Visualization of asphaltene precipitation and deposition in a uniformly patterned glass micromodel

Precipitation and deposition of asphaltene are among chronic operational problems for recovering oil from reservoirs of high asphaltene content. The present experimental study aimed at investigating the process of precipitation and deposition of asphaltene in a uniformly patterned glass micromodel. This was carried out by the injection of n-heptane while setting the other operating conditions, such as temperature, pressure and flow rate unchanged. Synthetic oil solutions containing toluene and n-heptane with asphaltene content of 5 wt% were prepared and injected to the micromodel under different wettability conditions. Precipitation of asphaltene gradually started once n-heptane was introduced to the micromodel. It was found that asphaltene precipitation occurred as injected n-heptane diffused into the oil phase and destabilized the dissolved asphaltene. The destabilization of dissolved asphaltene occurred along with the formation of a cloud-like, semi-solid phase which evolved from the oil phase due to the diffusion of n-heptane molecules indicating the onset of asphaltene precipitation. As soon as precipitation took place, the color of oil phase changed from black to grey due to loss of dissolved dark asphaltenes. Asphaltene precipitation in the oil-flooded micromodel was more likely to occur due to the deposition of asphaltene onto the micromodel surface and passages. Finally, it was found that not all precipitated asphaltene particles would deposit, instead it was more likely occurrence (i) for the oil-flooded micromodel; (ii) micromodels passages with tortuosity and complicated flow paths which have been generated by the deposition of precipitated asphaltenes and (iii) the interface of n-heptane and the oil phase.