Optimization of CO 2 Huff-n-Puff in Unconventional Reservoirs with a Focus on Pore Confinement Effects, Fluid Types, and Completion Parameters

Aaditya Khanal () and Md Fahim Shahriar
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Aaditya Khanal: The Jasper Department of Chemical Engineering, The University of Texas at Tyler, Tyler, TX 75799, USA
Md Fahim Shahriar: The Jasper Department of Chemical Engineering, The University of Texas at Tyler, Tyler, TX 75799, USA

Energies, 2023, vol. 16, issue 5, 1-23

Abstract: The cyclic injection of CO 2 , referred to as the huff-n-puff (HnP) method, is an attractive option to improve oil recovery from unconventional reservoirs. This study evaluates the optimization of the CO 2 HnP method and provides insight into the aspects of CO 2 sequestration for unconventional reservoirs. Furthermore, this study also examines the impact of nanopore confinement, fluid composition, injection solvent, diffusivity parameters, and fracture properties on the long-term recovery factor. The results from over 500 independent simulations showed that the optimal recovery is obtained for the puff-to-huff ratio of around 2.73 with a soak period of fewer than 2.7 days. After numerous HnP cycles, an optimized CO 2 HnP process resulted in about 970-to-1067-ton CO 2 storage per fracture and over 32% recovery, compared to 22% recovery for natural depletion over the 30 years. The optimized CO 2 HnP process also showed higher effectiveness compared to the N 2 HnP scenario. Additionally, for reservoirs with significant pore confinement (pore size ≤ 10 nm), the oil recovery improved by over 3% compared to the unconfined bulk phase properties. We also observed over 300% improvement in recovery factor for a fluid with a significant fraction of light hydrocarbons (C 1 –C 6 ), compared to just a 50% improvement in recovery for a fluid with a substantial fraction of heavy hydrocarbons (C 7 + ). Finally, the results also showed that fracture properties are much more important for CO 2 HnP than natural depletion. This study provides critical insights to optimize and improve CO 2 HnP operations for different fluid phases and fracture properties encountered in unconventional reservoirs.

Keywords: CO 2 huff-n-puff; nanopore confinement; unconventional reservoir; optimization; CO 2 sequestration (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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