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NMR relaxation mechanism of rock pore fluid
Три разных механизма релаксации, свободный отдых, поверхностная релаксация и диффузионная релаксация, существуют в ЯМР-релаксации поровых жидкостей горных пород. В целом, the three relaxation behaviors exist simultaneously.
1. Бесплатный отдых
Бесплатный отдых, то есть, the body relaxation phenomenon unique to fluids, the relaxation time is determined by the physical properties of the fluid (вязкость, химический состав, и т. д.) and the environment (температура, давление, и т. д.) 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. Однако, когда нефть и газ в порах гидрофильной породы относятся к несмачивающей фазе, 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. Релаксация поверхности
Механизмом релаксации поверхности пор породы является поверхностная релаксация, which is specifically manifested as the relaxation phenomenon between the pore fluid and the rock-solid surface.
3. Диффузионная релаксация
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, размер пор, структура развития пор, 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.
В целом, для гидрофильных пород, время релаксации Т2 воды в порах определяется главным образом поверхностной релаксацией; для тяжелой нефти, 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.