Investigation of Low-Salinity Waterflooding in Secondary and Tertiary Enhanced Oil Recovery in Limestone Reservoirs

Abstract

Improved oil recovery from oil-wet low-permeability limestone reservoirs is a great challenge by altering the reservoir rock wettability. The purpose of this study is to compare the results of low-salinity waterflooding in secondary and tertiary modes to decrease the residual oil saturation from limestone reservoirs. Three different stock-tank crude oils and limestone cores are used in this study. All of the coreflooding experiments were performed at 60 °C and 2000 psi by injection of actual formation and seawater, with brine solutions containing single-component salt, such as MgSO 4 , KCl, Na 2 SO 4 , CaCl 2 , MgCl 2 , and NaCl, with a wide range of salinity levels. During low-salinity flooding in secondary recovery, the dominant displacement-suggested mechanism is snap-off, which results in an oil recovery factor with different values for the various wettability conditions. The most interesting result is that tertiary low-salinity recovery was never observed in these coreflooding experiments. The measured effect of tertiary low-salinity waterflooding from limestone core experiments was rock dissolution, as a result of surface reactions, and an increase in water relative permeability.

Enhancing Oil Recovery from Chalk Reservoirs by a Low-Salinity Water Flooding Mechanism and Fluid/Rock Interactions

“…Recovery results were compared by flooding Na 2 SO 4 , NaCl, and MgCl 2 brines as secondary mode [18]. They suggested that low salinity brine enriched in (SO 4 2− ) and depleted in monovalent ions is suitable in oil recovery.…”

Impact of water saturation and cation concentrations on wettability alteration and oil recovery of carbonate rocks using low-salinity water

“…The wettability alteration may occur via various EOR methods such as smart water injection (Gandomkar and Rahimpour 2015;Rivet et al 2010), low-salinity water injection (Tang and Morrow 1997a;Shehata and Nasr El-Din 2015;Samira et al 2018), and Nano EOR (Hendraningrat et al 2013). There exist some conventional experimental methods to investigate the occurrence and contribution of wettability alteration during various EOR techniques such as contact angle measurement (Mahani et al 2015a), flotation test (Anderson 1986), adhesion test (Anderson 1986;Tiab and Donaldson 2004), spontaneous imbibition (Shehata and Nasr El-Din 2015), core-flooding (Wickramathilaka et al 2011), and capillary pressure measurement (Anderson 1986;Shaker Shiran and Skauge 2012).…”

“…The recovery from outcrop chalk cores was not affected by low-salinity water, both at ambient and reservoir temperature (Zahid et al 2012). Most of these works indicated that the ion concentration should be changed during low-salinity water injection to wettability alteration that occurs (Shehata and Nasr El-Din 2015;Rivet et al 2010;Gandomkar and Rahimpour 2015); however, various mechanisms have been proposed for this phenomenon (as mentioned above) (Tang and Morrow 1999;McGuire et al 2005b;RezaeiDoust et al 2009;Ligthelm et al 2009;Austad et al 2010;Mahani et al 2015b;Lager et al 2008). In addition, if the low-salinity water injection method is performed as a tertiary oil recovery method, at least a portion of saturated water is diluted as a result of secondary water injection.…”

Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding

“…Improved recovery during CSW in carbonates appears to be observed when the initial wetting state is mixed- or oil-wet, and the wettability changes to become more water-wet after injecting water with modified composition8912152122242526. As the reservoir first fills with oil, polar functional groups on the molecules in the oil may adsorb onto the mineral surfaces, rendering them oil-wet.…”