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Surfactant flooding

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Surfactant flooding is an Enhanced Oil Recovery technique in which the mobility of residual oil in the reservoir is increased by reducing the Interfacial Tension (IFT) between the injected fluid and the reservoir oil.[1]


Schematic of a surfactant-based flooding process applied to a petroleum field.  [2]











Overview of surfactant flooding

Surfactant flooding is a chemical Enhanced Oil Recovery technique (cEOR) in which a small amount of surfactant (0.3-1.0 volume%) is mixed with the injected fluid (water) to sweep the reservoir oil[3]. Surfactants are blended with co-surfactants which acts as active agents to enhance the properties of surfactant solution and helps to sustain optimal conditions with respect to pressure, temperature and salinity.

In EOR techniques a fluid or gas is injected in the reservoir to displace residual crude oil from the reservoir. In this chemical Enhance Oil Recovery (cEOR) technique, surfactants along with aqueous solution are injected forming a micro emulsion[4]. These injected fluids interact with the reservoir rock and oil trapped in pores resulting in oil production by controlling the phase behavior properties in the oil reservoir and by reducing residual oil in the pore spaces of the matrix rocks.

The presence of surfactants also improves the wettability (oil-wet to water-wet) of reservoir rock to enhance the recovery of oil. Surfactants also improve the recovery of residual oil through other mechanisms like micro-emulsification of trapped residual oil and by changing the interfacial rheological properties.[5]

In primary and secondary recovery only one third of oil can be produced and the residual oil gets trapped in the pores due to capillary forces and viscous forces[6]. Therefore, in chemical enhance oil recovery (cEOR), surfactant solution is injected into the reservoir which increases the capillary number by lowering the interfacial tension or by achieving Ultralow Interfacial Tension and its range should be reduced to 0.001mN/m. This chemical EOR technique has been reviewed recently[1].

Surfactants types used

The surfactants are primarily divided into four categories[3]

  • Cationic surfactant
  • Anionic surfactant
  • Non-ionic surfactant
  • Amphoteric
Molecular structure and classification of various surfactant molecules[7]








Mechanisms of surfactant flooding

Micelle formation in surfactant flooding

Micro emulsions are formed in surfactant flooding between water and oil as two immiscible phases and by lowering interfacial tension and viscosity which increases mobility of oil[8].

Surfactant adsorption

Adsorption process occurs when the surfactant accumulates on the surface of reservoir rock forming micelles and surface charge at the solid and liquid interface. The surfactant concentration must not exceed the value of CMC. Surfactant properties alter considerably based on the critical micelle concentration (CMC). Each surfactant has their unique CMC value based on temperature, salinity and hydrophobic chain length. CMC value for ionic surfactant decreases by factor of 2 and by factor of 3 for non-ionic surfactant[9]. To obtain lower IFT and good foam stability the surfactant concertation should be greater than the CMC value.

Reservoir compatibility

Carbonate reservoirs are generally suitable for cEOR techniques. However, it is not suitable for surfactant flooding since carbonate reservoir are composed of calcite (CaC03), magnesite (MgCO3), anhydrites (CaSO4) etc. which have high conductivity and a  low permeability matrix and mostly has oil wet/mixed wet conditions. Sandstone Reservoirs are homogenous and are more suitable of cEOR.  

Future challenges

  • High temperature, High Salinity, fractured Carbonate reservoirs.
  • Low temperature and low salinity conditions are optimal, but sulphonate based surfactants can be used for high temperature and low salinity conditions.
  • High Adsorption and precipitation of surfactant is challenging for high temperature and high salinity sandstone reservoirs.

References

  1. 1.0 1.1 Ali, S.M. Farouq, and S. Thomas. "The Promise And Problems of Enhanced Oil Recovery Methods." J Can Pet Technol 35 (1996): No Pagination Specified. doi: https://doi.org/10.2118/96-07-07
  2. Gurgel, Alexandre & Moura, Maria & Castro, Tereza & Barros Neto, E. & Dantas Neto, Afonso. (2008). A review on chemical flooding methods applied in enhanced oil recovery. Braz. J. Pet. Gas. 2. 10.5419/bjpg.v2i2.53.
  3. 3.0 3.1 Ali, H. (2016, November 13). Surfactant flooding reservoir simulation. Retrieved March 16, 2021, from https://www.slideshare.net/heshammokhtar2031/surfactant-flooding-reservoir-simulation
  4. Mai, A., Bryan, J., Goodarzi, N., & Kantzas, A. (2009). Insights into non-thermal recovery of heavy oil. Journal of Canadian Petroleum Technology, 48(03), 27-35. doi:10.2118/09-03-27
  5. Mai, A. & Bryan, J. & Goodarzi, N. & Kantzas, A.. (2009). Insights Into Non-Thermal Recovery of Heavy Oil. Journal of Canadian Petroleum Technology - J CAN PETROL TECHNOL. 48. 27-35. 10.2118/09-03-27.
  6. Selby, R., Alikhan, A., & Ali, S. F. (1989). Potential of non-thermal methods for heavy oil recovery. Journal of Canadian Petroleum Technology, 28(04). doi:10.2118/89-04-02
  7. Nakama, Y. (2017, March 10). Surfactants. Retrieved March 12, 2021, from https://www.sciencedirect.com/science/article/pii/B978012802005000015X?via%3Dihub
  8. Cristina, V., Castro Dantas, T. N., & Dantas Neto, A. A. (2012). The use Of Microemusion systems in oil industry. Microemulsions - An Introduction to Properties and Applications. doi:10.5772/36803
  9. Kamal, M. S., Hussein, I. A., & Sultan, A. S. (2017). Review on Surfactant Flooding: Phase behavior, RETENTION, Ift, and field applications. Energy & Fuels, 31(8), 7701-7720. doi:10.1021/acs.energyfuels.7b00353