Smart Water for EOR by Membranes Remya Ravindran Nair , Evgenia Protasova, Skule Strand and Torleiv Bilstad University of Stavanger, 4036 Stavanger, Norway [email protected] Introduction • Smart water enhances oil recovery (EOR) by changing wettability. • Smart water comprises high divalent and low monovalent ion concentrations for a chalk reservoir. • Smart water is produced by modifying the ionic composition of seawater(SW) . • Smart water can also be produced from diluted produced water (PW). • Smart water is currently produced by adding proper chemicals to fresh water. • Smart water is alternatively produced by nanofiltration membranes (NF) (Figure 1 and 2). • Smart water research is to analyze technical and economical limits for ion separation by membranes. Theory Membranes • NF membranes have a negative surface charge with pore sizes between 0.1 and 1 nm thereby separating monovalent and divalent ions. • Retentate from NF membrane have a high divalent ion concentration and a low monovalent ion concentration. Smart water in chalk reservoirs Main criteria for smart water is low Na + and Cl - and high SO 4 2- , Ca 2+ and Mg 2+ concentrations. Mechanism for wettability alteration • Injection of brines into reservoirs at high temperatures results in enhanced oil recovery by spontaneous imbibition (Figure 3). • SO 4 2- adsorbs onto the positively charged rock surfaces thereby reducing the surface charge. • Reduced electrostatic repulsion increases the concentration of Ca 2+ at the rock surface and Ca 2+ binds to the negatively charged carboxylic group of oil, releasing it from the rock. • High Na + and Cl - concentrations have an adverse effect on oil recovery. Results and Discussion Acknowledgement The authors acknowledge the Research Council of Norway and the industry partners; ConocoPhillips Skandinavia AS, BP Norge AS, Det Norske Oljeselskap AS, Eni Norge AS, Maersk Oil Norway AS, DONG Energy A/S, Denmark, Statoil Petroleum AS, ENGIE E&P NORGE AS, Lundin Norway AS, Halliburton AS, Schlumberger Norge AS, Wintershall Norge AS of The National IOR Centre of Norway and University of Stavanger for support. Conclusions Separation efficiencies by NF membranes with seawater as feed • 99 % rejection for SO 4 2- and 15 % rejection for Na + (Figure 4) • Rejection of monovalent ions decreased with increased divalent ion concentration in feed (Figure 5 and 6). • Substituting sulphate with phosphate decreased monovalent ion rejection (Figure 7). Figure 1. A membrane unit Figure 2. Membrane performance Figure 3. Wettability alteration model induced by smart water Figure 4. Rejection of ions Treatment of deoiled PW • Presence of barium in PW will result in BaSO 4 scaling. • Experiments with 3 different NF membranes on de-oiled PW as feed for removing barium. • 81 % barium removed by NF (Figure 8) Figure 8. Barium rejection by NF Why Nanofiltration? Process chosen after calculating the power consumption, foot print and unit price (Figure 9). Figure 10. Proposed final combination of PW reinjection • Smart water is produced from seawater and oil free produced water by membranes. • Retentate from NF is rich in divalent ions required for smart water. • Power consumed by NF to produce smart water is 48 KWh/m 3 whereas for flash distillation is 1820 KWh/m 3 . • Fresh water consumption is insignificant. • NF is cost efficient, environmentally friendy with no added chemicals. References Bilstad, T. (1992). Sulphate separation from seawater by Nanofiltration. Environmental Science Research, v.46. T. Austad, “Water based EOR in carbonates and Sandstone: New chemical Understanding of the EOR-Potential Using ¨ Smart water¨,” 2012 J. Fathi, T. Austad and S. Strand, “Water-based Enhanced Oil Recovery (EOR) by ¨Smart Water¨ in Carbonate Reservoirs,” Society of Petroleum Engineers, 2012. B. Tansel, J. Sager, J. Garland, R. F. Strayer, L. Levine, M. Roberts, M. Hummerick and J. Bauer, “Significance of hydrated radius and hydration shells on ionic permeability during nanofiltartion in dead end and cross flow modes,” Seperation and Purification Technology ,51, pp. 40-47, 2005. Figure 9. Energy consumption Figure 5. Cl - rejection with increasing SO 4 2- concentration Figure 6. Na + rejection with increasing Mg 2+ concentration Figure 7. Monovalent rejection by increased concentration of SO 4 2- and PO 4 3-