Carbon dioxide injection is used for tertiary oil recovery and can recover significant amount of residual oil. CO2 injection has been used successfully as an enhanced oil recovery (EOR) method for several decades. Recently, CO2 flooding method has gained popularity due to the growing concerns over the global warming issue. Hence, many light and medium reservoirs are subjected to Immiscible, miscible, and near-miscible CO2 flooding. In CO2 or hydrocarbon flooding, the asphaltene to resin ratio of crude oil is altered, causing asphaltene precipitation and thereby its deposition.
The deposition of asphaltene in an oil reservoir during production causes formation damage and productivity decline. The severity of this damage is different during miscible and immiscible flooding. In this study, asphaltene deposition due to miscible and immiscible carbon dioxide flooding and its effect on porous media damage are experimentally investigated. A high-pressure, high-temperature coreflood set-up is designed to work under reservoir conditions up to 6000 psia and 150 ºC.
Dynamic displacement experiments were carried out to study the process of asphaltene deposition and permeability reduction during CO2 injection in core samples. For this purpose, the pressures along the core were measured at 4 different points to study the damage distribution. Damage index were measured in different sections and compared during miscible and immiscible flooding and the effect of residual gas saturation in permeability reduction is studied as well.
The results showed that two parameters could change the permeability of the medium. At pressure lower than MMP trapped gas in the pores may also reduce the permeability and at pressure above the MMP asphaltene deposition is the main factor for the porosity and permeability reduction. The maximum damage index occurs in miscible flooding which was equal to 0.79.