Research On The Acoustic-Intensity Response Of Different Density Cement Stone With Hollow Density Reducer

Low-pressure and easy-to-leakage formations are often encountered in cementing,and the ultra-low and low-density cement slurry system is an effective measure to solve the easy-to-pressure-leak formations and cement slurry leakage during the cementing process and improve the cementing quality.Due to the addition of density-reducing materials,the acoustic and strength characteristics of cement stones are very different from those of conventional density cement stones,resulting in the acoustic impedance of ultra-low and low-density cement stones being lower than those of conventional density cement stones.The existing cementing quality evaluation standards can no longer accurately evaluate the cementing quality of ultra-low and low-density cement slurry systems.Therefore,it is necessary to improve the cementing quality evaluation standards to make them suitable for different low-density cement slurry systems,and to provide certain guidance for on-site cementing quality evaluation.Based on the performance evaluation of cement slurry systems with different densities,this paper studies the sound velocity,compressive strength,and flexural strength development laws of cement slurry systems with different densities under different curing conditions,and establishes a relationship between the acoustic properties and strength characteristics of cement stones.Using X-ray diffraction and scanning electron microscope analysis methods to analyze the hydration products and microstructure,reveals the internal reasons for the sound wave propagation and intensity development of cement stone under different conditions.According to the law of sound velocity development,the optimal logging time of different density cement slurry systems at different temperatures is determined,and the evaluation criteria of ultra-low and low density cement slurry systems are theoretically studied and improved using the improved method of cementing quality evaluation index.Finally,the feasibility and accuracy of the theoretical study were verified through indoor and outdoor logging response simulation experiments,and improved cementing quality evaluation standards for different low-density cement slurry systems were proposed,and established a correction chart of cementing quality evaluation index based on compressive strength.Research shows that:cement slurry systems of various densities meet the requirements of cementing construction.In the early period of curing,the sound velocity and strength of cement stones of different densities increase with the increase of temperature,but in the later period of curing,the temperature has an effect on the sound velocity and strength of cement stones.The development has little effect;as the density increases,the sound velocity and strength of the cement stone increase,and the denser the cement stone interior.Regression fitting shows that the acoustic impedance and compressive strength of cement paste systems with different densities have a good quadratic relationship,and when the same compressive strength is reached,the acoustic impedance of low-density cement stone is very different from that of conventional density cement stone.When the temperature is 50-80℃,the best logging time for ultra-low and low-density cement slurry systems is about 72 h.This paper combines theoretical and experimental results to obtain:the cementing quality evaluation index of the cement slurry system of 1.10-1.20 g·cm^-3 is 30%and 50%;the cementing quality evaluation index of the cement slurry system of 1.25-1.33 g·cm^-3 is 25%and 45%;the cementing quality evaluation index of low-density cement slurry system above 1.50 g·cm^-3 is 20%and 40%.The improved cementing quality evaluation standard and correction chart are of great significance to field work.