Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: Methods and apparatus for making directional measurements of earth formations surrounding a borehole. New antenna coil shield designs are utilized to provide selective attenuation of at least one electromagnetic energy field component as the component interacts with the shield. The new shields are implemented in several downhole tool configurations to provide azimuthally focused formation measurements. In effect, the new shield filters interacting electromagnetic energy field components to pass those components corresponding to a magnetic dipole oriented at an angle from the tool axis. The shields thereby alter a coil's envelope of influence to electromagnetic energy. The new shields also form part of a system for making directional measurements while drilling.

Abstract: The present invention is directed to a method for removing periodic errors from well log data. The method comprises defining a parametric model of well log data to identify periodic errors due to the borehole environment are present, and removing the periodic errors from the well log data.

Abstract: The present invention relates generally to a method and apparatus for evaluating the resistivity of invaded formations at high apparent dip angle. A multi-array induction tool having a plurality of arrays is disposed in a borehole. Signals from a subset of coils of the array are selected to probe different volumes of the formation surrounding the borehole. The maximum entropy method is used to process data from the subset of coils to effectively remove distortions produced by shoulder and dip effect in the presence of shallow, moderate, or deep invasion. An advantage of the invention is a computer program that accurately predicts the response of induction arrays in an assumed layered formation with dip. After processing the data, the resulting multi-array induction log will indicate a conductivity profile for the subset of coils which is substantially identical to that of an array in a thick bed, without dip or layering, with the same invasion profile.

Abstract: In a well logging truck computer which phroduces an induction log, a dip correction algorithm, stored in a memory of the computer, corrects an error introduced in the induction log by dip effect. The dip effect error is introduced into the induction log when an array induction tool is disposed in a deviated borehole at an apparent dip angle with respect to a formation having a plurality of bedding planes, and subsequently develops formation parameter data. This formation parameter data, which contains the dip effect error, is displayed on the induction log. The dip effect algorithm eliminates the dip effect error by multiplying or convolving inverse filters "h" as a function of dip angle "a" with a plurality of the formation parameter data "sigma(j-n)" to thereby produce a corresponding plurality of corrected formation parameter data "sigma.sub.F ", the corrected formation parameter data being reproduced on an induction log output record medium.

Abstract: Induction logging sonde including transmitter and receiver solenoid coils mounted on a support and axially separated from each other. The support is made of conductive material and comprises at least one first longitudinal portion for mounting the coils and second longitudinal portions on each side of the first portion. At least the first portion has a substantially continuous and axisymmetric outer surface so as to favor the flow of eddy currents around the surface, whereby the electric field on that surface is substantially cancelled.

Abstract: An electrical induction sonde for measuring a characteristic of an earth formation traversed by a borehole having improved vertical resolution and excellent depth of penetration. The sonde has two or more transmitter-receiver spacings preselected to provide at least two separate induction signals received from the formation that, when combined, produce a response function indicative of formation physical properties with no zeros in the spatial frequency response function over the frequency domain of interest.

Abstract: A method and apparatus for enhancing the resolution of an induction logging tool at a desired depth of investigation comprising receiving an induction signal from the formation corresponding to the desired depth of investigation, receiving a second signal from the formation having no zeroes in the spatial frequency domain and filtering and combining the received signals to provide high frequency signal information from the second signal to augment and enhance the first signal. Additional corrections, such as for skin effect and shoulder effect are also made.

Abstract: A method for determining a sonde error characteristic of an induction tool is disclosed. The method includes the step of measuring an electrical characteristic which may be the real or quadrature component of conductivity, at two or more different heights above the earth. The sonde error characteristic is determined as a function of a predetermined relationship between the desired sonde error characteristic and the measurements of that characteristic at two or more different heights above the earth. The method may be performed with the tool disposed substantially parallel to the earth. Alternatively, the tool may be disposed substantially perpendicularly to the earth.

Abstract: Induction logging sonde including transmitter and receiver solenoid coils mounted on a support and axially separated from each other. The support is made of conductive material and comprises at least one first longitudinal portion for mounting the coils and second longitudinal portions on each side of the first portion. At least the first portion has a substantially continuous and axisymmetric outer surface so as to favor the flow of eddy currents around the surface, whereby the electric field on that surface is substantially cancelled.

Abstract: A method and system for processing induction measurements of sub-surface formations taken by an induction logging system at various depths in a borehole is disclosed. The method reduces the effects of variations in the sonde response function with formation conductivity (skin effect). A filtering function is applied to the quadrature-phase X component measurement of each log measurement to obtain a correction component measurement representative of the change in the sonde response function as a function of formation conductivity. The correction component measurements are then summed with the in-phase R components to obtain a skin effect compensated log.

Abstract: A method and system for processing induction measurements of sub-surface formations taken by an induction logging system at various depths in a borehole is disclosed. The method reduces the unwanted contributions in the measurements from induction currents flowing in the formations spaced apart from each measurement depth (shoulder effect) and the effects of variations in the logging system transfer function with variations in the conductivity of the formations being investigated (skin effect). Shoulder effect is reduced by generating a spatial deconvolution filter which when convolved with the sonde response function sharpens the main lobe and reduces the sidelobes to near zero. The skin effect is reduced by filtering the quadrature-phase component measurements according to a non-linear spatial filtering function to obtain a correction component measurement representative of the change in the sonde response function as a function of the formation conductivity.