Experimental investigation on continuous N₂ injection to improve light oil recovery in multi-wells fractured-cavity unit

Abstract

The purpose of this experimental study is to evaluate the feasibility and oil recovery efficiency of continuous N₂ injection in a multi-well fractured-cavity reservoir. In this study, the similar criterion of physical simulation was firstly discussed. In order to reveal the mechanism of remaining oil startup and production performance characteristic by continuous N₂ injection, a visualized two-dimensional fractured-cavity model and a three-dimensional pressure resistant model were designed and fabricated respectively based on the similar theory. And the 2D visualized physical experiments and 3D physical experiments were performed with the simulated oil and brine reservoir samples in Tahe oilfield. Four groups of experiments in 2D and 3D model were performed, each of which included bottom water depletion driving, water injection and N₂ injection. The 2D visualized experiments indicated the main mechanism of N₂ developing remaining oil was to occupy the high position and replace the attic oil due to gravitational differentiation. Furthermore, both the 2D and 3D experiments demonstrated that higher oil recovery factor could be achieved if N₂ was injected through high positional wells. The 3D physical model is closer to the real reservoir condition, so the production performance can reflect the real field production process. This paper confirmed the efficiency of continuous N₂ flooding in the light oil saturated fractured-cavity reservoir.

Keywords

Continuous N₂ injection / Similar criterion / 2D visualized model / 3D pressure resistant model / Oil recovery factor

Acknowledgements

The Authors wish to thank the National Natural Science foundation of China (NO. 51174216) and State Key Science & Technology Project of China (NO. 2011ZX05009-004 and NO. 2011ZX05052) for their financial support to carry out this research. The insightful and constructive comments of the anonymous reviewers are also gratefully acknowledged.

References

[1] Z.H. Chen, C.H. Liu, J. Yang, et al., Development strategy of fractured-vuggy carbonate reservoirs-taking Ordovician oil/gas reservoirs in main development blocks of Tahe oilfield as examples, Oil Gas Geol. (2005), 0253-9985 (2005) 05e0623 e 07.

[2] S.Q. Zheng, Y. Li, H.F. Zhang, Fracture-cavity network model for fracturecavity carbonate reservoir, J. China Univ. Pet. (2010), 1673-5005 (2010) 03-0072-04.

[3] J.H. Du, X.Y. Zhou, Q.M. Li, et al., Characteristics and controlling factors of the large carbonate petroleum province in the Tarim basin, NW China, Pet. Explor. Dev. (2011), 1000-0747 (2011) 06-0652-10.

[4] T. Xu, Z.M. Lun, X.H. Zhang, et al., Gravity drainage in oil-wet carbonate matrix rock system, Pet. Explor. Dev. (2010), 1000-0747 (2010) 03-0358-05.

[5] P. Popov, L.F. Bi, Y. Efendiev, et al., Multiphysics and multiscale methods for modeling fluid flow through naturally fractured vuggy carbonate reservoirs, SPE (2007), 105378.

[6] M.H. Lu, C. Zhang, J.X. Xu, et al. Inverse-scattering imaging of cavern models, Pet. Explor. Dev. (, 2010), 100020747 (2010) 0320330208.

[7] Z.J. Chen, L. Liu, W. Wang,Characteristics and controlling factors of the upper Ordovician petroleum reservoirs in the Tazhong No. 1 fault belt, Tarim basin, Pet. Explor. Dev. (2010), 1000-0747 (2010) 04-0409-07.

[8] X.B. Lu, Heterogeneity of karst-vuggy carbonate reservoir rocks, Xinjiang Pet. Geol. (2003), 1001-3873(2003) 04-0360-03.

[9] E.S. Poole, Evaluation and implementation of CO₂ injection at the dollarhide Devonian unit, SPE (1986), 17277.

[10] V.B. Karpov, V.I. Kokorev, Gas utilizing methods-a new technology of oil recovery factor improvement, SPE (2008), 117373.

[11] J.Y. Li, H.Q. Jiang, J.J. Li, et al., The feasibility study for fractured and vavernous carbonate reservoir by injection nitrogen, Inn. Mong. Petrochem. Ind. 23 (2008) 84-87.

[12] A. Kantzas, B. Nikakhtar, P. de Wit, et al., Design of a Gravity Assisted Immiscible Gas Injection Program for Application in a Vuggy Fractured Reef, PETSOC-93el0, 2010.

[13] Kaveh Dehghani, Jairam Kamath, High temperature blow-down experiments in a vuggy carbonate core, SPE (1999), 56542.

[14] X. Xie, W.W. Weiss, Improved oil recovery from carbonate reservoirs by chemical stimulation, SPE (2005), 89424.

[15] J.L. Sanchez, A. Astudillo, F. Rodriguez, et al., Nitrogen injection in the Cantarell complex: results after four years of operation, SPE (2005), 97385.

[16] R.B. Zhao, W.Q.., H. Wu, et al., Enhanced heavy oil recovery from fractured vuggy carbonated reservoir of Tahe oilfield with N2/CO₂ gas mixture, SPE (2010), 132247.

[17] Z.C. Liu, J.R. Hou, J.l. Li, et al., Study of residual oil in Tahe 4th Block Karstic/fractured heavy oil reservoir, SPE (2012), 151592.

[18] D.Y. Yuan, J.R. Hou, Z.J. Song, et al., Residual oil distribution characteristic of fractured-cavity carbonate reservoir after water flooding and enhanced oil recovery by N2 flooding of fractured-cavity carbonate reservoir, J. Pet. Sci. Eng. (2015). S0920- 4150(15) 00123-0.

[19] J.Y. Li, H.Q. Jiang, J.J. Li, The feasibility study for fractured and cavernous carbonate reservoir by injection nitrogen, Inn. Mong. Petrochem. Ind. 34 (23) (2008) 84-87.

[20] P.F. Liu, H.Q. Jiang, H. Xu, The laboratory simulation study of fracturedvuggy reservoirs, Oil Drill. Prod. Technol. 31 (5) (2009) 72-76.

[21] H.B. Li, J.R. Hou, W. Li, Laboratory research on nitrogen foam injection in fractured-vuggy carbonate reservoir for enhanced oil recovery, Pet. Geol. Recovery Effic. 21 (4) (2014) 93-96.

[22] J.R. Hou, H.B. Li, Y. Jiang, et al., Macroscopic three-dimensional physical simulation of water flooding in multi-well fracture-cavity unit, Pet. Explor. Dev. 41 (6) (2014) 784-789.