Mechanistic investigation of bypassed-oil recovery during CO2 injection in matrix and fracture

CO2 injection is currently one of the most popular EOR (Enhanced Oil Recovery) methods in the world, as its MMP (Minimum Miscibility Pressure) with oil is lower than other common injected gases. In this work, miscible, near-miscible and immiscible CO2 injection was investigated experimentally for both fracture and matrix systems. Different driving forces (such as diffusion, gravity, viscous and capillary) were studied with a system of hydrocarbon components with well-known properties in porous media, following a rational design and procedure. To ensure experiments were representative of reservoir conditions and to demonstrate the relative importance of active forces, pore and core scale dimensional analyses were conducted. CO2 injection in fracture, near-critical tests provided the highest recovery. Significant impact of gravity, swelling and vaporization was inferred from “ultimate recoveries,” “variations of pore pressure,” “the status of oil production,” “recovery rate of corresponding pre-equilibrated test,” and “dimensional analysis.” In CO2 injection in matrix, the maximum recovery was achieved for the first-contact-miscible displacement, as a result of IFT (Interfacial Tension) reduction.