Evaluation Method for Cementing Quality of Ultra-Low-Density Cement

For an accurate cementing quality evaluation of ultra-low-density cement slurry, an indoor experiment was carried out to study the influence of parameters such as curing time, temperature, and density on the strength and acoustic properties of ultra-low-density cement stone. The relationship equation between the compressive strength of cement stone with different density and the acoustic velocities of P-waves and S-waves was obtained by mathematical fitting. In combination with the downhole acoustic field analysis of cased wells, an improved algorithm of relative acoustic amplitude was developed for the evaluation of ultra-low-density cement slurry logging based on compressive strength, and a correction type-curve of relative acoustic amplitude was built on that basis. The verification results showed that for the cement slurry of cenospheres, the relative acoustic amplitude corresponded well to compressive strength, and with the increase in compressive strength, the relative acoustic amplitude decreased. Under the same compressive strength, the relative acoustic amplitude was reduced with the growth of cement slurry density. The research demonstrates that the application of the correction type-curve of relative acoustic amplitude for the cementing quality evaluation of ultra-low-density cement slurry can significantly improve the accuracy and pertinence of cemen-ting quality evaluation.