Simulation Study On Downhole Flow Measurement Method Based On Ultrasonic Doppler Effect

In production logging,in order to evaluate reservoirs and predict production capacity,it is necessary to accurately determine the flow and properties of different layers of fluids in the well.However,the traditional measuring instruments' accuracy and resolution are affected in the harsh environment,only a small number instruments can be applied.Given that Openfield Technology designed the logging tool with stepped-structure transducer arrays by using ultrasonic pulse wave Doppler can improve the situation,domestic research on this technology is imminent.This paper has carried out theoretical research on this method.Firstly,the method and characteristics of flow measurement by two mode wave Doppler effect are introduced,which are continuous wave and pulse wave.Next,the numerical calculation of continuous wave Doppler theory is carried out.The sound field model of uniform motion sound source is established,which is divided into two cases: sound source and receiver are on the same line and on different lines,to verify the Doppler Effect and influencing factors.Then,the corresponding numerical simulation of ultrasonic pulse wave Doppler method is carried out,and an idealized sound field model is established according to the downhole transducer array measurement circumstance.The feasibility of the method and the influencing factors of the flow measurement are also explored in two cases.The results show that in both cases,main frequency of the received signal increases when the moving sound source is close to the receiver,and it decreases when the moving sound source is far away.The number of sound sources has almost no effect on the Doppler shift,that is,the problem of sound field of multiple moving sound sources can be simplified to a single moving sound source's problem,but the increase in the number of sound sources will increase the amplitude of received signal.Well,Doppler shift is proportional to the moving velocity of the sound source and the frequency of the transmitted signal,indicating that the method of inverting velocity and flow according to the change of received signal's frequency is feasible,and the selection of transmitted signal's main frequency also has an important impact on this result.