Sectorial Scanning Electromagnetic Logging Opens Up New Frontiers in Downhole Corrosion Identification
Authors: Abdulghani A. , Muailu H. , Alghunaim E. , Hasan E. Murad , Miftakhov I. 
Published: May 2024

Quantifying downhole corrosion is one of the persistent challenges in the oil and gas industry. The aim is to prevent the ingress of undesirable fluids into the well-bore or to the surface. Various physical methods are employed to assess well-integrity, with electromagnetic (EM) technology standing out as one of the most popular. This paper proposes a novel solution, introducing a technology that employs electromagnetic field measurements with array sensors focused on specific areas of the pipe.

The combination of an array pulse and a traditional electromagnetic tool incorporates a generating-and-receiving electromagnetic coil wound on a core. The primary function of these tools is to capture signal decay in the time domain within receiver coils after emitting a magnetic pulse along the pipe during a survey. The induced ring currents in the pipe body generate an electromagnetic field in the receiver coils.

In contrast to the conventional electromagnetic tool, the array tool is equipped with eight identical sectorial sensors strategically positioned radially symmetrically. The small-sized and radially symmetric sensors make them sensitive to the metal thickness within a one-eighth radial sector. This approach allows for azimuthal localization of defects.

Integrating these technologies helps to overcome limitations in the existing well-integrity assessment methods, providing a comprehensive and accurate evaluation of tubular conditions. The utilization of array sensors enhances the spatial resolution of electromagnetic measurements, offering a detailed understanding of localized conditions within the well structure. Incorporating eccentricity measurement further contributes to a thorough assessment, ensuring proper tool placement and overall well-integrity.

The survey output from the array tool comprises eight sectorial thickness measurements for the first barrier, typically the tubing and liner. On the other hand, the conventional electromagnetic tool provides an average thickness of 360 degrees. The survey can be conducted during a logging up or down pass. This methodology enhances the accuracy and reliability of the data collected during the inspection.

The array pulse tool represents a cutting-edge electromagnetic survey method with comprehensive sensing capabilities. Its effectiveness extends to chrome completion and exhibits insensitivity to surface deposits. Furthermore, it has a major advancement during logging coated tubular pipes, such as Glass Reinforced Epoxy (GRE) in comparison with mechanical logging tools. It operates seamlessly in various fluid environments, including gas within the well-bore.

The utilization of sectorial pulse logging proves invaluable in ensuring localized metal loss zones. Moreover, specific eccentricity sensors play a crucial role in identifying any decentralization of the tool within the tubing and the tubing within the casing. This integrated approach provides comprehensive and precise assessments of the condition within the well, thereby optimizing the corrosion logging process.