Experimental and numerical study of the EOR potential in liquid-rich shales by cyclic gas injection

One of the limitations of gas or water injection in tight shale oil reservoirs is that the fluid injectivity is low due to the nature of very low permeability of shale. Another challenge of gas flooding is that the injected gas is subject to early breakthrough in densely fractured shale gas or oil reservoirs, resulting in poor performance. Cyclic gas injection (CGI) in a single horizontal well is not affected by early gas breakthrough. Compared to gas flooding, cyclic gas injection is an effective recovery process in tight shale oil reservoirs. This paper presented our experimental work on using nitrogen cyclic injection in shale rocks. We analyzed the experimental data using numerical simulation approaches. Coreflooding and simulation outputs showed that it is favorable to implement cyclic gas injection enhanced oil recovery process in shale oil reservoirs.

Our experimental data and simulation results have demonstrated the potential of gas huff-n-puff injection to improve oil recovery in shale oil reservoirs. We also examined the effect of diffusion on improved oil recovery performance by cyclic injection process. The objective of this paper is to investigate significance of possible factors on gas huff-n-puff recovery process in shale oil reservoirs via experimental work and simulation approaches. Our simulation results benchmarked with experimental observations showed that molecular diffusion played a significant role in the mobilization of oil in lab scale.