2D Magnetic Resonance Imaging Of Two-phase Flow

On-line monitoring of two-phase flow in pipelines of oil and gas wells is an important guarantee for optimizing reservoir management.The measurement of its flow parameters is of great significance for dynamic reservoir management and monitoring of single well productivity.Due to the continuous changes of the flow pattern and fluid state of the two-phase flow,the traditional techniques and methods are not ideal in the measurement of two-phase oil/water flow parameters,and there are certain technical limitations.The emergence and development of nuclear magnetic resonance technology overcomes the shortcomings of traditional measurement methods and penetrates into the medium in a non-contact manner,opening up a new way for the measurement of two-phase flow parameters.In order to meet the requirements of NMR two-phase flow 2D imaging measurement,this paper has completed a three-stage improved Halbach magnet structure,designed a transmitting unit with adjustable frequency amplitude and high driving power,and we established the relationship between the NMR inversion spectrum and the two-phase oil/water flow parameters,and realized the 2D NMR image reconstruction of the two-phase oil/water flow with a specific flow pattern was realized.The specific work and innovations of this paper are as follows:(1)We complete the optimization design of the magnet parameters of the low-field nuclear magnetic resonance system.In order to meet the requirements of low-field nuclear magnetic resonance,this paper first uses particle swarm optimization to optimize and simulate the traditional Halbach structure parameters.In order to reduce the influence of the end effect of the Halbach structure,based on the optimized parameters,a three-stage improved Halbach magnet structure is proposed.The end effect is reduced,the shimming range of the original Halbach structure is increased by 120%,and the non-uniformity is reduced to 16.09%.Correlative verification experiments are carried out to test the actual effect of the magnetic field.The results show that the magnetic field strength and magnetic field uniformity,etc.All indicators meet the theoretical requirements.(2)We design the transmitting unit circuit of magnetic resonance imaging system.In order to meet the requirements of excitation waveform and improve imaging quality,based on DDS technology,a transmitting unit circuit with adjustable frequency amplitude,high frequency resolution,frequency stability and spectrum purity is designed,and carried out software and hardware debugging.The results show that the frequency and amplitude and other indicators of the transmitting circuit meet the system requirements,verifying the feasibility of the transmitting circuit design.(3)We established the relationship between nuclear magnetic resonance inversion spectrum and two-phase oil/water flow parameters.Based on the spectrum inversion interpretation,combined with the nuclear magnetic resonance 2D image reconstruction method,completed a more comprehensive analysis of the two-phase oil/water flow characteristic parameters.Firstly,the phase holdup and flow velocity of the two-phase oil/water flow are accurately analyzed through characteristic parameters such as the relaxation time and waveform integration of the nuclear magnetic resonance signal,the peak value of the inversion spectrum,the relaxation time and the waveform area.Then use the MRI method to reconstruct the image of the two-phase oil/water flow,and analyze the difference between the water content of the reconstructed two-phase oil/water flow and the actual model according to the relative error and the absolute error.The simulation results show that both the nuclear magnetic resonance spectrum inversion and 2D image reconstruction methods have obtained accurate two-phase oil/water flow parameter information,which verifies the rationality and feasibility of the spectrum inversion and 2D image reconstruction methods.To sum up the main work done for this paper,it provides an important idea and theoretical basis for the design of magnetic resonance imaging two-phase flow imaging system,and it lays a foundation for magnetic resonance imaging two-phase flow image reconstruction.