Abstract
The miscible gas injection has been a successful technique to overcome the low oil recovery by improving the oil mobility due to viscosity reduction. While many experimental studies defined the fundamentals of gas injection in heavy oil reservoirs, experimental studies of gas injection into condensate oil reservoirs are scarce. Therefore, this study provides a comprehensive investigation of the impact of the injection pressure and reservoir permeability on the efficiency of CO2 to improve oil recovery from oil condensate reservoirs. The efficiency of the injected gas at different injection pressure into different permeability rocks is evaluated as a function of the recovery factor and the viscosity reduction experimentally.
Miscible gas injection experiments of different shale rock samples with different permeabilities saturated with condensate oil were conducted at 5 different injection pressures. The recovery factor will be used to investigate the effect of injection pressure in two distinctly saturated rock samples. These samples are saturated with condensate oil from the Eagle Ford formation. The Minimum Miscible Pressure is predicted from the compositions of the fluids, which is determined using gas chromatography. The gas is injected at different pressures, and the recovery factor is calculated at the gas breakthrough, the end of the injection (Injecting 3 PV), and at the abandonment pressure (100 psi). The viscosity of the collected oil at the end of each run is measured to determine the viscosity reduction value.
The experimental results proved the success of CO2 injection in improving condensate oil production. A proportional relationship between the injection pressure and the recovery factor was observed. Moreover, a proportional relation was observed between the production and the permeability. However, the permeability and the viscosity reduction were observed to be inversely proportional. This observation was extended to the immiscible injection, where the oil viscosity was reduced by a small percentage. This reduction is translated to an existence of some level of miscibility within the pores of the lower permeability sample. This phenomenon could be caused due to the higher nanopore confinement pressure in the lower permeability samples.
