Cement-sheath integrity preventing interzonal communication is closely related to static gel strength (SGS). API Standard 65-2 puts importance on the critical gel strength period (CGSP) measurement, which begins when the critical static gel strength (CSGS) is developed and ends when 500 lbf/100 ft2 is attained. The three methods accepted in the industry to measure SGS development are continuous and intermittent rotation, followed by ultrasonic measurement. A laboratory-based study is presented in the complete paper that compares these measurement methods.
SGS Measurement Methods
Continuous-Rotation Device. The continuous-rotation device used for direct SGS measurement is equipped with a pressure vessel capable of maintaining the set temperature and pressure that simulates actual cementing conditions. The paddle drag created by the continuous movement is converted and measured as SGS by means of correlation.
Intermittent-Rotation SGS Device. This device keeps the cement slurry to be evaluated in a static condition inside a pressure vessel at controlled temperature and pressure.
