METHOD OF TREATMENT OF WATER PRODUCED BY CHEMICAL FLOCCULATION USING ANIONIC SURFACTANT AND CATIONIC POLYELECTROLYTE AND USE OF THE SAME

Abstract

A method of treating produced water on offshore platforms and onshore facilities is described. The method can be applied to or integrated into other already-installed processes and/or technologies for the treatment of produced water, being characterized by the combined addition of anionic surfactant and cationic polyelectrolyte for the destabilization and flocculation of oily emulsions characteristic of produced water, preliminarily to the separation steps (hydrocyclones and/or flotators). The different points and alternatives of reagent injection combinations are adaptable to equipment and units already in operation.

Claims

1. A chemical method of destabilization and flocculation of water produced on offshore oil extraction platforms, the method comprising: sequentially adding 5 to 300 ppm of an anionic surfactant and 5 to 300 ppm of a cationic polyelectrolyte to an effluent as flocculation reagents for the generation of surfactant-polymer complexes and destabilization/aggregation of the dispersed oil droplets; and removing one or more formed flocs by dissolved air flotation (DAF).

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. The method of claim 19, wherein the injection of the combination of the anionic surfactant with the cationic polyelectrolyte is, upstream of the three-phase separator.

7. (canceled)

8. (canceled)

9. (canceled)

10. The method of claim 19, wherein the injection of the combination of anionic surfactant with the cationic polyelectrolyte is downstream of the three-phase separator and upstream of the one or more hydrocyclone batteries.

11. The method of claim 19, wherein the injection of the combination of anionic surfactant with the cationic polyelectrolyte is downstream of the electrostatic treater and upstream of the one or more hydrocyclone batteries.

12. The method of claim 19, wherein the injection of the combination of anionic surfactant with the cationic polyelectrolyte is downstream of the one or more hydrocyclone batteries and upstream of the flotation.

13. (canceled)

14. The method of claim 1, wherein the anionic surfactants comprises one or more of: carboxylate, sulfonate, sulfate ions, sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), anionic tannins, and anionic lignins.

15. The method of claim 1, wherein the cationic polyelectrolytes comprise water-soluble polymeric organic flocculants with ionizable species of positive charge.

16. The method of claim 15, wherein the cationic polyacrylamide has a charge density between 15% and 75% and a molecular weight between 6 and 9 MDa.

17. The method of claim 1, further comprising mixing the anionic surfactant, the cationic polyelectrolyte, and the effluent for 5-60 seconds prior to removing the one or more flocs.

18. (canceled)

19. The method of claim 1, wherein the offshore oil extraction platform comprises a system comprising a three-phase separator, an electrostatic treater, one or more hydrocyclone batteries, and a flotation.

20. The method of claim 15, wherein the water-soluble polymeric organic flocculants with ionizable species of positive charge comprise polyacrylamide, polyalkyleneimines, or polyethyleneamine.

21. A method of destabilization and flocculation of water produced on offshore oil extraction platforms, the method comprising: adding 5 to 300 ppm of an anionic surfactant for conditioning a dispersed oil droplets; subsequently adding 5 to 300 ppm of a cationic polyelectrolyte to an effluent for forming surfactant-polymer complexes and the flocculation of the conditioned oil droplets; and removing one or more formed flocs by dissolved air flotation.

22. The method of claim 21, wherein the offshore oil extraction platform comprises a system comprising a three-phase separator, an electrostatic treater, one or more hydrocyclone batteries, and a flotation.

23. The method of claim 22, wherein adding anionic surfactant comprises injecting the anionic surfactant upstream of the three-phase separator.

24. The method of claim 22, wherein adding anionic surfactant comprises injecting the anionic surfactant downstream of the three-phase separator and upstream of the one or more hydrocyclone batteries.

25. The method of claim 22, wherein adding anionic surfactant comprises injecting the anionic surfactant downstream of the electrostatic treater and upstream of the one or more hydrocyclone batteries.

26. The method of claim 22, wherein adding cationic polyelectrolyte comprises injecting the anionic surfactant downstream of the three-phase separator and upstream of the one or more hydrocyclone batteries.

27. The method of claim 22, wherein adding cationic polyelectrolyte comprises injecting the anionic surfactant downstream of the electrostatic treater and upstream of the one or more hydrocyclone batteries.

28. The method of claim 22, wherein adding cationic polyelectrolyte comprises injecting the anionic surfactant upstream of the flotation and downstream of the one or more hydrocyclone batteries.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0028] To assist in identifying the main characteristics of the present invention, the figures to which references are made are presented, as follows:

[0029] FIG. 1 illustrates a simplified schematic flowchart, typical of a conventional offshore produced water treatment system.

[0030] FIG. 2 presents the detailed flowchart of a conventional offshore produced water treatment system. Points A, B, C and D indicate the possible reagent injection points, as claimed in the present invention.

[0031] FIG. 3 presents the results of bench studies of treatment of produced water simulated by flocculation-flotation by dissolved air under the following conditions: OGC and residual turbidity as a function of SDBS concentration; 20 mg/L cationic polyacrylamide (15% charge density, Molar Mass between 6 and 9 MDa, emulsified product with 35% active matter) and pH=6.5.

[0032] FIG. 4 shows the results found for bench studies of treatment of produced water simulated by flocculation-flotation by dissolved air, under the following conditions: OGC and residual turbidity as a function of the concentration of cationic polyacrylamide (PAA); SDBS at 20 mg/L and pH=6.5.

[0033] FIG. 5 shows digital images of oily flocs formed in saline with 20 mg/L of PAA (CE 814) and 20 mg/L of SDBS.

DETAILED DESCRIPTION OF THE INVENTION

[0034] Preliminarily, it should be highlighted that the description that follows will start from a preferred embodiment of the invention. As will be apparent to technician skilled on the subject, however, the invention is not limited to that particular embodiment.

[0035] Thus, it should be noted that the present invention is not limited by the characterization of the application of reagents (surfactants and polyelectrolytes) in produced water treatment systems characterized by the flowcharts in FIG. 1 or FIG. 2, and may be characterized by the sequential/consecutive/combined use of the reagents (anionic surfactant and cationic polyelectrolyte) in any produced water treatment system with specific layout, and with injection of reagents at any point upstream or downstream of hydrocyclones and/or flotators.

[0036] Suitable anionic surfactants include (but are not limited to these only) those containing carboxylate, sulfonate and sulfate ions and other groups whose interaction with the aqueous medium will produce anionic charge. Examples of recommended anionic surfactants include medium to long chain sulfonates and alkylaryl sulfonates, such as sodium dodecylbenzene sulfonate and sodium dodecyl sulfate. More than one surfactant can be used, being added jointly or separately during the produced water treatment process. Further, surfactants with a carbonic base (chain) of natural origin, such as tannins and lignins, chemically modified by the introduction of sulfonated radicals or not, are also encompassed by the method described by this invention.

[0037] Suitable cationic polyelectrolytes include (but are not limited to) water-soluble polymeric organic flocculants with positively charged ionizable species. Examples of recommended organic flocculants include, but are not limited to, polyacrylamide, polyalkyleneimines and polyethyleneamine. It is suggested the use of a cationic polyacrylamide with charge density between 15 and 75% and molecular weight, preferably, between 6 and 9 MDa (mega Daltons).

[0038] FIG. 1 illustrates a simplified schematic flowchart of a conventional produced water treatment system for marine disposal or reinjection into oil extraction wells. Such a figure shows the produced water outlets from the three-phase separator and the electrostatic treater, containing dispersed oil and dissolved organic compounds. In general, this oily water is directed to the hydrocyclone battery, where the gravimetric separation of the larger dispersed oily fraction takes place, at a cut-off diameter of droplets between 50 and 150 μm. Then, the chemical flocculation reagents are added upstream of the flotators, which aim at obtaining a stream of treated water with a residual OGC concentration of less than 29 mg/L.

[0039] FIG. 2 shows a simplified flowchart of a conventional offshore produced water treatment system, and the possible addition points of the reagents claimed in this invention. Points A, B and C are possible injection points for the upstream or downstream piping of the three-phase separator and the electrostatic treater and hydrocyclones. Point D is where normally the flocculation reagents are added, upstream of the flotators, for final treatment of produced water for disposal. The different possibilities for altering the conventional treatment process proposed in this invention are described in the next paragraphs.

[0040] At point A, the addition of reagents is made upstream of the three-phase separator, it being possible to add only the anionic surfactant (between 5 and 300 ppm), or the combination of the surfactant with the cationic polyelectrolyte (between 5 and 300 ppm), being added sequentially. If only the surfactant is added, the entire three-phase mixture (oil, water and gas) will be mixed with the anionic reagent, and due to the amphiphilic nature of the molecules, the dispersed oil fraction will preferentially react with the hydrophobic region of the amphiphilic molecules, resulting in the phenomenon of “conditioning” of oil droplets. The purpose of this alternative is to increase the contact time between the reagents and to provide conditions for complete mixing, for the formation of micellar complexes on the surface of oil droplets conditioned with surfactant, right after the addition of the cationic polyelectrolyte, in a later step at addition points B, C, and/or D.

[0041] In the case of the sequential addition of the reagents at point A, the instantaneous formation of micellar precipitates from the interaction of the surfactant with the polyelectrolyte will occur at the inlet of the three-phase separator. The objective of this alternative is to promote the capture and flocculation of oil droplets in the first step of separation between the oily and aqueous phases, maximizing the oil production capacity and reducing the dispersed and dissolved oil content of the water produced for the following treatment steps.

[0042] Points B and C indicate the locations with the possibility of adding the reagents upstream of the gravimetric separation step in the hydrocyclone batteries. Point B refers to the outlet of the three-phase separator, and point C to the outlet of the electrostatic separator. The possible combinations of reagents to be added, each in a concentration between 5 and 300 ppm, can be considered for both points, or for each of the points individually.

[0043] One of the alternatives for adding reagents at points B and C comprises adding the anionic surfactant (between 5 and 300 ppm), individually, for conditioning the oil droplets present in the oil and water mixture and subsequent addition of the cationic polyelectrolyte at point D (between 5 and 300 ppm), upstream of the flotator. This alternative aims at promoting the conditioning of the oil droplets dispersed with the anionic surfactant molecules, using the contact time and mixing intensity promoted in the hydrocyclone.

[0044] Another possibility at points B and C comprises injecting the cationic polyelectrolyte alone (between 5 and 300 ppm), when the oily waters were previously conditioned with anionic surfactant, injected alone at point A (between 5 and 300 ppm). In this way, the micellar precipitates will form instantly after the injection of the cationic polyelectrolyte on the surface of the oil droplets conditioned by the surfactant molecules.

[0045] An alternative is the injection of both reagents (anionic surfactant and cationic polyelectrolyte) together, at points B and/or C, aiming at the formation of micellar precipitates and the flocculation of dispersed droplets prior to the separation in the hydrocyclone, maintaining the same recommended concentrations. This alternative aims at increasing the number of oil droplets to be separated in the hydrocyclone, possibly resulting in greater oil recovery and the generation of a stream of treated water with less dispersed oil content, for subsequent treatment by flotation.

[0046] The alternatives presented in the paragraphs above, depending on the characteristics of the produced water effluent from the three-phase and electrostatic separators, may result in a removal of OGC by gravimetric separation in the hydrocyclone battery, reaching the quality of treated water with adequate specification for marine disposal, wherein the flotation step is unnecessary, when the objective is the disposal of treated produced water.

[0047] Finally, the injection of reagents at point D, where flocculant reagents are normally added, upstream of the flotators, includes the possibility of injecting the cationic polyelectrolyte alone (between 5 and 300 ppm), for the formation of micellar precipitates in oily water previously conditioned with anionic surfactant (between 5 and 300 ppm), added at points A and/or B and/or C, or in the addition of both reagents (anionic surfactant and cationic polyelectrolyte) together, for the instantaneous formation of micellar precipitates and flocculation of oil droplets.

[0048] Thus, based on the above description, the present invention provides possibilities for the application of non-conventional reagents for the treatment of produced water, highlighting their forms and the points of addition in the process, allowing different methodologies to be used in order to adapt the treated water for the intended purposes. In addition to increasing the treatment capacity of existing facilities, other advantages can be achieved through the present invention, by developing new equipment and/or systems for treating produced water optimized for specific scenarios.

[0049] In this context, the innovations and advantages proposed by the present invention comprise: [0050] a. Combination of reagents (anionic surfactant plus cationic polyelectrolyte) with the aim of destabilizing the oily emulsion and aggregating dispersed oil droplets, through the mechanism of formation of precipitated complexes (insoluble) that strongly interact with the dispersed oil; [0051] b. Description of possible reagent injection points, in water treatment plants produced on offshore platforms or in fixed facilities onshore; and/or [0052] c. Reduction of the residence time necessary for the formation of flocs and consequent increase in the treatment capacity of existing facilities.

[0053] In addition, the main advantages expected from the execution of the present invention are related to the following aspects:

[0054] —Economic/Productivity:

[0055] The increase in the treatment capacity of existing facilities will allow for an increase in oil production, solving the problem of production “bottleneck” in unforeseen scenarios of water production flow rate. Savings in the treatment process obtained by reducing the use of conventional reagents, especially if the acidification of the produced water is required. Further, the treated water can, when applicable, be reinjected, generating a reduction in the costs of obtaining reinjection water and greater oil extraction efficiency.

[0056] —Health/Safety:

[0057] Maintaining and adapting the quality of treated water to the levels required by environmental legislation will guarantee the conditions for the discharge of offshore produced water, conserving the integrity of marine and coastal ecosystems.

[0058] —Reliability:

[0059] The robustness and resilience of the treatment process are proven by the operation ability to adapt to different scenarios of characteristics of the produced water to be treated (operational and physical-chemical parameters, such as total oil and grease content, dissolved solids, salinity, temperature and other process interferents) by adjusting the concentration of reagents, especially the anionic surfactant, aiming at maintaining the formation of flocculant species (PSC).

[0060] —Environmental:

[0061] Removing oil dispersed in treated water reduces/minimizes environmental impacts at the disposal site and related to the operation. The invention should contribute to comply with current legislation on offshore disposal of produced water, to reduce oily problems at disposal points close to platforms and to reduce the ecotoxicity of treated effluents. Improved quality of treated water also makes it possible to use it for reinjection, reducing water consumption and disposal. Maintaining and adapting the quality of treated water to the levels required by environmental legislation will ensure the conditions required for the discharge of offshore produced water, conserving the integrity of marine and coastal ecosystems.

[0062] —Other Advantages:

[0063] Possibility of designing and installing future produced water treatment compact units using the flocculation technique and the different proposed reagent injection points.

EXAMPLE OF EMBODIMENT

[0064] The method to be protected was tested in bench studies of produced water treatment simulated by flocculation-flotation by dissolved air under the following conditions (according to FIGS. 3 and 4): [0065] 1) Residual OGC and Turbidity as a function of SDBS concentration; 20 mg/L cationic polyacrylamide (15% charge density, Molar Mass between 6 and 9 MDa, emulsified product with 35% active matter) and pH=6.5; and [0066] 2) Residual OGC and Turbidity as a function of cationic polyacrylamide (PAA) concentration; SDBS at 20 mg/L and pH=6.5.

[0067] In this way, the destabilization (flocculation) of synthetic produced water (oily emulsions prepared in saline solutions, with an average droplet diameter of 5 μm) was evaluated by the combination of anionic surfactants (sodium dodecylbenzene sulfonate SDBS, or sodium dodecyl sulfate—SDS) and a cationic polyelectrolyte (cationic polyacrylamide with 15% charge density and molecular weight between 6 and 9 mega Daltons). The flocculation of the dispersed droplets was promoted with 2 minutes of conditioning the emulsion with the anionic surfactant, followed by the injection of flocculant polymer at the base of the column. The mixing time for the formation of flocs, after the polymer injection, was 15 seconds.

[0068] Next, the formed flocs were removed by dissolved air flotation, using a benchtop saturator vessel coupled to a needle valve for bubble generation, with 20% recycle rate and 5 minutes of separation. The results obtained with both surfactants showed that the treated water presented a residual OGC compatible with the environmental disposal parameters in a wide range of reagent concentrations, and the best results indicated a treated water with residual OGC lower than 15 mg/L. FIG. 5 shows images of the flocs formed by the polymer-surfactant interaction.

[0069] Numerous variations affecting the scope of protection of the present application are allowed. This reinforces the fact that the present invention is not limited to the above-described particular configurations/embodiments.

[0070] The technicians skilled on the subject will value the knowledge presented herein and will be able to reproduce the invention in the forms presented and in other variants, encompassed by the scope of the appended claims.