Experimental Study On Downhole Ultrasonic Viscosity Measurement Technology

Petroleum is a very important fossil energy.With the continuous consumption of petroleum,numbers of oil fields have entered the stage of tertiary oil recovery,in which polyacrylamide aqueous solution i s most commonly used as oil-displacing agent.The oil displacement properties of polyacrylamide aqueous solution are closely related to its high viscosity,so it is important to be able to detect the real-time viscosity of polyacrylamide aqueous solution downhole.Although there are many methods for measuring fluid viscosity,due to the harsh downhole environment and small space,only the ultrasonic attenuation method is expected to achieve the final aim.At present,the ultrasonic attenuation method has not been commercialized,and there is no mature equipment that can be directly applied.Therefore,it is of practical significance to research and design downhole ultrasonic viscosity measurement devices and methods.The work in this article is divided into four parts,as follows:In the first part,we propose the technical scheme of downhole ultrasonic viscosity measurement.According to the principle of ultrasonic attenuation method to measure viscosity,a downhole ultrasonic viscosity measurement method and device are raised.According to the method of measurement and formula derivation,it is found that the downhole ultrasonic viscosity measuring device can only obtain the longitudinal viscosity of the oil-displacing agent but cannot directly obtain the shear viscosity.To obtain the shear viscosity of the downhole oil displacing agent,a laboratory measuring device is needed.In the second part,we introduce the design and working principle of the laboratory ultrasonic viscosity measuring device.Firstly,we use the viscometer to measure the shear viscosity of polyacrylamide aqueous of solutions different concentrations at different temperatures.Secondly,we measure the sound velocity and the attenuation of the sound amplitude when the ultrasonic wave passes through the polyacrylam ide aqueous solution at different temperatures using the laboratory ultrasonic viscosity measuring device.Combining with the previously measured dynamic viscosity values,we can establish a database of the relationship between the dynamic viscosity and the sound velocity and the sound amplitude attenuation,respectively.The parameters of the laboratory viscosity measuring device are the same as those of the downhole ultrasonic viscosity measuring device.Therefore,regardless the influence of pressure,as long as the temperature in the device and the sound velocity or sound amplitude attenuation of the sound wave are measured,the shear viscosity of acrylamide oil displacing agent can be obtained by comparing with the experimental measurement database.In the third part,we describe the preparation of polyacrylamide aqueous solution and the measurement of shear viscosity in detail.First,we prepare polyacrylamide aqueous solutions of different concentrations using the polyacrylamide powder.Then,we measure the shear viscosity with a rotary viscometer and monitor the real-time temperature of the solution by using a temperature sensor.The process of the shear viscosity measurement will be under two different kinds of conditions,which is to hold the temperature and the concentration of the solution unchanging,separately.Finally,we can obtain the relationship among the concentration,temperature and dynamic viscosity of the solution,and prepare for the next operation of experiment.In the fourth part,we discuss the relationship between the shear viscosity of polyacrylamide aqueous solution and the speed and attenuation of ultrasonic waves.We have obtained the relationship among the shear viscosity,solution concentration and temperature of the polyacrylamide aqueous solution in the third part.Therefore,in order to achieve the convenience of calculation,we can directly explore the relationship between the solution concentration and both latter ones and then relationship between the dynamic viscosity with the latter can be converted.In operation,we use the laboratory ultrasonic viscosity measuring device to measure the sound velocity and attenuation of ultrasonic waves passing through different concentrations of polyacrylamide aqueous solution at different temperatures to acquire the relationship between dynamic viscosity and sound velocity and attenuation,and then we could establish the corresponding database.In the fifth part,Design and simulation of piezoelectric viscosity measuring device.Aiming at the problem of unsatisfactory results in measuring the viscosity of the oil-displacing agent by the ultrasonic attenuation method,a piezoelectric shear driving beam was designed to measure the viscosity of the fluid by using the resistance effect of the viscous fluid on the moving objects in the fluid.In order to verify the correctness of the designed device,the COMSOL Multiphysics simulation software was used to simulate the movement of the device in polyacrylamide aqueous solutions of different viscosities.The results showed that the greater the viscosity,the smaller the displacement of the beam movement.The relationship can be measured by measuring the pressure.The displacement of the electric drive device is used to measure the viscosity of the downhole oil-displacing agent.