Relationship between Surfactant Injectivity, Phase Behaviour and Retention in Porous Medium

Transcription

1 Relationship between Surfactant Injectivity, Phase Behaviour and Retention in Porous Medium Limei Sun, Kristine Spildo, Ketil Djurhuus and Arne Skauge, (CIPR), Bergen, Norway IEA EOR Workshop, Aberdeen, Oct. 2010

2 Key question Can you have low loss of surfactant (retention) at ultralow interfacial tension (IFT)?

3 Sor EOR by lowering oil-water IFT 0,35 0,30 0,25 N c v : viscosity v: linear flow rate σ: interfacial tension (IFT) 0,20 0,15 0,10 0,05 Ncc ~1x10-5 Low IFT gives high Nc and thus low Sor 0,00 1,00E-07 1,00E-06 1,00E-05 1,00E-04 1,00E-03 1,00E-02 1,00E-01 Remaining oil saturation (S or ) is a function of capillary number Nc Trapping at high IFT Mobilisation at low IFT

4 Some surfactant selection criteria Low IFT. Closely related to surfactant phase behaviour Retention: total loss of surfactant in a porous medium. Low retention: more efficient process/better economics High retention: process not efficient, costly Solubility : surfactant formulation should have solution properties, i.e. stable solutions and good solubility to guarantee good injectivity.

5 Phase behavior of oil/brine/surfactant Increasing salinity Oil Oil Oleic Na + Na + Na + Na + Na + Na+ Aqueous Na + Brine Na + Na + Brine Na + Winsor I/Type II- Winsor III/Type Centre III for Integrated Winsor Petroleum II/Type Research II+

6 Experiments Solubility evaluation (20 0 C) Phase behaviour (20, 50 and 90 0 C) and IFT study (20 and 50 0 C) Dynamic retention measured on Berea cores (20 0 C) Surfactant formulation: 1 % internal olefin suifonate (IOS) surfactant + 1% isoamyl alcohol (IAA) Varying NaCl concentration Oil: heptane CH 3 (CH 2 ) m CH(CH 2 ) n CH 3 IOS SO - Na + Centre for Integrated 3 Petroleum Research

7 Scope of experiments For a certain surfactant formulation, investigate the interrelationship between solubility, phase behaviour (IFT) and retention as functions of salinity. Find the best condition(s) for combined low IFT, low retention, and good injectivity in a surfactant flooding process.

8 Solubility evaluation: visual inspection and activity Activity Ci Co 100 C i : concentration in centrifuged sample C 0 : initial conc. in non centrifuged sample C T P P O C: Clear T: Turbid P: Precipitate O: Oleic phase Good solubility : Clear solution and high activity.

9 Phase behaviour and IFT Vo,1 Vo,2 VE SP SP w o V V V V w s o s V V V Vs V Vs w, 1 o, 1 w,2 o,2 Vs = surfactant volume Vw,1 Vw,2 IFT: 0,3 ( SP) 2 Before After Solublization parameters were used to estimate the IFTs of type III systems. IFTs for two-phase systems were measured using a spinning drop tensiometer

10 Retention Berea cores, dried, vacuumed, saturated with brine. Injection sequence: Brine preflush 2 PV surfactant solution (0.2 PV for low retention samples) 5 PV brine Total retention: surfactant injected surfactant recovered

11 Results Solubility as a function of salinity 1% surfactant + 1% IAA NaCl (wt %) Appearance * C C C C P P T P P P O Activity * After centrifugation C: Clear P: Precipitate T: Turbid O: Oleic phase Good surfactant solubility in the aqueous phase is found at low salinities Increasing salinity reduces the repulsion between ionic head groups and thus forces the surfactant to salt out.

12 IFT/(mN/m) Phase behaviour and IFT as functions of salinity (20 0 C) 10 1 WII- WIII WII+ 0,1 EOP/MEP MEP/EWP 0,01 0, NaCl/wt% NaCl % , S* Phase behaviour II- II- II- II- II- II- III III III II+ II+ II+ IFT/(mN/m) 2,18 0,46 0,21 0,075 0,077 0,05 ~0,013 0,0015 ~0,006 0,013 0,023 0,061 Phase behaviour against heptane follows usual trends. II- phase behaviour gives low IFT near the three-phase region

13 Retention as a function of salinity (20 0 C) NaCl (%) Appearance Activity Retention (mg/g rock) 1 C 100 0,14 3 C 100 0,15 6 T 100 1,50 9 P 98 1,76 At low salinity (0-3%) retention is quite low, while at high salinity, the retention is high. Retention increases with increasing salinity. Clear solutions with high activity gives low retention High surfactant activity, but with turbid solutions, gives high retention.

14 Correlation between solubility, retention and phase behaviour NaCl wt% Appearance C C C C P P T P P P O Activity Retention (mg/g) 0,14 0,15 1,5 1,76 IFT (mn/m) 2,18 0,46 0,21 0,075 0,077 0,05 0,0015* 0,013 0,023 0,061 Phase behaviour WII- WIII WIII WII+ WII+ WII+ * IFT at S* = 6.6 Alternative?

15 Conclusions At optimum salinity (S*) ultralow IFT is obtained, but in our study solution properties are poor and surfactant retention is high. The search for an optimum surfactant formulation has to consider solution properties and retention in addition to the low IFT. Type II- phase behaviour can also result in low interfacial tensions. At these salinities solubility is good and retention is low. This implies a possibility for a potentially better and more successful surfactant flooding. Type II- phase behaviour may be the best option for a compromise between the properties in question.

16 Statoil and Shell are gratefully acknowledged for supporting surfactant research at CIPR The Norwegian Research Council is also gratefully acknowledged for supporting EOR research at CIPR through the PETROMAKS program

17 Thank you for your attention!

18 II - III II + Increasing salinity It is well established that IFT is related to phase behaviour: Ultra low IFTs are found for systems in the III phase area, with the lowest value obtained at optimal salinity, S* Important questions related to applicability: What is the solubility of the injected surfactant solution at S*? What is the adsorption/retention of surfactant at S*?