Well integrity and zonal isolation are crucial in deepwater wells requiring accurate cement bond log analysis. These wells require high mud weights and/or thick-wall casing strings that can prevent the use of some tools and, in the best case, result in a significantly reduced response and senstivity to the presence of cement. Guided Shear Horizontal (SH) modes generated by electromagnetic acoustic transducers (EMATs) provide an enhanced dynamic range response and are immune to any borehole content, either liquid or gas.
The response of SH modes is evaluated over a range of different casing diameters and thicknesses commonly encountered in deepwater wells in Brazil. This analysis includes analytical and numerical modeling that shows the changing attenuation response to varying cement properties. The unique feature of the SH modes is their response to only a solid coupled to the casing, enabling a straightforward analysis and interpretation. These results are also compared to standard compressional attenuation, demonstrating the enhanced sensitivity that the EMAT measurement provides.
The results demonstrate that the enhanced dynamic range of the SH modes often provides 300% or larger cement attenaution response over the standard compressional methods. This enhanced SH mode range shows the ability to use these data to directly determine the shear modulus of the material coupled to the casing, enabling a straightforward method for determining the presence of cement and its properties in-situ. This approach contrasts with conventional ultrasonic systems that respond to the compressional impedance, which can often have complications with heavy settled-solids behind the pipe. In addition, a case study shows the ability to see the formation-squeeze in heavy wall pipe. This evidence demonstrates the ability of SH guided modes generated by EMATs to provide enhanced cement evaluation in thick-wall casing. These modes provide an enhanced dynamic range and a straightforward and unique means determining the presence of a solid and its properties.