Abstract: An induction logging sonde is disclosed for detecting the resistive properties of formations traversed by a wellbore. The transmitting and receiving circuitry of the induction sonde comprises triads of orthogonally wound transmitters and receivers that are capable of being driven in such a fashion as to electrically rotate the coils to emulate coils that are either perpendicular or parallel to the bedding planes in a dipping formation. These rotations can be varied at any depth by using the information of the dip and strike angles obtained from a pulsed method of operation of the sonde. Once the dip angle and strike angles are ascertained, the electronic rotation is chosen to orient the coils parallel to the bedding planes, thereby producing logs which are devoid of horns, while at the same time producing regional dip and strike angles. In addition, the electronic rotation is also chosen to orient the coils perpendicular to the bedding planes to measure electrical anisotropy.

Abstract: At least one transmitting coil 1 and at least one receiving coil 2 are disposed along the bore axis 18 of a borehole 7 such that these coils are inclined and face each other, thus causing these coils to have directivity for examining electric characteristics of a formation around the borehole. More specifically, a method of and an apparatus for directional induction logging are provided, which permit measurement of the electric conductivity distribution of a formation in the circumferential direction in a range of several meters around the borehole and also imaging reflecting the electric conductivity.

Abstract: A slot antenna has a square aperture and two current probes at angles to each other in the aperture. The two current probes are excited simultaneously or separately with different signals. By adjusting the amplitude or phase of the signals in the current probes, the angle of the magnetic moment of the antenna can be adjusted. An array of such antennas in an electromagnetic propagation tool for a well-logging device simultaneously provides better standoff performance by adjusting tile magnetic moment to be parallel to a borehole axis, and better image response by adjusting the magnetic moment to be perpendicular to the formation bed. The array can be excited to function as an endfire and broadside array of an electromagnetic propagation tool.

Abstract: The method and apparatus relies on a modified induction approach and preferably is incorporated into a metal drill collar for MWD measurements. Directional nulls are created in a primary changing magnetic field formed in a formation by a transmitting antenna which is in a groove on the surface of the drilling collar. Detecting antennas are placed at the directional nulls to enable the primary magnetic field to be decoupled from the same and allow it to be distinguished from the secondary field caused by the current induced in the formation by such primary field. The drill collar also carries a plurality of current detectors which detect the value of current induced in the formation to provide a resistivity profile immediately adjacent the borehole. A preferred embodiment uses a hybrid modified induction and electrical approach.

Abstract: A second receiver coil system (45a,45b) at right angles to the primary receiver coil system (40) in an induction logging tool (10) detects the skewness in the logging tool field pattern caused by the presence of assymmetrical formation structures (30). This skew signal, which provides a composite measure of the asymmetry of the formation structures (30), can be used to correct for horns produced in formation conductivity logs when the logging tool sonde (14) traverses interfaces between dipping beds. The skew signal can also be used to determine the dip and strike angles between such dipping beds.

Abstract: The invention relates to a device for the determination, in a borehole, of the slope and of the azimuth of a discontinuity layer in a homogeneous terrain. It includes three emitting induction coils (1a, 1b, 1c) and three receiving induction coils (2a, 2b, 2c), means for supplying each of the emitting coils with alternating electric current, means for measuring the responses of each of the receiving coils and for isolating in each of the three responses the part resulting from the excitation of each of the emitting coils, and means (7) for deducing from the parameters thus obtained the slope and the azimuth of a layer crossed by the device.

Abstract: A method and apparatus for determining the distance and direction of a well from a borehole. A toroidal inductor surrounds a drill stem within a borehole. The inductor acts as a primary for a transformer, with the drill stem, the earth surrounding the borehole, and electrically conductive material at the target well forming a single loop transformer secondary. An oscillator is connected to the primary to produce an induced AC current in the secondary. Secondary current flowing in the target well produces an AC secondary magnetic field which is detected at the borehole.

Abstract: An anisotropic well logging system includes a well logging tool including a first transmitter coil spatially arranged within the well logging tool in a first predetermined manner and a second transmitter coil spatially arranged within the well logging tool in a second predetermined manner which ultimately transmits electromagnetic energy into the formation at a frequency which enables electromagnetic energy to propagate through the surrounding earth formation. A first pair of receiver coils spaced a predetermined distance from each other and from the first transmitter coil and spatially arranged within the well logging tool in the same manner as the first transmitter coil provides signals in accordance with the received electromagnetic energy.

Abstract: Apparatus and method are disclosed for determining properties of subsurface formations surrounding a borehole by induction logging. The properties which can be determined include the formation dip angle and dip azimuth angle. Indications of formation anisotropy can also be obtained. An array of individually energizable transmitter coils is provided, preferably including three coils having mutually orthogonal axes. Electronic transmitter steering circuitry is provided for controlling the energizing means to electronically steer the direction of the magnetic moment resulting from the magnetic field components generated by the transmitter coils. An array of receiver coils is also provided along with receiver processing circuitry for processing signals induced in the receiver coils. The array of receiver coils preferably includes three receiver coils having mutually orthogonal axes.

Abstract: Two mutually orthogonal radiating antennas each transmit electromagnetic radiation to three mutually orthogonal receiving antennas. The transmitted electromagnetic radiation carries data characterizing the phase and magnetic moment of the electromagnetic radiation. Measurement of the two transmitted signals as received by the set of three orthogonal receiving antennas produces information which, in combination with two known position or orientation parameters, is sufficient to determine in a noniterative manner the six position and orientation parameters of the receiving antennas with respect to the radiating antennas. Use of only two radiating antennas increases the speed of the system and simplifies the transmitter. Alternatively, three radiating antennas and two receiving antennas may be provided to simplify the receiver.

Abstract: An induction well logging apparatus and method is disclosed for determining dip and/or anisotropy parameters of formations surrounding a borehole. A transmitter is provided and includes a first transmitter coil having an axis which is substantially parallel to the borehole axis and a second transmitter coil having an axis which is substantially perpendicular to the borehole axis. A receiver is provided and includes first and second receiver coils having axes which are substantially mutually orthogonal. Each of the receiver coils is substantially perpendicular to the borehole axis. The transmitter and receiver are mounted in a mechanically passive manner on a support member adapted for movement through the borehole. The transmitter coils are energized in a manner which permits the separate detection at the receivers of the currents induced in the formations by each of the two transmitter coils.

Abstract: Measuring of mixed phased flows to determine flow regime through the use of circumferentially shifted electric fields and measurement of resultant diametral and chord conductances with certain combinations of ratios of diametral to cord conductances serving as a signature of flow regime.

Abstract: The probe comprises two inductance windings mounted in opposition and conted to an a.c. generator, a measurement winding placed at right angles between the two inductance windings and a measurement voltage detector. A compensation winding is placed coaxially and symmetrically with the measurement winding in relation to the axis of the inductance windings, thus permitting enhanced sensitivity of the probe and a directional effect. Potential applications include continuous recording of magnetic susceptibility along a vertical borehole wall and ore sorting on a conveyor belt.

Abstract: An instrument is disclosed for mapping vertical conductive fractures in a resistive bedrock, magnetically inducing eddy currents by a pair of vertically oriented, mutually perpendicular, coplanar coils. The eddy currents drive magnetic fields which are picked up by a second, similar pair of coils.