Through-Tubing Casing Deformation and Tubing Eccentricity Image Tool for Well-Integrity Monitoring and Plug Abandonment

Abstract

Casing deformation and tubing eccentricity is a concern in the oil and gas industry for safety and operational reasons. Casing deformation or tubing eccentricity originates from various sources such as well completion, corrosion, formation swelling, collapse, and salt dome creep. It is important to implement a well-integrity surveillance program covering all casing and tubing strings for the full well life cycle from initial completion to abandonment. However, there has been no effective through-tubing logging method to evaluate the casing string for deformation and eccentricity. This paper describes a new Deformation-and-Eccentricity (DEC) tool that is based on electromagnetic technology and designed to measure casing deformation and tubing eccentricity while logging inside completion tubing. The DEC tool generates a unique compressed-and-focused magnetic field that provides an increased signal-to-noise ratio (SNR). The tool then employs an array of magnetic sensors to measure the magnetic flux density distributions azimuthally around the tool. The tool’s compressed-and-focused magnetic field is designed to (1) saturate the magnetic flux of the tubing, (2) to inject more magnetic flux into the first casing behind the tubing, and (3) to increase the signal measurement sensitivity and SNR. The sensor matrix measures flux density changes that correspond to variations in distance between tubing and casing. The high-resolution azimuthal magnetic sensor matrix delivers high-accuracy measurements that are used to image the flux density changes. A finite-element-based forward modeling and an optimized Gaussian processes regression method have been developed to process the raw logging data. The DEC tool has a built-in orientation measurement capability that is based on gyroscopes and accelerometers that are used to align the deformation and eccentricity images and index curves as well as the tubing thickness image. The tool specifications state accuracies of 1% of the eccentricity ratio and 5% of the deformation ratio in the range of casing OD up to 13.375 in. DEC technology provides an advanced answer product for through-tubing casing deformation and eccentricity measurements in downhole well-integrity and plug-abandonment applications. When combined with other well-integrity measurements such as a multifinger caliper and multipipe thickness log tool, a complete well-integrity evaluation can be achieved throughout the life cycle of a well. For example, significant casing deformation can often indicate possible damaged cement behind the casing. Other applications for the technology include locating tubing clamps for fiber-optic cables and control lines and determining the orientation of multistring tubing completions. Performances of the tool have been validated through research simulations, lab tests, and field trials. This paper includes a field case study of a deviated gas production well with tubing buckling and casing micro dogleg.