Background
Supercritical CO₂ (sCO₂) foam injection represents a promising advancement over traditional surfactant-alternating gas (SAG) techniques for enhanced oil recovery (EOR), offering superior mobility control and sweep efficiency in porous media. This method leverages the unique properties of sCO₂, such as its low viscosity and high diffusivity, to enhance oil displacement and secure long-term carbon storage. This study investigates sCO₂ foam's stability and mobility under a variety of operational conditions, specifically tailored to mimic real reservoir settings using a heterogeneous sand pack system.
Approach
The experimental setup involved injecting sCO₂ and a surfactant-brine mixture at flow rates from 90 to 180 ml/min. Foam qualities were varied from 65% to 97%, maintained under a constant pressure of 1,200 psig, with temperatures ranging from 50°C to 150°C. These elevated flow rates are crucial for evaluating foam performance under conditions that approach pilot-scale applications, thereby bridging the gap between laboratory experiments and real-world implementations. The system's design allowed for detailed monitoring of viscosity, pressure, and temperature. Viscosity measurements before and after the sand pack installation were captured using rheometers, while real-time visualization of the foam structure was facilitated by strategically placed sight glasses.
Accomplishments
Significant findings from the research indicated that pre-generated ScCO₂ foam demonstrated higher apparent viscosity, particularly at critical foam qualities approaching 95%, as shown in Figure 1. This is essential for maintaining structural integrity through porous media. Enhanced viscosity was observed with increasing flow rates, suggesting potential for optimizing sweep efficiency in Enhanced Oil Recovery (EOR) operations. Notably, lower temperatures were correlated with higher viscosities, indicating better foam stability under reduced thermal stress. Additionally, experiments showed that downflow conditions slightly increased viscosity, likely due to the supportive effect of gravity, which is beneficial for vertical injection strategies in EOR.
These findings highlight the potential of ScO₂ foam as an effective method for both EOR and Carbon Capture, Utilization, and Storage (CCUS). By using a heterogeneous sand pack to simulate realistic reservoir conditions, the study provided relevant insights that can be applied to field scenarios. Understanding ScCO₂ foam behavior under different operational parameters supports the development of optimized foam injection strategies, which can enhance sweep efficiency and improve CO₂ sequestration in various reservoir settings.
Figure 1: Visual observation of CO2 foam before and after the sand pack. These images show CO₂ foam at 150 ml/min and 150°C, with foam qualities from 65% to 97%. The critical 95% foam quality marks a significant increase in viscosity and stability, essential for enhancing sweep efficiency in EOR and CO₂ sequestration by improving foam performance in porous media.