Low Salinity Waterflooding in Carbonate Reservoirs: Review of Interfacial Mechanisms

Abstract

Carbonate rock reservoirs comprise approximately 60% of the world's oil and gas reserves. Complex flow mechanisms and strong adsorption of crude oil on carbonate formation surfaces can reduce hydrocarbon recovery of an oil-wet carbonate reservoir to as low as 10%. Low salinity waterflooding (LSW) has been confirmed as a promising technique to improve the oil recovery factor. However, the principal mechanism underpinning this recovery method is not fully understood, which poses a challenge toward designing the optimal salinity and ionic composition of any injection solution. In general, it is believed that there is more than one mechanism involved in LSW of carbonates; even though wettability alteration toward a more desirable state for oil to be recovered could be the main cause during LSW, how this alteration happens is still the subject of debate. This paper reviews different working conditions of LSW, previous studies, and field observations, alongside the proposed interfacial mechanisms which affect the colloidal interactions at oil-rock-brine interfaces. This paper provides a comprehensive review of studies on LSW in carbonate formation and further analyzes the latest achievements of LSW application in carbonates, which helps to better understand the challenges involved in these complicated multicomponent systems and potentially benefits the oil production industry.

Low-salinity-based enhanced oil recovery literature review and associated screening criteria

“…Therefore, as far as the underlying mechanisms of low-salinity waterflooding are concerned, clays are not included. In a recent survey by Derkani et al (2018), they categorized the LSWF mechanism according to intrinsic or given parameters such as reservoir characteristics and extrinsic factors such as the injection brine. These are summarized here and a brief screening criterion has been provided.…”

“…Formation waters in carbonate reservoirs tend to be relatively more saline compared to those in sandstones. Derkani et al (2018) noted the importance of formation water composition from the standpoint of reservoir souring and plugging when designing LSWF. As far as initial water saturation (S wi ) is concerned, similar to sandstones, water wetness is directly proportional to water saturation in carbonates also.…”

“…From the perspectives of extrinsic parameters, obviously the ionic composition of the (low salinity) injection brine is one of the most important in carbonates as well. However, temperature has also been discussed as one of the influential parameters in carbonates (Derkani et al 2018). Unlike sandstones, the literature suggests that for the most part LSWF tends to focus on dilution or modification of seawater, which contains possible potential determining ions Ca 2+ and SO 4 2− , that impart favorable wetting characteristics improving the recovery (Derkani et al 2018;Zhang and Austad 2006).…”

“…However, temperature has also been discussed as one of the influential parameters in carbonates (Derkani et al 2018). Unlike sandstones, the literature suggests that for the most part LSWF tends to focus on dilution or modification of seawater, which contains possible potential determining ions Ca 2+ and SO 4 2− , that impart favorable wetting characteristics improving the recovery (Derkani et al 2018;Zhang and Austad 2006). Based on the various cases discussed by Derkani et al (2018), two main points, that are beneficial for enhancing oil recovery from carbonates, emerge; the injection brine should contain Ca 2+ and/or Mg 2+ and SO 4 2− and temperature above 70 °C.…”

“…Unlike sandstones, the literature suggests that for the most part LSWF tends to focus on dilution or modification of seawater, which contains possible potential determining ions Ca 2+ and SO 4 2− , that impart favorable wetting characteristics improving the recovery (Derkani et al 2018;Zhang and Austad 2006). Based on the various cases discussed by Derkani et al (2018), two main points, that are beneficial for enhancing oil recovery from carbonates, emerge; the injection brine should contain Ca 2+ and/or Mg 2+ and SO 4 2− and temperature above 70 °C. The synthetic seawater cases discussed by Derkani et al (2018) include oil recovery as a function of varying SO 4 2− concentration between 0-4 times present in the original seawater while keeping the Ca 2+ constant and vice versa, with temperatures in the range of 70-130 °C.…”