A Laboratory Instrument to Continuously Monitor The Compressive Strength of Cement Slurries

The "Ultrasonic Cement Analyzer" (UCA) is the name given a new generation device (Fig. 1) that continuously monitors strength development of oil well cement compositions. A single sample of cement slurry is placed in the instrument under pressure and heated to simulate downhole conditions. Measurements of the cement's ultrasonic velocity are started during the fluid state and continue through initial set to any desired point of partial or final strength development. Strength values are continuously computed and displayed until the test is terminated. The result is a complete and precise history of initial set and strength development which can be plotted versus time at any point of interest. The UCA functions with little operator attention aside from start up and shut down. The same information from standard API compressive strength crush tests would require curing a multitude of specimens to preselected test times, with no guarantee that the first test would be short enough or the final test long enough to accurately provide the critical information for the job. Since its introduction some two years ago, the principal advantage of the UCA has been simply to speed collection of reliable compressive strength data. For example, one technician with an eight-chamber UCA can produce more data than eight technicians and 64 separate curing autoclaves. In addition, human error and the opportunity for bias is greatly reduced with the UCA.