Detection Technology Of Fluid Dynamic Distribution In Core During CO₂ Flooding Under Reservoir Conditions

Real-time detecting the dynamic distribution of each phase fluid in the core during CO₂flooding under reservoir conditions provides important experimental evidence for understanding the migration process of fluids,oil displacement mechanism and permeability rule in pores of the core.To study the dynamic measurement of each phase fluid saturation,the visualization of fluid spatial distribution,the migration process of fluids and the migration rule during CO₂ flooding,this paper proposed a non-intrusive method based on ultrasonic transmission for real-time monitoring the fluid dynamic distribution in the core during supercritical CO₂ flooding.The main research works are summarized as follows:Ultrasonic test platform was designed based on original displacement equipment.Twenty-five pairs of ultrasonic probes were evenly placed on the upper surface and lower surface of the core model（30cm in length,30cm in width and 6cm in height）.Water flooding and CO₂ flooding experiments were performed under reservoir conditions（high temperature and high pressure）.Waveform data that ultrasounds transmitted through the core were measured.Data consist of 6521 sets of water flooding experimental data and32175 sets of CO₂ flooding experimental data.Ultrasonic signals received from receiver probes contained much feature information inside the core.The change of each phase fluid saturation in the core would lead to the change of two sensitive features（average ultrasonic velocity and ultrasonic amplitude attenuation）.Thus average ultrasonic velocity and ultrasonic amplitude attenuation were used to reflect the feature information inside the core.Displacement front were detected by finding the catastrophe point of average ultrasonic velocities or ultrasonic amplitudes attenuation that ultrasounds transmitted through the core.When the average ultrasonic velocity of a certain position in the core had a sudden change,it indicated that each phase fluid saturation in the core had a sudden change.It was the sudden change moment that displacement front arrived.In the same way,when the ultrasonic amplitude attenuation of a certain position in the core had a sudden change,fluid saturation changed suddenly and the displacement front arrived.Water flooding oil saturation mathematical model based on ultrasonic velocity was built.The first break time was used to reflect the average ultrasonic velocity.Oil saturation was linear with the first break time.The spatial dynamic distribution of two phase fluids（oil and water）during water flooding could be obtained by considering different moments,positions of different injection wells and withdrawal wells and distribution position of ultrasonic probe array.Water flooding oil saturation mathematical model based on ultrasonic attenuation was built as well.The amplitude of first wave was used to reflect the ultrasonic amplitude attenuation.Oil saturation was nonlinear with the amplitude of first wave.The results of oil and water spatial distribution were inferior to the results based on ultrasonic velocity.CO₂ flooding fluid saturation mathematical model was built based on ultrasonic velocity and amplitude attenuation comprehensively.Parameters of mathematical model were obtained by measurement,calculation and least squares estimation.Linear least squares solutions with constraints（oil,gas and water saturation）were calculated by the mathematical model.The spatial dynamic distribution of three phase fluids during CO₂flooding could be obtained by considering different moments,positions of different injection wells and withdrawal wells and distribution position of ultrasonic probe array.