Abstract
The FM fault-controlled fractured-vuggy volatile oil reservoir is characterized by strong heterogeneity and insufficient natural energy, which limits the effectiveness of conventional water flooding due to early water breakthrough and significant attic oil retention. To optimize post-waterflood development strategies, this study conducted a series of full-diameter physical simulation experiments using multi-fractured-vuggy cores under reservoir conditions. Experiments with different gas injection media revealed that the stage recovery rates for N2, hydrocarbon gases, and CO2 are 78.85%, 64.36%, and 59.96%, with an identical gas injection volume of 0.77 HCPV. Based on these findings, along with the results from phase behavior experiments, N2 is recommended as the preferred gas injection medium. The cumulative oil recovery after continuous water flooding was about 75%. The subsequent water-alternating-gas (WAG) injection effectively increased oil recovery by approximately 6.6–8.8% relative to waterflooding alone by improving sweep efficiency and mobilizing residual oil in branch fractures. Finally, connectivity-controlled case studies demonstrate that gas injection in upper-connected fractured-vuggy unit provides an additional 11.68% incremental recovery compared with lower-connected unit due to delayed gas breakthrough and expanded sweep volume. Overall, direct continuous gas injection results in earlier gas breakthroughs, premature oil production at the core outlet, reduced gas consumption per ton of oil, and favorable extraction outcomes. Therefore, it is recommended to implement a direct continuous gas injection in the well group following water flooding to enhance crude oil recovery.
Data availability
The datasets generated during and/or analysed during the current study are not publicly available due to confidentiality concerns but are available from the corresponding author on reasonable request.
References
Yao, J. et al. The construction of carbonate digital rock with hybrid superposition method. J. Pet. Sci. Eng. 110, 263–267 (2013).
Manrique, E. J., Muci, V. E. & Gurfinkel, M. E. EOR field experiences in carbonate reservoirs in the United States. SPE Res. Eval Eng. 10, 667–686 (2007).
Wu, Y. B. et al. Application status of CO₂ flooding in low permeability reservoir to enhance oil recovery. Xinjiang Oil Gas. 6, 36–54 (2010).
Li, F. & Yang, Y. C. Study of carbon dioxide drive in Pu 1–1 well and pilot experiment result analysis of Sha 1 reservoir in Pucheng Oilfield. Offshore Oil. 29, 56–60 (2009).
Hu, R. R. et al. Study on EOR mechanism by gas injection replacing oil in fractured-vuggy carbonate reservoir of Tahe Oilfield. J. Xi’an Shiyou Univ. (Nat Sci. Ed). 30, 49–59 (2015).
Heidari, P. & Kordestany, A. Gas injection into fractured reservoirs above bubble point pressure. Petrol. Sci. Technol. 30, 534–543 (2012).
Mohsenzadeh, A. et al. Non-hydrocarbon gas injection followed by steam–gas co-injection for heavy oil recovery enhancement from fractured carbonate reservoirs. J. Pet. Sci. Eng. 144, 121–130 (2016).
Lyu, X. R. et al. Mechanism and influencing factors of EOR by N2 injection in fractured-vuggy carbonate reservoirs. J. Nat. Gas Sci. Eng. 40, 226–235 (2017).
Guo, W. J. et al. Experimental research on the mechanisms of improving water flooding in fractured-vuggy reservoirs. J. Pet. Sci. Eng. 213, 110383. https://doi.org/10.1016/j.petrol.2022.110383 (2016).
Lyu, X. R. et al. Technical policy study of single well N₂ injection for EOR in complex fractured-vuggy carbonate reservoirs. J. Southwest. Petrol. Univ. (Sci Technol. Ed). 43, 101–109 (2021).
Parvizi, R. & Ghaseminejad, E. An experimental investigation of gravity drainage during immiscible gas injection in carbonate rocks under reservoir conditions. J. Petrol. Sci. Technol. 4, 63–71 (2014).
Shi, F. G. et al. Experimental study on oil flooding by full diameter core gas injection in fractured-vuggy reservoir. Adv. Fine Petrochem. 17, 9–11 (2016).
Olabode, O. A. et al. Effect of foam and WAG (water alternating gas) injection on performance of thin oil rim reservoirs. J. Pet. Sci. Eng. 171, 1443–1454 (2018).
Olabode, O. A. Effect of water and gas injection schemes on synthetic oil rim models. J. Pet. Explor. Prod. Technol. 10, 1343–1358 (2020).
Wu, X. M. et al. Effect of bottom water on subsequent water flooding and gas drive in fractured-vuggy carbonate oil reservoir. Petrol. Geol. Recovery Eff. 23, 111–115 (2016).
Kang, B. et al. A preferred method of gas injection unit in the fractured-vuggy reservoir. Sci. Technol. Eng. 13, 7629–7633 (2013).
Shi, Y. Z. et al. Experiment on effect evaluation of nitrogen displacement of fractured-vuggy reservoir. Contemp. Chem. Ind. 49, 2194–2202 (2020).
Hui, J. et al. Study on the mechanism of gas injection and oil substitution in fracture-vuggy reservoirs in Tahe Oilfield. Drill. Prod. Technol. 36, 55–57 (2013).
Allal, M. A. et al. Miscible water alternating gas injection WAG field scale application in Algeria: An effective way to improve oil recovery, rejuvenate mature field and develop opportunities to stream gas sales. Proc. ADIPEC Conf.; (2023). https://doi.org/10.2118/216168-MS
Shedid, S. A. et al. Microscopic rock characterization and influence of slug size on oil recovery by CO2 miscible flooding in carbonate oil reservoir. Proc. SPE Int. Improved Oil Recovery Conf.; (2005). https://doi.org/10.2118/97635-MS
Hou, R. J. et al. Influencing factors on EOR nitrogen flooding in fractured-vuggy carbonate reservoir. Petrol. Geol. Recovery Eff. 22, 64–68 (2015).
Wang, Z. H. et al. Gas-water flowing characteristics under high temperature and high pressure in fractured cavity carbonate gas reservoir. Petrol. Reserv. Eval Dev. 7, 47–52 (2017).
Wang, L. et al. Visual experiments on the occurrence characteristics of multi-type reservoir water in fracture-cavity carbonate gas reservoir. Acta Pet. Sin. 39, 686–696 (2018).
Chen, X. J. Visualized gas drive EOR experiments in fractured-vuggy reservoirs after waterflooding in Tahe oilfield. Xinjiang Petrol. Geol. 39, 473–479 (2018).
Su, W. et al. Experimental investigation on continuous N₂ injection to improve light oil recovery in multi-wells fractured-cavity unit. Petroleum 3, 367–376 (2017).
Li, J. et al. Experimental study on the simulation of water flooding mechanism in fracture-vuggy carbonate reservoirs. Nat. Gas Explor. Dev. 31, 41–84 (2008).
Xiong, Y. et al. Physical simulation of the full diameter of different development methods of fracture-vuggy carbonate condensate gas reservoirs. Xinjiang Oil Gas. 8, 58–61 (2012).
Zheng, Z. Y. et al. Visible research on remaining oil after nitrogen flooding in fractured-cavity carbonate reservoir. Petrol. Geol. Recovery Eff. 23, 93–97 (2016).
Acknowledgements
We extend our gratitude to Hanmin Tu and Zhouhua Wang for their intelligent discussions and support.
Funding
This work was supported by China National Petroleum Corporation Major Science and Technology Project: Research on the Scaled Reserve Increase and Production and Exploration and Development Technology of Marine Carbonate Oil and Gas (No.2023ZZ16); Research on the Efficient Development and Improved Recovery of Ultra-deep Fault-controlled Marine Carbonate Reservoirs (No.2023ZZ16YJ02).
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Investigation: X.D., Z.L., J.Z. Methodology: Z.W., H.T. Project administration: X.D., Z.L., G.L. Supervision: X.D., Z.L., P.W. Writing–original draft: Z.L., H.T., J.Z., C.Z. Writing–review & editing: X.D., Z.W., Z.L. Funding: X.D., Z.L.
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Deng, X., Liu, Z., Zhang, J. et al. Evaluating miscible gas injection patterns for enhanced oil recovery in fault controlled fractured vuggy volatile oil reservoirs. Sci Rep (2026). https://doi.org/10.1038/s41598-026-45923-1
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DOI: https://doi.org/10.1038/s41598-026-45923-1
