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Low-salinity water flooding

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Low-salinity water flooding (LSW) is an EOR method that injects water containing low concentrations of soluble solids into a reservoir. Its potential of improving oil production has been proved through laboratory experiments. Unlike the conventional water flooding, low-salinity water flooding can change the wettability of the reservoir rock in order to increase oil recovery. It is usually used as tertiary oil recovery technology and has great potential for oilfield development.


Laboratory tests have produced many research results on low-salinity water flooding, but there are still some controversies in the study of oil displacement mechanism. There are only a limited number of successful applications of Low salinity water flooding in field trials. Due to the limited field successes, factors that claims to be influencing oil production in lab studies need to be evaluated more carefully prior to large field implementation. Based on research, some factors that influence oil recovery by low salinity water flooding include but are not limited to:

  • Wettability
  • Temperature
  • Porosity and permeability correlation
  • Reservoir fluid properties
  • Fracture and caves

Main factors

When operating low-salinity waterflood in oil reservoirs, it is necessary to clarify the main controlling factors that may affect low-salinity waterflooding, which determines the success of oil recovery. Those main factors have been summarized and are outlined below[1]

  • Mineral surface
  • Brine
  • Oil
  • Temperature
  • Wettability
  • Injection brine concentration
  • Connate water salt concentration

Mechanisms of operating in different types of reservoirs

Regardless of whether it is sandstone or carbonate reservoirs, the understanding of its dominant mechanism has not yet reached a consensus. The potential displacement mechanisms are mainly fines migration[2], multicomponent ionic exchange (MIE)[3], electrical double layer[4],  and pH effects[5].

Fines migration:

Figure 1. Effect of clay fine migration on recovery improvement by LSW[6]

Fine-grain migration was first proposed in 1999. The migration of fine particles from the rock surface may change the wettability of the rock surface and make it more water wet. It may also block the high permeability channels and increase the water sweep efficiency.

Multicomponent ionic exchange (MIE):

This mechanism is generally used to explain the low-salinity water drive mechanism in carbonate rocks. The main mineral of carbonate rock is calcium carbonate. Calcium ions accumulate on the surface of calcium carbonate to give it a positive charge. Crude oil inside carbonate reservoir contain carboxyl group which is negatively charged. Under reservoir conditions, the carboxyl groups in the crude oil and the positive charges on the surface of the carbonate rock attract each other to cause the oil-wet or mixed-wet condition of the carbonate rock. During the low-salinity water flooding process, the positive charge on the rock surface decreases. Therefore, the process reduces the attraction between carbonate rocks and crude oil. As a result, the oil recovery after low salinity water flood could increase.

Electrical double layer:

Figure 2. Effect of salinity on electrical double layer[7]

It was proposed that the mechanism of enhanced oil recovery in which the expansion of the electric double layer leads to the wetting modification of the reservoir. In high salinity reservoir, the electric double layer is more compact allowing less oil between the clay particles to be released. When the water in the reservoir is less saline, the double layer expands allowing oil between clay particles to be produced. In a typical saline reservoir environment, the outside of the clay particle is composed a negatively charged diffusion layer, and the inside of the clay particle is composed of a positively charged adsorption layer. The positive ions are mainly divalent cations. When the salinity decreases, the double layer expands, and sodium ions replace the divalent cations. The water wettability increases due to electrostatic repulsion of crude oil components away from the rock.

pH effects

In sandstone reservoirs, the organic matter of crude oil is desorbed from the clay surface by the increase of local pH at the clay-water interface, resulting in increased water wettability and enhanced oil recovery.


Water flooding is currently the most widely used improved oil recovery (IOR) technology. Low-salinity water flooding injects diluted seawater or river water to the formation. Some advantages of low salinity water flood include high effectiveness, simple injection, low cost, and low capital investment.


  1. Katende, A., and Sagala, F. 2019. A Critical Review of Low Salinity Water Flooding: Mechanism, Laboratory and Field Application. Journal of Molecular Liquids. Journal of Molecular Liquids 278 (15):627-649.
  2. Tang, G., and Morrow, N. R. 1999. Influence of Brine Composition and Fines Migration on Crude Oil/Brine/Rock Interactions and Oil Recovery. Journal of Petroleum Science and Engineering 24(2-4):99-111.  
  3. Lager, A., Webb, K.J., Black, C.J.J., Singleton, M., and K.S. Sorbie. 2008. Low Salinity Oil Recovery - An Experimental Investigation." Petrophysics 49 (2008): No Pagination Specified.
  4. D.J. Ligthelm, J. Gronsveld, J. Hofman, N. Brussee, F. Marcelis, H. van der Linde, Novel Waterflooding Strategy By Manipulation Of Injection Brine Composition, EUROPEC/EAGE Conference and Exhibition, 8–11 June, Amsterdam, The Netherlands, 2009,
  5. T. Austad, A. Rezaeidoust, T. Puntervold, Chemical Mechanism of Low Salinity Water Flooding in Sandstone Reservoirs, SPE Improved Oil Recovery Symposium, 24–28 April, Tulsa, Oklahoma, USA, 2010,
  6. Yazdani Sadati, E., Sahraei, E., Rahnema, M. et al. The effect of CO2-enriched water salinity on enhancing oil recovery and its potential formation damage: an experimental study on shaly sandstone reservoirs. J Petrol Explor Prod Technol 10, 3791–3802 (2020).
  7. T. Knott, Less Salt, More Oil, BP Magazine of Technology and Innovation (2009), pp. 1-12, Accessed 11th Apr 2018