Effect of surfactants C12PO6 and SW320 on oil/CO2 minimum miscibility pressure of unconventional liquid reservoirs - molecular dynamics simulation study

Abstract

CO₂ flooding has been identified as an effective method for enhancing the recovery rate of unconventional oil and gas. However, in many oilfields, the miscibility pressure of CO₂ with crude oil exceeds the oilfield pressure, preventing them from achieving miscibility. This impedes the desired recovery outcomes. Surfactants present a solution to this challenge, as they can reduce the miscibility pressure between CO₂ and crude oil, thereby elevating the recovery rate. Yet, the microscopic dynamics of how surfactants modulate the MMP in CO₂ flooding within ULRs remain under-explored.

This research aims to delve into this gap, using molecular dynamics to elucidate the underlying mechanisms and potential benefits of surfactant inclusion in CO₂ flooding applications for unconventional reservoirs.

Our study, rooted in molecular dynamics, seeks to demystify these dynamics and understand surfactants' role more profoundly. Delving into the CO₂-n-decane system, we discovered that C₁₂PO₆ and SW320 significantly alter the interfacial width by forming a molecular film, which enhances CO₂'s solubility in crude oil. Notably, SW320 emerged as more potent than C₁₂PO₆ in this regard. Both C₁₂PO₆ and SW320 managed to reduce the MMP of the CO₂-n-decane system by more than 15 %. However, in terms of cost-effectiveness, C12PO6 offers a compelling balance between performance and affordability compared to SW320. Further insights revealed that the structure of the C₁₂PO₆ surfactant plays a crucial role in determining its MMP reduction capacity. Intriguingly, the addition of low carbon alcohols, especially n-pentanol, enhances the C₁₂PO₆ surfactant's surface activity, underscoring its superiority over ethanol in reducing interfacial tension.

In essence, this research offers a microscopic lens to view the intricate dance of surfactants in CO₂ flooding within ULRs. Our findings provide a robust framework for refining recovery strategies in unconventional reservoirs, potentially transforming the landscape of CO₂ flooding methodologies to ensure more sustainable and efficient oil and gas extraction.