The Evaluation of CO2 Immiscible Displacement in Ultra-Low Permeability Reservoir

CO2 flooding is currently one of the main means to increase crude oil recovery rate. This study mainly used laboratory experiments and numerical simulation methods to analyze and evaluate the enhanced recovery rate of CO2 immiscible flooding in ultra-low permeability reservoirs. Firstly, the high pressure physical properties of crude oil in the study area were tested, and then the properties of light oil-CO2 systems with different CO2 flooding concentrations were measured to research the phase characteristic of light oil-CO2 systems. Test results indicate that the miscible pressure of the ultra-low permeability reservoir in the study area was high, and the system expanded by 30% and the oil viscosity decreased by 60% after the CO2 injection. Which means CO2 immiscible flooding in this area is also can enhance oil recovery remarkably and there is a linear relationship between the content of each pseudo-component and the amount of CO2 injected. Secondly, the method of numerical simulation is used to analyze the matching of laboratory test. The influences of reservoir permeability, reservoir thickness, oil saturation to CO2 immiscible flooding in ultra-low permeability reservoir were analyzed on the basis of well simulation matching. It indicates that ultra-low permeability mechanism reservoir with higher permeability, forming CO2 immiscible flooding and earlier gas channeling. With the suitable reservoir thickness (8 m–19 m in this paper) can delay gas channeling. Reservoir with low oil saturation are suitable to product with large volume of gas injection.