Miscibility

Residual oil

Permeability (electromagnetism)

Geotechnical engineering

Materials science

Petroleum engineering

Relative permeability

Biochemistry

Saturation (graph theory)

Geology

Supercritical fluid

Porosity

Polymer

Organic chemistry

Membrane

Mathematics

Porous medium

Composite material

Enhanced oil recovery

Combinatorics

Chemistry

Viscous fingering

Energy

Supercritical CO2 (ScCO2) injection is a potential way to enhance oil recovery (EOR). The displacement effect varies significantly with the difference of miscible degree and pore scale. However, studies in this field are rarely reported. In this paper, relative permeability curves of three miscible types are firstly measured. Interestingly, the ultimate oil recovery of near-miscible flooding is found to be comparative with that of miscible flooding due to the obvious decrease of gas relative permeability under higher residual oil saturation. On this basis, four main zones in the vicinity of oil-ScCO2 contact are divided in view of the multiple contact miscibility mechanism. A new threshold pressure gradient (TPG) considering both pressure sensitivity and oil properties, is proposed as the indicator of the seepage capacity for the reservoir fluids. The seepage resistance of different cores is greatly reduced due to the ScCO2 injection, especially for the permeabilities less than 5 × 10−3 μm2. The modified TPGs decreased exponentially with the increase of mobility indicating that the seepage capacity of reservoir fluids can be enhanced significantly by strong and sufficient interactions of ScCO2 and oil. Thus, CO2 soaking-alternating-gas (CO2-SAG) flooding is proposed and evaluated to verify the importance of contact time and mass transfer.

Effects of miscible degree and pore scale on seepage characteristics of unconventional reservoirs fluids due to supercritical CO2 injection