Development Of Key Components Of Low Field DNP Spectrometer And Research In Porous Media

Reservoir rocks are rich in a large amount of oil and gas resources,and the analysis of porous structural and the study of internal fluids dynamic are essential for reservoir assessment and development.Magnetic resonance technology has the advantages of non-destructive and in-situ measurement,and thus is widely applied in the research of porous media.The NMR/MRI technology can obtain the structural characteristics of materials,fluids quantitative information and transport in that,which is critical for the reservoir assessment,understanding the recovery process and improving the oil recovery.Due to the magnetic field gradient root in the magnetic susceptibility difference between solid and liquid phase,NMR signal in small pores is rapidly attenuated or even invisible at high field.Therefore,the study of the porous media e.g.reservoir rocks is always carried out at low field.However,the low NMR signal-to-noise ratio greatly increases the measurement time,especially for the 2D NMR and MRI experiments,which may take as long as several hours.Moreover,it serious influencing the reliability and efficiency at low field,and further cannot fulfill the requirements of accurate and real time measurement.In order to improve the issues caused by low NMR SNR,it is necessary to develop new methods or adopt new technology to increase the NMR sensitivity.Dynamic nuclear polarization technology can effectively improve the polarization of the nucleus,and providing a solution to solve unfavorable factors at the low field.In present dissertation,the development of key components of 0.06T DNP spectrometer and the study of porous materials were carried out by combing the research requirements of porous materials.Firstly,the research actuality of porous media was summarized and the limitations of DNP in that were discussed,and the requirements of DNP spectrometer were also proposed.Then the NMR and DNP principles were briefly introduced,and the key components of the spectrometer were studied and developed,and then the integration and measuring of the spectrometer was implemented.Finally,the research and discussion on the materials structure characterization,identification and characterization of oils and water in oil-water mixtures,and the visual distribution of two fluids phase via DNP were carried out.Specifically,the work and the innovations of the present dissertation are as follows1)The microwave transmitter and magnetic field control system of the DNP spectrometer were designed and developed based on the requirements of the study,and then spectrometer system was integrated and tested.The polarization enhancement of 1H was higher than-180,and the sample heating effect was lower than 3?,which is beneficial to the study of porous media at low field.2)The structure characterization of porous media via DNP.The porous models with a pore size distribution of 9.4 to 72.4 ?m was constructed by calibrated glass beads.The enhancements of oils and water were measured,and the variation of the enhancement were analyzed.The result shows that the enhancement of wetting phase decreased with the pore size due to the influence of surface characteristics of the materials,while the enhancement of non-wetting phase was approximately uniform with the variation of the pore size.Therefore,a method to study the wettability and structure of porous media via DNP enhancement was proposed.The results of calibrated glass beads can be seen as a scale,which provides a basis for rapid evaluating the structure parameters such as pore size,specific surface area,and permeability.3)The identification and characterization of oils an water.Aiming at the issues of large difference between oils and water,and the selective radical is rarely and costly,the method to separation oils and water via combining regular radical and selective relaxation agent was proposed.Where the free radical was used to enhance the NMR signal,and the relaxation agent was the inhibitor of the NOE for the unconcerned fluids.Based on the selective enhancement the real value of oils in oil-water mixture was obtained though data processing of delayed acquisition.And then a method to separate and sort the types of oils via the DNP enhancements was applied.The combination of selective enhancement and delayed acquisition can obtain the enhancement of concerned fluids without considering the content ratio of different fluids.What's more,it still retains the original informal of the sample,thereby facilitating the subsequent quantitative analysis.4)Visualization distribution of oil and water.The DNP-MRI was implemented to improve the issues e.g.low NMR SNR,long time-consuming measurement and indistinguishable for oil and water at low field.The feasibility of DNP-MRI in improving the image contrast and measurement efficiency was analyzed,and the verification tests were performed by oil and water containing TEMPO.And then we proposed a DNP-MRI method to enhance and distinguish the distribution of oil and water.The oil distribution can be enhanced and identified via the enhanced image.The separation and distinguishing of oil and water via DNP-MRI is directly relied on the large image contrast,and thus is not influenced by the relaxation characteristics of the samples.Therefore,it can be widely used to study materials with complex structure such as reservoir rocks,and provide the real time visual distribution information for the dynamic process e.g.forced displacement oil by brine and the drainage against capillary forces,which is critical for understanding the oil recovery,and predicting the field scale performance in the reservoir.