Method for measuring diffusion coefficient of carbon dioxide in crude oil

Abstract

The invention belongs to the technical field of oil-gas field development and discloses a method for measuring diffusion coefficient of carbon dioxide in crude oil. The method includes following steps: 1), filling crude oil of V0 in volume into an airtight container of VC in volume; 2), maintaining the airtight container filled with the crude oil in the step 1) at measuring temperature T constantly; 3), feeding carbon dioxide gas into the constant-temperature airtight container in the step 2), and measuring pressure P (t) of the carbon dioxide gas once from starting time t0 every other delta ttime until balanced pressure is realized; 4), utilizing expansion coefficient beta of the crude oil dissolved with carbon dioxide and combining with a relation between diffusion time t and the pressure P (t) to obtain the diffusion coefficient DAB of carbon dioxide in the crude oil, wherein a formula in the step 4) is show as follows. The method takes the circumstance that the crude oil expands in volume after carbon dioxide is diffused into the crude oil into consideration, so that the diffusion coefficient of carbon dioxide in the crude oil can be measured more accurately.

Description

technical field [0001] The invention belongs to the technical field of oil and gas field development, in particular to a method for measuring the diffusion coefficient of carbon dioxide in crude oil. Background technique [0002] In the development of oil and gas fields, the use of carbon dioxide flooding can enhance the recovery of crude oil, so carbon dioxide oil recovery technology has been widely used. The steps of using carbon dioxide to recover oil are as follows: First, a certain amount of carbon dioxide gas is injected into the oil layer, then the well is shut down to balance the diffusion of carbon dioxide in the crude oil, and finally the well is opened for oil recovery. In order to predict the time when carbon dioxide reaches equilibrium in crude oil, it is necessary to know the diffusion coefficient of carbon dioxide in crude oil. If the diffusion coefficient is inaccurate, the equilibrium time cannot be accurately confirmed, which will adversely affect oil recov...

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Problems solved by technology

However, in the process of establishing the model, the expansion of the liquid phase volume caused by the diffusion of carbon dioxide was not considered.

[0006] The standard for the determination of the diffusion coefficient of hydrocarbon gases in rocks (Petroleum and Natural Gas Industry Standard of the People's Republic of China, SY / T 6129-1995), by fixing the core in the holder, the diffusion chambers at both ends of the core are respectively injected with nitrogen and hydrocarbons Gas, through gas chromatography to measure the composition of gas at both ends under different time conditions, and the diffusion coefficient of hydrocarbon gas in porous media can be obtained through processing. ; Second, sampling the gas in the diffusion chamber at both ends will destroy the diffusion balance and cause large experimental errors

In addition, none of these measurement methods can obtain an accurate diffusion coefficient of carbon dioxide gas, and therefore cannot accurately confirm the equilibration time of carbon dioxide gas in crude oil, thereby adversely affecting oil recovery

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