Investigation of asphaltene adsorption in sandstone core sample during CO_2 injection: Experimental and modified modeling

摘要

In this work, asphaltene adsorption in a sandstone core sample under dynamic conditions and during miscible CO_2 injection was studied using live oil sample which is close to real conditions in petroleum reservoirs. In order to investigate of damage in sandstone core sample by the deposited material such as asphaltene, the morphology analysis of sandstone core sample using scanning electron microscopic method was studied. Also analyses of the adsorbed material in sandstone core sample by Soxhlet extraction using an azeotrope mixture and with SARA method were performed. The experimental results show that by increasing the flow rate of injected CO_2, the amount of asphaltene in retained material within sandstone core sample and consequently permeability and porosity reduction increased significantly. It can be observed that the accumulation of deposited asphaltene is more in inlet section than outlet section and decreases along the core sample. The elemental and SEM analyses of sandstone core sample indicate that the asphaltene is adsorbed as multilayer with formation of large clusters of asphaltene on surface of studied core sample during dynamic condition. Also, the SEM images indicate that the pore throats are blocked and no discernible holes are present on surface of core sample after CO_2 flooding. It can be found by increasing the flow rate of injected CO_2; the surfaces seem rougher due to the more adsorbed asphaltene on surface of sandstone core sample. Also, a modified model based on multilayer adsorption theory was compared with existing models based on monolayer adsorption theory to account asphaltene adsorption in sandstone core sample during gas injection. These results show that the asphaltene adsorption behavior in core sample is far from monolayer kinetic adsorption model and is closer to modified model which is based on multilayer behavior. It can be concluded that the modified model is capable of predicting the permeability reduction experimental data with AADs of 1.1-1.3%, whereas modeling based on monolayer kinetic adsorption is less accurate in the modeling of CO_2 flooding processes with AADs 5.7-7.4%. Therefore, the developed model based on multilayer adsorption theory is more accurate than models based on monolayer adsorption theory and is in good agreement with the experimental data reported in this work.