Summary
Studies on the application of transition-metal catalysts for heavy-oil or bitumen in-situ upgrading were conducted in the absence of a porous medium, mainly measuring the characteristics of heavy oil in reaction with metal ions at static conditions with the help of a magnetic stirrer. Metal species in ionic form are not soluble in oil phase. Therefore, metal particles, as inhomogeneous catalysts, are considered in this paper. Furthermore, dynamic tests in porous media are needed to clarify the injection possibility of the metal particles and their effect on in-situ upgrading of heavy oil. Injection of metal particles may deteriorate the recovery process by damaging porous media because of attractive forces such as van der Waals and electrostatic forces between particles and porous rock. A better understanding of these forces and their importance in the retention of particles is required.
In this paper, the catalysis effect of pure nanometer-sized nickel during steam-injection application was compared with that of an industrial catalyst such as micron-sized Raney nickel. The changes in the viscosity, refractive index, and asphaltene content were measured after each test to analyze the catalysis effects. Nickel nanoparticles showed a better catalysis compared with Raney nickel. The approximate optimum concentration of the catalysts was determined. Then, the catalysis effect of nickel nanoparticles was studied in the presence of sandpack as a porous medium. The results showed accelerated catalysis in presence of the sands. Also, nickel nanoparticles improved the oil recovery factor.
The next phase of this paper studies the injectivity and transport of nickel particles. The injected suspension was stabilized by use of xanthan gum polymer and ultrasonication. The effect of solution pH, which controls the magnitude of the repulsive electrostatic forces, was clarified. Stabilization of the metal particles’ suspension was studied at different pH values through zeta-potential measurements. Also, the zeta potential of the recovered suspensions was studied to confirm the stability of the suspension during travel through the porous medium. Depending on the size, particles carry different charges and have different settling velocities. Therefore, the stabilization pH and dispersant concentration were different from one sample to another. The results of the injectivity tests confirmed the lower retention and better injectivity of nanoparticles in comparison with micron-sized particles.
Environmental assessment: tar sand in situ steam injection experiment
