The Impact of LoSal™ on Oil Recovery from a Selected Carbonate Reservoir in Abu Dhabi-An Experimental Approach

Abstract

Low-salinity water flooding LoSal™ has been used to improve oil recovery for many decades. Historically, the physical mechanism behind this improvement in oil recovery was attributed to the pressure maintenance and displacement of oil by injected water. Recently, evidence from laboratory and field tests indicated that water flooding also involves chemical processes and that modifying of the injection brine salinity and its ionic composition can significantly impact the oil recovery. Several theories regarding the mechanism of LoSal™ flooding have been discussed in the literature. These include interfacial tension reduction, wettability alteration (cation exchange), change in pH (increase), emulsion formation, and clay migration. There is no agreement, however, among the researchers regarding the mechanism of LoSal™ flooding and although limited work has been done on carbonates, some studies have concluded that LoSal™ have no effect on oil recovery. This work presents the results of flooding tests on selected carbonate core samples taken from Bu Hasa field in Abu Dhabi using sea water and two field injection waters, Um-Eradhuma (UER) at 197,584 ppm and Simsima (SIM) at 224,987 ppm. These results were used to evaluate the effects of brine salinity and ionic composition on the possible interactions of limestone rock/ brine/ and oil system and to identify the oil recovery mechanism. The field injection waters were diluted to salinities of 5000 and 1000 ppm and the optimum salinity was determined and then modified by varying the sulfate and calcium ion concentrations. Wettability alteration was determined by contact angle measurements. Interfacial tension measurements of the studied systems were also performed in an attempt to evaluate the flow mechanism with LoSal™ flooding. The experimental results revealed that a significant improvement in the oil recovery can be achieved through alteration of the injection water salinity. Reducing the salinity of UER water from 197,362 ppm to 5000 ppm resulted in an improvement of oil recovery from 63% to 84.5% of OOIP and the latter salinity was used to evaluate the impact of changing the sulfate and calcium ion concentrations on oil recovery. Results also indicated that sulfate concentration has a significant effect on the flooding process and that increasing the sulfate concentration beyond some optimum concentration of 47 ppm resulted in a negative effect on the flooding process. Contact angle measurements indicated that lowering the solution salinity could shift the wettability of the system towards intermediate wettability levels and that the UER water exhibits higher shift toward intermediate wettability compared to other waters. Results also indicated that there is no clear correlation between the improvements in oil recovery and interfacial tension and the pH of the studied systems.

Similarities and Differences of Low Salinity Polymer and Low Salinity LPS (Linked Polymer Solutions) for Enhanced Oil Recovery

“…Secondary mode 10-fold diluted sea water injection recovered 10% additional oil compared to the sea water injection in secondary mode. Similar results have been reported by other researchers all indicating improved oil recovery by low salinity injection in carbonate rocks, either by diluting the high salinity brine or by manipulation of the determining ions in the injected brine (Zahid et al, 2012, Romanuka et al, 2012, Al-Attar et al, 2013, and Al-Shalabi et al, 2013.…”

Oil Recovery Efficiency and Mechanism of Low Salinity-Enhanced Oil Recovery for Light Crude Oil with a Low Acid Number

“…The trends in IFT values observed in this study are similar to the one observed for a pure alkane−brine system in our previous study. 34 Al-Attar et al 35,36 have reported crude oil−seawater IFT values for crude oil from the Bu Hasa oilfield and seawater from Arabian Gulf (40 980 ppm). They have observed a continuous increase in IFT with brine dilution.…”

Effect of Ca2+, Mg2+ and SO42− ions on the zeta potential of calcite and dolomite particles aged with stearic acid

“…However, the affinity of Mg 2+ ions increases with the temperature; and they can substitute Ca 2+ ions from the carbonate lattice [17][18][19]23]. It is reported that increasing the concentration of Ca 2+ ions resulted in a decreased ultimate recovery during core flooding experiments [44]. SO 4 2− ions are reported in literature as strong PDIs towards carbonate surfaces.…”