Open Access

ARTICLE

Performance Analysis of Gas-Soluble Surfactants for Reducing Minimum Miscibility Pressure in CO₂-Injection Development of Ultra-Low Permeability Reservoirs

Bo Jing^1,2, Yuejun Zhu^1,2, Bo Huang^1,2, Engao Tang^1,2, Mingda Dong^3,*, Anfeng Xiao³, Ziming Wang³
1 State Key Lab of Offshore Oil & Gas Exploitation, Beijing, China
2 CNOOC Research Institute Ltd., Beijing, China
3 College of Oil and Gas Engineering, Chongqing University of Science and Technology, Chongqing, China
* Corresponding Author: Mingda Dong. Email:
(This article belongs to the Special Issue: Enhanced Oil and Gas Recovery in Unconventional Reservoirs)

Energy Engineering https://doi.org/10.32604/ee.2026.077925

Received 19 December 2025; Accepted 28 February 2026; Published online 18 May 2026

Abstract

CO₂ miscible flooding is a crucial technology for enhancing oil recovery in ultra-low permeability reservoirs. However, the relatively high minimum miscibility pressure (MMP) has restricted the application of this technology. To reduce the MMP of the CO₂/crude oil system, gas-soluble surfactants have been widely adopted in CO₂ miscible flooding technology. In this paper, gas-soluble surfactants were taken as the research object. Firstly, a cloud point pressure test system with high-pressure visual autoclave and an illuminance sensor as the core equipment was established. The cloud point pressure method was used to determine the solubility of three surfactants, namely Span 80, AOT and TXIB, in CO₂ under reservoir temperature. Then, slim-tube experiments were conducted to evaluate the effect of different surfactants on reducing the MMP of the CO₂/crude oil system, analyze the differences in MMP reduction efficiency between non-ionic and ionic surfactants, and screen out the optimal gas-soluble surfactant suitable for the target reservoir. The results show that TXIB has the highest solubility at all mass fractions, while AOT has the lowest. Meanwhile, the MMP reduction rate of the non-ionic surfactant TXIB reaches as high as 16.35%, which is much higher than that of the anionic surfactant AOT. Compared with anionic surfactants, non-ionic surfactants can form weak interactions with CO₂ through ester groups and long-chain hydrophobic groups, thus achieving miscibility at lower pressure and being more suitable for the target reservoir.

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Keywords

CO₂ miscible flooding; MMP; gas-soluble surfactants; cloud point pressure

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