Borehole Conductivity Simulator Verification and Transverse Coil Balancing

Abstract

Calibration of the arrays of a multicomponent induction logging tool is achieved by positioning the tool horizontally above ground. The upper and lower housings of the tool are connected by a borehole conductivity simulator which as a resistance comparable to that of a borehole. Axial and radial positioning of the transmitter coils is done by monitoring outputs at receiver coils to achieve a minimum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is best understood with reference to the accompanying figures in which like numerals refer to like elements and in which:

FIG. 1 (prior art) shows schematically a wellbore extending into a laminated earth formation, into which wellbore an induction logging tool as used according to the invention has been lowered;

FIG. 2A (prior art) illustrates a conventional resistivity measurement in the vertical direction;

FIG. 2B (prior art) illustrates a resistivity measurement in the horizontal direction;

FIG. 3 is an overall flow chart of the procedures of the present invention;

FIG. 4 illustrates a borehole conductivity simulator (BCS) used in the present invention;

FIG. 5 illustrates an assembly for calibrating of transverse arrays in a logging tool;

FIG. 6 illustrates an assembly for calibrating longitudinal arrays in a logging tool;

FIGS. 7-8 illustrate assemblies for calibrating XY cross-component arrays; and

FIGS. 9-10 illustrate assemblies for calibrating XZ cross-component arrays.

Claims

1. A method of preparing a multicomponent induction logging tool having a plurality of transmitter coils and a plurality of receiver coils, the method comprising: (a) positioning the logging tool in a calibration area substantially free from components capable of interfering with magnetic and electric fields produced by the said tool;(b) coupling a first conductive housing of the tool with a second conductive housing of the tool through a borehole conductivity simulator (BCS) having an impedance similar to that of a borehole environment;(c) activating a first coil of the plurality of transmitter coils and measuring a signal in a first coil of the plurality of receiver coils;(d) moving the first coil of the plurality of transmitter coils relative to a conductive feed-through pipe between the first housing and the second housing to reduce a magnitude of the signal; and(e) moving the first coil of the plurality of receiver coils relative to the feed-through pipe until the magnitude of the signal is substantially equal to zero.

2. The method of claim 1 further comprising positioning the first coil of the plurality of receiver coils in an eccentered position in the logging tool prior to step (d).

3. The method of claim 1 further comprising orienting the logging tool with its longitudinal axis substantially parallel to the ground.

4. The method of claim 1 wherein the first coil of the plurality of transmitter coils has an axis that is one of (i) substantially parallel to a longitudinal axis of the tool, and (ii) substantially orthogonal to a longitudinal axis of the tool.

5. The method of claim 1 wherein the first coil of the plurality of receiver coils has an axis that is one of (i) substantially parallel to a longitudinal axis of the tool, and (ii) substantially orthogonal to a longitudinal axis of the tool.

6. The method of claim 1 further comprising: (i) rotating the tool about a longitudinal axis of the tool;(ii) activating a second coil of the plurality of transmitter coils and measuring an additional signal in a second coil of the plurality of receiver coils; and(iii) moving the second coil of the plurality of transmitter coils with respect to the feed-through pipe to reduce a magnitude of the additional signal.

7. The method of claim 1 further comprising: (i) magnetically coupling the tool to a calibrator;(ii) activating the first coil of the plurality of transmitter coils;(iii) determining from a signal received at a specific coil of the plurality of receiver coils a transfer function between the specific coil and the first coil of the plurality of transmitter coils.

8. The method of claim 1 wherein the tool is positioned inside the calibrator.

9. The method of claim 1 wherein the moving is in a direction selected from (i) substantially parallel to a longitudinal axis of the tool, and (ii) substantially orthogonal to a longitudinal axis of the tool.

10. An apparatus for evaluating performance of a multicomponent induction logging tool having a plurality of transmitter coils and a plurality of receiver coils, the tool being positioned in a calibration area substantially free from components capable of interfering with magnetic and electric fields produced by the said tool, the apparatus comprising: (a) a borehole conductivity simulator (BCS) having an impedance similar to that of a borehole environment the BCS coupling a first housing of the tool with a second housing of the tool;(b) a processor configured to activate a first coil of the plurality of transmitter coils;(c) a first coil of the plurality of receiver coils configured to provide a signal responsive to the activation of the first coil; and(d) a device configured to: (A) move the first coil of the plurality of transmitter coils relative to the first coil of the plurality of receiver coils to reduce a magnitude of the signal; and(B) move the first coil of the plurality of receiver coils relative to the conductive feed-through pipe until the magnitude of the signal is substantially zero.

11. The method of claim 10 wherein the device is further configured to position the first coil of the plurality of receiver coils in an eccentered position in the logging tool.

12. The apparatus of claim 10 wherein the first coil of the plurality of transmitters has an axis that is one of (i) substantially parallel to a longitudinal axis of the tool, and (ii) substantially orthogonal to a longitudinal axis of the tool.

13. The apparatus of claim 10 wherein the first coil of the plurality of receivers has an axis that is one of (i) substantially parallel to a longitudinal axis of the tool, and (ii) substantially orthogonal to a longitudinal axis of the tool.

14. The apparatus of claim 10 further comprising a calibrator and wherein: (i) the logging tool is magnetically coupled with the calibrator, and(ii) the processor is further configured to determine from the signal a transfer function between the first coil of the plurality of transmitters and the first coil of the plurality of receivers.

15. The apparatus of claim 10 wherein the logging tool is positioned within the calibrator.

16. The apparatus of claim 9 wherein the device is configured to produce movement in a direction selected from (i) substantially parallel to a longitudinal axis of the tool, and (ii) substantially orthogonal to a longitudinal axis of the tool.