Polymer surfactants as viscosity reducers for ultra-heavy oil: Synthesis and viscosity reduction mechanism

Polymeric surfactants have poor viscosity-reducing effect and little adaptability on ultra-heavy oils. We synthesized a novel polymeric surfactant, named PAMOs, by introducing 2-acrylanmido-2-methylpropanesulfonic acid (AMPS) and sodium alpha-olefin sulfonate (AOS) into the acrylamide (AM) backbone for viscosity reduction in ultra-heavy oil. The PAMOs with high surface and interfacial activity, strong emulsification, good molecular efficiency and viscoelasticity, which emulsified ultra-heavy oil effectively. The formed oil in water (O/W) emulsions with small droplet size and high stability. PAMOs also reduced the oil-water mobility ratio. At a concentration of 3 mg/mL, PAMOs reduced viscosity by more than 90% for different ultra-heavy oils (>15000 mPa·s), showing a broad range of suitability. Combining experimental and molecular dynamics simulation results, polymeric surfactants penetrate into the asphaltene molecular layers to form a "sandwich" structure, weakening the interaction forces between asphaltenes. The structure obtained via the ion-pair dipolar coupling between the polar groups, such as amide and sulphonic acid, and the asphaltene molecules. By strong hydrogen bonding between PAMOs and asphaltene, the supramolecular structure of asphaltene is destroyed and transformed into a low molecular structure. At the meantime, re-agglomeration is prevented by the steric hinerance of hydrophobic long chains, thus achieving viscosity reduction of ultra-heavy oil. It shown that polymeric surfactants have unique advantages in the field of viscosity reduction for ultra-heavy oil.