An Electromagnetic Wave Based Water Cut Meter and the Influence Factors of Measuring Accuracy

Abstract Most of oil fields in China have stepped in the development stage of high water cut. The accurate measurement of downhole water cut is the key to master the developing status, upon which injection and production adjustment could be implemented to improve oil recovery. This paper proposed an electromagnetic wave based water cut meter, which can realize full-range measurement of the water cut with high resolution and accuracy. The measuring sensor is equipped with two coaxial cylindrical conductors, the oil-water mixture flows between the two conductors during the measurement. When electromagnetic wave transmits in the coaxial sensor full of mixed fluid of water and oil, the wave phase shifts regularly. The water cut of the mixed fluid is calculated through the measured phase variation. Based on the analysis of polarization principle, dielectric property, transmission law, and the circuit implementation, this paper established the mathematical model of electromagnetic wave phase variation, and determined the frequency of electromagnetic wave. Then an electromagnetic wave based water cut meter was proposed. Through simulations and experiments, the paper studied the influence factors of measuring accuracy, including the mixed fluid's temperature, salinity, pollution to the conductors, and emulsive state. The temperature and salinity show associated effects on the measuring result. If the salinity is low, the response of water cut meter decreases with temperature rising. If the salinity is high, the response is just the opposite. Under different emulsive states, the response frequency of the mixed fluid exhibit same tendency, although the frequency value may show some difference. The oil films adhered to inner or outer conductor both give rise to measuring errors, while the pollution to the inner conductor produces more obvious influence. The response characteristics of water cut meter were also summarized in the paper and the compensation methods to eliminate or reduce the interference were confirmed. At present, in most cases, the downhole water cut are measured during well logging or separate-layer producer testing. This paper proposes an electromagnetic wave based water cut meter, which can be equipped in the downhole production regulator and realize automatic production adjusting.