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NMR relaxation mechanism of rock pore fluid
Tres mecanismos de relajación diferentes, relajación libre, relajación superficial y relajación por difusión, existen en la relajación por RMN de los fluidos de los poros de las rocas. Generalmente, the three relaxation behaviors exist simultaneously.
1. Relajación libre
Relajación libre, eso es, the body relaxation phenomenon unique to fluids, the relaxation time is determined by the physical properties of the fluid (viscosidad, composición química, etc.) and the environment (temperatura, presión, etc.) where the fluid is located.
In the process of nuclear magnetic research in the petroleum industry because the rock surface is solid, the fluid surface relaxation in the rock pores is usually stronger than the body relaxation. Sin embargo, cuando el petróleo y el gas en los poros de la roca hidrófila pertenecen a la fase no humectante, the existence of cracks in the rock causes less contact between the fluid and the solid surface, and the viscosity of the fluid such as heavy oil is high, the free relaxation between the fluid and the rock pores is impossible. Ignore, the influence of free relaxation and surface relaxation needs to be considered at the same time.
2. Relajación superficial
El mecanismo de relajación de la superficie de los poros de la roca es la relajación superficial., which is specifically manifested as the relaxation phenomenon between the pore fluid and the rock-solid surface.
3. Relajación por difusión
Molecules undergo self-diffusion during the process of Brownian motion. Diffusion relaxation is the relaxation characteristic of protons in a gradient magnetic field due to molecular diffusion.
Conditions such as the type of pore fluid in the rock, tamaño de poro, estructura de desarrollo de poros, petrophysical properties of the pore surface, and the wettability of the rock particle surface determine whether the three relaxation mechanisms work for the fluid in the pores.
Generalmente, para rocas hidrófilas, El tiempo de relajación T2 del agua en los poros está determinado principalmente por la relajación de la superficie.; para petróleo pesado, the T2 relaxation time is mainly determined by free relaxation; while the T2 relaxation time of light oil is It is jointly determined by free relaxation and diffusion relaxation and is related to the viscosity of oil; natural gas due to the diffusion characteristics of gas molecules, its T2 relaxation time is mainly controlled by diffusion relaxation.