X-ray Imaging Method Improves Well Intervention Diagnostics

Abstract

Technology Update Poor well performance and downhole failures have a significant effect on operator profitability. To combat this, operators spent nearly USD 10 billion in 2013 on time-consuming and costly well interventions to retrieve and repair completions hardware. A major factor contributing to the high cost of interventions is the lack of reliable information about the current condition of the downhole equipment. The ability to accurately visualize equipment in a well allows an operator to execute the remedial work plan more efficiently, thus saving time and money. Several methods are available for visualizing hardware downhole. The oldest technique uses a block of lead lowered into the well to take an impression of the object. While fast and inexpensive, the impression is often difficult to interpret. A more recent technology involves using ultrasonic imaging to produce an image of an object inside a fluid-filled well. However, this technique requires a knowledge of the exact specifications of the well fluid at the investigation depth to determine the speed of sound in the fluid. Furthermore, if the well fluid contains too many gas bubbles or suspended particles, then an excessive absorption and scattering of the ultrasonic beam will result in poor image quality. As a third option, optical cameras provide images in well fluids that are transparent to visible light or in gas-filled wells, but even small traces of oil or particulates will distort the images. As a result, operator costs increase not only for cleaning the well, but also for changing out the original well fluid with an optically transparent fluid before running the camera. The shortcomings of these methods led to a joint industry project to investigate the use of downhole X-ray imaging. However, common applications of X-ray imaging in the medical and security fields require access to both sides of the object, which is generally not possible in an oil well. Instead, a new technique has been developed using X-ray backscatter imaging. In backscatter imaging, both the X-ray source and detector are positioned on the same side of the object of interest. Emitted from the source toward the object, the X-ray photons pass through the opaque fluid, scatter within the fluid and from the object, and pass back through the opaque fluid to enter the detector. A conventional backscatter image is obtained by recording the photons scattered by the object. However, the object of interest inside an oil well is usually metal, often steel or another highly dense material, and these materials readily absorb photons. Therefore, the signal received in the detector is mainly composed of photons that have been scattered by the fluid, which rules out conventional X-ray backscatter imaging.