| 摘要 |
<p>A downhole apparatus provides data communication by electromagnetic (EM) radiation between a downhole location and a surface station (50). Separate transmit and receive coils (52, 51) are provided downhole. The transmit coil (52) comprises a plurality of toroidal coils connected in parallel, while the receive coil (51) comprises a plurality of toridal coils connected in series, and all the individual coils are of identical construction. The coil axes are arranged to be aligned with the axis of an electrically conductive drill string (23 etc). The downhole installation is switchable by remote command between a mode in which the transmit coil (52) is arranged to be electrically connected to said drill string, and one in which it is electrically isolated from said drill string. A control system adapts the mode according to environmental conditions at the downhole location.</p> |
