Abstract: Apparatus and method for detecting the formation and dissociation of gas hydrates in a fluid. The apparatus used comprises a piezoelectric crystal sensor and a signal analyzer. The crystal sensor has a deposition surface in contact with the fluid. Under a range of pressures and or temperatures the resonant frequency or an electrical parameter dependent on the resonant frequency of the piezoelectric sensor is measured. There is a step change in the resonant frequency which occurs upon the formation or dissociation of a clathrate hydrate on the deposition surface, so that the formation or dissociation of said clathrate hydrate may be detected.

Abstract: Apparatus and method for detecting the dew point or bubble point phase transition in fluid. The apparatus used comprises a piezoelectric crystal sensor and a signal analyser. The phase transition of the fluid is measured by monitoring, directly or indirectly, change in the resonant frequency of the piezoelectric crystal sensor while said one of the temperature and pressure is varied, so as to detect a substantial change in said resonant frequency and/or in the rate of change in resonant frequency with change in the varying one of the temperature and pressure.