitters to cause an electromagnetic wave signal to propagate through said formation in first one direction and then another direction so that said electromagnetic wave signal induces said first and second receiving antenna to develop a first pair and then a second pair of pick-up signals, said first and second pick-up signals including error components attributable to at least one of:
• (1) transmitter amplitude output variation, (2) receiver sensitivity variation, (3) transmitter phase variation, and (4) receiver phase variation;
• processing said first pair of pick-up signals to produce a first sampled signal which includes said error components, and recording said first sampled signal;
• processing said second pair of pick-up signals to produce a second sampled signal which includes said error components;
• and
• processing the recorded first sampled signal and the second sampled signal by combining sampled signals to produce a signal that is a function of said electrical parameter of said formation but which is unaffected by said error components.

A logging apparatus for use in a wellbore, comprising:

• a housing;
• first and second transmitters, spaced apart a selected distance on said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through portions of said formation which surround said wellbore;
• first and second receivers, spaced apart a selected distance on said housing in a selected position relative to said first and second transmitters, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said formation which is disposed about said wellbore between said first and second receivers has a formation characteristic which is detectable from measurements of said electromagnetic interrogating signal taken by said first and second receivers;
• a controller member for alternately energizing said first and second transmitters in (a) a first sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said first receiver to said second receiver and (b) a second sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said second receiver to said first receiver, for selectively obtaining measurements of said electromagnetic interrogating signal with said first and second receivers, and for combining said measurements to eliminate by cancellation error components;
• a first drive circuit which is responsive to said controller member for energizing said first transmitter;
• a second drive circuit which is responsive to said controller member for energizing said second transmitter;
• wherein said first drive circuit is dedicated to said first transmitter and is located proximate said first transmitter and remote from said first and second receivers;
• wherein said second drive circuit is dedicated to said second transmitter and is located proximate said second transmitter and remote from said first and second receivers.

A logging apparatus for use in a wellbore for determining a selected formation characteristic of a 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;
• first and second transmitters, spaced apart a selected distance on said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through portions of said formation which surround said wellbore;
• first and second receivers, spaced apart a selected distance on said housing in a selected position relative to said first and second transmitters, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said formation which is disposed about said wellbore between said first and second receivers has a formation characteristic which is detectable from measurements of said electromagnetic interrogating signal taken by said first and second receivers;
• a controller member for alternately energizing said first and second transmitters in (a) a first sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said first receiver to said second receiver and (b) a second sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said second receiver to said first receiver, for selectively obtaining measurements of said electromagnetic interrogating signal with said first and second receivers, and for combining said measurements to eliminate by cancellation error components;
• a first drive circuit which is responsive to said controller member for energizing said first transmitter;
• a second drive circuit which is responsive to said controller member for energizing said second transmitter;
• wherein said first drive circuit is dedicated to said first transmitter and is located proximate said first transmitter and remote from said first and second receivers;
• wherein said second drive circuit is dedicated to said second transmitter and is located proximate said second transmitter and remote from said first and second receivers.

A logging apparatus for use in a wellbore, comprising:

• a housing;
• first and second transmitters, spaced apart a selected distance on said housing, each transmitter being individually and selectively actuable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through portions of said formation which surround said wellbore;
• first and second receivers, spaced apart a selected distance on said housing in a selected position relative to said first and second transmitters, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said formation which is disposed about said wellbore between said first and second receivers has a formation characteristic which can be determined from measurements of said electromagnetic interrogating signal taken by said first and second receivers;
• a controller member for alternately energizing said first and second transmitters in (a) a first sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said first receiver to said second receiver and (b) a second sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said second receiver to said first receiver, for selectively obtaining measurements of said electromagnetic interrogating signal with said first and second receivers, and for combining said measurements to eliminate by cancellation error components;
• a first drive circuit which is responsive to said controller member for energizing said first transmitter;
• a second drive circuit which is responsive to said controller member for energizing said second transmitter;
• and
• wherein a plurality of conductors extend through said housing for coupling said controller member, said first and second transmitters, said first and second driver circuits, and said first and second receivers, which carry at least one reference signal which at least in-part synchronizes operation of said controller member, said first and second transmitters, said first and second drive circuits, and said first and second receivers, said at least one reference signal having a frequency which is substantially different from said interrogation frequency of said electromagnetic interrogating signal.

A logging apparatus for use in a wellbore for determining an electrical parameter of a 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;
• first and second transmitters, spaced apart a selected distance on said housing, each transmitter being individually and selectively operable for producing an electromagnetic interrogating signal at a selected interrogation frequency for passage through portions of said formation which surround said wellbore;
• first and second receivers, spaced apart a selected distance on said housing in a selected position relative to said first and second transmitters, each receiver being tuned to receive electromagnetic signals at said interrogation frequency to the exclusion of other frequencies;
• wherein a portion of said formation which is disposed about said wellbore between said first and second receivers has an electrical parameter value which can be derived from at least one of (a) amplitude attenuation of said electromagnetic interrogating signal directed between said first and second receivers as determined from measurements of said electromagnetic interrogating signal taken by said first and second receivers and (b) phase shift of said electromagnetic interrogating signal directed between said first and second receivers as determined from measurements of said electromagnetic interrogating signal taken by said first and second receivers;
• a controller member for alternately energizing said first and second transmitters in (a) a first sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said first receiver to said second receiver and (b) a second sample mode of operation with said electromagnetic interrogating signal passing through said formation in a direction from said second receiver to said first receiver, for selectively obtaining measurements of said electromagnetic interrogating signal with said first and second receivers, and for combining said measurements to eliminate by cancellation error components;
• a first drive circuit which is responsive to said controller member for energizing said first transmitter;
• a second drive circuit which is responsive to said controller member for energizing said second transmitter;
• wherein a plurality of conductors extend through said housing for coupling said controller member, said first and second transmitters, said first and second drive circuits, and said first and second receivers, which carry at least one reference signal which at least in-part synchronizes operation of said controller member, said first and second transmitters, said first and second drive circuits, and said first and second receivers, said at least one reference signal having a frequency which is substantially different from said interrogation frequency of said electromagnetic interrogating signal;
• wherein said first and second receivers simultaneously provide a low impedance for magnetic fields and a high impedance for electrical fields to minimize susceptibility of said first and second receivers to undesirable electrostatic noise and thus minimize need for electrostatic shielding on said first and second receivers.

A logging apparatus for use in a wellbore which is surrounded by a formation, comprising:

• a housing;
• a plurality of transmitters located at selected axial positions along said housing;
• at least one driver for selectively energizing selected ones of said plurality of transmitters and causing electromagnetic radiation to propagate through portions of said formation;
• a plurality of receivers located at selected axial positions along said housing for detecting at least one characteristic of said electromagnetic radiation;
• processor means for determining at least one formation property from a plurality of readings, taken with said plurality of receivers, of said at least one characteristic of said electromagnetic radiation;
• wherein radial penetration of said electromagnetic radiation depends at least in-part upon a propagation path length as defined between selected transmitters and receivers;
• and
• wherein said plurality of transmitters and said plurality of receivers include at least one formation interrogation subsystem including first and second receivers spaced apart a selected distance on said housing in a position intermediate first and second transmitters, with said first and second receivers and said first and second transmitters being substantially symmetrically positioned.