Abstract: A method for performing a formation physical action includes: transmitting a first time-domain transient electromagnetic (EM) signal into a borehole and the formation using a downhole EM wave propagation tool, the first EM signal having frequency domain components in a range of at least 1 MHz to 1 GHz; receiving a second time-domain transient EM signal due to the transmitting of the first EM signal, the second EM signal having frequency domain components in the range of at least 1 MHz to 1 GHz; calculating attenuation and phase shift S-parameters as a function of frequency using the first and second EM signals; assigning to the formation at least one of a resistivity value and a permittivity value of a reference that matches or is within a selected range of the attenuation and phase shift S-parameters; and performing the physical action using the at least one of the resistivity value and the permittivity value.

Abstract: Systems, devices, and methods for evaluating an earth formation. Method embodiments may include conveying a carrier in a borehole, the carrier including a conducting tubular having a plurality of transmitters and a receiver non-collocated with the plurality of transmitters; inducing a first current in the earth formation using a first transmitter of the plurality of transmitters; measuring with the receiver a first time-dependent transient electromagnetic (TEM) signal induced by the formation responsive to the first current; inducing a second current in the earth formation using a second transmitter of the plurality of transmitters; measuring with the receiver a second TEM signal induced by the formation responsive to the second current; and using at least one processor to estimate a value of a resistivity property of the earth formation using a bucked signal derived from the first time-dependent TEM signal, the second time-dependent TEM signal, and a bucking coefficient K(t).

Abstract: A method for performing a formation physical action includes: transmitting a first time-domain transient electromagnetic (EM) signal into a borehole and the formation using a downhole EM wave propagation tool, the first EM signal having frequency domain components in a range of at least 1 MHz to 1 GHz; receiving a second time-domain transient EM signal due to the transmitting of the first EM signal, the second EM signal having frequency domain components in the range of at least 1 MHz to 1 GHz; calculating attenuation and phase shift S-parameters as a function of frequency using the first and second EM signals; assigning to the formation at least one of a resistivity value and a permittivity value of a reference that matches or is within a selected range of the attenuation and phase shift S-parameters; and performing the physical action using the at least one of the resistivity value and the permittivity value.

Abstract: Systems, devices, and methods for evaluating an earth formation. Apparatus include an electrically conducting tubular; at least one transmitter configured to propagate an electromagnetic field in the earth formation; and at least one receiver configured to receive an electromagnetic signal resulting from interaction of an electromagnetic field with said earth formation. The at least one transmitter and at least one receiver may employ antenna assemblies comprising: a recess in the conducting tubular defined by at least one radially extending surface substantially perpendicular to a longitudinal axis of the conducting tubular and non-radially extending surfaces; an antenna in the recess; and conductive shielding, the conductive shielding having a conductivity significantly more than a conductivity of the conducting tubular and covering the whole of each of the plurality of radially extending surfaces.

Abstract: A method for estimating a property of an earth formation penetrated by a borehole, the method comprising generating a first transient electromagnetic fields with a transmitter on a carrier located outside of the borehole and receiving associated signals, calculating a bucking coefficient using the measured signals, conveying the carrier through a borehole, generating a second transient electromagnetic field and receiving associated signals, calculating, a bucked signal using the bucking coefficient and the downhole signals, calculating synthetic formation signals, calculating synthetic formations signals by applying a Duhamel's integral to the measured signals and the synthetic formation signals, calculating a synthetic bucked signal, and performing an inversion of a formation model to estimate a property of the formation such that an inverted synthetic bucked signal and an inverted bucked signal coincide within a predetermined range.

Abstract: A method for imaging an earth formation includes estimating an apparent resistivity (AR) value and an apparent distance to a bedding plane (AD2B) value for each of a plurality of samples derived from measurements of a time-dependent transient electromagnetic signal, estimating an inversion-based resistivity value (IB-R) and an inversion-based distance to a bedding plane (IB-D2B) value at a first sample of each consecutive depth interval, wherein each depth interval includes a plurality of consecutive samples, and determining a difference between apparent values and the corresponding inversion-based values. The method further includes generating an image of the earth formation using the AR and AD2B values for the entire interval if the difference is less than a threshold value and generating an image of the earth formation using IB-R and IB-D2B values for the entire interval if the difference is greater than the threshold value.

Abstract: Methods, systems, and devices for evaluating an earth formation. Methods may include conveying the carrier into a formation borehole; and using measure electrodes, in one mode of measurement, to make current measurements by applying a voltage to each measure electrode in a first set of sensor arrays while making first current measurements; and applying another high frequency voltage to each measure electrode in a second set of sensor arrays while making second current measurements. Optionally, methods include using the measure electrodes, in another mode of measurement, to make further resistivity measurements by applying a voltage to each measure electrode in both sets of sensor arrays while making third current measurements. Methods include combining first current measurements, second current measurements, and third current measurements to simulate a virtual impedance for each measure electrode. Optionally, any two consecutive sensor arrays around the circumference of the tool body are in different sets.

Abstract: Systems, devices, and methods for evaluating an earth formation. Apparatus include an electrically conducting tubular; at least one transmitter configured to propagate an electromagnetic field in the earth formation; and at least one receiver configured to receive an electromagnetic signal resulting from interaction of an electromagnetic field with said earth formation. The at least one transmitter and at least one receiver may employ antenna assemblies comprising: a recess in the conducting tubular defined by at least one radially extending surface substantially perpendicular to a longitudinal axis of the conducting tubular and non-radially extending surfaces; an antenna in the recess; and conductive shielding, the conductive shielding having a conductivity significantly more than a conductivity of the conducting tubular and covering the whole of each of the plurality of radially extending surfaces.

Abstract: Methods and apparatus configured to evaluate a volume of interest of an earth formation intersected by a borehole. Apparatus comprise a transceiver electrode on the tool body configured to provide electrical current to the earth formation; a return electrode configured to receive the electrical current returning from the earth formation; a multi-function electrode on the resistivity imager tool; and an electrical system configured to provide current measurements at the transceiver electrode. In the first operational mode, the electrical system maintains the tool body at a first electrical potential, and maintains the multi-function electrode and the transceiver electrode at a second electrical potential; and in the second operational mode, the electrical system maintains the tool body at the first electrical potential, maintains the multi-function electrode at the first electrical potential, and maintains the transceiver electrode at the second potential.

Abstract: A method for estimating a property of an earth formation penetrated by a borehole, the method comprising generating a first transient electromagnetic fields with a transmitter on a carrier located outside of the borehole and receiving associated signals, calculating a bucking coefficient using the measured signals, conveying the carrier through a borehole, generating a second transient electromagnetic field and receiving associated signals, calculating, a bucked signal using the bucking coefficient and the downhole signals, calculating synthetic formation signals, calculating synthetic formations signals by applying a Duhamel's integral to the measured signals and the synthetic formation signals, calculating a synthetic bucked signal, and performing an inversion of a formation model to estimate a property of the formation such that an inverted synthetic bucked signal and an inverted bucked signal coincide within a predetermined range.

Abstract: Methods and apparatus configured to evaluate a volume of interest of an earth formation intersected by a borehole. Apparatus comprise a transceiver electrode on the tool body configured to provide electrical current to the earth formation; a return electrode configured to receive the electrical current returning from the earth formation; a multi-function electrode on the resistivity imager tool; and an electrical system configured to provide current measurements at the transceiver electrode. In the first operational mode, the electrical system maintains the tool body at a first electrical potential, and maintains the multi-function electrode and the transceiver electrode at a second electrical potential; and in the second operational mode, the electrical system maintains the tool body at the first electrical potential, maintains the multi-function electrode at the first electrical potential, and maintains the transceiver electrode at the second potential.

Abstract: A logging tool for performing resistivity measurements on the sidewall of a borehole in an earth formation is provided with a circumferential series of evenly-spaced measurement electrodes providing complete circumferential coverage of resistivity measurements. In one embodiment, the measurement electrodes are carried on a conductive pad circumferentially surrounding an elongate mandrel or tubular. The conductive pad is held at a voltage adapted to focus measurement current into the sidewall of the borehole. Preferably, the pad has dimensions relative to the measurement electrodes and a standoff distance between the measurement electrodes and said borehole wall to effectively focus the measurement current into the borehole wall. In accordance with one aspect of the invention, the measurement electrodes are spaced apart by a distance that is less than the width of each measurement electrode, thereby ensuring full circumferential resolution.

Abstract: Systems, devices, and methods for evaluating an earth formation. Method embodiments may include conveying a carrier in a borehole, the carrier including a conducting tubular having a plurality of transmitters and a receiver non-collocated with the plurality of transmitters; inducing a first current in the earth formation using a first transmitter of the plurality of transmitters; measuring with the receiver a first time-dependent transient electromagnetic (TEM) signal induced by the formation responsive to the first current; inducing a second current in the earth formation using a second transmitter of the plurality of transmitters; measuring with the receiver a second TEM signal induced by the formation responsive to the second current; and using at least one processor to estimate a value of a resistivity property of the earth formation using a bucked signal derived from the first time-dependent TEM signal, the second time-dependent TEM signal, and a bucking coefficient K(t).

Abstract: A three-coil bucking system is used for determination of a formation resistivity property ahead of the drill bit. The conductive drill pipe is provided with non-conductive inserts in the proximity of at least one transmitter and at least two receivers. Transient electromagnetic signals are processed to give the estimate of the resistivity property and for geosteering.

Abstract: A system and method of estimating properties of a subsurface formation are described. The method includes transmitting an excitation current pulse into the formation, receiving an induced pulse used to generate input data, and performing an inversion on the input data using a lookup table based on a shape of the excitation current pulse to estimate the properties of the subsurface formation.

Abstract: Systems, devices, and methods for evaluating an earth formation. Methods may include inducing a current in the formation; measuring a time-dependent transient electromagnetic (TEM) signal induced by the formation responsive to the current; and estimating apparent resistivity values for each of a plurality of samples derived from the TEM measurement, wherein each sample corresponds to a discrete time window of the TEM measurement. Estimating the apparent resistivity values for each of the samples includes determining for each sample a simulated homogeneous formation that provides a best fit for the sample. The apparent resistivity values may be used to estimate distance to an interface. The apparent resistivity values or the estimated distance may be logged and the log displayed. The apparent resistivity values, the estimated distance, or the log may be used to conduct further operations in a borehole, including geosteering.

Abstract: Systems, devices, and methods for evaluating an earth formation. Apparatus may include a carrier configured for conveyance in a borehole including a conducting tubular comprising a reduced conductivity portion made of reduced conductivity material adjacent at least one of (i) at least one transmitter antenna, and (ii) at least one receiver antenna on the carrier. The material may be a composite and may have a resistivity of between 10?4 and 102 ohm-meters. Methods and apparatus may be configured for producing time-dependent transient electromagnetic (TEM) signals using the transmitter(s) and receiver(s) and estimating a value of a resistivity property using the signals. The apparatus may be used in drilling and may include a bottom hole assembly with a drill bit, and the value may be indicative of a portion of the earth formation ahead of the bit. The value may be used to conduct further operations in a borehole, including geosteering.

Abstract: A method for imaging an earth formation includes estimating an apparent resistivity (AR) value and an apparent distance to a bedding plane (AD2B) value for each of a plurality of samples derived from measurements of a time-dependent transient electromagnetic signal, estimating an inversion-based resistivity value (IB-R) and an inversion-based distance to a bedding plane (IB-D2B) value at a first sample of each consecutive depth interval, wherein each depth interval includes a plurality of consecutive samples, and determining a difference between apparent values and the corresponding inversion-based values. The method further includes generating an image of the earth formation using the AR and AD2B values for the entire interval if the difference is less than a threshold value and generating an image of the earth formation using IB-R and IB-D2B values for the entire interval if the difference is greater than the threshold value.

Abstract: A transmitter on a bottomhole assembly (BHA) is used for generating a transient electromagnetic signal in an earth formation. A processor estimates the distance to a resistivity interface using a signal produced by a receiver on the BHA. The transmitter-receiver distance may be less than 1 m. The estimation of the distance is done in real time using a thin conductive sheet approximation.

Abstract: A method and apparatus for estimating a parameter of interest of an earth formation ahead of a carrier within borehole. The method including estimating one or more functions based on received signals that may reduce the sum of the signals received by a first receiver, and estimating the parameter of interest based on signals received by one or more additional receivers by applying the one or more functions and, if necessary, a defocusing factor, such that reception of information from downhole of a selected downhole location is enhanced relative to reception of information uphole from the selected location. The apparatus including two or more transmitters, two or more receivers, and a processor to estimate one or more functions, and, based on these functions, the parameter of interest.