An Experimental Approach to Investigating Permeability Reduction Caused by Solvent Induced Asphaltenes Deposition in Porous Media

Abstract

Utilizing hydrocarbon solvents such as propane, butane, pentane, hexane, and heptane has shown to be a promising method for reducing the amount of energy required for exploiting the underground heavy oil reservoirs. However, there is an unintended consequence of using the aforementioned solvents in heavy oil recovery processes. The interaction between oil and the aforementioned solvents results in the precipitation of a solid material called asphaltenes. Asphaltenes are the most common solid material dissolved in oil. It belongs to a solubility class that is soluble in light aromatics such as benzene and toluene but insoluble in lighter paraffins. Precipitated asphaltenes can deposit inside porous media and restrict the flow of oil. Reservoir engineers rely on reservoir simulation software to calculate the permeability reduction that results from solvent induced asphaltenes deposition in underground heavy oil reservoirs. Two questions must be answered in order to calculate the permeability reduction. First, how much asphaltenes is deposited in each section of the porous media and second, how much is the reduction in permeability associated with the asphaltenes deposition. This research strives to answer these questions by conducting laboratory experiments and computer simulation. Most of the published literature considers the asphaltene-related permeability reduction to be similar to formation damage by fine particles invasion. This approach does not capture the physics of asphaltene deposition during solvent flooding, since during solvent injection the asphaltene particles form and deposit inside the porous medium whereas during the fine particle invasion process, solid particles have already formed outside porous medium before injection. In this study, the deposition of asphaltene in porous media has been investigated in a way that allows the asphaltene particles to form and deposit within the porous medium. More importantly, a procedure has been developed that allows one to simultaneously measure the changes in asphaltene deposition and the resulting reduction in permeability along the flow path. This had not been accomplished before. Although the reversibility of asphaltenes deposition has been experimentally investigated by a number of researchers, the procedure developed in this work is unique in the sense that, for the first time, reversibility of asphaltenes deposition has been investigated during flow through realistic porous media. Reversibility of asphaltenes deposition was evaluated and it was found that maltene can totally re-dissolve asphaltenes if temperature is above 80°C. Due to the lack of experimental data in the literature, the numerical simulation studies have assumed an ad hoc value for the deposition rate of asphaltenes during a solvent injection process. In this work, values for the deposition rate of asphaltenes has been obtained by history matching the experimental data with a numerical simulator.