Abstract: Apparatus and methods for estimating a value of a resistivity property of an earth formation intersected by a borehole. Apparatus may include a carrier conveyable in the borehole; a tri-axial induction antenna assembly along the carrier; and a magnetically transparent sleeve enclosing the antenna assembly. The antenna assembly includes panels circumferentially arrayed about a portion of the carrier to form at least three collocated antennas. Each panel includes a magnetic core, an axially sensing coil that is transversely wound about the magnetic core, and a laterally sensing coil that is longitudinally wound about the magnetic core. The axially sensing coil of each panel may be electrically connected to the axially sensing coils of the other panels to form an axial antenna. Corresponding lateral coils may be electrically connected to form a lateral antenna. Each panel may be individually removable from the carrier, and assembled together may form a cylinder.

Abstract: Apparatuses and methods are provided herein that may improve sensitivity to transient signals. For example, an electromagnetic sensor for downhole measurements that includes a plurality of sectors (e.g., four quadrants) is provided herein. Each quadrant may include a magnetic core formed of a material with a high initial magnetic permeability to improve sensitivity to transient signals. A sensor for continuous wave induction tools is also provided, and may include a magnetic core formed of a material with a high initial magnetic permeability. Forming each sector magnetic core of a material with a high mechanical reliability may allow the magnetic core of the corresponding sensor to be pliable and flexible and not brittle and prone to breaking. Furthermore, the corresponding sensor may have enhanced sensitivity, greater stability of sensitivity relative to temperature changes, and high mechanical reliability.

Abstract: Apparatus and methods for estimating a value of a resistivity property of an earth formation intersected by a borehole. Apparatus may include a carrier conveyable in the borehole; a tri-axial induction antenna assembly along the carrier; and a magnetically transparent sleeve enclosing the antenna assembly. The antenna assembly includes panels circumferentially arrayed about a portion of the carrier to form at least three collocated antennas. Each panel includes a magnetic core, an axially sensing coil that is transversely wound about the magnetic core, and a laterally sensing coil that is longitudinally wound about the magnetic core. The axially sensing coil of each panel may be electrically connected to the axially sensing coils of the other panels to form an axial antenna. Corresponding lateral coils may be electrically connected to form a lateral antenna. Each panel may be individually removable from the carrier, and assembled together may form a cylinder.

Abstract: Apparatuses and methods are provided herein that may improve sensitivity to transient signals. For example, an electromagnetic sensor for downhole measurements that includes a plurality of sectors (e.g., four quadrants) is provided herein. Each quadrant may include a magnetic core formed of a material with a high initial magnetic permeability to improve sensitivity to transient signals. A sensor for continuous wave induction tools is also provided, and may include a magnetic core formed of a material with a high initial magnetic permeability. Forming each sector magnetic core of a material with a high mechanical reliability may allow the magnetic core of the corresponding sensor to be pliable and flexible and not brittle and prone to breaking. Furthermore, the corresponding sensor may have enhanced sensitivity, greater stability of sensitivity relative to temperature changes, and high mechanical reliability.

Abstract: An apparatus for measuring a characteristic of an earth formation includes a drill collar configured to be inserted into a borehole of the earth formation, an electromagnetic sensor on the drill collar, and a non-conductive sleeve surrounding a circumference of the drill collar including the electromagnetic sensor and configured to press directly against the electromagnetic sensor.

Abstract: An apparatus and method for providing a downhole acoustic source is disclosed. The acoustic source includes a piston configured to oscillate in an axial direction of the acoustic source and produce an acoustic signal in a medium in contact with an exterior surface of the piston, and an elastomer disposed on an interior side of the piston, an acoustic impedance of the elastomer selected to match an acoustic impedance of the piston. A permanent magnet is configured to provide a permanent magnetic field oriented in the axial direction, and a coil disposed on an interior side of the piston produces an alternating magnetic field in the region of the permanent magnetic field. The elastomer may be, for example, a silicon rubber, a silicone jelly, and a silicone oil. A plurality of acoustic sources may be arranged to produce an acoustic dipole configuration or an acoustic quadrupole configuration.

Abstract: An apparatus and method for providing a downhole acoustic source is disclosed. The acoustic source includes a piston configured to oscillate in an axial direction of the acoustic source and produce an acoustic signal in a medium in contact with an exterior surface of the piston, and an elastomer disposed on an interior side of the piston, an acoustic impedance of the elastomer selected to match an acoustic impedance of the piston. A permanent magnet is configured to provide a permanent magnetic field oriented in the axial direction, and a coil disposed on an interior side of the piston produces an alternating magnetic field in the region of the permanent magnetic field. The elastomer may be, for example, a silicon rubber, a silicone jelly, and a silicone oil. A plurality of acoustic sources may be arranged to produce an acoustic dipole configuration or an acoustic quadrupole configuration.