Dynamic Adsorption of Sulfate Propoxylate and Alkylbenzene Sulfonate Surfactants: Correlation with 3D Pore Geometry in Highly Heterogeneous High-Salinity Carbonate Reservoirs

Abstract

Surfactant flooding is a well-established method for enhancing oil recovery in carbonate reservoirs with hydrophobic properties. The adsorption of surfactants onto carbonate rock surfaces alters wettability to a more hydrophilic state, improving oil extraction. However, surfactant adsorption can lead to losses, reducing the cost-effectiveness of the technique. This study evaluates the adsorption mechanisms of sulfate propoxylate and alkylbenzene sulfonate surfactants through dynamic adsorption experiments and 3D micro-CT analysis. Dynamic adsorption experiments were conducted following a classical methodology, including core preparation, brine saturation, surfactant solution flooding, and periodic fluid sampling to quantify adsorption. Core samples from Bashkirian and Vereian horizons, differing in pore structure, were analyzed. Low-resolution (57 µm) 3D micro-CT provided an overview of pore distribution and effective porosity, while high-resolution (6.4 µm) 3D micro-CT revealed ultra-small pores in the Bashkirian core. Dynamic adsorption and 3D micro-CT scans results indicated higher surfactant adsorption in the Vereian core, despite its lower effective porosity and total pore surface area. In the Bashkirian core, surfactant flooding predominated in larger connected pores (> 0.1 mm), while smaller pores (< 0.1 mm) were weakly or not involved. In contrast, the Vereian core’s more uniform large-pore distribution provided a higher accessible contact area for surfactants.