Experimental Coreflooding and Numerical Modeling of CO2 Injection With Gravity and Diffusion Effects

Abstract

Abstract In some high pressure and low temperature reservoirs the density of CO2 may be substantially higher than the oil density. Upon mixing of CO2 and oil, a gas phase with a high content of methane (C1) may also appear; when the C1 content is high, this gas phase may have a lower density than the oil. In relation to the above, we have conducted three comprehensive experiments studying CO2 injection from the top and bottom of a vertical core and injection in a horizontal core. The injection rate is i PV/day. The low rate which may correspond to field scale condtions allows the study of the effect of diffusion. The core diameter used in this work is 3.8 cm and the length is 27.3 cm. The tests are conducted at a pressure of 441 bar and temperature of 60°C. The coreflood results give a recovery of 98% for bottom injection, 84% for top injection, and 92% for horizontal injection. We have also conducted an extensive set of measurements to determine swelling, viscosity and density for the calibration of an equation of state. We simulate the experiments using a state-of-the-art higher-order finite element two-phase compositional model. The simulations show that Fickian diffusion should be taken into account, and that even in the horizontal injection there is a considerable gravity effect. One main conclusion is that there may be vast differences between CO2 injection in a 1D slim tube and in a core where there may be a 2D flow. A related conclusion is that analysis of CO2 core flooding at low injection rate may provide important insights into the process.