Primary Study On Phase Fraction Measurement Of Two-phase Flow With High Water Cut Based On Coaxial Capacitance Sensor

The water cut of crude oil is an important parameter in the petrochemical industry. The measurement of this parameter is significant for the exploitation, dehydration and gathering process. Because of the complex nature of oil water two-phase flow, it is difficult to measure the phase fraction and there is a lack of the precise equipment to satisfy requirements of the water cut measurement up to now. The real-time, accurate measurement of the water cut has become a critical problem to be solved in the oil field.The dielectric property of oil and water is different. The relative dielectric constant of the oil is about 2.3, while the one of the water is 80.The oil-water mixture with different water cut have different dielectric properties. In order to get water cut, dielectric property is measured by capacitance method in this paper.In this paper, the main work is shown as follows:1. In order to measure the water cut of oil/water two phase flow with high water fraction, a new method based on imaginary and real part demodulation was presented. The dielectric information of the mixture was obtained accurately, and then the relationship between dielectric and water cut was analyzed.2. With regard to the edge effect, spatial filtering effect, phase slip of oil water mixture and pressure loss, the coaxial capacitance sensor was optimized design. By using the circuit theory, the impedance of oil water mixture in the sensor and the influence of salinity on the result under different frequency were analyzed so as to get the proper exciting frequency.3. Based on the modularization method, an imaginary and real part demodulation system was designed. The demodulation board was designed, and a program of host computer was composed. A whole measuring system was constructed. The results of experiments proved that the measuring system was stably and reliably.4. The feasibility experiments results showed that the salinity has little influence on the imaginary part of the measured impedance, which is the foundation of the further study.Finally, some improvement suggestions are presented at the end of the thesis.