Open Access

ARTICLE

Experimental Study on the Critical Conditions for Hydrate Formation during CO₂ Driving Oil Recovery

Min Li¹, Haijun Luan¹, Ming Chi¹, Sen Chen¹, Yang Chen¹, Jiarui Cheng^2,*, Tian Xie^2,*, Rui Wang²
1 Oil Extraction Technology Research Institute, CNPC Xinjiang Oilfield Branch, Karamay, China
2 School of Mechanical Engineering, Xi’an Shiyou University, Xi’an, China
* Corresponding Author: Jiarui Cheng. Email: ; Tian Xie. Email:

Frontiers in Heat and Mass Transfer https://doi.org/10.32604/fhmt.2026.081419

Received 02 March 2026; Accepted 08 April 2026; Published online 29 April 2026

Abstract

This study used simulated formation water (15 g/L CaCl₂) from a certain area of Xinjiang Oilfield as the experimental medium., and employed a high-pressure sealed reaction vessel and a sapphire window to systematically investigate the effects of water content (30%–70%), initial pressure (2–14 MPa), and the intervention of CH₄ on the critical point of CO₂ hydrate formation. The differences between the ‘visual confirmation’ method and the temperature-pressure curve inflection point method for determining hydrate formation were also compared. The study found that in a single CO₂ system under a constant pressure of 5 MPa and a water content of 30%–70%, no visible hydrate was observed with the naked eye. However, the inflection point method showed that the theoretical critical temperature and pressure increased with the increase in water content. For a 50% water content system, there was a threshold pressure range of 8–11 MPa. Only when the initial pressure was higher than this threshold would visible hydrates form, and the critical point shifted upward with the increase in pressure. In the CO₂-CH₄ mixed system, the critical point under a constant pressure of 10 MPa showed a V-shaped trend with changes in gas ratio, with a minimum point at a 1:1 ratio; the constant ratio and variable pressure experiment indicated that the intervention of CH₄ significantly increased the critical temperature and pressure. Furthermore, the introduction of CH₄ changed the growth position of hydrates, shifting them from the gas-liquid interface to the liquid phase matrix. The study revealed the pressure threshold effect of CO₂ hydrate formation in high mineralization degree formation water systems and the gas component competition mechanism: when the ratio of the two components is balanced, the competitive effect is minimized, forming the optimal formation conditions; as the proportion of CH₄ increases, its competitive advantage strengthens, not only increasing the critical temperature and pressure, but also driving the shift of the hydrate growth position, demonstrating the decisive regulatory role of gas components on the equilibrium and formation kinetics of hydrates, providing experimental basis for the risk prevention of hydrates in the CO₂ flooding process.

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Keywords

CO₂ flooding; hydrate formation; water content; pressure

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