Oil and gas wells extend from the surface to one or more subterranean formations of rock containing oil and/or gas. The well is typically cased by cementing a steel or other suitable casing in the well bore. The casing stabilizes the sides of the well bore, prevents pollution of fresh water reservoirs and/or prevents fluids from zones other than oil and gas producing zones from entering the well bore.
Cementing operations pump wet cement slurry down a well bore to fill the space between the casing and the rock walls. The cement protects the casing and prevents water and other fluids from flowing vertically in the space between the casing and rock walls of the well bore. Typically, cementing operations are designed and supervised by engineers. Laboratory technicians test and select the cement slurry and additives.
Cement compositions are designed for a variety of well bore conditions, which may vary in depth, temperature and pressure. In designing a cement composition for a well bore, a number of potential slurries are typically tested for mechanical properties. Mechanical properties are often determined using circular cylinder samples. The samples are cured at pressure and temperature, depressurized, machined to proper geometry and dimensional tolerances, placed in a pressure vessel, re-loaded hydrostatically to a predetermined confining pressure, and then tested to failure. Another method for establishing mechanical properties is to measure acoustic velocities and calculate mechanical properties based on linear elastic theory and various empirical correlations. These dynamic measurements are performed at extremely high loading rates and the data is corrected for lower loading rates expected under in situ conditions.