Patent FR-2845416-A1 (FR)
Title: Electrical diagraph probe, for measuring resistivity of bore wall, has electrodes held against bore wall by flexible extensible element inflated by pressurized fluid
Inventor: LE TROQUER YANN
IPC: E21B47/01
Filed: 2002-10-02
Abstract: Each electrode is fixed on the outside of a tube-shaped flexible, extensible element with satisfactory elasticity (9, 10), carried by the support (2) and defining a closed space (11, 12) between this element and the support. This is connected to a source of pressurized fluid inside the support, which inflates the flexible element to place the electrodes in contact with the bore wall  A hollow tubular support (2) for at least two separate metal electrodes (21) at a distance from each other at the periphery of the support on its outside. The support is introduced and moved in an un-lined bore made in the ground to be brought to a zone internal to the bore. The electrodes are connected outside the bore to a controller which contains an electrical generator and a device for measuring electrical resistivity. The closed space between the support and the flexible element is connected to the source of pressurized fluid by orifices in the wall of the support. The flexible element carrying the electrodes is an elastic sleeve surrounding the outside of part of the support, with the ends applied against the external surface of the support, to close the space, for example by external gripping rings made of metal or plastic. Each electrode is made of a series of metal bars at equal distance from each other on the surface of the flexible element, in at least two layers on top of each other and with one layer connected to the next by leaf springs to ensure mechanical connection and electrical continuity between the bars in the two layers. Alternatively, the electrodes are lozenges or other metal elements glued to or fixed by other means to the external surface of the flexible element and spread over its circumference. The electrode are connected to the electrical generator and the controller outside the tubular support by cables or linking wires passing inside the support after passing through holes in its wall. These cables or wires are at least as long as the depth of penetration of the support inside the bore. The support is closed at one end and connected at the other in a sealed manner to a flexible tube to feed the support with the pressurized fluid. The flexible feed tube is connected to a compressor via a manometer and control valve with a purge valve. The flexible feed tube encloses or supports the cables or linking wires. The closed end of the support includes ballast in the case of a vertical bore. The flexible element has a rigid hollow part fixed perpendicular to the electrodes and passing through the wall of the support by one of the orifices communicating with the closed space. Each electrode is carried by the flexible element with interposition between them of a thin band to allow humidification of the soil near the electrode. The humidification band is an extendable circular sleeve of hydrophilic cotton with an appropriate elasticity or other similar textile. The support carries several electrodes, in particular two, three or four connected separately or together to the controller.