Cements have numerous applications in the drilling, completion, work-over, and abandonment of wells. For each application, the cement is designed with special properties and is given additives that provide predictable slurry density, volume, viscosity, compressive strength, and thickening time. Thickening time, or the time a cement slurry remains able to be pumped into the well, is the most critical properties in designing a cement. A short thickening time is desired, while maintaining the special properties of the cement's design. The thickening time of a cement can be measured in a laboratory by testing a sample of the cement slurry in a Pressurized Consistometer. The elapsed time between an initial application of pressure and temperature on the slurry sample and the development of 100 Bearden units of consistency (Bc) is the thickening time for the sample at a particular specification test schedule [Table 8.2, API Spec 10(1)].
The Pressurized Consistometer incorporates a rotating, cylindrical Slurry Cup equipped with a stationary paddle assembly enclosed in a pressure chamber designed for a working pressure of 275 MPa (40,000 psi) at a maximum temperature of 315°C (600°F). (An air-operated hydraulic pump generates pressure to the cylinder assembly.) The hydraulic system incorporates a reservoir, piping, valves and filters. Heat is supplied to the chamber by a 5000-watt, internal, tubular heater controlled by the automatic temperature control system program. Thermocouples are provided for determining the temperatures of the oil bath and cement slurry.
The programmable temperature controller will automatically control the rate of temperature rise of the slurry (i.e. temperature gradient). When the slurry reaches the desired maximum temperature, the controller will hold the slurry temperature at that level. Pressure settings are maintained through the control of a pressure release valve and air pressure available to the pump.
The slurry container is rotated at a constant speed of 150 +/- 15 rpm by a Magnetic Drive. Drive torque is transmitted from a set of outside drive magnets, through a non-magnetic housing, to permanent magnets attached to the rotating shaft within the cylinder. Permanent, rare earth magnets are used to ensure high torque and a long magnetic-field life.