Smart Water for EOR by MembranesRemya Ravindran Nair, Evgenia Protasova, Skule Strand and Torleiv Bilstad

University of Stavanger, 4036 Stavanger, Norway remya.nair@uis.no

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 SO42-, Ca2+ and Mg2+ concentrations.

Mechanism for wettability alteration

• Injection of brines into reservoirs at high temperatures results in enhanced oil recovery by spontaneous imbibition (Figure 3).• SO4

2- adsorbs onto the positively charged rock surfaces thereby reducing the surface charge.• Reduced electrostatic repulsion increases the concentration of Ca2+ at the rock surface and Ca2+ 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 industrypartners; ConocoPhillips Skandinavia AS, BP Norge AS, Det Norske Oljeselskap AS, EniNorge 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 Stavangerfor support.

Conclusions

Separation efficiencies by NF membranes with seawater as feed

• 99 % rejection for SO42- and 15 % rejection for Na+ (Figure 4)

• Rejection of monovalent ions decreased with increaseddivalent 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 modelinduced by smart water

Figure 4. Rejection of ions

Treatment of deoiled PW

• Presence of barium in PW will result in BaSO4 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, footprint 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/m3 whereas for flash

distillation is 1820 KWh/m3 .• 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¨,” 2012J. 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 ionicpermeability 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 increasingSO4

2- concentration

Figure 6. Na+ rejection withincreasing Mg2+ concentration

Figure 7. Monovalent rejection by increased concentration of SO4

2- and PO43-