Surfactant losses due to adsorption in the hydrocarbon reservoir is a major concern in surfactant based chemical enhance oil recovery (chemical EOR) methods because it results in the loss of optimum concentration required for adequately reducing oil-water interfacial tension (IFT). Much higher concertation of surfactant than the optimally designed concentration in the EOR formulation has to be injected in order to account for the surfactant losses in the reservoir which often makes the whole EOR process uneconomical. Although extensive research has been performed with surfactants and nanoparticles in porous media as separate entities, but not much work has been done to understand their combined effects on oil mobilization and adsorption in clay containing reservoirs. The objective of this work is to study uniquely surface modified silica nanoparticles and understand their influence in reducing surfactant adsorption in clay containing reservoirs and develop appropriate injection strategies.
Thermally stable negatively charged silica nanoparticles were developed via surface modification. Static and dynamic adsorption studies were conducted at 80 °C in seawater brine. Static adsorption studies were conducted in the glass vials without any agitation or movement of the fluids. Dynamic adsorption experiments were conducted on the sandpack flow setup. Total of 190 grams of 20/40 mesh gravel pack sand and 10 grams of Kaolinite clay were used to make 9 inches tall column. Two injection strategies for nanoparticles treatment was evaluated – Single Step Injection and Two Steps Injection. In single step, nanoparticles and surfactant were mixed to form single injection fluid, while in the case of two steps injection, porous medium was pre-treated with the nanoparticles before surfactant injection. Thermogravimetric weight loss analysis was used to measure surfactant concentration in the eluting samples. Particle count analysis using dynamic light scattering technique was used to measure the silica nanoparticles concentration.
Negatively charged silica nanoparticles were found to adsorb at a much lower rate than surfactants. Static adsorption tests showed that Kaolinite clay containing samples adsorbed significantly more surfactant compared to the samples without Kaolinite clay and the surfactant adsorption was much lower in the presence of negatively charged nanoparticles. Dynamic adsorption results showed nanoparticles injection significantly reduced the surfactant adsorption in the column and the two steps injection was several times more effective in reducing the surfactant adsorption compared to the single step injection.
This work evaluated two injection strategies for the nanoparticles treatment in clay containing reservoir. Static and dynamic adsorption testing results demonstrated significant reduction in surfactant adsorption at 80 °C temperature in seawater. The findings from this work are helpful in designing more efficient surfactant EOR methods.