| 摘要 |
A method and apparatus provided for reducing the effect of magnetic materials, such as magnetite, in an earth formation on the electrical A.C. signal induced by protons of earth formation fluids precessing under the influence of the earth's magnetic field after the establishment and interruption of a polarizing field,d in an earth formation traversed by a wellbore. In accordance with the present invention, before the polarizing field, say of magnitude Hp gauss, is established within the earth formation (by passing a direct current through a field coil in a normal, first direction) the direction of the polarizing current, itself, is reversed for a predetermined time interval. Using only a single reversal of current (not oscillating)-suprisingly-demagnetizes enough of the magnetic particles within the earth formation which could cause inhomogeneities in the proton precessional field that the response characteristic of the subsequently detected A.C. signals are significantly improved, say, by twenty percent without hindering important digital control aspects of the logging process. The magnitude of the reverse
|
