| 摘要 |
In accordance with illustrative embodiments of the present invention, a technique is disclosed for substantially eliminating noise from measurements of the spontaneous potential made in a borehole drilled into the earth. An exploring system in the borehole carries two electrodes and the potential is measured between one of these electrodes and an electrode remotely located therefrom to provide a first measurement. The potential between the two exploring device electrodes is measured to provide a second measurement. A low-frequency function of the first measurement and a high-frequency function of the second measurement are utilized to provide a substantially error-free spontaneous potential measurement. The two electrodes carried through the borehole can comprise the armor of a cable which supports a well tool in the borehole and an electrode mounted on the well tool. Alternatively, these two electrodes can take the form of two closely spaced electrodes on the well tool so as to give a differential or gradient-type measurement. This gradient measurement could also be obtained by measuring the naturally occurring current flow in the borehole. |
