| Water content of crude oil is a key index in the production process of oilfield,which is directly related to the judgment of the water yield of oil wells and oil producing horizon,and of great significance to estimate crude oil production and predict the development life of oil wells.Capacitance method has an important application in online measurement of water content in crude oil because of its advantages of high sensitivity,simple structure,reliable operation and low cost.However,in practical application,the measurement results are greatly affectd by parasitic capacitance,leakage resistance and environmental factors such as temperature,salinity and other factors,so the measurement accuracy can not be guaranteed.This paper studies the probe structure design and environmental impact compensation,designs the triaxial shielding structure capacitance sensor probe,proposes the joint compensation method of temperature and salinity,develops the online measurement system for water content in crude oil,and completes the experimental verification.The main work of this paper is as follows:A capacitance sensor probe based on active excitation shielding is designed.The sensing model of the coaxial cylindrical capacitive sensor is established,and the environmental interference factors affecting the capacitive sensor are defined.A triaxial probe structure is constructed by using insulation layer and shielding layer.The influence of parasitic capacitance and leakage resistance is shielded by equipotential excitation.The simulation results show that the sensor structure based on triaxial shielding structure can significantly reduce the influence of parasitic capacitance and leakage resistance on the accuracy of moisture content measurement.A simplified temperature-salinity joint compensation method is proposed.The correlation models of temperature-capacitance and salinity-capacitance were established.Combined with the correlation function of temperature-salinity-dielectricconstant,the simplified model of temperature-salinity joint compensation for water cut measurement is constructed by polynomial regression to compensate the influence of temperature and salinity.The experimental results show that the maximum measurement error of water content measurement system in the temperature range of30～55 ℃ and salinity range of 0～62.25 g/L is reduced from 4.38% to less than 0.1%,which effectively reduces the influence of environmental factors on the measurement of water content of crude oil and improves the measurement accuracy of water content of crude oil.An on-line measurement system of water content of crude oil based on capacitance method is developed.Based on Lab VIEW platform,the upper computer software program is developed,and the system performance test experiment and environmental impact compensation experiment are carried out.The experimental results show that the measurement accuracy of the system is better than 0.1%,which meets the requirements of the system. |
