| 摘要 |
<p>An instrument (10) is disclosed for measuring resistivity of Earth formations from within a conductive pipe (12) inside a wellbore drilled through the formations. The instrument includes a plurality of housings (18) connected end to end and adapted to traverse the wellbore. At least one electrode (A,P0-P6) is disposed on each housing. Each electrode is adapted to be placed in electrical contact with the inside of the pipe. The instrument includes a source of electrical current (32), a digital voltage measuring circuit (35B,35B*) and a switch. The switch is arranged to connect the source of electrical current between one of the electrodes and a current return at a selectable one of the top of the pipe (34B) and a location near the Earth's surface (34B*) at a selected distance from the top of the pipe (12), and to connect selected pairs of the electrodes to the digital voltage measuring circuit. The pairs are selected to make voltage measurements corresponding to selected axial distances and selected lateral depths in the Earth formations.</p> |
