Methods and Means for Simultaneous Casing Integrity Evaluation and Cement Inspection in a Multiple-Casing Wellbore Environment

Abstract

An x-ray based cement evaluation tool for measurement of the density of material volumes within single, dual and multiple-casing wellbore environments is provided, wherein the tool uses x-rays to illuminate the formation surrounding a borehole, and a plurality of detectors are used to directly measure the density of the cement annuli and any variations in density within The tool uses x-rays to illuminate the casing surrounding a borehole and a plurality of multi-pixel imaging detectors directly measure the thickness of the casing The tool includes an internal length having a sonde section, wherein the sonde section further includes an x-ray source; a radiation shield for radiation measuring detectors; sonde-dependent electronics; and a plurality of tool logic electronics and PSUs. Other systems and subsystems appropriate for carrying out the foregoing are also disclosed, as are a plurality of example methods of use therefor.

Claims

1. An x-ray based cement evaluation tool for measurement of the density of material volumes, wherein the tool uses x-rays to illuminate a formation surrounding a borehole and a plurality of detectors are used to measure the density of the cement annuli and variations in density within, said tool further comprising: an internal length comprising a sonde section, wherein said sonde section further comprises an x-ray source; a radiation shield for radiation measuring detectors; sonde-dependent electronics; and a plurality of tool logic electronics and PSUs.

2. The tool of claim 1, further comprising a detector that is used to measure casing standoff such that other detector responses are compensated for tool stand-off and centralization.

3. The tool of claim 1, wherein said shield further comprises tungsten.

4. The tool of claim 1, wherein the tool is configured so as to permit through-wiring.

5. The tool of claim 1, wherein a plurality of reference detectors is used to monitor the azimuthal output of the x-ray source.

6. The tool of claim 1, wherein the shortest-axial offset imaging detector array is configured to distribute incoming photons into energy classifications such that photoelectric measurements may be made.

7. The tool of claim 1, wherein the x-ray source energy is capable of being modulated to modify the optimum-detector axial offset in order to assist with the creation of response sensitivity functions.

8. The tool of claim 1, wherein the tool is combinable with other measurement tools comprising one or more of neutron-porosity, natural gamma and array induction tools.

9. The tool of claim 1, wherein an azimuthally segmented acoustic measurement is integrated into the tool.

10. The tool of claim 1, wherein the tool determines the position, distribution and volume of fractures, either natural or artificial, within the formation surrounding the cased wellbore.

11. The tool of claim 1, wherein the tool is integrated into a logging-while-drilling assembly.

12. The tool of claim 1, wherein the tool is powered by mud-turbine generators.

13. The tool of claim 1, wherein the tool is powered by batteries.

14. The tool of claim 1, wherein the tool is configured so as to permit through-wiring.

15. The tool of claim 1, wherein a plurality of reference detectors is used to monitor the output of the x-ray source.

16. The tool of claim 1, wherein the shortest-axial offset detector is configured to distribute incoming photons into energy classifications such that photoelectric measurements may be made.

17. The tool of claim 1, wherein the x-ray source energies are modulated to modify the optimum-detector axial offset in order to assist with the creation of response sensitivity functions.

18. The tool of claim 1, wherein the tool is combinable with other measurement tools comprising one or more of neutron-porosity, natural gamma and array induction tools.

19. The tool of claim 1, wherein azimuthally segmented acoustic measurements are integrated into the tool.

20. The tool of claim 1, wherein the tool determines the position, distribution and volume of fractures, either natural or artificial, within the formation surrounding the cased wellbore.

21. The method of x-ray based cement evaluation for measuring the density of material volumes within single, dual and multiple-casing wellbore environment, wherein said method comprises: illuminating the formation surrounding a borehole using x-rays; using a plurality of detectors to measure the density of the cement annuli and any variations in density within; and illuminating the casing surrounding a borehole using x-rays and then using a plurality of multi-pixel imaging detectors to measure the thickness of the casing.

22. The method of claim 21, further comprising: measuring casing standoff such that other detector responses can be compensated for tool stand-off and centralization.

23. The method of claim 21, further comprising using a plurality of reference detectors to monitor the azimuthal output of the x-ray source.

24. The method of claim 21, further comprising: configuring the shortest-axial offset imaging detector array to distribute incoming photons into energy classifications such that photoelectric measurements may be made.

25. The method of claim 21, further comprising modulating the x-ray source energy source to modify the optimum-detector axial offset to aid the creation of response sensitivity functions.

26. The method of claim 21, further comprising combining the tool with other measurement tools comprising one or more of neutron-porosity, natural gamma and array induction tools.

27. The method of claim 21, further comprising integrating an azimuthally segmented acoustic measurement into the tool.

28. The method of claim 21, further comprising determining the position, distribution and volume of fractures, either natural or artificial, within the formation surrounding the cased wellbore.

29. The method of claim 21, further comprising using a plurality of reference detectors to monitor the output of the x-ray source.

30. The method of claim 21, further comprising configuring the shortest-axial offset detector to distribute incoming photons into energy classifications such that photoelectric measurements may be made.

31. The method of claim 21, further comprising modulating the x-ray source energies so as to modify the optimum-detector axial offset in order to aid the creation of response sensitivity functions.

32. The method of claim 21, further comprising determining the position, distribution and volume of fractures, either natural or artificial, within the formation surrounding the cased wellbore.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 illustrates an x-ray-based tool being deployed into a borehole via wireline conveyance. Regions of interest within the materials surrounding the borehole are also indicated.

[0029] FIG. 2 illustrates one example of the azimuthal placement of near-field imaging detector arrays, arranged so as to enable imaging of the inner-most casing.

[0030] FIG. 3 illustrates one example of the axial placement of near-field imaging detector arrays, arranged so as to enable imaging of the inner-most casing while illuminated by a conical beam of x-ray, while an array of longer offset detectors interrogate the materials surrounding the borehole using the same conical x-ray beam.

[0031] FIG. 4 illustrates how manipulation of an arrangement of collimators/shields can be used to select between a fixed plurality of x-ray beams, or a rotating set of x-ray beams, and further illustrates how the casing imaging detectors would be arranged.

BRIEF DESCRIPTION OF SEVERAL EXAMPLE EMBODIMENTS

[0032] The methods and means described herein for simultaneous casing integrity evaluation, through x-ray backscatter imaging combined with x-ray-based cement inspection in a multiple-casing wellbore environment, is deployed in a package that does not require direct physical contact with the well casings (i.e., non-padded). Furthermore, the method and means employ an actuated combination of collimators, located cylindrically around an X-ray source within a non-padded concentrically-located borehole logging tool, together with a single or plurality of two dimensional per-pixel collimated imaging detector array(s) used in certain embodiments as the primary fluid/offset compensation detectors. The capability of actuation of the collimators permits the operator, the opportunity between a fixed collimator mode, that provides the output of an azimuthal array of a plurality of x-ray beams (from said x-ray source), or to select through actuation, a mode that produces a single or plurality of individual azimuthally arranged x-ray beams that ‘scan’ azimuthally, through the rotation of one of the collimators.

[0033] In one example embodiment, an electronic-source-based borehole logging tool [101] is deployed by wireline conveyance [104] into a cased borehole [102], wherein the density of materials surrounding the borehole [103] are measured by the tool. In a further embodiment, the tool is enclosed in a pressure housing, which ensures that well fluids are maintained outside of the housing.

[0034] FIG. 2 further illustrates how an azimuthal plurality of per-pixel collimated two-dimensional detectors [201] can be used to create a plurality of two-dimensional images of the well casing [202] as the tool [203] is logged. The output from each pixel can be summated as a function of depth to provide tool offset (eccentricity) data which acts as a key-input into the fluid compensation of the detectors that possess a larger axial offset (cement evaluation detectors), and hence, a deeper depth of investigation into the materials surrounding the borehole.

[0035] FIG. 3 illustrates that as the x-ray beam [309] (shown as a cone) interacts with the media surrounding the tool [307] within the borehole [301, 302, 303, 304, 305], the counts that are detected at each axially offset group of detectors [310, 311, 312, 313, 314] is a convolution of the various attenuation factor summations of the detected photons as they travelled through and back through each ‘layer’ of the borehole surroundings [301, 302, 303, 304, 305]. The data each detector may be deconvoluted through the use of the data collected by the 1st order detector group [310], to compensate for fluid-thickness and casing variations alone. As the first order detector [310] is a per-pixel collimated imaging detector array, the detectors are also capable of creating backscatter images of the casing [305] itself. When the tool is actuated axially (through wireline logging) the images, collected as a function of axial offset/depth, can be tessellated to produce long two-dimensional x-ray backscatter images of the casing [305]. The backscatter images may also contain spectral information, such that a photo-electric or characteristic-energy measurement may be taken, such that the imaged material may be analyzed for scale-build up or corrosion, etc.

[0036] In one embodiment, cylindrical collimators are used to provide directionality to the output of an x-ray source located within the pressure housing of a borehole logging tool. An x-ray beam or plurality of beams, rotating azimuthally around the major axis of the bore tool, interacts with the annular materials surrounding the wellbore within a single or multi-string cased hole environment to produce both single and multi-scatter responses, depending upon the axial offset of a plurality of fixed detectors that are employed to measure the incoming photons resulting from said scatter. In a further embodiment, an azimuthal plurality of per-pixel collimated two-dimensional detectors can be used to create a plurality of two-dimensional images of the well casing as the tool is logged.

[0037] FIG. 4 further illustrates the rotation of the collimator [404], which permits an increase of the discrete resolving power of the azimuthal location of density variations in the annular materials surrounding the wellbore in multi-string cased-hole environments. An axial plurality of fixed collimated detector-sets [401] can be used to measure the multiple-scatter signal resulting from the interaction of the beam with the casings and annular materials. The collimator sleeves [405] may be actuated to enable the selection of varying x-ray beam output modes [402, 403]. In one example of such an arrangement, a non-rotating plurality of azimuthally located x-ray beams [402] is provided, wherein each beam is accompanied by an axially-paired two dimensional per-pixel collimated imaging detector array [401]. In another example of such an arrangement, the axial actuation of one sleeve [405] and the rotation of another [404] produce a single or multi-element azimuthally rotating beam [403] (similar to a lighthouse). The azimuthal plurality of detectors [401] rotates with the source collimation sleeve, such that the result is a multi-helical ribbon image that can be re-formatted to create a complete image of the 360 degrees of the casing as a function of depth/axial-di stance.

[0038] In yet another embodiment, the collimators are used to provide directionality to the output of an x-ray source are square, formed tubes disposed within a shielding material. In a further embodiment, the collimators are used to give directionality to the output of an x-ray source are rectangular formed tubes within a shielding material.

[0039] In one embodiment, the output from each pixel is summated as a function of depth to provide tool offset (i.e., eccentricity) data which acts as a key-input into the fluid compensation of the detectors that possess a larger axial offset (cement evaluation detectors), and hence, a deeper depth of investigation into the materials surrounding the borehole.

[0040] In another embodiment, the backscatter images may also contain spectral information, such that a photo-electric or characteristic-energy measurement may be taken, such that the imaged material can be analyzed for scale-build up or casing corrosion, etc.

[0041] In a further embodiment, machine learning would be employed to automatically analyze the spectral (photo electric or characteristic energy) content of the images to identify key features, such as corrosion, holes, cracks, scratches, and/or scale-buildup.

[0042] In a further embodiment, the per-pixel collimated imaging detector array would be a single ‘strip’ array (i.e., one pixel wide) and multiple pixels long—the imaging result is a ‘helical’ ribbon image, that can be re-formatted to create a complete image of the 360 degrees of the casing as a function of depth/axial-distance.

[0043] In a further embodiment, the tool is maintained stationary in the well, and the source collimator would be rotated, the per-pixel collimated imaging detector array would be a single ‘strip’ array (i.e., one pixel wide) and multiple pixels long—the imaging result would be a ‘cylindrical’ ribbon image. Further passes of the rotating source/detector collimator could be accumulated such that the statistical accuracy (and therefore resolution) of the image is improved for each pass.

[0044] In a further embodiment, the tool is maintained stationary in the well, and the source collimator would be rotated, the per-pixel collimated imaging detector array would be a single ‘strip’ array i.e. one pixel wide, and multiple pixels long—the imaging result is a ‘cylindrical’ ribbon image. The tool could be moved axially (for example, by either a wireline-winch or with a stroker) and a new image set taken, such that a section of casing could be imaged by stacking cylindrical ribbon images/logs.

[0045] In a further embodiment still, machine learning is employed to automatically reformat (or re-tesselate) the resulting images as a function of depth and varying logging speeds or logging steps, such that the finalized casing and/or cement image is accurately correlated for azimuthal direction and axial depth, by comparing with CCL, wireline run-in measurements, and/or other pressure/depth data.

[0046] The foregoing specification is provided only for illustrative purposes, and is not intended to describe all possible aspects of the present invention. While the invention has herein been shown and described in detail with respect to several exemplary embodiments, those of ordinary skill in the art will appreciate that minor changes to the description, and various other modifications, omissions and additions may also be made without departing from the spirit or scope thereof.