Downhole optical imaging tools and methods
A disclosed downhole optical imaging tool includes a light source and a camera enclosed within a tool body having at least two sidewall windows. A first window transmits light from the light source to a target region in the borehole, while a second window passes reflected light from the target region to the internal camera. The target region is spaced along the borehole away from the second window in a direction opposite the first window. In some embodiments, this configuration is provided by angling the first and second windows with respect to the sidewall, or by shaping the windows to cast and receive light from a “forward” direction. Some tool embodiments include motion and/or orientation sensors that are employed by a processor to combine separately captured images into a panoramic borehole image. It can be employed during drilling operations employing air or a substantially transparent liquid as a drilling fluid.
1. An optical imaging tool for downhole use, the tool comprising:
a light source;
a camera; and
a tool body having a sidewall with:
a first window that transmits light from the light source to a target region in a borehole; and
a second window that passes reflected light from the target region to the camera, wherein the target region is downhole from the second window.
2. The tool of claim 1 , wherein at least one of the first and second windows has an outer surface that is angled with respect to the sidewall.
3. The tool of claim 1 , wherein the second window has an inner surface that is tilted relative to the sidewall.
4. The tool of claim 1 , wherein the tool body is mounted on a drill string.
5. The tool of claim 4 , wherein the drill string comprises coil tubing.
6. The tool of claim 1 , wherein the tool body is suspended from a wireline.
7. The tool of claim 1 , wherein the light source operates in at least one of the spectra in the group consisting of: infrared light, visible light, and ultraviolet light.
8. The tool of claim 1 , further comprising:
a tool motion or orientation sensor; and
a processor coupled to the sensor and the camera to combine multiple images into a panoramic borehole image that is compressed and transmitted to the surface.
9. A method for imaging while drilling, the method comprising:
using a drillstring to convey an optical imaging tool into a borehole containing a fluid;
illuminating a target region in a borehole via a first window in a sidewall of said tool; and
capturing an image of the target region via a second window in the sidewall of said tool, wherein the second window is downhole from the first window, and wherein the target region is downhole from the second window.
10. The method of claim 9 , wherein at least one of the first and second windows has an outer surface that is angled with respect to the sidewall.
11. The method of claim 9 , wherein the second window has an inner surface that is tilted relative to the sidewall.
12. The method of claim 9 , further comprising:
combining multiple captured images to form a panoramic image; and
transmitting a compressed representation of the panoramic image uphole.
13. The method of claim 12 , wherein said combining includes tracking tool motion and relating the multiple images based at least in part on said motion.
14. The method of claim 9 , further comprising determining fracture size and orientation based at least in part on said captured image.
15. The method of claim 9 , further comprising steering the drillstring based at least in part on said captured image.
16. The method of claim 9 , further comprising adjusting a parameter of a stimulation process based at least in part on said captured image.
17. The method of claim 9 , further comprising conducting a milling operation based at least in part on said captured image.
18. The method of claim 9 , wherein the fluid is a gas or a transparent liquid.
19. An optical imaging tool for downhole use, the tool comprising:
a tool body having a sidewall with at least one viewing window; and
a camera positioned within the tool body, wherein the camera captures images of a target region in a borehole downhole from the at least one viewing window.
20. The tool of claim 19 , further comprising at least one light source inside the tool body that illuminates the target region via an illumination window in the sidewall, wherein the illumination window is positioned uphole from said at least one viewing window.
21. The tool of claim 20 , wherein said at least one viewing window has parallel surfaces that are inclined relative to the sidewall.
22. The tool of claim 20 , wherein said at least one viewing window has an inner surface that is not parallel to the sidewall.
23. The tool of claim 19 , further comprising a second camera paired with the first camera to provide binocular three-dimensional images.
24. The tool of claim 19 , further comprising a processor coupled to the camera, wherein the processor measures temperature variation with respect to time.
25. A downhole logging method that comprises:
using a camera to collect measurements indicative of borehole wall temperature;
processing the measurements to determine rates of temperature change; and
displaying a borehole wall image based at least in part on measured rates of temperature change.
26. The method of claim 25 , wherein pixel values of the borehole wall image represent rates of temperature change.
27. The method of claim 25 , wherein pixel values of the borehole wall image represent heat capacity.
28. The method of claim 25 , further comprising heating or cooling a borehole fluid to cause changes in the borehole wall temperature.
29. The method of claim 25 , further comprising illuminating the borehole wall with an infrared source to cause changes in the borehole wall temperature.