Shale gas reservoir gas diffusion coefficient experiment test method

Abstract

The invention discloses a shale gas reservoir gas diffusion coefficient experiment test method. According to a method, a one-dimensional diffusion mathematic model is built by monitoring pressure attenuation data in a shale plunger rock sample under effective stress conditions of methane gas with a certain initial pressure in a constant-temperature closed system with the micro-pore structure and the gas existence state of a shale reservoir as bases, the diffusion coefficient of the gas (methane) in shale is calculated, and the diffusion mass-transfer capacity of the gas (methane) in the shale is quantitatively assessed. In the experiment testing process, the diffusion process of gas in the shale gas reservoir can be effectively simulated, and influences of effective stress, gas adsorption/desorption and other factors on the diffusion coefficient are reflected. Besides, the method can overcome influences of gas free expansion stage data in a traditional adsorption/desorption method on the diffusion coefficient. The method can assess the diffusion mass-transfer capacity of the gas in the shale and provide experiment support for researches in the aspects of shale gas reservoir productivity models, productivity prediction and the like.

Description

technical field [0001] The invention relates to the technical field of experimental evaluation methods for gas mass transfer capacity of unconventional oil and gas reservoirs, and relates to an experimental method for simulating the diffusion process of gas (methane) in shale gas reservoirs and testing the diffusion coefficient. Background technique [0002] Shale gas is a typical unconventional natural gas, which is produced in the reservoir rock series dominated by organic-rich shale with extremely low porosity and permeability, and belongs to source rock gas pool. The recoverable resources of shale gas in my country are about 25.08×10 12 m 3 , equivalent to conventional natural gas resources. In shale gas reservoirs, shale gas mainly occurs in free and adsorbed states. After the gas well is put into production, the free gas is produced first; at the same time, with the transmission of the pressure wave, the adsorbed gas in the organic matter pores of the shale will gra...

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Problems solved by technology

However, the adsorption / desorption method also has the following disadvantages: first, the powder sample (60-80 mesh) is used for testing, and the characterization scale is extremely small, and the measured diffusion coefficient is affected by the size of the sample; second, the sample preparation of powder sample is tedious , and cannot reflect the effect of effective stress changes on the pore structure and diffusion process

But they are either very different from the experimental conditions and engineering applications, or the instruments and equipment are complicated and expensive, and it is difficult to popularize them.

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