Method for determining diffusion coefficient of carbon dioxide in porous medium

Abstract

The present invention provides a method for determining the diffusion coefficient of carbon dioxide in a porous medium. The method comprises: sealing all surfaces of rock core saturated with crude oil; placing the sealed rock core in a diffusion cylinder; heating the diffusion cylinder to achieve a desired temperature, and maintain the constant temperature; opening a valve, pressurizing a carbon dioxide container to achieve a desired pressure, and maintaining the constant pressure; opening a valve, and injecting CO2 into the diffuser cylinder under the constant pressure; measuring the rock core in the diffusion cylinder through a nuclear magnetic resonance system to obtain a T2 spectrum; calculating the volume proportions of the CO2 and the crude oil in the rock core by using the peak area in the T2 spectrum; and calculating the molar concentration of the CO2 in the rock core, calculating the molar concentration C of the CO2 in the rock core under different diffusion time conditions to obtain an average concentration C<->, and substituting the average concentration C<-> into a formula defined in the specification to obtain the diffusion coefficient D. According to the present invention, with the method, the visualized calculation and the quantitative analysis of the diffusion coefficient by using the T2 magnetic resonance spectrum is achieved.

Description

technical field [0001] The invention relates to the field of oil and gas field development, more specifically, relates to a method for measuring CO by using nuclear magnetic resonance T2 spectrum 2 A method for diffusivity in dense porous media saturated with crude oil. Background technique [0002] The methods for measuring the diffusion coefficient of gas in porous media in the current literature are generally divided into two categories: direct method and indirect method. Whether it is direct or indirect measurement, it can only describe the concentration or diffusion of the gas in the diffusion medium, but cannot directly measure the diffusion coefficient of the gas, that is, the diffusion coefficient of the gas in the porous medium must be determined by the laboratory combined with the model Calculations can be determined. [0003] (1) Direct method: sample the fluid at different times and different diffusion distances, then analyze these samples to obtain the gas con...

AI Technical Summary

Problems solved by technology

The gas-liquid diffusion process is detected by MRI technology, which realizes the microscopic visualization and quantitative analysis of the gas-liquid system diffusion process in porous media, and quantitative analysis of important parameters such as porosity, permeability and saturation of porous media; the device of this patent Through MRI technology, the proton density image, longitudinal and transverse relaxation time, apparent diffusion coefficient and diffusion tensor distribution image of the fluid in the porous medium can be measured in real time, intuitively and without damage, so as to realize the visualization of the entire diffusion process, but This invention does not mention the use of nuclear magnetic resonance technology to obtain the diffusion coefficient of gas and liquid, but can determine the diffusion coefficient of gas in a rock core saturated with liquid through an improved double-chamber pressure decay method

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