The mechanisms of plugging due to scaling and fines migration and the change characteristics of relative permeability curve after CO2 flooding

Abstract Since the exploitation of Block 8 of Jinglou Oilfield, owing to the constant increase in water influx, coupled with low system pressure (8.9 MPa), the water influx affected by the water injection wells every year has been near 2×10 4 m 3 , the formation pressure has exhibited a year-by-year ascending trend, and the contradiction of water injection well plugging removal has been increasingly prominent. In view of these problems, the following experiments were carried out: the experiment on scaling laws of inorganic scale under the interactions of CO 2 at different concentrations with formation water, the experiment on laws of plugging due to fines migration caused by CO 2 flooding, the experiment on mechanisms of plugging by organic scale after CO 2 flooding and on plugging removal, and the evaluation experiment on oil-water relative permeability curve after CO 2 flooding. The results show that there is a CaCO 3 scaling trend existing between CO 2 and formation water in the flooding process under reservoir conditions. After CO 2 flooding, there is plugging effect due to conglomeration of inorganic scale, organic scale and fines, causing the seepage capacity of the reservoir to become poor, with a loss of core permeability of 69.6%. After the reservoir is washed with toluene and absolute alcohol, its seepage capacity is recovered slightly, with a recovery of core permeability of 42.2%. It can be discerned from the shape of the relative permeability curves that the change characteristics of two-phase relative permeability curves before and after CO 2 flooding exhibit rightward shift for all cores with different permeability values, with the bound water saturation increasing (more than 35%), indicating that the CO 2 -water-rock karstification caused by CO 2 flooding enlarges the pore space and seepage channels, enhancing the water injectivity. This study is of great theoretical and practical significance for plugging removal and augmented injection in water injection wells.