Induction Resistivity Tool that Generates Directed Induced Fields
In one aspect of the present invention, an induction resistivity tool includes an induction transmitter and an induction receiver located along the length of the tool. The transmitter is located adjacent at least one induction bucking coils of the tool. When activated the bucking coils are configured to direct a field transmitted by the induction transmitter away from the tool at an angle from the central axis of the tool.
1 . An induction resistivity tool, comprising:
at least one induction transmitter and at least one induction receiver disposed along a length of the tool;
the transmitter being disposed adjacent at least one induction bucking coil of the tool;
wherein when activated the at least one bucking coil is configured to direct a field transmitted by the induction transmitter at an angle less than 90 degrees from a central axis of the tool.
2 . The tool of claim 1 , wherein at least one bucking coil is in electrical communication with separate power sources.
3 . The tool of claim 1 , wherein at least one bucking coil is disposed at different heights.
4 . The tool of claim 1 , wherein at least one bucking coil is disposed at different distances from the transmitter.
5 . The tool of claim 1 , wherein the transmitter is positioned at an angle with respect to the central axis.
6 . (canceled)
7 . The tool of claim 1 , wherein at least one bucking coil is electrically isolated from another.
8 . The tool of claim 1 , wherein the transmitter comprises at least one coil wrapped around a circumference of the tool.
9 . The tool of claim 1 , wherein the transmitter comprises a plurality of units spaced along the circumference of the tool, wherein the units are electrically isolated from one another.
10 . The tool of claim 1 , wherein at least one of the bucking coils is in communication with a central processing unit.
11 . The tool of claim 1 , wherein at least one bucking coil is positioned at a distance from the transmitter greater than a distance of another bucking coil from the transmitter.
12 . The tool of claim 1 , wherein the induction field approaches, overlaps, or extends beyond the axial position of the bottom of the tool or a drill bit secured to the tool.
13 . The tool of claim 1 , wherein the at least one bucking coil has significantly more wire turns or wire of a different diameter or shape than another bucking coil.
14 . The tool of claim 1 , wherein the tool is part of a down-hole tool string.
15 . The tool of claim 1 , wherein the tool is part of a wireline assembly.
16 . A method for taking an induction resistivity measurement, comprising the steps of:
providing at least one induction transmitter and at least one induction receiver disposed along a length of the tool, and
projecting an induction field from the transmitter at an angle less than 90 degrees from a central axis of the tool,
processing the measurement based on the tool orientation within the borehole.
17 . The method of claim 16 , wherein the method comprises activating at least one induction bucking coils in any combination or pattern on either side of the transmitter.
18 . The method of claim 16 , wherein the method comprises an additional step of energizing one or more of the bucking coils more than one or more other coils.
19 . The method of claim 16 , wherein the method comprises an additional step of individually adjusting the field strength of the bucking coils.
20 . The method of claim 19 , wherein the step of adjusting the field strength of the bucking coils cause the angle of the induction field to sweep over a range of angles.