The Mechanism Reseach Of NMR Surface Relaxation In Porous Media

Micro-pore structure(micrometer to millimeter scale)is usually the main factor that affect the physical and chemical properties of porous media.Accurately obtaining microscopic pore structure information is of great significance for studying rock and other porous media.The NMR method directly measures the hydrogen nuclei information of fluids in the formation and can accurately obtain important reservoir parameters such as porosity,permeability,and saturation,and has been widely used in underground oil and gas exploration and laboratory rock physical analysis.In addition,compared with mercury intrusion,semi-permeable separators and other methods,NMR technology has the advantages of rapidness,non-destructiveness,and no pollution,and has become an important means for quantitative evaluation of pore structure.Because of the similarities between the mercury intrusion orifice throat distribution curve and the T2 relaxation time spectrum,domestic and foreign experts used various mathematical transformations and successfully converted the T2 relaxation time spectrum into an aperture distribution curve.However,in this transformation process,the accurate surface relaxivity is often the key to the calibration of relaxation time distribution and pore size.The relaxation rate of rock surface is affected by the physical and chemical properties of the surface of the solid skeleton,and the surface relaxation mechanism is complex.In view of the controllability of nanoparticles,we injected different concentrations of paramagnetic zirconia nanoparticle dispersion into the glass beads.Due to the electrostatic force between the nanoparticles and the glass beads,the paramagnetic zirconia nanoparticles are adsorbed on the surface of the glass beads,thereby changing the surface relaxivity of glass beads.The saturated glass beads were washed with deionized water,so that a few nanoparticles that were free in the pore fluid werecompletely discharged,and the relaxation characteristics of the fluid before and after the rinsing were compared to research the relationship between the amount of adsorped zirconia nanoparticles and the concentration of the dispersion liquid.Nuclear magnetic resonance measurements were performed on the washed glass beads,and different methods for measuring the surface relaxivity were compared to investigate the relationship between the surface relaxivity and the amount of adsorped paramagnetic zirconia nanoparticles.This work starts from three aspects: 1)verifying the adsorption of paramagnetic nanoparticles on the surface of glass beads;2)exploring the relationship between the amount of adsorbed nanoparticles and the concentration of dispersion;3)the relationship between the surface relaxivity and the amount of adsorped paramagnetic nanoparticles.