Experimental and numerical evaluation of the potential of improving oil recovery from shale plugs by nitrogen gas flooding

Production from tight formation resources leads to the growth in U.S. crude oil production. Compared with chemical flooding and water flooding, gas injection is a promising enhanced oil recovery (EOR) approach in shale reservoirs. A limited number of experimental studies concerning gas flooding in the literature have focused on unconventional plays. This paper presents experimental work for applying an immiscible N₂ flooding process in oil-saturated shale plugs. To investigate the effect of injection pressure on recovery performance, multiple core-flood tests were performed at the injection pressures of 1000 psi, 3000 psi, and 5000 psi, respectively. A lab-scale numerical simulation model was built to match the experimental data. Based on this model, we conducted sensitive studies and analyzed the recovery process.

The potential of N₂ flooding for improving oil recovery from shale core plugs has been demonstrated by the experimental observations and simulation results. Under a certain injection pressure, the results show that the oil was produced with a high and stable production rate at the initial period of the recovery process, before gas breakthrough. After that, the incremental RF decreased with the increase of a flooding period, and a much longer time had less effect on extracting more oil. We also examined the effect of injection pressure on gas breakthrough time, ultimate RF, and oil recovery history. This study illustrates that gas flooding could be considered as an improved oil recover (IOR) approach in shale oil reservoirs.