Visuray is using x-rays to give operators detailed 3-D pictures of the inside of their wells
What if you could see inside your well? The instinctive is answer is that with various imaging techniques, we already can. Cameras, electrical, acoustic and combination imaging techniques already offer a multitude of methods which enable us to examine or map the condition and layout of the wellbore – yet the value of those images depends on what exactly you need to do.
The major problem with optical imaging is that it requires a transparent fluid to be of any help – few cameras can see through opaque liquids. Ultrasonic techniques work with clear fluids but are less useful for fluids contaminated with particulates.
Stuck tools represent a particular problem. If a tool gets stuck downhole during a well intervention, options are limited in terms of its retrieval, especially when intervention engineers or slickline operators cannot see exactly what is going on. Impression blocks can be used, but do not offer much clearer insight than that suggested by a misshapen block of metal. Furthermore, even if the tool can be located and its position established, it is usually very difficult to retrieve it one piece with such a limited view.
Visuray’s approach is a departure from the industry norm; in a process called fluid-based surface imaging, it uses x-ray backscatter to produce highly detailed 2-D and 3-D images of hardware in the well.
Seeing is believing
The firm offers downhole x-ray imaging as a commercial service to operators looking to their wells in greater detail – particularly useful when undertaking well interventions. Its proprietary system, the VR90®, is a downward-facing x-ray tool which can be deployed downhole via coiled tubing and run via all types of electric wireline.
Inside the VR90 is a digital x-ray detector with a pixelated array based on applications from the medical sector, as well as a miniaturised, high-output x-ray source.
To power this, Visuray developed a compact, ultra-high output power supply which enables the 180-kV source to emit high-energy x-rays, using an electron beam current of 1mA. All of this is housed in a system measuring 3 5/8” (92mm), around 27.5 feet (8.4m) in length and weighing 236kg.
Miniaturising this technology was one of the Visuray team’s greatest challenges. The firm’s founding CEO and chief technologist, Phil Teague, explained to InnovOil: “We generate and control very high voltages within a very narrow grounded tool housing. State-of-the-art industrial power supplies of an equivalent voltage are similar in size to an oversized suitcase but only operate at room temperature – so reducing the size of such power supplies into a wireline deployable 3 5/8” tool while designing for high-temperature functionality was one of the key successes of the technology development.”
The detector itself is made up of six individual tiles measuring 128x128 pixels, each pixel of which measures 100 square micrometres. Information gathered by the array is then sent back to the surface for processing, generating 2-D and 3-D images for analysis by the operator. Rather than this being taken away to be processed, images can be produced in near real time, allowing intervention managers to make faster decisions about their wells.
The actual process enabling this is more complicated than it may sound. In backscatter imaging, the radiating source and the detector are positioned on the same side of the examined object. Traditionally, the detector is calibrated to form an image from the photons which are scattered and returned by the object – yet the metals used in oil wells tend to be very dense and will readily absorb photons. In addition since the object is immersed in the well fluid, the signal which returns is mostly comprised of backscatter from the fluid. That rules out using a simple x-ray backscatter setup.
Visuray navigates this problem using its proprietary technique. Fluid-based surface imaging assumes that photon scattering occurs mainly in the fluid with only a negligible contribution from the object itself. That means that the amount of scattering observed indicates the distances between the detector and the face(s) of the metal object. Using this principle, Visuray’s system reconstructs a 2-D and 3-D image of the object based on these spatial variations.
This inherently safe method can deliver a clear picture across all production fluids, even when they contain particulates such as sand or rust. It can also image hardware as it lies, without the need for cleaning, additional fluid displacement or chemical conditioning, all of which offers a considerable time and cost saving compared to other techniques.
Another particular advantage – though by no means a necessity – is that the 3-D image can be rendered in other ways. In conversation with InnovOil, Visuray demonstrated a 3-D printed resin model of a wrench, which had been modelled from a 3-D x-ray image. While it is unlikely to be useful to all operators, having an actual model of the tool to examine is a powerful physical tool to show just how accurate and informative the technique can be.
Currently, the VR90 works at temperatures of up to 100 °C and pressures of 20,000 psi, though recent improvements will see a 125 °C-rated model brought to market later in 2016. Teague says that this covers temperatures found in “the majority of wells,” but rules out high-temperature applications for the moment. “Wells with significantly higher temperatures, such as 150 °C, are currently prohibitive to the technology. However, we are continuing to increase the temperature rating of the technology and believe that we will be able to service the [these] wells in the future.”
Visuray remained drawn on the provisional cost of the service – Teague told InnovOil that the service was “comparable to the cost of running other imaging services” – but added that once the technology had proved its worth, a value pricing method would be agreed with its customers. Promisingly, those potential customers could be major operators – Statoil, BP and Royal Dutch Shell all contributed funds to the company’s initial start-up, with additional funding supplied in a later round by other joint industry partners.
So far, Teague said, “industry response to the technology has been very positive.” Late 2015 saw the company secure its first commercial well operation, where it used the VR90 to take 2-D and 3-D images of a coiled tubing BHA disconnect in an onshore well in the Netherlands, for TAQA Energy. As a result of the image accuracy, the assembly was retrieved in a single fishing run.
Beyond its direct use in imaging, Teague believes the technology holds a number of other possibilities that the company hopes to explore in future, adding: “It is possible to envision applications where it can be employed as a well integrity diagnostic method. The way in which we produce X-rays also eliminates the use of radioactive isotopes, [meaning that] many of the traditional oilfield measurements which rely on radioactive materials could be replaced with this core technology, in addition to new techniques and measurements.”
Overall, it is a highly promising innovation for an industry just beginning to get to grips with x-ray techniques in areas such as asset integrity and inspection. With even more focus being placed on cost and time efficiency, in new wells and old, the accuracy offered by the VR90 could make it an invaluable tool for the tech-savvy well manager.