Fig. 2. VR90 is a wireline tool that incorporates the thermoionic X-ray tube with the imaging system components.
Te X-ray source and detector are both positioned on nearly the same side of the object of interest such that photons pass through the barrier, scatter from the object, and pass through the barrier again to enter the detector.
Contrast in an X-ray backscatter image
arises from differences in the number of photons scattered by the object of interest as compared to the background. Backscatter imaging works best when the object of interest scatters strongly and the background material does not, for example metallic or organic objects in air. Furthermore, the barrier cannot be too thick; otherwise it will scatter too strongly or absorb too many photons as they pass through. Visuray, a Stavanger, Norway-based
company, has developed a new wireline tool that creates X-ray backscatter images of objects within a production well. Tis novel technique turns the ‘noise’ into the desired signal by creating a reconstruction
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of the surface of an object based on the amount of scattering arising from the fluid between the source/detector and the object. Visuray calls this technique ‘fluid- based surface imaging’.
improved visibility enabled by Visuray’s VR90 X-ray based imaging tool allows oil companies to plan any well interventions precisely and efficiently.
H
To perform X-ray backscatter imaging in oil wells using the fluid-based surface imaging technique, a purpose-built thermoionic X-ray tube is installed along the axis of the tool. It is shielded such that X-rays are emitted as a broad beam primarily through the bottom nose of the tool. Te tube is operated at a voltage above 150 kVp and an electron beam current of 1 mA.
istorically oil companies have had no reliable means of imaging a well’s physical condition. The
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