Double-Functionalized Silica Nanomaterials for Effective CO ₂ Foam Stabilization in Harsh Carbonate Reservoirs

Foam flooding is a well-known technique for effective conformance control, especially in highly heterogeneous and depleted oil and gas reservoirs. It helps to divert the fluid flow from high-permeability zones into the low-permeability, bypassed, or untapped regions of the reservoir, thereby contributing to improved sweep efficiency and yielding incremental oil recovery. However, foam stability and propagation still pose significant challenges, particularly in harsh and complex reservoirs such as Saudi Arabian carbonate formations. They are typically strongly oil-wet and exhibit a diverse range of porosity, permeability, mineralogy, and pH. This study investigates the effect of the functionalized silica nanoparticles, focusing on their influences, especially the type/degree of surface functionalizations, specifically single (S1 and S2)- and double-functionalized silane nanoparticles (S12) as novel additives for enhancing CO2 foam stability under reservoir-representative conditions. Initially, all three types of silane nanoparticles were successfully synthesized and characterized in detail. Later, static (bulk) foam experiments were conducted using a nonionic surfactant (FS-31) with the addition of S12 at various concentrations (0–2.5 wt/v %) and using CO2 as the foaming gas. The foam stability was evaluated by measuring the half-life (H0) of the generated foams. In this screening, the double-functionalized silanes increased the foam half-life by at least 2–4 times higher than the neat surfactant solution of FS-31, in the CO2 system. Subsequently, the interfacial measurements of the SW–CO2 systems were also studied with and without S12, and the addition of S12 particles reduced the IFT significantly from 68 to 55.4 mN/m, indicating their surface activity. Later, dynamic foaming and displacement experiments were also demonstrated in porous media using the high-temperature, high-pressure (HTHP) coreflood setup. These tests were mainly conducted under reservoir-representative conditions of 70 °C, 3200 psi (pore pressure), and 67 kppm salinity using the best-performing formulation identified in the bulk tests. The observed pressure drops further support the strong foam generation with the addition of S12 over the neat FS-31-based SAG flooding. Additionally, the mobility reduction factor and apparent viscosity calculations of these tests further supported the stronger foam generation in the case of the S12-added system, dynamically. Overall, the double-functionalization of the silanes proved to be an effective nanoadditive for improving CO2-foam stability and conformance of the CO2-foam under harsh carbonate reservoir conditions.