Electromagnetic Shear and Flexural Attenuation Combination to Overcome Cement Evaluation Challenges in Modern Wells

Cement integrity is very important in oil and gas industry and recently light weight cement slurries have been extensively used in modern wells due to multiple challenges i.e depleted reservoirs, small window of Equivalent Circulating Density (ECD). Evaluating such slurries has been always a challenge due to its very low acoustic impedance and the narrow dynamic range of compressional attenuation-based tools Electro Magnetic Acoustic Transducers (EMATs) are utilized to generate and measure acoustic guided waves directly on the casing. EMATs consists of an arrangement of coils, magnets, and conductive casing. The acoustic waves are generated by driving current through the coil, which creates eddy currents in the casing. Having this sensors setup allows for generation of shear and flexural waves directly on the casing and minimizes corrections required for borehole fluid. Typically, shear wave attenuation can be used as a solid identifier as it can propagate through solids no matter how light is it, which allows to confidently differentiate between light weight cement and liquid. on the other hand, the flexural waves attenuation measurement allows micro annulus detection without the need for additional pressure passes. Both waves attenuation responses are compared against conventional pulsed echo-based tool across light weight cement intervals. The horizontal shear measurements showed a clear attenuation response across light weight cemented sections as compared to lower attenuation from the compressional based tool light weight cement detection due to its unique ability to propagate across solids no matter its density. The flexural wave has a particle movement that's perpendicular to the casing plate which allows for its attenuation to overcome the micro-annulus effect and respond to the cement present behind the liquid filled micro-annulus while having the shear and compressional attenuation response close to free pipe attenuation range. The comparison clearly shows the value of using shear and flexural attenuation response to overcome typical cement evaluation challenges of micro-annulus and light weight contaminated cement with low acoustic impedance. This study shows the value of shear / flexural combination to overcome light weight cement evaluation challenge as well as liquid micro-annulus challenges with no need of additional pressure pass