Study On Probe Optimization And Rapid Measurement Method And Application For Downhole NMR Fluid Analyzer

As a sophisticated tool,NMR fluid analyzer is widely used for fluid property identification and content calculation,which can provide key parameters for building programme in nearly every aspect in petroleum industry.According to the new demands and new challenges during the applicaitons of NMR fluid analyzer,the research contents of the thesis incorporate the following four parts:?1?Optimization and implementation of a multi-parameter and multi-functional NMR fluid analyzer;?2?Design and validation of rapid measurement methods;?3?Flow velocity and relaxation time determination for flow fluids;?4?Identification and verification of fluid properties.Downhole is an important application site of NMR fluid analyzer.In this circumstance,the system needs to face with many adverse factors,such as high temperature,high pressure,limited volume,temperature changes,fluid flow and rapid measurement requirement,et al.In order to accurately obtain the NMR properties of downhole fluids,a new set of NMR fluid analyzer was developed with the characteristics of high magnetic field homogeneity,high pre-polarization efficiency and high measurement efficiency:?1?The system adopts the special-ring shaped magnet structure to avoid the twist between adjacent magnetic blocks,this can help to generate a homogeneous magnetic field;?2?The system uses a four-stage magnet structure,the first three sections are pre-polarized magnets,the last section is the measured area,which effectively improves the pre-polarization for flow fluids;?3?The system adopts a combined antenna structure to perform rapid multi-parameter and multi-functional measurements.Measurement efficiency is a significant factor for economy evaluation of downhole applications of NMR fluid analyzer.Confronted with this urgent problem,the paper improves the dilemma by new designed pulse sequence and observational modes.Firstly,Driven Equilibrium?DE? pulse sequence was used to acquire T₁-T₂ correlation map as few as two scans.In addition,based on the combined antenna structure,two observational modes were developed,which can help the system make the most use of the polarization time.By this way,it can double the measurement efficiency of the system.Measurement of flowing fluids is a more efficient mode.Meanwhile,the relaxation mechanism will be more complicated.The measured relaxation time will be affected by both bulk relaxation and fluid flow velocity.In this paper,with the designed fluid analyzer and the combined antenna structure,two different methods are used to obtain the high flow fluid and low flow fluid velocities,respectively.Then,by the acquired flow velocity,the relaxation time spectrum can be corrected free from flow velocity.Finally,through the obtained NMR responses with the fluid analyzer,some typical oil properties can be obtained.By partial least squares regression?PLSR? method,the NMR relaxation time spectrum was used to establish the evaluation model for oil viscosity and hydrogen index.Then,according to the different NMR responses of asphaltene and soft asphaltene,two methods for measuring the asphaltene concentration of crude oil were proposed.