Abstract: This disclosure relates to a sensor for imaging boreholes with improved durability to impact along the wall of the borehole, which may protect the sensor from premature wear. Such an apparatus may include a housing, one or more button electrodes coupled to the housing, one or more current return electrodes couple to the housing, and a guard electrode disposed at least partly around the one or more button electrodes. The one or more button electrodes may transmit or receive an electrical or electromagnetic signal through the underground formation, and the one or more current return electrodes receive or transmit the signal. The guard electrode may block portions of the electrical or electromagnetic signal that did not pass through the underground formation. In addition, the guard electrode may include a number of holes to enable the guard electrode to couple to the housing while providing additional structural durability.

Abstract: This disclosure relates to a sensor for imaging boreholes with improved durability to impact along the wall of the borehole, which may protect the sensor from premature wear. Such an apparatus may include a housing, one or more button electrodes coupled to the housing, one or more current return electrodes couple to the housing, and a guard electrode disposed at least partly around the one or more button electrodes. The one or more button electrodes may transmit or receive an electrical or electromagnetic signal through the underground formation, and the one or more current return electrodes receive or transmit the signal. The guard electrode may block portions of the electrical or electromagnetic signal that did not pass through the underground formation. In addition, the guard electrode may include a number of holes to enable the guard electrode to couple to the housing while providing additional structural durability.

Abstract: The techniques herein relate to a pressure compensation system. The system includes a downhole tool and one or more pressure compensators positionable in the downhole tool. Each pressure compensator includes a first compensating fluid section having a first compensating fluid, at least one second compensating fluid section having a second compensating fluid, and a convoluted membrane between the first and second fluids in the first and second compensating fluid sections, respectively. The first or second compensating fluid sections, or both, may include a porous disk positioned at a hole in the fluid section. The pressure compensator may also include a switch configured to indicate a fluid condition in the pressure compensator and a relief valve configured to release fluid from the pressure compensator.