Effects of Gravity Drainage Mechanism on Asphaltene Deposition Pattern in Porous Media during Miscible Displacement

Asphaltene deposition in porous media during miscible injection, as an enhanced oil recovery method, results in permeability impairment and thus formation damage. The degree of the permeability reduction due to asphaltene deposition is a function of the asphaltene deposition pattern. In this study, the effects of viscous and gravitational forces on the deposition pattern of asphaltene during miscible displacement of oil in a glass micromodel were studied. Dead oil was dissolved in a toluene/gasoil mixture to prepare model oil. A homogeneous micromodel with the pore and throat sizes of 160 and 80 μm, respectively, was prepared and employed for the miscible displacement of the model oil by normal hexane at the injection flow rate of 0.04 mL/h. The flow rate leads to a very low Reynolds number which is a characteristic of laminar flow in the porous media. To shed light on the contribution of the gravitational force to the deposit amount and deposition pattern, the displacement tests were conducted at the dip angles of 0, 10, and 20 degree in the injection direction. It is found that the deposition mechanism of asphaltene is divided into three main categories of deposition on surface, pore throat blocking, and internal filter formation. The deposition mechanism and thus deposition pattern of asphaltene depend on whether the viscous or diffusion/dispersion force is the dominant force in the porous media. The breakthrough time and thus the oil recovery factor is improved in the tilted displacements. In addition, in comparison to horizontal flow, the deposit amount of the asphaltene is decreased by 70.5 and 82.3% at the dip angles of 10 and 20 degree, respectively. Diffusion/dispersion increases the deposit amount of asphaltene, leading to a harsh damage. However, the viscous force may either strengthen or weaken the asphaltene deposition.