Research On Measurement Method And System Of Nmr Two-phase Flow

Two-phase flow is a common flow form in the production process of the petroleum industry.In the exploitation of oil reservoirs,timely acquisition of various parameters of the fluid in the reservoir is of great significance to the protection of the reservoir and the improvement of crude oil recovery,but due to the complex and variability of its composition and flow process,the traditional measurement method is not ideal for the practical application of two-phase flow.In recent years,the rapid development of nuclear magnetic resonance technology has made up for the defects of traditional measurement methods that damage the fluid and are greatly affected by the distribution of each phase.In this thesis,based on the basic principles of nuclear magnetic resonance and fluid properties,a nuclear magnetic resonance measurement system for two-phase flow measurement has designed and the T₂ spectrum inversion of the measured echo string signal was studied to realize the identification of different fluids.The main research work and periodic results of this article are as follows:First,for the characteristics of high frequency and low amplitude of the echo string signal generated by the two-phase flow excited by the nuclear magnetic resonance pulse sequence,a signal conditioning circuit module based on matching tuning,pre-amplification and mixing filtering has designed to achieve the following Functions:?1?The matched and tuned signal reaches the resonance state at 4.26 MHz,and maintains 50? impedance matching with the coaxial cable;?2?The high-gain and low-noise characteristics of up to 80 dB in the two-stage preamplifier circuit It satisfies the requirement of amplifying weak echo signals well;?3?After being mixed with the local oscillator signal,it can filter signals higher than 100 kHz,and has a good passband and cutoff value,which is beneficial to the post-stage Signal acquisition.Secondly,a high-precision data acquisition module with ARM + FPGA as the dual core and external high-speed A / D conversion as the architecture has designed to realize the functions of acquisition,processing,storage,and communication of the two-phase flow signal of nuclear magnetic resonance.Among them,FPGA controls the ADC to discriminate and filter out some interference pulse signals that are lower than the threshold value in the collected echo string signals,which reduces the amount of data and improves the signal quality.The processed data is buffered by the dual-port RAM,and the high-speed real-time data exchange between ARM and FPGA is realized through the FSMC bus.Finally,in order to identify the two-phase flow,the SVD-based NMR T₂ spectrum inversion method is adopted,and the accuracy of the inversion is improved by the selection of singular value cutoff values and the optimization processing of non-negative constraints.And the laboratory experiment of the designed nuclear magnetic resonance two-phase flow measurement system and inversion method was carried out.The simulation inversion results have high stability,verify the feasibility of the measurement system and inversion method described in this article,and have a good practical application effect.