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Special Topics & Reviews in Porous Media: An International Journal
ESCI SJR: 0.259 SNIP: 0.466 CiteScore™: 0.83

ISSN Imprimer: 2151-4798
ISSN En ligne: 2151-562X

Special Topics & Reviews in Porous Media: An International Journal

DOI: 10.1615/SpecialTopicsRevPorousMedia.v9.i2.40
pages 145-154

ENHANCING CO2 FLOODING EFFICIENCY BY CHEMICAL FLOODING: A NUCLEAR MAGNETIC RESONANCE STUDY

Hui Gao
School of Petroleum Engineering, Xi'an Shiyou University, Xi'an, China, 710065; Engineering Research Center of Development and Management for Low to Ultra- Low Permeability Oil and Gas Reservoirs in West China, Ministry of Education, Xi'an, China, 710065
Chen Wang
School of Petroleum Engineering, Xi'an Shiyou University, Xi'an, China, 710065; Engineering Research Center of Development and Management for Low to Ultra- Low Permeability Oil and Gas Reservoirs in West China, Ministry of Education, Xi'an, China, 710065; School of Mining and Petroleum Engineering, Faculty of Engineering, University of Alberta, Edmonton, AB, Canada T6G 2W2
Lanxiao Hu
School of Mining and Petroleum Engineering, Faculty of Engineering, University of Alberta, Edmonton, AB, Canada T6G 2W2
Huazhou Andy Li
School of Mining and Petroleum Engineering, Faculty of Engineering, University of Alberta, Edmonton, AB, Canada T6G 2W2

RÉSUMÉ

Due to large reservoir heterogeneity, there is still much residual oil remaining in the reservoir after miscible CO2 flooding. This research attempts to improve CO2 flooding performance using chemical-flooding methods, including foam-gel flood and surfactant flood. Nuclear magnetic resonance (NMR) technique is used to determine how CO2 flooding and chemical flooding alter the oil-saturation distribution in core samples. Single-core flood experiment shows that the foamed gel alone does not increase recovery efficiency, but after the foamed-gel treatment, CO2 flooding can displace the residual oil distributed in T2 < 10 ms and T2 > 100 ms pores, enhancing the ultimate recovery by 15.99%. The foamed gel added in the CO2 flooding process can decrease the residual oil contained in the smaller pores, remarkably improving the recovery efficiency. Parallel-core experiments using a high-permeability core and a low-permeability core are conducted to examine the effect of macro-scale heterogeneity on the performance of combined CO2/surfactant flooding. As for the low-permeability core, surfactant flooding alone only slightly increases the recovery factor, while the follow-up CO2 flooding greatly increases the recovery factor by 28.24% and efficently displaces oil residing in T2 > 10 ms pores. The results of the NMR tests show that most of the residual oil is confined in the pore range of T2 < 100 ms. Due to reduction in oil–water interfacial tension after surfactant treatment, a higher recovery factor and a more uniform displacement front can be achieved in the subsequent CO2 flooding. In comparison, as for the higher-permeability core which does not go through surfactant flooding, the second CO2 flooding results in much less additional oil recovery.