Method for cement evaluation using acoustical logs

摘要

An improved method to determine the quality of a material disposed in an annular space behind a casing (or a liner) in a wellbore. A transit time of a sound wave to travel through a specimen of the material is determined, and a pulse velocity is calculated. The slurry density and mixing rate of the material are determined at a wellsite, and the slurry volume can then be calculated by multiplying the amount of time that the slurry remains at the slurry density by the mixing rate. The slurry has a theoretical acoustical impedance that is equal to the slurry density multiplied by the pulse velocity. The true annular displacement volume and a theoretical acoustical impedance map, an attenuation rate map, and a voltage map are than drawn. After running an acoustical log, a calculated acoustical impedance is derived, and is compared to the theoretical acoustical impedance to detertmine the quality of the material.