Abstract: Measurements made with a multicomponent logging system oriented in a horizontal position above the surface of the earth must satisfy certain relationships. These relationships are used to establish calibration errors in the system.

Abstract: Cross-component measurements made at a plurality of toolface angles are processed to remove bias. The amplitude of the resulting sinusoid is used to estimate a distance to an interface in an earth formation.

Abstract: Measurements made by multiarray and multicomponent induction resistivity measurements in a borehole are used for determining the orientation and length of fractures in an earth formation when the fractures have a fluid with a resistivity different from that of the earth formation. The apparatus and method may also be used in anisotropic earth formations where the vertical and horizontal resistivities are different.

Abstract: Data are acquired using multi-array logging tool in a borehole having an angle of inclination to a normal to the bedding plane of earth formations. The multi-array measurements are filtered using angle dependent filters to give a filtered curve corresponding to a target one of the multi-array measurements using angle dependent filters. Correlation coefficients are determined for a set of possible dip angles and a relative dip angle is estimated from the correlation coefficients. This dip angle estimate together with bed boundaries obtained from the multi-array measurements are used for inverting multi-component measurements alone or jointly with multi-array measurements to refine the relative dip angle interpretation and give horizontal and vertical formation resistivity.

Abstract: An artificial neural network, ANN, and method of training the ANN for inversion of logging tool signals into well logs of formation parameters is disclosed. Properly selected synthetic models of earth formations are used to train the ANN. The models include Oklahoma and chirp type of formations. In each model parameter contrasts of from 10 to 1 to about 100 to 1 are included. Models including maximum and minimum parameter values spanning the operating range of the selected logging tool are included. Parameter contrasts at interfaces are limited to realistic values found in earth formations. The selected models are used to generate synthetic tool signals, which are then used as inputs to the ANN for training. When the ANN coefficients are properly adjusted to produce an output matching the original models, the ANN can be used for inversion of any real signals from the selected logging tool.

Abstract: The invention is a method of determining horizontal and vertical resistivity in an anisotropic formation using a combination of orientable triaxial and array antennae conveyed downhole. Measurements are taken at various azimuthal angles about a measuring device at a given depth. Values at each azimuthal orientation can be fit to a curve to yield information on the surrounding formation. Multiple measurements at a given depth and azimuthal orientation can be weighted to obtain an average value. Values from the curve fitting process are used in subsequent inversion processing and reduce the uncertainty of the inversion processing result. Utilization of a three dimensional geometry enables a unique resolution of the orientation of the principle axis of anisotropy, and consequently of horizontal and vertical resistivity, and dip.

Abstract: The invention is a method of determining horizontal and vertical resistivity in an anisotropic formation using a combination of orientable triaxial and array antennae conveyed downhole. Measurements are taken at various azimuthal angles about a measuring device at a given depth. Values at each azimuthal orientation can be fit to a curve to yield information on the surrounding formation. Multiple measurements at a given depth and azimuthal orientation can be weighted to obtain an average value. Values from the curve fitting process are used in subsequent inversion processing and reduce the uncertainty of the inversion processing result. Utilization of a three dimensional geometry enables a unique resolution of the orientation of the principle axis of anisotropy, and consequently of horizontal and vertical resistivity, and dip.

Abstract: Measurements made with a multicomponent logging instrument when used in a substantially horizontal borehole in earth formations are diagnostic of the direction of beds relative to the position of the borehole. When the logging instrument is conveyed on a drilling assembly, the drilling trajectory may be maintained to follow a predetermined trajectory or to maintain a desired distance from a boundary such as an oil-water contact.

Abstract: A coil array for high resolution induction logging comprises a transmitter, a first receiver set positioned at a first distance from the transmitter and a second receiver set positioned at a second distance from the transmitter, and the second receiver set includes at least one portion of the first receiver set. Also disclosed is a method for deriving an apparent conductivity log from at least one induction well log that comprises a plurality of depth samples, comprising the steps of raising each depth sample of the apparent conductivity signal to several predetermined powers to generate a plurality of powers of conductivity, convolving in depth the powers of conductivity with a plurality of filters, where each power has a distinct filter, and summing the results of all of the convolutions to produce a conductivity log that is substantially free from the effects of adjacent beds and the nonlinear effects of true conductivity.

Abstract: A coil array for high resolution induction logging comprises a transmitter, a first receiver set and a second receiver set. The second receiver set includes at least one portion of the first receiver set. A method for deriving an apparent conductivity log from at least one induction well log that comprises a plurality of depth samples comprises raising each depth sample to several predetermined powers, convolving in depth the powers of conductivity, and summing the convolutions to produce a conductivity log. An apparatus for measuring the resistivity of an earth formation, comprises a transmitter energized by a time-varying, periodic voltage, a set of receivers generating a receiver voltage, an analog-to-digital converter that outputs a digitized voltage signal, and a processor that receives the digitized voltage signal.

Abstract: A coil array for high resolution induction logging comprises a transmitter, a first receiver set and a second receiver set. The second receiver set includes at least one portion of the first receiver set. A method for deriving an apparent conductivity log from at least one induction well log that comprises a plurality of depth samples, comprises raising each depth sample to several predetermined powers, convolving in depth the powers of conductivity, and summing the convolutions to produce a conductivity log. An apparatus for measuring the resistivity of an earth formation, comprises a transmitter energized by a time-varying, periodic voltage, a set of receivers generating a receiver voltage, an analog-to-digital converter that outputs a digitized voltage signal, and a processor that receives the digitized voltage signal.

Abstract: A coil array for high resolution induction logging comprises a transmitter, a first receiver set positioned at a first distance from the transmitter and a second receiver set positioned at a second distance from the transmitter, and the second receiver set includes at least one portion of the first receiver set. Also disclosed is a method for deriving an apparent conductivity log from at least one induction well log that comprises a plurality of depth samples, comprising the steps of raising each depth sample of the apparent conductivity signal to several predetermined powers to generate a plurality of powers of conductivity, convolving in depth the powers of conductivity with a plurality of filters, where each power has a distinct filter, and summing the results of all of the convolutions to produce a conductivity log that is substantially free from the effects of adjacent beds and the nonlinear effects of true conductivity.

Abstract: A coil array for high resolution induction logging comprises a transmitter, a first receiver set positioned at a first distance from the transmitter and a second receiver set positioned at a second distance from the transmitter, and the second receiver set includes at least one portion of the first receiver set. Also disclosed is a method for deriving an apparent conductivity log from at least one induction well log that comprises a plurality of depth samples, comprising the steps of raising each depth sample of the apparent conductivity signal to several predetermined powers to generate a plurality of powers of conductivity, convolving in depth the powers of conductivity with a plurality of filters, where each power has a distinct filter, and summing the results of all of the convolutions to produce a conductivity log that is substantially free from the effects of adjacent beds and the nonlinear effects of true conductivity.

Abstract: Data are acquired using multi-array logging tool in a borehole having an angle of inclination to a normal to the bedding plane of earth formations. The multi-array measurements are filtered using angle dependent filters to give a filtered curve corresponding to a target one of the multi-array measurements using angle dependent filters. Correlation coefficients are determined for a set of possible dip angles and a relative dip angle is estimated from the correlation coefficients. This dip angle estimate together with bed boundaries obtained from the multi-array measurements are used for inverting multi-component measurements alone or jointly with multi-array measurements to refine the relative dip angle interpretation and give horizontal and vertical formation resistivity.

Abstract: A method for determining the azimuthal direction of a maximum in a series of gamma ray count measurements that are each assigned to an azimuthal sector, comprising: determining the x- and y-components of the gamma ray counts for each sector, averaging the component values to obtain averaged x- and y-components, and calculating the corresponding aximuthal angle for the maximum by computing the arctangent of the ratio of the averaged y- and x-components.

Abstract: A method for estimating the apparent conductivity of a formation comprises the steps of: providing layer conductivity data over a range of points in the formation outside the borehole along a portion of a borehole, calculating an apparent conductivity at a first series of points in the range, calculating a Doll-generated conductivity at each of the first points, calculating a skin effect by calculating a difference value between the Doll-generated conductivity and the apparent conductivity at each of the first points, calculating a Doll-generated conductivity at a second series of points that are different from the first points, calculating an interpolated difference value for each of the second points, and adding to interpolated difference value to the corresponding Doll-generated conductivity at each of the second points.

Abstract: A system and method for performing inversion and for correcting for shoulder bed effect. The method enhances the resolution of wave propagation resistivity logs and corrects the logs for adjacent bed effects, whereby the resulting logs have a vertical response as good as wireline high-resolution induction logs. The method first performs logging while drilling on a formation to obtain LWD resistivity log data. The method then selects one or more control depths at one or more locations of each of a plurality of detected beds in the formation. The present invention includes a novel method for selecting bed boundaries from the log data, and the control depths are then determined based on the determined bed boundaries. The method then estimates the resistivity of each bed only at the selected control depths to produce an estimated resistivity of the beds. The method then computes a simulated log value at each control depth using a current estimate of the resistivity of the beds.

Abstract: A typical nuclear well logging tool forms a count rate data stream including statistical noise. A robust single pass partially deconvolved smoothing filter matched to the tool response is applied to the count rate data to enhance vertical resolution while minimizing the statistical noise increase. The smoothing filter is partially deconvolved by the application of a three point deconvolution characteristic of the cusp portion of a related cusp function and a box function representative of the tool response.

Abstract: Variable frequency induction well logging methods and apparatus are disclosed having an approximately constant vertical response function. The frequency of operation is automatically selected to minimize propagation effects. These techniques permit an N point deconvolution of apparent formation conductivity to yield an approximation of the true conductivity of incremental layers of cylindrically symmetrical earth formations, including formations having adjacent layers of arbitrary thicknesses and conductivities.

Abstract: Induction well logging methods and apparatus are disclosed for deconvolving apparent conductivity measurements obtained for a induction logging coil system. The well logging system is operated so that it has a substantially fixed vertical response. The fixed vertical response function is used to design an inverse (deconvolution) filter by using a minimum Tchebycheff norms technique. The inverse filter function is stored and employed to convert (deconvolve) signals obtained from the induction coil system to signals functionally related to the actual conductivity of an incremental layer of a formation being logged.