This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. This invention also relates to a method and apparatus for steering a downhole tool during a drilling operation in order to maintain the borehole within a desired earth formation. The steering capability is enabled by computing the difference or the ratio of the phase-based or amplitude-based responses of the receiver antennas which are mounted in planes that are not parallel to the planes of the transmitter antennas. Although this invention is primarily intended for MWD or LWD applications, this invention is also applicable to wireline and possibly other applications.

Electromagnetic wave resistivity tool having a tilted antenna for geosteering within a desired payzone

This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. Although this invention is primarily intended for MWD or LWD applications, this invention is also applicable to wireline and possibly other applications.

Electromagnetic wave resistivity tool having a tilted antenna for determining the horizontal and vertical resistivities and relative dip angle in anisotropic earth formations

Disclosed herein are electromagnetic resistivity logging systems and methods that employ an antenna configuration having at most two transmitter or receiver antenna orientations that rotate relative to the borehole. The measurements made by this reduced-complexity antenna configuration enable the determination of at least seven components of a coupling matrix, which may be determined using a linear system of equations that express the azimuthal dependence of the measurements. For increased reliability, measurement averaging may be performed in azimuthally spaced bins. The coupling matrix components can then be used as the basis for determining logs of various formation parameters, including vertical resistivity and anisotropy.

Antenna coupling component measurement tool having rotating antenna configuration

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.

Apparatus and method for determining parameters of formations surrounding a borehole in a preselected direction

Systems and methods for performing bed boundary detection and azimuthal resistivity logging with a single tool are disclosed. Some method embodiments include logging a borehole with an azimuthally-sensitive resistivity logging tool; deriving both a resistivity log and a boundary detection signal from measurements provided by said tool; and displaying at least one of the boundary detection signal and the resistivity log. The resistivity log measurements may be compensated logs, i.e., logs derived from measurements by one or more symmetric transmitter-receiver arrangements. Though symmetric arrangements can also serve as the basis for the boundary detection signal, a greater depth of investigation can be obtained with an asymmetric arrangement. Hence the boundary detection signal may be uncompensated.

Tool for Azimuthal Resistivity Measurement and Bed Boundary Detection

IN ACCORDANCE WITH ILLUSTRATIVE EMBODIMENTS OF THE PRESENT INVENTION, METHODS AND APPARATUS FOR DETERMINING THE POSITIONING OF FORMATION BEDDING PLANES BY ROTATING ONE OR MORE ELECTROMAGNETIC FIELDS THROUGH FORMATIONS SURROUNDING A BOREHOLE ARE ILLUSTRATED. IN ONE EMBODUMENT, A SOLENOID-TYPE COIL IS ENERGIZED WITH CURRENT AND ROTATED AT A SUBSTANTIALLY CONSTANT VELOCITY ABOUT AN ADJUSTABLE AXIS. AN AMPLITUDE MODULATED SIGNAL WILL THEN BE PRODUCED IN THE COIL IF THERE IS A CONDUCTIVITY CONTRAST OR GRADIENT IN THE FORMATION PLANE WHICH DEFINES THE SWEEP OF THE ELECTROMAGNETIC FIELD. THIS AMPLITIDE MODULATED SIGNAL IS THEN DEMODULATED AND THE RESULTING MODULATION SIGNAL IS SYNCHRONOUSLY DETECTED BY THE SIGNAL WHICH CAUSES THE COIL ROTATION. THIS PRODUCES PHASE COMPONENTS WHICH ARE USED FOR BRINGING THE AXIS OF ROTATION OF THE COIL INTO A SUBSTANTIALLY PERPENDICULAR DIRECTION TO THE LOW GRADIENT FORMATION PLANE AND INDICATING THE POSITIONING OF THIS PLANE. IN ANOTHER EMBODIMENT, TWO ELECTROMAGNETIC FIELDS ARE ROTATED AROUND A BOREHOLE AT SPACED APART DEPTH LEVELS BY SEQUENTIALLY COUPLING A PLURALITY OF CIRCUMFERENTIALLY SPACED COIL PAIRS TO THE ADJOINING FORMATIONS. THE SIGNALS FROM EACH COIL OF THE COIL PAIRS ARE COMBINED IN SELECTED RELATIONSHIPS TO PRODUCE A COMPOSITE SIGNAL FOR EACH COIL PAIR. THESE COMPOSITE SIGNALS ARE THAN USED TO ADJUST THE RELATIONSHIP WITH WHICH THE INDIVIDUAL COIL SIGNALS ARE COMBINED UNTIL EACH COMPOSITE SIGNAL HAS SUBSTANTIALLY THE SAME AMPLITUDE THUS INDICATING THE POSITIONING OF THE LOW CONDUCTIVITY GRADIENT FORMATION PHASE.

Loeb Julien M

Papers

Methods and apparatus for investigating earth formations utilizing rotating electromagnetic fields