| 摘要 |
<p>A borehole guidance system for guiding reference well includes a multi-sectioned casing (14) in the reference well (10). A selected section of the casing (46), usually the lowest section, is electrically conductive and the next adjacent section (44) is electrically nonconductive. A wireline (60) connects a current source on the surface to the selected conductive section to produce a reference current (I) in the well. The reference current is injected into the earth and dissipated so that the current produces a reference magnetic field (100) surrounding the well which is unaffected by return currents.</p> |
