A Study of CO2 and WAG Injection Induced Asphaltene Precipitaion

Asphaltene is high molecular weight component of crude oil that exists in the oil as colloidal suspension, and is peptized or stabilized by resin that absorbed on its surface. Asphaltene might loss its stability during different phases of production and specially during carbon dioxide flooding. The precipitation of asphaltene during CO2 injection might lead to formation damage, wellbore plugging and recovery reduction. Water-alternating-gas (WAG) injection is the mobility enhancement method of CO2 injection and it is believed that the presence of water could reduce the asphaltene precipitation.
In this work, dynamic core flooding experiments were conducted to study the effect of CO2 injection and WAG injection on the amount of asphaltene precipitated. Core properties after displacement were inspected for any porosity, permeability and wettability alteration to study the effect of asphlatene precipitation on rock properties. The recovered oil is collected over a time interval and the change in asphaltene content was reported against pore volume of injection. The reduction of the asphaltene content in the effluent oil indicates the amount of asphaltene precipitated inside the core.
The laboratory data had justified that WAG injection gives less asphaltene precipitation compared to CO2 injection. Higher porosity and permeability reduction were observed with CO2 injection. It was also found out that during CO2 injection, the presence of asphaltene would altered the rock wettability to more oil wet. However, in the presence of water film during WAG injection, the initial water wet condition of the rock remained and contributed to higher oil recovery. Overall, WAG injection gives less asphaltene precipitation, less formation damage, and higher oil recovery compare to CO2 injection.