Research On Core Pore Based On NMR Measurement

Nuclear magnetic resonance(NMR)is a rapid and nondestructive technique for measuring core pore size distribution in recent years.However,it directly reflects the relation between the H1 relaxation time of the fluid in the core and its frequency distribution,and cannot directly reflect the pore diameter distribution of the core.According to the relaxation mechanism of H1,we also need to obtain the relaxation rate between the core and the fluid,so as to combine the nuclear magnetic resonance spectrogram to obtain the pore diameter distribution law of the core.There are many factors that influence the relaxation rate,and there is not a particularly good way to measure its value at home and abroad.It is a reasonable value to match the NMR T2 spectrum with other measurement methods.This article in view of the low permeability and ultra-low permeability reservoir cores of the pore characteristics of the fluid to be ignored under the condition of relaxation,relaxation and diffusion to the surface relaxation on behalf of the entire relaxation phenomenon,put forward a kind of test core surface relaxation rate combined with nuclear magnetic spectra characterization of core pore size distribution method,and by using the mercury injection and other methods,the results were compared.The results show that this method can be used to characterize the pore size distribution of sample core,and it can be used to test speed,no damage to samples,and less sample usage.By comparing 4 tight sandstone with similar properties and similar properties,we find out the experimental conditions and find that each sample at a certain speed has enough centrifuge for 1 hours to make the remaining oil in this state no longer change,and in contrast to the traditional weighing method,the NMR signal can be used to accurately characterize the middle flow of rock samples.On the basis of the tight sandstone,this paper expands the range of samples and finds that the method can accurately represent the pore diameter distribution of natural rock core or outcrop core or artificial core.In this paper,the gas permeability of core is up to 10mD.At the same time,the core pore size distribution is divided into five types by the use of NMR relaxation time,and the abundance of pore distribution in the core is directly presented by using the magnetic resonance imaging technique.