Document Type : Research Paper
Engineering Department, National Iranian South Oil Company, Ahwaz, Iran
Asphaltene precipitation causes a decrease in the effective mobility of hydrocarbon through pore throats plugging and, as a result, the rock permeability. Moreover, by changing the reservoir rock wettability, asphaltene reduces the effective oil permeability and increases the amount of residual oil in porous media. Furthermore, change in the fluid viscosity should also be considered as a determining factor. This study aims to model asphaltene precipitation in the reservoir and evaluate this phenomenon’s consequences regarding the effects on the wells’ Productivity Index (PI). After developing a thermodynamic asphaltene model based on Cubic Peng-Robinson EOS, the fluid model was exported into a commercial compositional simulator using in-house PVT software. Besides, asphaltene behavior was described using the solid model. Then, the dynamics of the precipitated asphaltene were investigated using deposition, porosity reduction, permeability reduction, and viscosity change models in the mentioned simulator. Additionally, a sensitivity analysis was done to see how deposition model parameters and the production rate can probably affect the formation damage and final Wells’ PI under natural reservoir depletion. Finally, the most significant parameters triggering asphaltene damage were identified. The results indicated that the damage triggered by asphaltene deposition, through plugging and decreasing porosity and permeability, and a change in viscosity was disclosed as a decline in wells’ PI. The results also showed that although adsorption significantly affects the decrease in wells’ PI, plugging is a more determining mechanism.