Abstract: A resistivity logging apparatus has an array of electrodes projecting from imaging pads. The electrodes penetrate nonconductive mud lining the borehole wall. Some of the electrodes are moveable in and out of the pad while others of the electrodes can be fixed. The electrodes, which are arranged in an array along a circumferential portion of the borehole wall, are able to make contact with the borehole wall. Sequencing electronics causes one electrode to be a source, another to be a measuring electrode, with the measurements of source electrode and measuring electrode moving along the array in order to log a circumferential portion of the borehole wall.

Abstract: In an apparatus and method for actuating arms used on a borehole data-logging tool to deploy measuring instruments against a borehole wall, a mandrel is provided. At least one arm carried by the mandrel is mounted to the mandrel to move between an expanded position, in which a part of the arm projects from the mandrel, and a retracted position. A resilient biassing compression spring provides a resilient biassing force on each arm for biassing the arm towards its expanded position. A hydraulic piston and cylinder assembly associated with each arm restrains the arm against movement towards its expanded position. A drive piston and cylinder assembly acts upon the resilient biassing compression springs for adjusting the resilient biassing force acting upon each arm.

Abstract: In an electrical measurement apparatus and method for measuring an electrical characteristic of an earth formation, such as in a hole drilled for the exploration for hydrocarbons, a detection portion has an operational amplifier operating in voltage follower mode, with a measurement resistor in the feedback loop. The detection portion will typically include a plurality of sensor elements, and the operational amplifier can be switched between the sensor elements. The apparatus also includes a measurement portion adapted to measure the current flow through the measurement resistor, the calculation portion including an integrator.

Abstract: In an electrical measurement apparatus and method for measuring an electrical characteristic of an earth formation, such as in a hole drilled for the exploration for hydrocarbons, a detection portion has an operational amplifier operating in voltage follower mode, with a measurement resistor in the feedback loop. The detection portion will typically include a plurality of sensor elements, and the operational amplifier can be switched between the sensor elements. The apparatus also includes a measurement portion adapted to measure the current flow through the measurement resistor, the calculation portion including an integrator.

Abstract: A tubular cutting tool includes two or more sets of electrically actuated retractable anchoring legs (52,54) mounted at longitudinally spaced apart locations and an electrically driven rotary cutting head (14) with a retractable cutting blade (14). The anchoring legs can be arranged such that they are capable of compensating for variations in the internal radii of the tubular to be cut, thereby ensuring that the cutting tool is clamped rigidly in position.

Abstract: In an apparatus and method for actuating arms used on a borehole data-logging tool to deploy measuring instruments against a borehole wall, a mandrel is provided. At least one arm carried by the mandrel is mounted to the mandrel to move between an expanded position, in which a part of the arm projects from the mandrel, and a retracted position. A resilient biassing compression spring provides a resilient biassing force on each arm for biassing the arm towards its expanded position. A hydraulic piston and cylinder assembly associated with each arm restrains the arm against movement towards its expanded position. A drive piston and cylinder assembly acts upon the resilient biassing compression springs for adjusting the resilient biassing force acting upon each arm.