In order to design a successful miscible CO2 gas injection-EOR project, it is important to understand the physics and mechanisms by which the CO2 displaces oil in porous medium.
CO2 gas, under proper conditions of pressure and temperature, and in the presence of favorable reservoir oil composition, can become miscible with reservoir oil, helping remobilize and produce the oil remaining in the reservoir. The development of miscibility between the injected CO2 gas and the reservoir oil is through in-situ composition changes that occur from multiple fluid contacts and mass transfer between the reservoir oil and CO2 gas.
Trapping and mobilization of fluids in a porous medium are known to depend on (i) Pore Structure, (ii) Fluid/Fluid Interaction (reflected in interfacial tension (IFT) and mobility), and (iii) Fluid/Rock Interaction (related to wettability). Trapping and mobilization mechanism is related to the above factors in a complex way which can be described by complex interactions between viscous, gravity and capillary forces. EOR processes from fields typically involves altering the relative importance of these forces.
This paper discusses several aspects of miscible CO2 flooding and describes how these relate to the experimental and modeling studies required for a successful compositional simulation of miscible CO2-EOR processes.
The phase behavior experiments and EOS modeling of CO2-reservoir fluid system, as critical factors for an accurate performance prediction for miscible CO2-EOR projects, are reviewed.
In addition to PVT experiments, special coreflood experiments and numerical coreflood simulations to determine the micro-scale conformance of the CO2 displacement, identify CO2 breakthrough characteristics and longitudinal dispersion coefficient, are discussed in detail.
Finally, the importance of water injection and other factors related with CO2 injection, which could extend the miscible CO2-EOR technology to a broader range of oil reservoirs, has been given considerable attention.