Decomplexation of chelated hardness at high pH

Abstract

A process for removing metals and chelators from SAGD liner flowback that can be implemented at the wellhead using temporary tankage and equipment. In the first step, caustic is added to the flowback until the concentration of hydroxyl ion is high enough for the metals (Fe, Ca, Mg) to dissociate from the metal-chelate complexes and precipitate as hydroxides. In the second step, hydrogen peroxide is added and allowed to react until all of the chelator molecules are oxidized and decomposed. Once treated, the flowback can proceed to the CPF.

Claims

1. A method of treating flowback from stimulating a SAGD well with chelators, said method comprising: a) collecting a flowback from a SAGD well that has been stimulated by treatment with chelators, said flowback having a high concentration of metal-chelate; b) treating said flowback with a base until at least 90% of said metal-chelate separates into chelator and metal, and said metal precipitates as a metal hydroxide, thus producing a supernatant; c) optionally separating said supernatant containing said chelator from said metal hydroxide precipitate; d) treating said supernatant with H.sub.2O.sub.2 until 90% of said chelator degrades; and e) routing said treated supernatant to a central processing facility for further treatment.

2. The method of claim 1, wherein said collecting is in tank at or downstream from a wellhead.

3. The method of claim 1, wherein said collecting is in a pipeline downstream from a wellhead.

4. The method of claim 1, wherein said separating step c uses a flocculent or coagulant or both.

5. The method of claim 1, wherein said separating step c uses gravity segregation.

6. The method of claim 1, wherein said separating step occurs after treatment step d.

7. The method of claim 1, wherein said separating step occurs before treatment step d.

8. The method of claim 1, wherein said separating step uses gravity segregation and uses a flocculent or coagulant or both.

9. The method of claim 1, wherein said separating step uses a filter.

10. The method of claim 1, wherein said chelator is ethylenediamine tetraacetic acid (EDTA).

11. The method of claim 1, wherein said chelator is diethylenetriamine pentaacetic acid (DTPA).

12. An improved method of treating flowback from stimulation of a well with chelator to remove metals, wherein an initial volume of flowback from said stimulated well that contains high volumes of metal-chelate are sequestered and disposed of in a hazardous waste disposal facility, the improvement comprising collecting said initial volume of flowback and treating it with a base to precipitate said metals, and then treating it with hydrogen peroxide such that 90% of said chelator and 90% of said metals are removed from said flowback, and then routing said treated flowback to a central processing facility.

13. An improved method of treating flowback from stimulation of a well with chelator to remove metals, wherein an initial volume of flowback from said stimulated well that contains high volumes of metal-chelate are sequestered and disposed of in a hazardous waste disposal facility, the improvement comprising i) treating an initial volume of flowback with a base to precipitate said metals, ii) treating said flowback with hydrogen peroxide to decompose said chelator, ii) separating said metal precipitate from a flowback supernatant, and then routing said flowback supernatant to a central processing facility, wherein said 90% of said metals and 90% of said chelator have been removed from said flowback supernatant as compared with said initial volume of flowback.

14. A method of treating a production fluid, comprising treating a production fluid comprising a crude oil and water emulsion plus metal-chelate with caustic to separate said metal-chelate into metal hydroxide and chelator, precipitating said metal hydroxide, treating a remaining production fluid with hydrogen peroxide to degrade said chelator, and routing a treated production fluid to a treatment facility for separating said water and said crude oil.

15. A method of treating flowback from stimulating a SAGD well with chelators, said method comprising: a) collecting a flowback from a SAGD well that has been stimulated by treatment with chelators, said flowback having a high concentration of metal-chelate; b) treating said flowback with a base until at least 90% of said metal-chelate separates into chelator and metal, and said metal precipitates as a metal hydroxide, thus producing a supernatant; c) separating said supernatant containing said chelator from said metal hydroxide precipitate; d) treating said supernatant with H.sub.2O.sub.2 until 90% of said chelator degrades; and e) routing said treated supernatant to a central processing facility comprising an oil and water separator, a water treatment unit, and a steam generator; f) separating oil and water in said oil and water separator, treatment of said separated water in said water treatment unit, and generation of steam in said steam generator with said treated water with less fouling than a method without steps b-d).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Solubility of metal hydroxides.

(2) FIG. 2. Solubility of metal hydroxides.

(3) FIG. 3 Overlay of solubility curves from FIG. 1 and FIG. 2.

(4) FIG. 4 Solubility curves for several metal hydroxides with changing pH.

(5) FIG. 5. EDTA and EDTA metal complexes.

(6) FIG. 6 Proposed and identified degradation pathways for EDTA.

(7) FIG. 7B. X-ray diffraction (XRD) spectra of the decomplexation precipitate and different components of the precipitate. This data was used to provide the estimated amounts in the table in FIG. 7A.

(8) FIG. 8. Schematic of method and equipment used therein.

DETAILED DESCRIPTION

(9) The invention provides a novel method of treating flowback from stimulated wells that has high levels of metal chelates. The flowback is shunted to a wellhead tank and treated with caustic until the metal chelates separate into metal hydroxides and chelator. The chelator is then degraded with the addition of hydrogen peroxide. The now treated flow has <90% of the original metal or chelator levels, and can be routed to the CPF and treated as any other production fluid. The invention has particular applicability to SAGD wells, which are susceptible to damage causes by the high temperature steam and sand and clay reservoirs, and thus are oft stimulated with chelators, but need not be so limited. Indeed, the method can be applied to any sand/clay based or EOR wells.

(10) Early proof-of-concept experiments demonstrated that metal hydroxides will precipitate from EDTA complexes in distilled water (data not shown). A second proof-of-concept experiment, described here, was intended to test whether the decomplexation and EDTA degradation will take place in a SAGD emulsion as opposed to a purely aqueous solution. It will also test just oxidation of the EDTA by hydrogen peroxide in emulsion, without prior decomplexation of the metal and chelator.

(11) To facilitate the observation of precipitation, the experiment used high concentrations of metals and chelator. First, we prepared a metal-chelate in a produced oil emulsion by mixing the following components in a stirred beaker:

(12) i. 150 ml of Produced Emulsion (E-151216-0031)

(13) ii. 24.6 g tetrasodium EDTA

(14) iii. 12.54 g magnesium chloride hexahydrate

(15) iv. NaOH added to solution as necessary to dissolve the ingredients

(16) We saved 10 ml samples for ICP and IC EDTA, as well as reserved about 40 ml of for later analysis.

(17) Next, we tested NaOH decomplexation of the metal-chelates, followed by oxidation of the chelate. We also tested direct oxidation of the metal-chelate in oil emulsion. The methodology was as follows: i. Titrate 50 mL of the metal-chelate in oil emulsion by adding NaOH and observe when precipitants appear. Use concentrated NaOH and add measured volumes (650 μL each) from a pipette. ii. Note pH and conductivity of the metal-chelate in oil emulsion after each addition of NaOH. If no precipitant appears by pH=14, note that as well. iii. Transfer fluid and any precipitant to a centrifuge tube and spin at 4000 rpm for 20 minutes to separate the supernatant from the precipitant. Note volume of precipitant and volume of supernatant. iv. Combine 20 mL of supernatant with 20 mL of 3% hydrogen peroxide and stir for at least two hours. v. Label and submit the H.sub.2O.sub.2 treated supernatant for ICP and IC EDTA analysis.

(18) To test for direct oxidation, we combined 20 mL of metal-chelate in oil emulsion solution with 20 ml of 3% hydrogen peroxide and stirred for at least two hours. The experiment was otherwise as described above.

(19) The samples are labelled as in Table 1:

(20) TABLE-US-00002 TABLE 1 Sample Description Sample ID Sample Description E170424-0002 Initial chelated metal solution E170424-0003 Chelated metal solution after NaOH + H.sub.2O.sub.2 treatment E170424-0004 Chelated metal solution after NaOH + H.sub.2O.sub.2 treatment E170424-0005 Chelated metal solution directly oxidized with H.sub.2O.sub.2

(21) The results are shown in Table 2. The caustic step removed >99% of the magnesium and 50% of the silicon. The silicon loss can be explained by the 50% dilution with hydrogen peroxide.

(22) TABLE-US-00003 TABLE 2 Results Emulsion + Mg + EDTA After NaOH + H2O2 After H2O2 Only E170424-0002 E170424-0004 E170424-0005 mg/l mg/l mg/l Al <0.05 <0.05 <0.05 B 29 13 15 Ba <0.1 <0.1 <0.1 Ca 18.25 11.2 9.6 Co <0.1 <0.1 <0.1 Cr <0.1 <0.1 <0.1 Cu <0.1 <0.1 <0.1 Fe <0.1 <0.1 <0.1 K 12 <0.05 <0.05 Li <0.1 <0.1 <0.1 Mg 7258 43 3739 Mn <0.1 <0.1 <0.1 Mo <0.1 <0.1 <0.1 Na 25890 24320 13700 Ni <0.1 <0.1 <0.1 P <0.1 32 29 S 15 6.2 9 Si 42 21 19 Sr <0.1 <0.1 <0.1 Ti <0.1 <0.1 <0.1 V 21 <0.1 11 Zn <0.1 <0.1 <0.1

(23) Table 3 shows the levels of EDTA remaining in the final solutions. The proposed pathway is successful: treatment with caustic breaks the EDTA-Mg complex and precipitates the Mg as Mg(OH).sub.2. Successive treatment with H.sub.2O.sub.2 oxidizes the EDTA, thus degrading it and rendering the fluid safe for return to the CPF.

(24) TABLE-US-00004 TABLE 3 Results EDTA mg/l E1700424-0002 88826 E1700424-0004 1778 E1700424-0005 24291

(25) FIG. 8 shows a schematic of exemplary equipment for use in the method (100), but variations are possible. In FIG. 8, we see the flowback (1) coming from the stimulated well (arrow) to the flowback tank (110). NaOH (2) is added into the tank (100) and mixed therein, and then the peroxide (3) is added and mixed. Samples (4) can then be withdrawn for lab analysis, and the remaining solution directed to the central processing facility (5) to separate oil from brine, etc.

(26) Although FIG. 8 shows the reaction occurring in a separate vessel, these reactions could also occur in the pipeline from the well, as it takes about 45″ for oil to traverse the distance, depending on where the pad and CPF are located. In such a case, the reactants are routed into the flowback pipeline in the requisite order, caustic being closest to the well, and peroxide closer to the CPF. In such case, it may be necessary to pass the flowback through a settling tank in order to collect and separate the precipitants, and this can be done before or after peroxide treatment.

(27) Although our preliminary results are very promising, we will continue this work to optimize the various parameters, including but not limited to: Test with DTPA Explore caustic dose and residence time Explore hydrogen peroxide concentration, dose, and residence time Explore reaction products and their side effects for the process Explore alternate oxidizers, e.g. sodium hypochlorite Explore particle size distribution and properties of precipitates; need for centrifugation or filtration Explore direct oxidation Explore analytical methods for field monitoring and control

(28) Once these parameters are optimized in bench-top experiments, the methodology will be confirmed in field trials.

(29) Other chelator degradation methods may be combined herewith. These include ultraviolet light, which has been used to speed degradation, as has catalytic photooxidation processes, where a semiconductor like TiO.sub.2 or iron doped TiO.sub.2 is used and activated by means of ultraviolet light. Other methods include ozone, gamma rays, γ-radiolysis, TiO photocatalysis, UV/O.sub.3, UV/H.sub.2O.sub.2, solar ferrioxalate/H.sub.2O.sub.2, UV/electrochemical treatment, Fenton treatment H.sub.2O.sub.2/Fe(II), CAT-driven Fenton reaction, H.sub.2O.sub.2 microwave-activated photochemical reactor treatment, among others.

(30) In some embodiments, catalysts are added to speed the degradation of EDTA. Metallophthalocyanines (MePcS) are effective catalysts for e.g., EDTA and DTPA. The most effective catalytic system under neutral conditions was FePcS-H.sub.2O.sub.2. In laboratory-scale experiments, a catalyst/substrate/H.sub.2O.sub.2 molar ratio of 4:100:2000 was found to be optimal for aqueous solutions, while the effective reaction temperature was 40-60° C. Of course, conditions would need to be optimized for the complex emulsion that is flowback, but these data provide a useful starting point.

(31) The following references are incorporated by reference in their entirety for all purposes. Rämöä J. & Sillanpää M., Degradation of EDTA by hydrogen peroxide in alkaline conditions, Journal of Cleaner Production 9(3): 191-195 (2001). Sillanpää M., Pirkanniemi K., & Sorokin A., Oxidation of EDTA with H.sub.2O.sub.2 catalysed by metallophthalocyanines, Environmental Technology 30(14): 1593-1600 (2009). Kudrashou Y. V., STIMULATION DESIGN AND EVALUATION OF HIGH TEMPERATURE SAGD WELLS, Master's Thesis (2015), online at oaktrust.library.tamu.edu/bitstream/handle/1969.1/155536/KUDRASHOU-THESIS-2015.pdf?sequence=1 &isAllowed=y.