NANOPARTICLE-SURFACTANT STABILIZED FOAMS

Abstract

Stabilized foams are provided, adapted in particular for subterranean applications in hydrocarbon recovery operations. The foams are stabilized with surfactant-decorated nanoparticles, and the decoration of the nanoparticles with surfactant may be titrated to tune the stabilization of the foam.

Claims

1. A foam composition comprising a surfactant-decorated nanoparticle, wherein the nanoparticle comprises a charged surface characterized by a capacity to bear a charge, and an oppositely-charged ionic surfactant non-covalently decorates only a portion of the charged surface of the nanoparticle, the surfactant and the nanoparticle being present respectively in the foam composition in a surfactant concentration and a nanoparticle concentration, wherein the surfactant-decorated nanoparticle is present in the foam composition in a surfactant-decorated nanoparticle concentration that stabilizes the foam in the presence of a hydrocarbon and/or in the presence of a saline aqueous medium, compared to the stability of a foam having only the surfactant present at the surfactant concentration or a foam having only the nanoparticle present at the nanoparticle concentration.

2. The foam of claim 1, wherein the nanoparticle is comprised of a metal or metalloid oxide, carbon nanotubes, cellulose nanocrystals or a mixture thereof.

3. The foam of claim 2, wherein the metal or metalloid oxide is silicon oxide, iron oxide or aluminum oxide.

4. The foam of claim 1, wherein the surfactant comprises: a sulfonate, a betaine, an amino acid derivative, an ethoxylated linear paraffin, an olefin, an alkylate, a soap; a carboxylate, a linear alkyl-amine, or an alkyl-ammonium.

5. The foam of claim 4, wherein the sulfonate is sodium dodecyl benzene sulfonate.

6. The foam of claim 4, wherein the betaine is dodecyl betaine.

7. The foam of claim 4, wherein the olefin is an alpha olefin sulfonate.

8. The foam of claim 4, wherein the alkyl-ammonium is dodecyl amine or lauryl amine.

9. The foam of claim 1, wherein the foam comprises a gas phase, and the gas phase comprises N.sub.2, CO.sub.2, air, CH.sub.4 or mixtures thereof.

10. The foam of claim 1, wherein the nanoparticle concentration in the foam is from 0.01 to 10 weight %.

11. The foam of claim 1, wherein the surfactant concentration in the foam is from 0.01 to 10 weight %, or from 0.01 to 2 weight %.

12. The foam of claim 1, wherein the charged surface of the nanoparticle is positively charged, and the surfactant is an anionic surfactant.

13. The foam of claim 1, wherein the charged surface of the nanoparticle is negatively charged, and the surfactant is a cationic surfactant.

14. (canceled)

15. (canceled)

16. (canceled)

17. (canceled)

18. A method for stabilizing a foam comprising forming the foam with a surfactant-decorated nanoparticle, wherein the nanoparticle comprises a charged surface characterized by a capacity to bear a charge, and an oppositely-charged ionic surfactant non-covalently decorates only a portion of the charged surface of the nanoparticle, the surfactant and the nanoparticle being present respectively in the foam composition in a surfactant concentration and a nanoparticle concentration, wherein the surfactant-decorated nanoparticle is present in the foam composition in a surfactant-decorated nanoparticle concentration that stabilizes the foam in the presence of a hydrocarbon and/or in the presence of a saline aqueous medium, compared to the stability of a foam having only the surfactant present at the surfactant concentration or a foam having only the nanoparticle present at the nanoparticle concentration.

19. The method of claim 18, wherein the nanoparticle is comprised of a metal or metalloid oxide, carbon nanotubes, cellulose nanocrystals or a mixture thereof.

20. The method of claim 19, wherein the metal or metalloid oxide is silicon oxide, iron oxide or aluminum oxide.

21. The method of claim 18, wherein the surfactant comprises: a sulfonate, a betaine, an amino acid derivative, an ethoxylated linear paraffin, an olefin, an alkylate, a soap; a carboxylate, a linear alkyl-amine, or an alkyl-ammonium.

22. (canceled)

23. (canceled)

24. (canceled)

25. (canceled)

26. The method of claim 18, wherein the foam comprises a gas phase, and the gas phase comprises N.sub.2, CO.sub.2, air, CH.sub.4 or mixtures thereof.

27. The method of claim 18, wherein the nanoparticle concentration in the foam is from 0.01 to 10 wt. %.

28. The method of claim 18, wherein the surfactant concentration in the foam is from 0.01 to 10 weight %, or from 0.01 to 2 weight %.

29. (canceled)

30. (canceled)

31. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic illustration of the exemplified foam flow system.

[0019] FIG. 2 is a schematic illustration, showing five conceptual stages of nanoparticle (NP) decoration, defined by the concentration ratio of the surfactant-nanoparticle mixture. In an exemplified embodiment, stage 5 (partial coverage of NP by surfactant) resulted in the most stable foam, with step-change dynamic stability during flow in porous media in the presence of oil. Large circles represent positively charged nanoparticles, which are variably covered by surfactant molecules.

[0020] FIG. 3 is a set of photographs, showing stability of foam with time (A) 0.1 wt % surfactant, (B) 0.1 wt % surfactant+0.1 wt % NP, (C) 0.1 wt % surfactant+1.5 wt % NP, (D) 1.5 wt % NP. Bottom row shows close-up of foam structure at location indicated by red ovals. Surfactant-only foam (A) and stage 1 foam (B) bubbles expanded, and structure changed from spherical to polyhedral, while stage 5 bubbles (C) remained small and round after 120 minutes. Nanoparticles alone (D) cannot generate foam. Sample C (stage 5) survived for more than a day while samples (A) and (B) collapsed after 6-8 hours.

[0021] FIG. 4: is a set of photographs, surfactant-only foam (F) and stage 5 foam (H) stability in the presence of heavy oil at 0 min, 30 min and 120 min (left to right).

[0022] FIG. 5 is a set of photographs, illustrating the stability of surfactant foam with 5.0 wt % NaCl (J) and stage 5 foam with 5.0 wt % NaCl (L) stability in the presence of heavy oil at 0 min, 30 min and 120 min (left to right).

[0023] FIG. 6 is a graph, showing the normalized pressure across the sandpack saturated with water of different foaming systems compared with averaged pressure drop of baseline. Baseline is water and gas injection without foam stabilizers.

[0024] FIG. 7 is a graph illustrating ratio of foam apparent viscosity in high salinity environment to foam in a salt-free system. Stage 5 foam (green curve) demonstrated better flow resistance with 5.0 wt % NaCl solution. In contrast, salinity reduced the apparent viscosity of surfactant-only foam (blue curve).

[0025] FIG. 8 is a graph illustrating the normalized pressure and apparent viscosity across the sandpack saturated with mineral oil at residual oil saturation to baseline. The baseline is water and gas injection without stabilizers into sandpacks saturated with mineral oil at residual oil saturation (18 cp, 10%). Surfactant-only foam and stage 1 foam collapsed when they encountered residual mineral oil. Stage 5 foam is the only stable system in the presence of mineral oil, and foam viscosity can be tuned based on nanoparticles concentration at stage 5.

[0026] FIG. 9 is a graph illustrating the normalized pressure profile and apparent viscosity of foam in sandpack saturated with mineral oil (18 cp, Soi=90%). Only stage 5 foam remains stable at this condition.

[0027] FIG. 10 is a graph illustrating stage 5 foam was stable in the presence of residual heavy oil (508 cp, Sor=40%), stage 1 foam and surfactant-only foam broke after contacting heavy oil.

[0028] FIG. 11 is a graph illustrating unlike surfactant-only foam, stage 5 foam has both good oil tolerance (508 cp, Sor=40%) and salinity tolerance (5.0 wt % NaCl) in the porous media.

[0029] FIG. 12 is a graph illustrating surfactant foam was most stable when there was neither oil nor salt in the system. The presence of oil or salt had detrimental effect on foam stability and flow behavior in the porous media.

[0030] FIG. 13 is a graph illustrating stage 1 foam was only stable when there was no oil or salt in the system. Additional nanoparticles at this stage has no contribution to the foam stability.

[0031] FIG. 14 is a graph illustrating stage 5 foam was the only system that demonstrated good foamability and stability in the presence of oil and salt.

DETAILED DESCRIPTION

[0032] The present invention harnesses the synergistic interaction of a nanoparticle and a surfactant, using the concentration ratio of the two components to tune the affinity of the nanoparticle/surfactant mixture for the gas/liquid interface. We define five adsorption stages, as shown in FIG. 2, based on the ratio of surfactant to nanoparticle. Stage 1 and Stage 5 are stable stages, where there is no significant nanoparticle aggregation (sedimentation) and the suspension is stable.

[0033] This present invention provides mixtures that include commercially available surfactants and nanoparticles, but is not limited to a certain type of surfactant or NPs. The appropriate ratio (i.e. stage 5 configuration) of either chemical in a mixture results in a foam system which is highly stable and tunable in the presence of high salinity water and crude oil which is crucial for underground applications. The surfactant or nanoparticle alone and more importantly the mixture of surfactant/nanoparticle at other ratios cannot create such a stable foam system. The interaction between nanoparticle and surfactant (electrostatic or hydrophobic interactions or any interactions that provide a system similar to stage 5) is necessary to have such a system. The pre-treatment of a nanoparticle surface is not necessary and its mixture with properly selected surfactant (i.e. oppositely charged here) is important. Here we demonstrate the stage 5 configuration with electrostatic interactions between nanoparticle and surfactant (i.e. oppositely charge), however, alternative interactions (i.e. hydrophobic) which result in the stage 5 configuration are also contemplated.

Static Foam Stability without Oil

[0034] FIG. 3 shows the foam texture at different times. These tests were conducted at 20° C. and ambient pressure condition. Surfactant foam showed good foamability since the initial foam height was the highest among all the samples. Although the foam height did not change much as time increased, the bubble size expanded, and the bubble structure changed from spherical to polyhedral. Thus the surfactant stabilized foam did not show good stability in the static test. Stage 1 foam behaved similarly to surfactant-only foam, as expected since the nanoparticles are covered with a bilayer of surfactant. Nanoparticles-only solution showed no foaming ability. Only Stage 5 foam showed both foamability and high stability.

Static Foam Test: Effect of Crude Oil and Salinity

[0035] FIG. 4 shows the static foam stabilities for surfactant-only foam (F), stage 5 foam (H), in the presence of heavy oil. In the surfactant-only system, oil entered the lamella and covered the bubble immediately. This caused small bubbles to break and collapsed the foam in the center of the tube, leaving bubbles only near the tube wall after about 30 minutes. In contrast, partially covered nanoparticles present in the foam structure prevented oil from entering the foam structure. The foam was stable for more than 120 minutes, and the bubble size did not change with the time.

[0036] FIG. 5 shows the stability of high salinity foams with the presence of heavy oil. Although salinity slightly improved the surfactant-only foam stability in the presence of oil, the stage 5 foam maintained good oil tolerance in high salinity environment.

Foam Flow in Porous Media in the Absence of Oil: Effect of Salinity

[0037] One major drawback of using surfactant stabilized foam in FOR process is surfactant loss due to partitioning into heavy oil which can be mitigated by carefully choosing an oppositely charge nanoparticle as explained here.

[0038] The surfactant concentration was set at 0.1 wt % since it is the lowest studied concentration where we can get strong and stable foam in porous media.

[0039] To compare the performance of foam for mobility control, the baseline was conducted in which DI water and methane gas were co-injected at 1 ml/min with gas/liquid ratio at 4/1. FIG. 6 shows the foam stability and flow behavior of different foaming systems in water saturated sandpacks.

[0040] The pressure profile of the flow tests is consistent with the static foam stability results. When the foaming system contained only nanoparticles, it cannot generate foam either in bulk or in the porous media. When the foaming system contained the only surfactant it can generate stable foam in bulk and in the porous media. When the foaming system contained a proper mixture of surfactant and nanoparticles solution, the bilayer coverage foam showed similar foam flow behavior as the surfactant foam, in that the surfactant fully covered the nanoparticles surface, and the mixture behaved like surfactant micelles and buried the nanoparticles. The partial monolayer coverage foam could also generate stable foams inside water-saturated the porous media.

[0041] As seen in FIG. 7, the addition of salt decreases the dynamic stability (i.e. apparent viscosity) of surfactant stabilized foam while interestingly the dynamic stability of foam at stage 5 increases with salt concentration. This performance shows the potential of surfactant/nanoparticle stabilized foam for high salinity conditions for underground applications.

Foam Flow in Porous Media in the Presence of Oil: EOR Potential

[0042] The goal of this section is to evaluate the performance and dynamic stability of foam contacting with oil inside a porous media. Foam should be stable in reservoir condition (i.e. high pressure, high salinity, and in contact with oil) to have a potential for EOR and generally underground applications.

Mineral Oil at Residual Oil Saturation.

[0043] After water and oil saturation, waterflood was conducted at 1 ml/min for 3 PV until no significant amount of oil was produced (water cut around 95%) and reached to a residual oil saturation. Thereafter, foam food was performed with different foaming solutions as seen in FIG. 8.

[0044] Surfactant-only foam collapsed when it contacted oil, and despite continued injection it did not re-generate within the sandpack. The apparent viscosity of surfactant foam was less than 10 cp. Stage 1 foam also collapsed upon contacting oil. In contrast the apparent viscosity of stage 5 foam was 280 cp at steady state which indicated a stable foam in the presence of residual oil. Apparent viscosity of stage 5 foam at lower nanoparticle concentration (0.1 wt % surfactant and 1 wt % NP) was about 150 cp.

Mineral Oil at Initial Oil Saturation

[0045] Foam at stage 1 and stage 5 were selected to flow in porous media saturated with mineral oil (initial oil saturation) as seen in FIG. 9. The results indicated foam at stage 5 was the only stable system with the presence of mineral oil. The apparent viscosity of foam at stage 5 and stage 1 at the end of 5 PV injection were about 650 cp and 50 cp, respectively.

Heavy Oil at Residual Oil Saturation

[0046] As shown in FIG. 10, surfactant-only foam and stage 1 foam are not stable when contacting the heavy oil in the sandpack, while stage 5 demonstrated good stability.

[0047] The foam flowing test results at residual oil saturation and high salinity condition (5 wt % NaCl), are shown in FIG. 11. Surfactant stabilized was not stable while nanoparticles stabilized foam at stage 5 showed both oil tolerance and salt tolerance in dynamic condition.

[0048] FIG. 14, FIG. 15 and FIG. 16 describe the surfactant foam, stage 1 foam and stage 5 foam flow behaviors in different conditions, respectively. In surfactant foam or stage 1 foam system, the highest foam flow resistance only appeared in water saturated sandpacks, and any addition of oil or salt had a negative effect on foam stability, which limit the further application of surfactant foam or stage 1 foam in the oil field. Synergy effect was achieved only at stage 5 coverage and it was the only stable system in the presence of mobile oil, residual oil or high salinity. High salinity (up to 5.0 wt %) improved the stage 5 foam stability with or without oil in the porous media.

EXAMPLES

[0049] These examples, the results of which are discussed above, illustrate the suitability of foams stabilized with a mixture of surfactant and nanoparticles for underground applications (i.e. EOR). Adding the appropriate amount of nanoparticles to the surfactant results in a foam system having a step change performance compared to that of surfactant stabilized foam, particularly for subterranean applications in the presence of oil and high salinity aqueous media.

[0050] The results illustrate that the foam is stable at stage 5 (partial coverage of NP with surfactant) when contacting both mineral oil and crude oil. Moreover, the resistance to flow (apparent viscosity) of the foam can be tuned by varying the nanoparticle concentration while keeping the NP surface coverage at partial stage (stage 5), higher nanoparticle concentration yields more flow resistance and a more stable foam.

[0051] A mixture of NP and surfactant at an appropriate ratio (stage 5) will demonstrably result in a foam system which is stable in high salinity conditions. Adding salt increased the stage 5 foam stability in porous media and under static testing. In contrast, the stability of foam stabilized by surfactant alone was significantly reduced in the presence of salt and oil.

Example 1: Foam Characteristics

Materials

[0052] Alumina-coated silica nanoparticles (ST-AK), containing 17.8% silica and 2% alumina, with a particle size of 10-15 nm—provided by Nissan Chemical Industries Co., Japan—was used as the positive-charged nanoparticle. Sodium fatty alcohol polyoxyethylene ether sulfate (AES: (CH.sub.3) (CH.sub.2).sub.11O(CH.sub.2CH.sub.2O).sub.3SO.sub.3Na) with 70% active content, purchased from Chengdu Aike Chemical Technology Co., China, was used as the anionic surfactant. ST-AK and AES were used without any treatment.

Methods

Sample Preparation

[0053] Dispersions were prepared by diluting the desired concentration of AES and ST-AK in separate vials of Milli-Q water, followed by adding the AES solution to the ST-AK solution all at once to ensure a homogeneous dispersion. To avoid any particle aggregation, all dispersions were sonicated using a Branson M2800 ultrasonic bath for 30 minutes. For some dispersions with high concentration and/or high total volume, a QSonica Q700 sonicator was used for 5 minutes to ensure adequate dispersion. In the case of QSonica Q700 sonicator, samples were kept in an ice bath to avoid any temperature increase. It worth mentioning that we used the abovementioned procedure for following results but the mixing procedure is not limited and can be done differently as long as we can achieve a homogenous solution (i.e. no particle sedimentation). For example, the order of mixing and the time and speed of mixing can be changed to achieve a homogenous solution.

Static Foam Test

[0054] Preliminary foam tests were conducted by a Bartsch shaking method. 5 ml of foaming solution were shacked vigorously for 20 seconds in a 15 ml plastic tube and then foam height and texture were monitored with time. The gas phase in the static test was air. All the mixed foaming solution were sonicated right before the static test. The static test was conducted at 20° C. and ambient pressure condition.

[0055] To observe the effect of oil on bulk foam stability, after foam generation, 1 ml of crude oil (508 cp) was injected into the liquid/foam interface through the liquid phase by a syringe. In the control test, 1 ml of the same foaming solution was injected into the interface by the same process. The bubble structure and foam stability (height) were monitored after contacting the heavy oil.

Foam Flow Test

[0056] Foam flood test was conducted in a sandpack with a 1.57 cm in diameter and 30 cm length. A foam generator (0.46 cm and 15 cm in diameter and length, respectively) was used to pre-generate the foam as shown in FIG. 1. The foam generator was packed with silica sand (100-140 mesh, provided by US Silica) and the sandpack was packed with silica sand (50-70 mesh, provided by US Silica) before each flood test. The sandpack was dry packed with vibration method. The properties (i.e. porosity and permeability) of sandpack and foam generator were kept the same for all tests as seen in Table 2. The gas/liquid ratio was set at 4/1 at the inlet of the foam generator corresponding to a foam quality of 80% at the inlet. The total injection rate was set at 1 ml/min. All flow tests were conducted under ambient temperature and pressure of 4 MPa (580 psi).

[0057] After packing the sandpack, the whole system was vacuumed and then saturated with DI water to determine porosity and then the permeability.

[0058] Methane gas and the foaming solution were co-injected into the foam generator until reached to a steady-state (stable pressure) before switching to the sandpack. The pre-generated foam was then injected into the sandpack. The downstream pressure of the experiment was maintained by a backpressure regulator (BPR), and the backpressure was set at 4 MPa. There were three pressure transducers installed at the inlet of the foam generator, between the foam generator and the sandpack, and the outlet of the sandpack. The transducers recorded the absolute pressure at the same time. The pressure difference across the foam generator and the sandpack were recorded as an indicator of foam stability inside the porous media.

Example 2: Oil Displacement

[0059] Oil displacement experiments evaluated foam generation and propagation behavior in the presence of mineral oil or heavy oil at initial or residual oil saturation. The dynamic stability of foam generated with surfactant alone was compared to that of surfactant+nanoparticles at different surface coverage (concentrating ratio). Oil saturation was performed at 1 ml/min until no water was produced at the outlet. The sandpack was placed horizontal and aged overnight to reach an equilibrium state. If the experiments were conducted at initial oil saturation, the foam pre-generation process and the foam injection process are the same as the foam flow test explained above. If the experiments were conducted at residual oil saturation, waterflood was performed at 1 ml/min ahead of the foam injection for about 3 PV.

REFERENCES

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