A new insight into modeling of wormhole propagation in the presence of asphaltene for carbonates

Carbonate acidization is the process of creating wormholes in carbonate rocks by injecting acid to increase reservoir permeability and consequent oil production. Nevertheless, some reservoir oils might contain certain amounts of asphaltenes that affect the wormholing process. During acidization in the presence of these asphaltenes, the injected acid might not effectively react with rock. This study illustrates the processes of interactions between acid, rock, and asphaltene. It is found that a cumbersome and intricate compound known as acid-asphaltene sludge is formed when the acid reacts with the deposited asphaltene. The formation of this sludge would reduce oil productivity and acid injectivity. In this study, a numerical model is developed to predict the amount of asphaltene deposition, acid-asphaltene reaction, and formation of acid-asphaltene sludge. A 1D numerical model was developed to predict the deposition of asphaltene and acid-asphaltene reaction in radial geometry. Then, the developed model was utilized to predict sludge formation and its related effect on reservoir permeability. Furthermore, the developed asphaltene deposition model was validated against two different sets of experimental data where various factors affecting sludge formation were determined. The detailed analysis showed that although sludge formation is few percent, its concentration increases with time and acid injection. The results also indicate that acid-asphaltene sludge causes an irreversible and permanent formation damage from 40 percent blockage to total pore blockage, depending upon the location of sludge deposition in pore body or pore throat, respectively. Hence, reduction in hydrocarbon productivity is expected at a much lower rate as opposed to that before the acidization job. In addition, the results showed that the amount of acid-asphaltene sludge formation depends on asphaltene percentage, acid concentration, acid flow rate, and flow period. To the best of our knowledge, there is no published work focusing on modeling acid-asphaltene sludge formation and its subsequent wormhole development. This paper provides more insight into the effects of asphaltene deposition and acid-asphaltene sludge formation on wormhole creation and propagation.