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______________________________________________________________________________________________________________________________1.1 Introduction

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.

______________________________________________________________________________________________________________________________1.2 Surfactant flooding and its types

Surfactant flooding is a chemical Enhance Oil Recovery technique (cEOR) in which a little amount of surfactant (0.3-1.0 volume%) is mixed with the injected fluid (water) to sweep the reservoir oil. Surfactants are blended with co-surfactants which acts as active agents to enhance the properties of surfactant solution and helps to sustain the optimal conditions with respect to Pressure, Temperature and Salinity.

The presence of surfactants also improves the wettability (oil-wet to water-wet) of the reservoir rock to enhance the recovery of oil. Surfactants also improves the recovery of residual oil through other mechanisms like micro-emulsification of trapped residual oil and by changing the interfacial rheological properties (Mai A, 2009).

Generally, in EOR techniques a fluid or gas is injected in the reservoir in order to displace residual crude oil from the reservoir. In this chemical EOR (cEOR) technique, surfactants along with aqueous solution are injected forming a micro emulsion (Mai A, 2009). These Injected fluids interacts 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 the residual oil in the pore spaces of the matrix rocks.

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 (Selby R, 1989). 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 IFT. IFT range should be reduced to 0.001mN/m The state of the art of this chemical EOR technique has been reviewed recently (Farouq Ali SM, 1996).  

1.2.1 Types of surfactants used in the surfactant flooding process:

The surfactants are primarily divided into four types

• Cationic surfactant,  
• Anionic surfactant,
• Non-ionic surfactant and
• Amphoteric

Figure 1. Molecular structure and classification of various surfactant molecules (Y. Nakama, 2007).

1.3 Mechanism of surfactant flooding:

1.3.1 Micelle Formation in Surfactant flooding:

Micro Emulsion are formed in surfactant flooding between water and Oil as two immiscible phases and by lowering IFT and Viscosity which increases mobility of oil (Santanna, Curbelo, Castro Dantas, & Dantas Neto, 2009).

1.3.2 Surfactant Adsorption:

Adsorption process occurs when the surfactant accumulates on the surface of the reservoir rock forming a micelles and surface charge at solid and liquid interface. The surfactant concentration must not exceed the value of CMC. Surfactant properties alters 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.

To obtain lower IFT and good foam stability the Surfactant concertation should be greater than the CMC value.

1.4 Reservoir Compatibility for surfactant Flooding:

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 has low permeability Matrix and mostly has Oil wet -Mixed wet Conditions. Whereas, Sandstone Reservoirs are homogenous and are more suitable of cEOR.    

1.5 Future Challenges of Surfacatant Flooding:

• Its challenging in High temperature, High Salinity, fractured Carbonate reservoirs.
• It works good for low temperature and low salinity conditions. However, sulphonate surfactants can be used for high temperature and low salinity conditions.
• High Adsorption and precipitation of surfactant is also a challenge for high temperature and High salinity sandstone reservoirs.

1.6 References  

[1] Santanna, V.; Curbelo, F.; Castro Dantas, T.; Dantas Neto, A.; Albuquerque, H.; Garnica, A. Microemulsion flooding for enhanced oil recovery. J. Pet. Sci. Eng. 2009, 66 (3), 117−120.

[2] 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.

[3] Mai A, Bryan J, Goodarzi N, Kantzas A. Insights into non-thermal recovery of heavy oil. J Can Petrol Technol 2009;48:27–35.

[4] Farouq Ali SM. Prospects of EOR techniques in Saskatchewan oil reservoirs. J Can Petrol Technol 1986;25:64–7.

[5] Siggel, L.; Santa, M.; Hansch, M.; Nowak, M.; Ranft, M.; Weiss,H.; Hajnal, D.; Schreiner, E.; Oetter, G.; Tinsley, J. A New Class ofViscoelastic Surfactants for Enhanced Oil Recovery. SPE Improved Oil Recovery Symposium, SPE-153969-MS, Apr. 14−18, 2012, Tulsa, OK, USA; Society of Petroleum Engineers: Richardson, TX, USA, 2012.

[6] Morvan, M.; Moreau, P.; Degre, G.; Leng, J.; Masselon, C.; Bouillot, J.; Zaitoun, A. New viscoelastic fluid for chemical EOR. SPE International Symposium on Oilfield Chemistry, SPE-121675-MS, Apr.20−22, 2009, The Woodlands. TX, USA; Society of Petroleum

Engineers: Richardson, TX, USA, 2009; pp 1−15, DOI: 10.2118/121675-MS.

[7] Hirasaki, G.; Miller, C.; Puerto, M. Recent Advances in Surfactant EOR. SPE J. 2011, 16 (4), 889−907.

[8] Abramov, V. O.; Abramova, A. V.; Bayazitov, V. M.; Altunina, L.K.; Gerasin, A. S.; Pashin, D. M.; Mason, T. J. Sonochemical approaches to enhanced oil recovery. Ultrason. Sonochem. 2015, 25(1), 76−81.