Potential of Low-Salinity Waterflood To Improve Oil Recovery in Carbonates: Demonstrating the Effect by Qualitative Coreflood

Abstract

Low-salinity waterflood (LSF) is a promising improved-oil-recovery (IOR) technology. Although, it was demonstrated that LSF is an efficient IOR method for many sandstone reservoirs, the potential of LSF in carbonate reservoirs is still not well-established because only a limited number of successful coreflood experiments are available in the literature. Therefore, the aim of this study was to examine the oil-recovery improvement by LSF in carbonate reservoirs by performing coreflood experiments.This paper proposes an experimental approach to qualitatively evaluate the potential of LSF to improve oil recovery and alter the rock wettability during coreflood experiments. The corefloods were conducted on core plugs from two Middle Eastern carbonate reservoirs with a wide variation of rock properties and reservoir conditions. Seawater (SW) and several dilutions of formation brine and SW were flooded in the tertiary mode to evaluate their impacts on oil recovery compared with formation-brine injection. In addition, a geochemical study was performed with PHREEQC software (Parkhurst and Appelo 1999) to assess the potential of calcite dissolution by LSF.The experimental results confirmed that lowering the water salinity can alter the rock wettability toward more water-wet, causing improvement of oil recovery in tertiary waterflood in plugs from the two reservoirs. Furthermore, SW is more-favorable for improved oil recovery than formation brine because injection of SW after formation brine resulted in extra oil production. This demonstrates that the brine composition plays an important role during waterflooding in carbonate reservoirs, and not only the brine salinity. It was also observed that oil recovery can be improved by injection of brines that cannot dissolve calcite on the basis of the geochemical modeling study. This implies that calcite dissolution is not the dominant mechanism of IOR by LSF.To conclude, this paper demonstrates that LSF has a good potential as an IOR technology in carbonate reservoirs. In addition, the proposed experimental approach ensures the verification of LSF effect, either it is positive or negative. However, further research is required to explore the optimum salinity and composition and the most-influential parameters affecting LSF response.

Low Salinity Waterflooding in Carbonate Reservoirs: Review of Interfacial Mechanisms

“…It was first shown that either altering the brine composition or reducing the salinity of injected brine below that of the initial formation water can lead to additional oil recovery for Berea sandstone [6][7][8][9][10][11][12]. Such results attracted many oil and gas companies, such as British Petroleum [13][14][15][16][17][18][19], Shell [20][21][22][23][24][25][26], ExxonMobil [27,28], Schlumberger [29][30][31], TOTAL [32,33], and Statoil [34,35] to investigate and further explore the potential and applicability of low salinity waterflooding (LSW) for improved oil recovery. LSW, also known as designer waterflood, advanced ion management, and smart waterflooding, injects brine with controlled ionic concentration and composition (also known as smart water or dynamic water) into the well [17,20,27].…”

Optical measurements of oil release from calcite packed beds in microfluidic channels

“…Most common are methods based on water injection (Goolsby and Anderson 1964;Rausch and Beaver 1964;Hussain et al 2013;Esmaeili and Maaref 2019), for which different strategies are followed: adding alkali, polymers, surfactants or nanoparticles, or adjusting the ion composition. The latter, also known as Smart Water Flooding (SWF) is a relatively recent technique which has been reported to give higher yields than conventional (sea) water injection, (Bernard 1967) in both sandstone (Tang and Morrow 1999;Morrow and Buckley 2011) and carbonate (Gupta et al 2011;Yousef et al 2011;Shehata et al 2014;Nasralla et al 2016Nasralla et al , 2018 reservoirs.…”

Experimental investigation of water composition and salinity effect on the oil recovery in carbonate reservoirs

“…In surveys conducted by Austad et al, the presence of sulfate ions as catalysts showed to make a difference in wettability regarding cationic surfactants [26]. Subsequently, Zhang and Austad [27] suggested the sulfate ion as the only adequate consideration to improve change of wettability in carbonate formations denying the use of surface-active agents especially avoiding high expense of application [28][29][30]. Published experimental data suggests that desorption of acidic oil components from rock surfaces make carbonate rocks more water-wet.…”