Abstract: Locating and/or marking equipment, such as a locate transmitter or locate receiver, a marking device, or a combined locate and marking device, may be communicatively coupled to and/or equipped with a mobile/portable device (e.g., a mobile phone, personal digital assistant or other portable computing device) that provides processing, electronic storage, electronic display, user interface, communication facilities and/or other functionality (e.g., GPS-enabled functionality) for the equipment. A mobile/portable device may be mechanically and/or electronically coupled to the equipment, and may be programmed so as to log and generate electronic records of various information germane to a locate and/or marking operation (e.g., locate information, marking information, and/or landmark information). Such records may be formatted in various manners, processed and/or analyzed on the mobile/portable device, and/or transmitted to another device (e.g., a remote computer/server) for storage, processing and/or analysis.

Abstract: Electrical property contrast difference maps of the subsurface formations may be produced using surface and/or near surface array of transmitters and receivers tuned to emit and receive electromagnetic (EM) signals. The electrical property may be resistivity or conductivity. The maps may be time based. A time based trend change may be used to predict the location and movement of fluids within the hydrocarbon bearing or any other subsurface zones where resistivity and/or conductivity values of the fluids within these zones change over time.

Abstract: Methods and apparatus to process measurements associated with drilling operations are described. An example method of modifying processing results during a subterranean formation drilling operation includes identifying a plurality of parameters and processing measurements associated with the subterranean formation obtained while drilling and the plurality of parameters to generate first results. Additionally, the example method includes processing measurements associated with the subterranean formation obtained while drilling is temporarily suspended and the plurality of parameters to generate second results and comparing the first and second results. Further, the example method includes, in response to the comparison of the first and second results, modifying the first results based on the second results to improve a quality of the first results.

Abstract: A method for determining mobile water saturation in a reservoir having a borehole extending through the reservoir is disclosed. The method involves obtaining a first borehole data log while the reservoir is subjected to first fluid conditions, and causing a mobile water displacement in the reservoir by changing the fluid conditions in the borehole to cause the reservoir to be subjected to second fluid conditions, the second fluid conditions differing from the first fluid conditions. The method further involves obtaining a second borehole data log under the second fluid conditions, and estimating the mobile water displacement using the first and second data logs, the estimated mobile water displacement providing an estimate of the mobile water saturation in the reservoir.

Abstract: A method for assigning a wettability or related parameter to a subvolume of formation located between two or more boreholes is described. The method includes the steps of obtaining measurements of resistivity at a subvolume, obtaining further parameters determining a relation between resistivity and saturation from logging measurements along the two or more boreholes, obtaining geological measurements defining geological or rock-type boundaries within the formation between the two or more boreholes, selecting the subvolume such that it is intersected by the geological or rock-type boundaries; transforming the resistivity measurements into the saturation at the subvolume; and using the saturation and/or the further parameters to determine the wettability or related parameter for the subvolume.

Abstract: Method for rapid inversion of data from a controlled-source electromagnetic survey of a subterranean region. Selected (51) common-receiver or common-source gathers of the data are reformed into composite gathers (52) by summing their data. Each composite gather is forward modeled (in the inversion process) with multiple active source locations (53). Computer time is reduced in proportion to the ratio of the total number of composite gathers to the total number of original common-receiver or common-source gathers. The data may be phase encoded to prevent data cancellation. Methods for mitigating loss of far offset information by data overlap in the summing process are disclosed.

Abstract: A technique provides a methodology for improving surveys of subterranean regions. The methodology comprises estimating macro anisotropy and an intrinsic or micro anisotropy of an overburden. A surface electromagnetic survey is conducted, and the data from the survey is inverted based on or including information gained from estimating the macro anisotropy and/or intrinsic anisotropy. A processor system can be used to conduct the inversion with the adjustments for anisotropy to improve the information provided by the survey.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may operate to receive down hole tool environmental temperature data, axial temperature data, radial temperature data, and log data. Further activity may include applying temperature effects compensation associated with the environmental temperature data and the down hole log data using a fitting function model obtained from a trained neural network to transform the down hole log data into corrected log data. Additional apparatus, systems, and methods are described.

Abstract: An apparatus and method for estimating a parameter of interest in a borehole penetrating an earth formation using a receiver and a transmitter, both disposed on a carrier, with aligned magnetic moments to correct for bending of carrier during borehole investigations. The apparatus may include a transmitter with at least two substantially perpendicular coils and a receiver with at least one coil oriented with at least one or the transmitter coils. The method may include aligning the magnetic moment of the transmitter and the magnetic moment of the receiver prior to estimating the parameter of interest. The method may include supplying a constant electric current to one of the transmitter coils while supplying a varying electric current to another of the transmitter coils. The method may include estimating a direction of bending or angle of bending of the carrier.

Abstract: Methods and systems for processing acoustic measurements related to subterranean formations. The methods and systems provide receiving acoustic waveforms with a plurality of receivers, deriving slowness of the formation based on the acoustic waveforms, and modeling dominant waveforms in the acoustic waveforms based on the formation slowness, wherein deriving the formation slowness comprises parametric inversion for complex and frequency dependent slowness and the derived complex slowness has real and imaginary parts.

Abstract: A method to obtain gain-corrected measurements. A measurement tool having one or more arrays is provided, wherein the arrays include two co-located triaxial transmitters and two co-located triaxial receivers. Measurements are obtained using the transmitters and the receivers. Impedance matrices are formed from the obtained measurements and the impedance matrices are combined to provide gain-corrected measurements. The apparatus may alternatively be a while-drilling logging tool having one or more arrays, wherein each array comprises a transmitter, a receiver, and a buck, and wherein the signal received by the receiver is subtracted from the signal received by the buck or vice versa. A slotted shield may be incorporated into either embodiment of the tool. The slots may form one or more island elements. A material is disposed in the slots. The islands and shield body have complementary tapered sides that confine the islands within the shield body.

Abstract: A method of passive surveying comprises generating one or more detected signals by passively detecting a signal generated within a subsurface earth formation due to a seismoelectric response or an electroseismic response in at least one porous subsurface earth formation containing at least one fluid, and processing the one or more detected signals to determine at least one property of the subsurface earth formation.

Abstract: Disclosed are various embodiments of a workflow or method for petrophysical rock typing of carbonates in an oil or gas reservoir or field comprising determining a Data Scenario (DS) for the reservoir or field, determining a plurality of Depositional Rock Types (DRTs) for the reservoir or field, determining a Digenetic Modification (DM) from a plurality of diagenetic modifiers or primary textures associated with the plurality of DRTs, selecting a Reservoir Type (RT) corresponding to the plurality of DRTs,determining at least one pore type, and determining, on the basis of the plurality of DRTs, the Diagenetic Modification (DM), and the at least one pore type, a plurality of Petrophysical Rock Types (PRTs) associated with the RT.

Abstract: A method of passive surveying comprises generating one or more detected signals by passively detecting a signal generated within a subsurface earth formation due to a seismoelectric response or an electroseismic response in at least one porous subsurface earth formation containing at least one fluid, and processing the one or more detected signals to determine at least one property of the subsurface earth formation.

Abstract: A method for identifying drilling induced fractures while drilling a wellbore into a formation is disclosed. The method includes: obtaining multi-component induction data collected by a drill string including a multi-component induction tool; processing the data to estimate values for principal components; and identifying drilling induced fractures from the principal components. An instrument and a computer program product are disclosed.

Abstract: A logging tool having a plurality of spatially separated antennas is provided and used to make propagation-style measurements in a formation. Tensors are formed using the propagation-style measurements and one or more quantities are computed using the tensors. A formation evaluation is performed using the computed quantities. The formation evaluation determines a formation property or parameter such as horizontal resistivity, vertical resistivity, relative dip, azimuthal dip, bed boundary location, or bed thickness. The computed quantities may include compensated phase shift resistivity, compensated attenuation resistivity, symmetrized phase shift resistivity, symmetrized attenuation resistivity, anti-symmetrized phase shift resistivity, and anti-symmetrized attenuation resistivity. The measurements may be corrected for antenna gain errors and an air calibration may be performed.

Abstract: A hydrocarbon exploration method is disclosed for generating anisotropic resistivity models of a subsurface reservoir from seismic and well data using a rock physics model. In one embodiment, the method comprises: selecting wells within a region of interest (101); obtaining a plurality of rock properties (102) and adjusting selected rock parameters (103) in the calibration of the rock physics model at the well locations; inverting porosity and shale content from seismic data (107); propagating the calibrated rock physics model to the region of interest (109) and calculating effective resistivity for the entire region of interest (109). The inventive method also provides for analyzing the uncertainty associated with the prediction of the resistivity volume.

Abstract: A method of processing geophysical data including at least measured potential field data from a potential field survey of a surveyed region of the earth to provide a representation of the geology of said surveyed region, the method comprising generating a first model of said surveyed region by fitting data predicted by said first model to said measured data for a specified frequency range; predicting full range potential field data for all measured frequencies using said generated first model; comparing said full range predicted data to said measured potential field data to provide full range residual data representing a difference between the full range predicted data and the full range measured data, and interpreting said full range residual data to provide a representation of said geology of said surveyed region.

Abstract: A method for processing well logging data includes method dividing the well logging data into a number of constant dimensional effect segments, where each constant dimensional effect segment defines an interval having a similar dimensional effect on the log response. The well logging data is taken from a highly deviated well. The method further includes dividing the constant dimensional effect segments into a number of constant property intervals, each constant dimensional effect segment including at least one corresponding constant property interval, and each constant property interval defining a wellbore distance over which a formation property is substantially constant that results in a log response having a low variance. The method further includes providing the constant property intervals to an output device.

Abstract: Disclosed are a production logging tool and method for evaluating fluid produced from a formation of an oilfield. The fluid is measured by a water sensor to determine if the fluid is water, and a chloride sensor to determine chloride levels of the fluid. Based on the chloride levels of the fluid, it can be determined whether the fluid is naturally occurring water, or if the fluid is an injection fluid.

Abstract: Current supplied to electrical submersible pumps in wells is monitored, and signal processing based on wavelet analysis and phase diagram analysis is performed on the data obtained from monitoring. An incipient malfunction of the electrical submersible pump, such as one due to scale build-up in and around the pump, can be detected at an early stage.

Abstract: Determining parameters associated with a hydrocarbon bearing formation beneath a sea bed. At least some of the illustrative embodiments are methods including: obtaining data gathered regarding a plurality of distinct readings by sensors, the readings responsive to a source of electrical energy towed in water above the hydrocarbon bearing formation, the sensors sense an electrical parameter associated with the source; combining a first datum associated with a first path of travel of the source with a second datum associated with a second path of travel of the source, the second path of travel distinct from the first path of travel, and the combining creates a first combined datum; and determining the parameter associated with the hydrocarbon bearing formation by evaluating the first combined datum.

Abstract: A method and system for producing look-ahead profiles measurements includes positioning an energy transmitter, such as a transmitting antenna, proximate to a borehole assembly tool. One or more energy receivers, such as receiving antennas, are positioned along a length of the borehole assembly. Next, energy is transmitted to produce look-ahead scans relative to the borehole assembly tool. Look-ahead graph data with an x-axis being a function of a time relative to the position of the borehole assembly tool is generated. The look-ahead graph is produced and displayed on a display device. The look-ahead graph may track estimated formation values based on earth models. The estimated formation values are displayed below a tool position history line that is part of the look-ahead graph. The estimated formation values in the look-ahead graph may be based on inversions of resistivity data from the look-ahead scans.

Abstract: Various embodiments include apparatus and methods of operation with respect to well logging. Apparatus and methods include a tool having an arrangement of transmitters and receivers that are operated at different positions downhole and a processing unit to process collected signals such that the arrangement of transmitters and receivers provides measurements that mimic operation of a different arrangement of transmitters and receivers. Additional apparatus, systems, and methods are disclosed.

Abstract: Methods and systems are provided for evaluating petrophysical properties of subterranean formations and comprehensively evaluating hydrate presence through a combination of computer-implemented log modeling and analysis. Certain embodiments include the steps of running a number of logging tools in a wellbore to obtain a variety of wellbore data and logs, and evaluating and modeling the log data to ascertain various petrophysical properties. Examples of suitable logging techniques that may be used in combination with the present invention include, but are not limited to, sonic logs, electrical resistivity logs, gamma ray logs, neutron porosity logs, density logs, NRM logs, or any combination or subset thereof.

Abstract: A method for drilling a wellbore proximate a salt structure includes measuring formation resistivity azimuthally. A map of spatial distribution of resistivity is determined from the azimuthal resistivity measurements. A distance from the wellbore to an edge of the salt structure is determined from the three dimensional volume map.

Abstract: Methods and related systems are described for analyzing electromagnetic survey data. Electromagnetic survey data of a subterranean formation is obtained using at least a downhole transceiver deployed in a borehole and a transceiver positioned on the surface or in another borehole. The electromagnetic survey data includes an incident wave component and a scattered wave component. The incident and scattered components are correlated so as to generate an image of the subterranean formation indicating spatial locations of one or more features, for example, electrical properties such as resistivity variations, in the formation. The image is based at least in part on one or more interference patterns of the incident and scattered wave components. The correlation preferably includes generating a simulation of the incident wave component propagated into the formation, and convolving the simulated propagated incident wave component with the scattered wave component.

Abstract: The present disclosure relates to a method to determine a characteristic of a subsurface formation using a downhole logging tool. A downhole logging tool having the ability to make substantially concurrent disparate measurements on the subsurface formation is provided and substantially concurrent disparate measurements on the formation using the downhole logging tool are made. Those measurements are used to solve a system of equations simultaneously and the solution to the system of equations is used to determine the characteristic of the subsurface formation.

Abstract: A method for determining orientation of an electrically conductive formation proximate an electrically substantially non-conductive formation includes measuring multiaxial electromagnetic induction response within the substantially non-conductive formation using an instrument disposed in a wellbore drilled through the formations. A difference from zero conductivity is determined for each component measurement of the multiaxial electromagnetic induction response. The differences are used to correct the measured response of each component measurement in the electrically conductive response. The corrected component measurements are used to determine the orientation of the conductive formation.

Abstract: Various methods are disclosed, comprising obtaining a plurality of raw depth measurements for a wellbore; obtaining survey data about a bottom hole assembly; obtaining depth compensation information; calculating a plurality of compensated depth measurements from the raw depth measurements and the depth compensation information and one or more additional corrections for residual pipe compliance, tide, and rig heave; calculating sag angle and correcting the survey data with the sag angle; determining a high fidelity wellbore trajectory from the compensated depth measurements and the survey data; and then employing the high fidelity wellbore trajectory in various drilling, formation evaluation, and production and reservoir analysis applications. Depth compensation information may comprise at least one of weight on bit, a friction factor, temperature profile, borehole profile, drill string mechanical properties, hookload, and drilling fluid property. The surveys may include both static and continuous surveys.

Abstract: Method for determining time-dependent changes [73] in the earth vertical and horizontal electrical resistivity and fluid saturations from offshore electromagnetic survey measurements. The method requires both online and offline data, which should include at least one electromagnetic field component sensitive at least predominantly to vertical resistivity and another component sensitive at least predominately to horizontal resistivity [62]. Using a horizontal electric dipole source, online Ez and offline Hz measurements are preferred. For a horizontal magnetic dipole source, online H2 and offline E2 data are preferred. Magnetotelluric data may be substituted for controlled source data sensitive at least predominantly to horizontal resistivity. Maxwell's equations are solved by forward modeling [64,65] or by inversion [66,67], using resistivity models of the subsurface that are either isotropic contrast, and [64,66] or anisotropic [65,67].

Abstract: Various logging-while-drilling (LWD) systems and methods provide resistivity logging coupled with deep detection of elongated anomalies at acute angles, enabling effective geosteering without disrupting drilling operations and without requiring intervention in the operations of the existing well. One LWD system embodiment employs a tool having tilted antennas as the transmitter and the receiver, where at least one of the antennas is placed in the vicinity of the bit, making it possible to detect existing wells at distances of 50-100 feet. In some cases, the detection distance is increased by enhancing the visibility of the existing well using a contrast fluid treatment on target well, either to fill the bore or to surround the well with treated cement or fluids that invade the formation. At least one inversion method separates the inversion of formation parameters from the inversion of parameters specifying distance, direction, and orientation of the existing well.

Abstract: Apparatus for in-situ wellbore measurements, said apparatus comprising one or more sensors arranged outside a wellbore, one or more actuators associated with the sensors, an electromagnetic transceiver situated inside a non-magnetic portion of wellbore conduit and mounted on an electric-line logging cable, a downhole interface unit also located on the electric-line cable for controlling communication to the apparatus. Also a method of in-situ wellbore measurements using said apparatus.

Abstract: The invention relates to a method and apparatus for determining the nature of a material in a cavity between one inner metal wall and one outer metal wall provided outside the inner metal wall. First a tool is located on the inside of the inner metal wall, where the tool comprises a pulse generator and a signal recorder. An electromagnetic short duration pulse is generated by means of the pulse generator, the pulse inducing mechanical vibrations in the walls. Data representing the reflections of the mechanical vibrations from said cavity is recorded by means of the signal recorder. The recorded data is analyzed to determine the nature of the material in the cavity.

Abstract: Certain embodiments described herein provide a measure of the misalignment of multiple acceleration sensors mounted in the downhole portion of a drill string. In certain embodiments, the measure of the misalignment corresponds to a measure of sag which can be used to provide an improved estimate of the inclination of the downhole portion of the drill string and/or the wellbore. Certain embodiments described herein provide an estimate of the magnetic interference incident upon a drilling system using multiple magnetic sensors mounted within a non-magnetic region of the downhole portion of the drilling system. Certain embodiments utilize the magnetic measurements to determine an axial interference resulting from one or more magnetic portions of the downhole portion and to provide an improved estimate of the azimuthal orientation of the downhole portion with respect to the magnetic field of the Earth.

Abstract: A method is provided for determining formation resistivity, anisotropy and dip from wellbore measurements includes moving a well logging instrument through subsurface formations. The instrument includes longitudinal magnetic dipoles and at least one of tilted and transverse magnetic dipoles. Formation layer boundaries and horizontal resistivities of the formation layers are determined from longitudinal magnetic dipole measurements. Vertical resistivities of the formation layers are determined by inversion of anisotropy sensitive measurements. Improved vertical resistivities of the formation layers and dips are determined by inverting symmetrized and anti-symmetrized measurements. Improved vertical resistivities, improved boundaries and improved dips are determined by inversion of the all dipole measurements. Improved horizontal resistivities, further improved layer boundaries and further improved dips are determined by inversion of all dipole measurements.

Abstract: A system and method for controlling a downhole portion of a drill string is provided. The method includes receiving signals from a first sensor package mounted at a first position to the downhole portion, the signals indicative of an orientation of the first sensor package. The method also includes receiving signals from a second sensor package mounted at a second position to the downhole portion, the signals indicative of an orientation of the second sensor package. The method further includes calculating a first amount of bend between the first and second sensor packages in response to the signals and transmitting control signals to an actuator which responds by adjusting the downhole portion to have a second amount of bend between the first and second sensor packages.

Abstract: The present disclosure relates to a method to determine a formation property of a subsurface formation. A downhole logging tool having two or more antennas, at least one of the antennas being a non-co-located triaxial antenna, is provided. Azimuthally sensitive measurements are obtained using the antennas of the downhole logging tool. The measurements are fitted to a Fourier series having Fourier coefficients and the non-co-location of the triaxial antenna is compensated for by adjusting the Fourier coefficients. Compensated measurements are determined using the adjusted Fourier coefficients and the formation property of the subsurface formation is determined using the compensated measurements. The compensating may use one or more scale factors that depend on an amplitude, phase, and/or frequency of the received signal, and an alignment angle between the triaxial antenna and another of the antennas of the logging tool.

Abstract: A method for determining a dip of a geological structure in a subterranean formation, involves generating, using a 3D resistivity analyzer, a first intermediate result describing the dip of the geological structure based on 3D resistivity data collected from a borehole penetrating the subterranean formation. The method further involves generating, using a borehole image analyzer, a second intermediate result describing the dip of the geological structure based on a borehole image collected from the borehole. The method further involves generating, by a computer processor combining the first intermediate result and the second intermediate result based on a pre-determined criterion, an integrated result describing the dip of the geological structure.

Abstract: The present disclosure relates to a method to determine a formation property of a subsurface formation. A downhole logging tool having two or more tri-axial antennas is provided and used to obtain azimuthally sensitive data. Borehole correction is performed on the obtained data and a ZD-inversion is performed on the borehole corrected data for all antenna spacing groups. A formation indicator flag is determined and, depending on the determined formation indicator flag, a 1D-axial inversion and/or a 1D-radial inversion is performed over selected zones, or neither is performed. The best ZD-inversion results are selected and the 1D-axial inversion results and/or the 1D-radial inversion results, if any, are combined with the selected best ZD- inversion results to form a composite inversion result. The formation property of the subsurface formation is determined using the composite inversion result.

Abstract: Various resistivity logging tools, systems, and methods are disclosed. At least some system embodiments include a logging tool and at least one processor. The logging tool provides transmitter-receiver coupling measurements that include at least direct coupling along the longitudinal tool axis (Czz), direct coupling along the perpendicular axis (Cxx or Cyy), and cross coupling along the longitudinal and perpendicular axes (Cxz, Cyz, Czx, or Czy). The processor performs a multi-step inversion of said transmitter-receiver coupling measurements to obtain values for model parameters. Based at least in part on the model parameters, the processor determines borehole corrections for the transmitter-receiver coupling measurements and may further provide one or more logs derived from the borehole corrected transmitter-receiver coupling measurements.

Abstract: A method of processing geological log data obtained from use of one or more logging tools and including at least a first log having a relatively poor attribute and a corresponding, second log having a relatively good said attribute comprises the step of incorporating into the first log characteristics of the second log that confer improvements in the said attribute, characterised in that the incorporating step includes modulating the extent of incorporation into the first said log of the said characteristics without distorting geologically significant information in the first log.

Abstract: Disclosed is a method for estimating a pore pressure of an earth formation penetrated by a borehole and an associated uncertainty. The method includes: conveying a carrier through the borehole; performing formation measurements relating to porosity at a plurality of depths in the borehole using a downhole tool coupled to the carrier; defining a first depth interval and a second depth interval deeper than the first depth interval, the first depth interval comprising a first set of formation measurement points and the second depth interval comprising a second set of formation measurement points; establishing a plurality of trendlines of depth versus porosity-related measurements using a processor with each trendline in the plurality of trendlines extending from a point in the first depth interval through a point in the second depth interval; and calculating a pore pressure line and associated uncertainty using the plurality of trendlines.

Abstract: Methods and related systems are described for analyzing electromagnetic survey data. Electromagnetic survey data of a subterranean formation is obtained using at least a downhole transceiver deployed in a borehole and a transceiver positioned on the surface, or in the same or another borehole. Limits are defined for casing correction coefficients that account for effects of the borehole casing. A constrained inversion process is performed solving for the casing correction coefficients within the defined limits, and for one or more parameters of a model representing attributes, such as resistivity, of the subterranean formation.

Abstract: In various embodiments, apparatus and methods are provided to determine formation resistivity associated with a well. Measurements taken using sub-arrays of a tool at different distances of investigation can be used to determine formation resistivity, where the sub-arrays are arranged to make azimuthal related measurements. Separations readings related to resistivity can be generated from signals received from different directions and can be analyzed to characterize validity of a measurement reading. Additional apparatus, systems, and methods are disclosed.

Abstract: Various resistivity logging tools, systems, and methods are disclosed. At least some tool embodiments include transmit and receive antennas that measure the electromagnetic response of the formation, at least one of which is tilted to provide a directional sensitivity. A processor converts the response (measured as a function of the tool's rotation angle) into a set of inversion parameters, which are then used to estimate the anisotropic properties of the formation. The set of inversion parameters includes at least one parameter based on an antipodal sum of the response signal, and may further include parameters based on an antipodal difference and an average of the signal response. Antipodal sum and difference values at different rotational orientations can be included in the set of inversion parameters, and they may be normalized to reduce environmental effects. Some tool embodiments collect the relevant formation measurements using parallel or perpendicular tilted antennas.

Abstract: A method for determining a formation type within a wellbore includes forming the wellbore such that the wellbore intersects fractures within a formation. Hydrocarbons are produced from the formation. An induction tool is disposed into the wellbore after producing the hydrocarbons. A resistivity of a portion of the formation is measured with the induction tool. The resistivity of the portion of the formation is compared with a known formation type. The formation type of the portion of the formation is determined based on the resistivity. A characteristic of the formation type is output.

Abstract: An apparatus and method for estimating a resistivity property of an earth formation involving electric current induced in an earth formation. The method may include reducing an error in a voltage received by a receiver coil due to excitation of a transmitter coil due to temperature effects. The voltage may include amplitude and/or phase errors. The method may modify the measured voltage by multiplying/dividing the voltage by a reduction factor. The reduction factor may be determined using polynomic curve fitting. The apparatus may be configured to perform the method. The apparatus may include at least one transmitter coil, at least one receiver coil, and at least one processes configured to perform the error reduction.

Abstract: In a method of processing resistivity log data, two or more resistivity log measurements of differing depths of penetration of an invaded formation are generated. The deepest and shallowest of the resistivity log measurements are combined in accordance with a non-linear combination algorithm that is modulated by a parameter. The value of the parameter used varies in dependence on a comparison between deep and shallow log measurements. The results of the comparison are forward modelled from sample data. A modified log output is generated as a result of combining the deepest and shallowest of the resistivity log measurements in accordance with the non-linear combination algorithm.

Abstract: Disclosed is an apparatus for estimating a property of an earth formation penetrated by a borehole. The apparatus includes a plurality of electrodes disposed downhole and configured to inject an electrical current into the earth formation using an applied voltage and/or measure electrical current resulting from an injection of the electrical current. The apparatus also includes a processor configured to perform a series of formation measurements that include injecting current into the earth formation using a unique subset of electrodes in the plurality of electrodes and measuring current in the earth formation using one or more electrodes not used for the current injecting. The processer sums the measured currents for the electrodes wherein the sum of electrical currents for at least one electrode that measured electrical current is substantially in phase with the applied voltage; and uses the sum of in phase currents to estimate the property.