Method for resistivity determination with borehole imagers

Patent metadata

Field	Value
Publication number	US-11249217-B2
Application number	US-201816605176-A
Country	US
Kind code	B2
Filing date	Nov 15, 2018
Priority date	Nov 15, 2018
Publication date	Feb 15, 2022
Grant date	Feb 15, 2022

Abstract

A method and system for resistivity imaging. A method may comprise disposing a downhole tool into a borehole, applying a voltage difference between the array of injector electrodes, constructing a first set of formation images for each of the plurality of frequencies, applying a mud effect removal algorithm to produce a second set of formation images for each of the plurality of frequencies, applying a dielectric correction algorithm to each of the plurality of frequencies to produce a third set of formation images for each of the plurality of frequencies, and combining the first set of formation images, the second set of formation images, and the third set of formation images to obtain a blended image. A system for resistivity imaging may comprise a downhole tool. The downhole tool may comprises a pad, an array of injector electrodes, and one or more return electrodes.

First claim

What is claimed is:

1. A method of resistivity imaging, comprising:
disposing a downhole tool into a borehole, wherein the downhole tool comprises:
a pad;
an array of injector electrodes; and
one or more return electrodes;

applying a voltage difference between the array of injector electrodes and the one or more return electrodes with a plurality of frequencies;
making an impedance measurement with the array of injector electrodes for each of the plurality of frequencies;
constructing a first set of formation images for each of the plurality of frequencies;
applying a mud effect removal algorithm to produce a second set of formation images for each of the plurality of frequencies;
applying a dielectric correction algorithm to each of the plurality of frequencies to produce a third set of formation images for each of the plurality of frequencies; and
combining every value from the first set of formation images, the second set of formation images, and the third set of formation images to obtain a blended image.

2. The method of claim 1 , wherein only two of the first set of formation images, the second set of formation images, and the third set of formation images are used in blending.

3. The method of claim 1 , wherein the blended image is formed based on a variation of first, second and third sets of images with frequency and wherein the variation is determined by taking a standard deviation of each pixel in the first set of formation images, the second set of formation images, and the third set of formation images over the plurality of frequencies for each set.

4. The method of claim 3 , further comprising applying a weighting function to each pixel of each of the first set of formation images, the second set of formation images, and the third set of formation images with weights that are inversely proportional to the standard deviation of each pixel to produce the blended image.

5. The method of claim 4 , wherein a switching algorithm is applied by setting the weights of any or all of the first set of formation images, the second set of formation images, and the third set of formation images to be zero for any pixel of the first set of formation images, the second set of formation images, or the third set of formation images.

6. The method of claim 4 , wherein the weighting function uses scaled versions of a standard deviations of the first set of formation images, the second set of formation images, or the third set of formation images.

7. The method of claim 6 , wherein a scaling factor is dependent on frequency, a design of the downhole tool, or is determined empirically.

8. The method of claim 1 , further comprising producing a processed image for each of the plurality of frequencies by combining the first set of formation images, the second set of formation images, and the third set of formation images for a specific frequency.

9. The method of claim 8 , further comprising applying a weighting function to each pixel of the processed image corresponding to the specific frequency in the first set of formation images, the second set of formation images, and the third set of formation images with weights that are inversely proportional to their standard deviations.

10. The method of claim 8 , further comprising obtaining the blended image from the processed image for each of the plurality of frequencies through a weighted averaging, a median selection, a minimum selection, or a maximum selection operation.

11. The method of claim 8 , further comprising designating a threshold, wherein real components of a pixel of the first set of formation images are designated as the pixel of the processed image if a standard deviation of both the second set of formation images and the third set of formation images are greater than the threshold for that specific pixel, and wherein the blended image is produced from a function of the processed image.

12. The method of claim 11 , wherein the threshold is based on the absolute value of the multi-frequency impedance measurement at a certain frequency.

13. A system for resistivity imaging, comprising:
a downhole tool, wherein the downhole tool comprises:
a pad
an array of injector electrodes; and
one or more return electrodes;

a conveyance for disposing the downhole tool in a borehole; and
an information handling system, wherein the information handling system is configured to measure an impedance for each of a plurality of frequencies and construct a first set of formation images from each impedance for each of the plurality of frequencies; apply a mud effect removal algorithm to produce a second set of formation images; apply a dielectric correction algorithm to produce a third set of formation images for each of the plurality of frequencies; and combine every value from the first set of formation images, the second set of formation images, and the third set of formation images to obtain a blended image.

14. The system of claim 13 , wherein the information handling system is configured to calculate a standard deviation for a variation over frequency of each pixel from the first set of formation images, the second set of formation images, and the third set of formation images.

15. The system of claim 14 , wherein the information handling system is further configured to apply a weighting function to each pixel of the first set of formation images, the second set of formation images, and the third set of formation images with weights that are inversely proportional to their standard deviations to produce the blended image.

16. The system of claim 13 , wherein the information handling system is further configured to use only two of the first set of formation images, the second set of formation images, and the third set of formation images in blending.

17. The system of claim 13 , wherein the information handling system is configured to produce a processed image for each of the plurality of the frequencies by combining the images from the first set of formation images, the second set of formation images, and the third set of formation images for a specific frequency using the variation of every pixel in each image set over frequency.

18. The system of claim 17 , wherein the information handling system is configured to produce the blended image from the processed images through a weighted averaging, a median selection, a minimum selection, or a maximum selection operation.

19. The system of claim 17 , wherein the information handling system is configured to designate a threshold, wherein real components of a pixel of the first set of formation images are designated as a processed image if the standard deviations of both the second set of formation images, and the third set of formation images for that specific pixel are greater than the threshold, wherein a blended image is produced from a function of the processed image.

20. The system of claim 19 , wherein the threshold is based on the absolute value of the multi-frequency impedance measurement at a certain frequency.

21. A method of resistivity imaging, comprising:
disposing a downhole tool into a borehole, wherein the downhole tool comprises:
a pad;
an array of injector electrodes; and
one or more return electrodes;

applying a voltage difference between the array of injector electrodes and the one or more return electrodes with a plurality of frequencies;
making an impedance measurement with the array of injector electrodes for each of the plurality of frequencies;
constructing a first set o

Assignees

• Halliburton Energy Services Inc

Inventors

• Guner Baris
• San Martin Luis Emilio

Classifications

• E21B47/00

  Survey of boreholes or wells (monitoring pressure or flow of drilling fluid E21B21/08) · CPC title

• G01V3/24 Primary

  using AC · CPC title

• G01V3/38 Primary

  Processing data, e.g. for analysis, for interpretation, for correction · CPC title

• G01V3/00

  Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation · CPC title

• G01V1/16

  Receiving elements for seismic signals; Arrangements or adaptations of receiving elements · CPC title