Since the discovery by Roentgen in 1895, X-rays have been used to “see” through otherwise opaque objects and very quickly were adopted by the medical community as a diagnostic tool. Almost everyone is familiar with chest X-rays, dental X-rays, and CT Scans. In all cases, the patient is radiated by X-rays, and the rays that penetrate and go through the patient are then recorded in some fashion. The equipment used to record the X-rays varies slightly from application to application, but in all cases, you must: 1. Generate the X-rays and 2. Record the transmitted or scattered X-rays.

The method of generating X-rays has not fundamentally changed since Roentgen’s discovery. Electrons are generated from a heated wire filament that heats a cathode inside a vacuum tube - like the filaments in incandescent lamps; subsequently, a high positive voltage is imposed on a metal electrode (anode) some distance away from the filament. The positive voltage on the metal electrode strips the electrons from the cathode and accelerates them toward the anode. Once the electrons slam into the metal target, X-rays are generated in all directions. The higher the voltage between the cathode and anode, the higher the kinetic energy of the electrons, resulting in higher energy X-rays with deeper penetrating power. To put things into perspective,  X-ray tubes are operated in the following voltage ranges for various applications: Dental 60-70 kV, CT 80-140 kV, X-ray Backscatter Devices 20-70 kV, and Structural Analysis 150-450 kV.

The VR360 application is similar to the higher end of the structural analysis application in that it requires an X-ray tube to be run at 380-400 kV or higher. At the same time, the imaging method used by the VR360 is closer to the method used in X-ray backscatter devices since the VR360 shines X-rays away from the borehole and subsequently detects and analyzes X-rays that have passed through the various layers in the oil well and scattered back to the VR360 detectors which are inside the well. This case is depicted below to the right in which a human being is imaged using an X-ray backscatter device. Conventional X-ray devices, on the other hand, use transmission X-ray imaging methods (see below to the right) since the X-rays are detected on the other side of the subject.

In all of these cases, a high-voltage generator and an X-ray tube are required to generate the X-ray radiation. This equipment (Generator plus X-ray tube) is established technology for most applications; however, it has never been developed to work at high temperatures in highly confined spaces afforded by oil and gas wells.

For example, a standard commercially available 450 kilovolt X-ray tube has a cylindrical shape and a diameter of ~ 6.7”, far too large to be put into an oil well outfitted with pipes with inner diameters as low as 3 ¾”. Just as important, a commercial tube is not designed to operate at high temperatures up to 150 °C and pressures up to 10,000 pounds per square inch—typical oil well conditions.

As a stepping stone to develop the VR360, Visuray developed a 1.95” diameter tube that functions at 220 kV and has been successfully tested in over 40 oil wells worldwide. A comparable commercially available X-ray tube has a diameter of 4.9”.  In the next step to develop the VR360, Visuray has developed a 400 kV X-ray tube with a diameter of 3.1”. Although this is small enough to be used in most wells in the North Sea, Visuray is now shrinking the 400 kV tube down to a diameter of 2.6” to access oil and gas wells with outfitted with small pipes such as ones found in the Gulf of Mexico and Australasia.

Visuray uniquely possesses the intellectual property rights for this technology in the oil and gas domain. Furthermore, no other company has even commenced trying to develop these compact high-voltage X-ray tubes.

A commercial X-ray tube is often sold with a high-voltage generator and an oil-based cooler to keep the anode from melting. Once again, commercially available systems are made for use at normal room temperature and pressure conditions with no constraints on the size of the equipment. A commercially available generator and cooler for use with a 450 kV X-ray tube occupies about 0.3 cubic meters of volume in the shape of large rectangular boxes with no dimension smaller than about 20”. At the same time, the equipment is not able to work at oil field temperatures and pressures. Once again, Visuray has developed a 180  kV generator with a diameter of about 2.3” and operates at oil well temperatures and pressures.

This system has been tested in over 40 oil wells worldwide. To generate 400 kV for the VR360, Visuray is developing two 200 kV generators with opposite polarity with diameters of 2.6” to drive the 400 kV tube. This represents a simple upscaling of the generator that the company has already qualified in real oil well tests. A cooler that operates at downhole temperatures and pressures and is used to cool the anode of the X-ray tube has been built and successfully tested in the laboratory.

Recording of X-rays in the recent past has shifted from using film to record transmitted or scattered X-rays to using electronic detectors. In the health and industrial applications mentioned above, the detectors are usually pixelated solid-state detectors using technology similar to what is inside a smartphone camera. Once again, these systems operate only at room temperature and will catastrophically fail at oilfield temperatures up to 150 °C.

In the oilfield, vacuum (photomultiplier (Extremely sensitive detectors that multiply the current produced by incident light by as much as 100 million times)) tubes mated with scintillating crystals such as NaI are used to detect scattered gamma rays emitted by radioisotopes to measure the bulk density of the earth formation that the well is penetrating to find deposits of oil. The typical commercial density measuring tool uses a 1.5 Ci ((for Curie) is a unit of radiation and is equal to 3.7×1010 particles emitted per second) source and 2 or 3 of these detectors. This is the closest the oil industry had come to developing a device to measure high energy photons (X-rays or gamma rays) in an oilwell until Visuray developed and tested a 180 kV, 10,000 Ci X-ray diagnostic tool in over 40 wells in 2016. The Visuray tool contained 6 pixelated detectors, each with 16,384 pixels. The detector was rated to 100 °C and was kept at a temperature of ~70 °C during its operation. The images collected by these detectors could distinguish features as small as 1 mm and were used to diagnose problems internal to the oil well.

These detectors have now been improved to operate at temperatures up to 150°C and are uniquely available to Visuray for the oil and gas domain. The VR360 will utilize up to 128 of these higher-temperature detectors, each with 1024 pixels, and generate about 40,000 Ci of radiation to penetrate multiple layers of steel and cement in the oil well. The VR360 would not be possible without a powerful X-ray source and sensitive solid-state detectors.