Abstract: An induction logging tool is used in an inclined borehole for determining properties of subsurface formations formation away from the borehole. Measurements are made at a plurality of transmitter-receiver (T-R) distances. After correction of the data for skin effects and optionally correcting for eddy currents within the borehole, the shallow measurements (those from short T-R spacing or from high frequency data) are inverted to give a model of the near borehole (invaded zone resistivity and diameter) and the resistivity of the formation outside the invaded zone. Using this model, a prediction is made of the data measured by the mid-level and deep sensors (long T-R spacings). A discrepancy between these predicted values and the actual measurements made by the midlevel and deep sensors is indicative of additional layer boundaries in the proximity of the wellbore.

Abstract: An apparatus for determining radial distribution of resistivity of earth formations surrounding a wellbore. The apparatus includes a sonde mandrel having an insulating exterior surface and electrodes disposed on the insulating surface at spaced apart locations. The electrodes are connected to circuits for measuring a focused current resistivity within a predetermined longitudinal span. The electrodes are also connected to circuits for measuring electrical impedance between pairs of electrodes spaced apart at a plurality of different longitudinal spacings. The preferred embodiment includes a voltage measuring circuit interconnected between a pair of electrodes which is positioned between a closest spaced pair of electrodes connected to the impedance measuring circuits, so that a vertical resolution of the impedance measurements can be limited to approximately the axial spacing of the pair of electrodes connected to the voltage measuring circuit.

Abstract: A differential array instrument for determining selected parameters of an earth formation surrounding a borehole, including an instrument mandrel carrying a single source electrode for injecting an electrical current of a predetermined value into the formation surrounding the borehole, and an array of a plurality of measurement electrodes uniformly and vertically spaced from said source electrode along the instrument mandrel. A predetermined group of the uniformly and vertically spaced electrodes are adapted to derive first and second difference potentials between the predetermined group of electrodes, wherein successive ones of a plurality of the predetermined group of selected measuring electrodes uniformly and vertically spaced at increasing distances from the source electrode axially of the borehole are adapted to derive a plurality of the first and second difference potentials between the predetermined group of electrodes.

Abstract: A single well transient electromagnetic ("TEM") apparatus and method is disclosed. The invention includes a wireline logging tool adapted for disposition in a borehole drilled in earth formations that has mounted thereon an electromagnetic transmitter and electric field transmitter for applying electromagnetic energy to the formation that will maximize the radial depth of penetration of the energy into the formation. The logging tool further includes an electromagnetic receiver and electric field receiver for detecting the electric field and magnetic field components created in the formation by the TEM transmitter. The electromagnetic transmitter and receiver preferably comprise three-axis electromagnetic coils, and the electric field transmitter and receiver preferably comprise three-axis electric dipole antenna elements. The tool may employ an array of the TEM transmitters and TEM receivers spaced axially along the tool in the borehole.

Abstract: A method of adjusting induction receiver signals for skin effect in an induction logging instrument including a plurality of spaced apart receivers and a transmitter generating alternating magnetic fields at a plurality of frequencies. The method includes the steps of extrapolating magnitudes of the receiver signals at the plurality of frequencies, detected in response to alternating magnetic fields induced in media surrounding the instrument, to a response which would obtain at zero frequency. A model of conductivity distribution of the media surrounding the instrument is generated by inversion processing the extrapolated magnitudes. Magnitudes of the receiver responses at the plurality of frequencies are synthesized based on the model of conductivity distribution.

Abstract: A method of determining selected parameters of an earth formation surrounding a borehole by first, obtaining at least one induction logging measurement of the selected parameters in a first predetermined volume of the formation surrounding the borehole having known first radial and vertical dimensions, then obtaining at least one galvanic logging measurement of the identical selected parameters in a second predetermined volume of the formation surrounding the borehole having known second radial and vertical dimensions that overlap the first radial and vertical dimensions of the first predetermined volume, whereby the overlapping volumes form a representative common volume of the formation, and then combining the induction and galvanic logging measurements using an inversion technique to obtain a measurement of the selected parameters of the earth formation surrounding the borehole in the representative common volume of the formation.

Abstract: A method of determining a plurality of formation models each of which will simulate the response of a well logging instrument. A measured response of the well logging instrument is used to generate an initial model using inversion processing. A response of the instrument to the initial model is synthesized. A singular value decomposition is performed on the synthetic response to generate eigenparameters of the initial model. Eigenparameters having the least significant overall contribution to the synthetic response are sequentially substituted with linear equations representing prior constraints on the initial earth model. A linear system, including the remaining ones of the eigenparameters and the linear equations is solved so that the eigenparameters are preserved exactly and the linear equations satisfy a least squares fit. An additional synthetic instrument response is generated for each solution to the linear system which falls below a predetermined error threshold.

Abstract: A method for producing synthetic tool responses for a well logging tool for an earth formation, the method including, in one aspect, generating wellbore logging data for a particular part of an earth formation with a wellbore logging system with a wellbore logging tool, the earth formation having at least one layer, producing an input earth model of the particular part of the earth formation based on the wellbore logging data, inputting the input earth model to a trained artificial neural network, e.g. resident in a computer, the computer with the trained artificial neural network processing the input earth model and producing synthetic tool responses for the wellbore logging tool for one point or for a plurality of points in the earth formation.

Abstract: A method of determining the conductivity of earth formations penetrated by a wellbore. The method includes inserting an induction well logging instrument into the wellbore. The instrument includes a transmitter, a source of alternating current connected to the transmitter, and a receiver. The transmitter is energized with the alternating current, voltages induced in the receiver are recorded, and area enclosed with respect to a baseline, by voltage peaks present in the recorded voltages is determined. The enclosed area corresponds to the conductivity.

Abstract: A method of measuring the conductivity of earth formations penetrated by a wellbore. The method comprises selectively passing an alternating current through transmitter coils inserted into the wellbore. Each of the transmitter coils has a magnetic moment direction different from the magnetic moment direction of the other ones of the transmitter coils. The alternating current includes a first and a second frequency. The amplitude at the first frequency has a predetermined relationship to the amplitude at the second frequency. The relationship corresponds to the first and the second frequencies. The method includes selectively receiving voltages induced in a receiver coil having a sensitive direction substantially parallel to the axis of the corresponding transmitter coil through which the alternating current is passed.