SPE Chemical EOR for Extra-Heavy Oil: New Insights on the Key Polymer Transport Properties in Porous Media

Transcription

1 Renewable energies Eco-friendly production Innovative transport Eco-efficient processes Sustainable resources SPE Chemical EOR for Extra-Heavy Oil: New Insights on the Key Polymer Transport Properties in Porous Media F. Rodríguez, PDVSA, Paris Diderot University; D. Rousseau and S. Bekri, SPE, IFP Energies nouvelles; M. Djabourov, ESPCI Paris Tech and C. Bejarano, PDVSA IFP Energies nouvelles PARIS-LA DEFENSE, JUNE 2015.

2 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 2

3 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 3

4 INTRODUCTION Heavy and extra-heavy oil: Significant reserves of heavy and extra-heavy oils in the world Fossil Fuel Resource Percentage of the world's total resources (Albooudwarej, H. et al) Conventional oil 30% Heavy Oil 15% Extra-heavy oil 25% Oil sand and bitumen 30% Low recovery factors heavy oil: 20-25% 25% ; extra-heavy oil: 3-18% ; conventional: 35% Extra-heavy oil in the Faja Petrolífera del Orinoco (FPO): 7-12 API T= C ηo > 1000 cp Reserves: 1.2 trillion barrels Recovery factor: 3-5% 4

5 INTRODUCTION Thermal EOR methods: Viscosity reduction at reservoir conditions Thermal methods: Injection of heat (steam flooding, in-situ combustion, SAGD, etc) SAGD needs pay thickness > 30 m Economic and environmental issues (degradation of air and water quality, high water consumption, etc.) Chemical EOR methods: Polymer flooding Surfactant flooding Alkali flooding 5

6 INTRODUCTION Chemical EOR for heavy and extra-heavy oils Polymer Flooding: to decrease the oil-water mobility ratio M = λw λ o = k k w o / ηw / η o η w Improvement in areal sweep of a homogeneous five-spot by use of polymers. Hydrosoluble polymers: polyacrylamidebased Polymer flooding increases the oil recovery rate in the short term (there is normally no impact on the ultimate recovery). Improvement in vertical sweep of a homogeneous five-spot by use of polymers. 6

7 INTRODUCTION Chemical EOR for heavy and extra-heavy oils Surfactant flooding: to mobilize the residual oil Sor Ca = u η γ w o / w SPE γ o/w 7 u ηw Ca = γ o / w S. Youssef et al., SCA Surfactant flooding: to decrease the interfacial tension between oil and water Impact on the ultimate recovery (tertiary recovery) Alkali is often considered: (a) for generation of in situ surfactants from reactions with the oil's acidic components (operational issues: scaling, transport of emulsion) ; (b) to reduce the adsorption of the synthetic surfactant

8 INTRODUCTION Chemical EOR for heavy and extra-heavy oils Comparison of Venezuelan Extra-heavy crude oil and Canadian/Chinese/Oman oils: Heavy/Extraheavy oil reservoir location API Acid number (mgkoh/g-oil) Oil viscosity (cp) Reservoir Temperature ( C) Canada China Oman Venezuela (FPO) 7-12 >2 >

9 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 9

10 MOTIVATIONS AND OBJECTIVE Motivations Displacement of extra-heavy oil might require high polymer viscosities (η > 100 cp?) Polymer flooding with high viscosity polymer solutions not extensively investigated in the literature Objective To give some insights into the transport properties of high viscosity polymer solutions in porous media under model conditions (approaching Venezuelan conditions). 10

11 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 11

12 EXPERIMENTAL METHODS AND MATERIALS Experiments: Standard HPAM (FP3630S) A model brine (20 g/l NaCl + 0,4 g/l NaN 3 ) C pol =0.8 to 2.5 g/l Model unconsolidated sandpacks: (ϕ = 40%, K = 4 D) Intermediate pressure taps Downstream capillary to detect polymer breakthrough T = 50 C Corefloods: Retention, Inaccessible Pore Volume, Over-retention, retention, In-depth transport and Injectivity 12

13 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 13

14 CHARACTERIZATION OF POLYMER SOLUTIONS TC/TN method: to determine the concentration of each polymer solution Typical flow curves: Marked shear thinning behavior 14

15 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 15

16 RETENTION AND INACCESSIBLE PORE VOLUME Method: analysis of the volume at breakthrough (V BT ) for two successive polymer slugs This method allow us to determine the irreversible component of polymer retention (usually attributed to polymer adsorption on the pore walls) Dead volumes are carefully determined V BT1 = V p + V ret IPV V BT2 = V p IPV = Dawson and Lantz, SPE3522 (1972) 16

17 RETENTION AND INACCESSIBLE PORE VOLUME 3 corefloods were performed by injecting 2 successive polymer slugs (for each fresh sand pack and each Cpol): CF1 0.8 g/l CF2 2 g/l CF3 2.4 g/l 17

18 RETENTION AND INACCESSIBLE PORE VOLUME Marked increase of retention with concentration Same trend is observed in recent literature (SPE ) for different conditions (brine salinity and T: 2% NaCl and 25 C) Marked increase of retention with concentration CF1= 0.8 g/l: 5 µg/g CF2= 2.0 g/l: 33 µg/g CF3= 2.4 g/l : 63 µg/g Increase of IPV with concentration CF1= 0.8 g/l: 0% PV CF2= 2.0 g/l: 2% PV CF3= 2.4 g/l : 5% PV 18

19 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 19

20 OVER-RETENTION EFFECT Additional polymer slugs were injected during a second step (after initial retention): both CF2 and CF3 were exposed to additional polymer slugs at Cpol=2.4 and 2g/L, respectively. It could be translated into a field injection strategy. 20

21 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 21

22 Results of Polymer In-Depth Transport: IN-DEPTH PROPAGATION HPAM 3630S C = 2,4 g/l HPAM 3630S C = 0,8 g/l P Mobility reduction: Rm P P: Measured pressure drop during the polymer injection P S : Measured pressure drop at initial pure water injection = Polymer propagation S involves more complex mechanisms at high concentration 22

23 IN-DEPTH PROPAGATION Results of Polymer In-Depth Transport: S1 S2 S3? R m Link between the bulk viscosity and Rm Bulk viscosity is computed at equivalent shear rate velocity (flow curves) P Sfinal R = k P S P app inj η k = = ini P ini η k S 0 inj = η reff Rk Effective viscosity becomes markedly lower than viscosity expected from bulk measurements. 23

24 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 24

25 DEPLETION EFFECT Numerical Approach: Analytical representation of the depletion layer effect (2 fluids model): Effective viscosity 1 η δ = eff R η bulk η depl η depl with: - η bulk : bulk viscosity ; η depl : viscosity in the depleted layer ; η eff : effective viscosity (Poiseuille's) - δ = thickness of the depleted layer ; R : pore throat radius 25

26 DEPLETION EFFECT Numerical Approach: 2D size exclusion effects Principle of the numerical simulation performed to assess for a depletion layer caused by steric exclusion between hard discs. Variation of the particle volume fraction ϕ depl in the depleted layer as a function of ϕ bulk, the "bulk" To translate the relationship between concentrations in a relationship between viscosities to determine η depl as a function of η bulk 26

27 DEPLETION EFFECT Hypothesis made: equivalent particle size = thickness of the depleted layer = adsorbed layer thickness S1 S2 S3 = (1- / ) = In the frame of the capillary bundle model 27

28 DEPLETION EFFECT Final results: S1 S2 S3 Good agreement between η reff /η rbulk calculated and η reff /η rbulk measured 28

29 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 29

30 POLYMER INJECTIVITY Impact of Polymer Concentration S1 S2 S3 Polymer injection at different flow rates (range of typical near-wellbore velocities) Interstitial velocity: v i = Q Sφ with: - Q: injection flow rate, - S: sand pack's section - ϕ: porosity For Cpol = 2.5 g/l, rheothinning appears to be more marked and rheothickening less marked than for Cpol = 0.8 g/l. 30

31 OUTLINE Introduction Motivations and objective Experimental methods and materials Characterization of polymer solutions Coreflood tests: Retention and inaccessible pore volume Over-retention effect In-depth propagation Depletion layer effect Polymer injectivity Conclusions and perspectives 31

32 CONCLUSIONS AND PERSPECTIVES The transport properties of viscous polymer solutions are very different to that of more conventional polymer solutions in terms of: 1. Irreversible retention which can be higher when viscosity is increased. 2. Adsorption at the pore walls might not be the only phenomenon responsible for the irreversible retention (complex rheological properties of viscous semi-diluted polymer solutions exposed to low deformations could also play a role). 3. A viscous polymer slug injected after a less viscous one can lead to significantly higher retention. Fortunately, the reverse does not appear to be true as no over adsorption is observed when concentration is decreased. This opens perspectives for field injection strategies to mitigate polymer adsorption. 32

33 CONCLUSIONS AND PERSPECTIVES 4. Apparent viscosity becomes markedly lower (up to 50% less) than bulk viscosity for viscous polymer solutions. This phenomenon can be modeled by depletion layer effects. 5. For polymer injectivity in porous medium, rheo-thinning appears to be more marked and rheo-thickening less marked for high viscosity than for low viscosity. 6. These specific properties of the transport of viscous polymer solutions in porous media illustrate that polymer flooding of the FPO extra-heavy oil require very careful preliminary/feasibility investigations. 33

34 CONCLUSIONS AND PERSPECTIVES Acknowledgements / Thank You / Questions We thank PDVSA and IFPEN for supporting this research project. Thanks to Philippe POULAIN and Nicolas ROUSSEAU at IFPEN for their advice regarding the procedures for the lab experiments. 34