CA2869823A1

CA2869823A1 - Method for purifying aqueous stream, system and process for oil recovery and process for recycling polymer flood

Info

Publication number: CA2869823A1
Application number: CA2869823A
Authority: CA
Inventors: Jonathan Karston Tait DUECK; Harish Radhakrishna Acharya; Qunjian Huang; Adbul Rafi KHWAJA; Yuchung Anthony Ku; Yangang Liang; Brian Christopher Moore; David Mathew POLIZZOTTI; Stephen Duane Sanborn; Yiwen Sun; Carl Joshua Vess; Rihua Xiong
Original assignee: General Electric Co
Current assignee: BL Technologies Inc
Priority date: 2011-04-08
Filing date: 2011-11-22
Publication date: 2012-10-11
Also published as: WO2012136064A1

Abstract

A method for purifying an aqueous stream comprising silica of a first concentration is provided. The method comprises: treating the aqueous stream with an electrocoagulation (EC) process to obtain a purified stream comprising silica of a second concentration lower than the first concentration. Optionally the aqueous stream may be produced water or have a temperature in a range of from about 60 °C to less than about 100 °C. At the same time, a system for enhanced oil recovery, a process for recycling polymer flood produced water and an oil recovery process are also provided.

Description

METHOD FOR PURIFYING AQUEOUS STREAM, SYSTEM AND PROCESS FOR OIL RECOVERY AND
PROCESS FOR
RECYCLING POLYMER FLOOD
FIELD
[0001] The invention relates generally to methods for purifying aqueous streams. In particular, the invention relates to methods for purifying aqueous streams at high temperature and methods of treating produced water.
BACKGROUND

[0002] Hot natural water, such as a geothermal aqueous stream and a coal bed methane aqueous stream at a high temperature of, e.g., at least 60 C, usually needs to be purified before being used and/or transported. Industrial processes, e.g., oil and gas recovery processes including steam assisted gravity drainage (SAGD), cyclic steam stimulation (CSS), etc., use a considerable amount of water and produce a significant amount of hot wastewater (an aqueous stream that may be called produced water) at a high temperature of, e.g., at least 60 C. The hot wastewater also needs to be purified before recycling or before discharge, especially where the natural water supply is insufficient.

[0003] Impurities in the hot aqueous stream (either natural water or wastewater) include silica (Si02, silicon oxide) among other suspended, colloidal and dissolved materials such as oil , or other organic contaminants and boron.

[0004] Using electrocoagulation to purify water at room temperature or a temperature a little higher than room temperature has been reported. For example, W02010/028097 discloses treating water at 120 F (49 C) to reduce silica et al.
However, silica exists in aqueous streams in both colloid and dissolved forms and more in dissolved form at high temperature because of higher silica solubility in hot aqueous streams.

[0005] A. Erdem Yilmaz et al. published in Journal of Hazardous Materials 153 (2008) 146-151 an article titled as, Boron removal from geothermal waters by electrocoagulation. In the article, it is noted that energy consumption of the EC

process increases when the temperature increases from 293 K (20 C) to 333 K
(60 C) because of formed gel on anode surface as a result of increasing solution temperature.

[0006] Other oil and gas recovery processes, including polymer flooding, use a considerable amount of water and produce a significant amount of wastewater, also called produced water. Polymer flooding involves the injection of large volumes of a polymer solution into a subterranean oil reservoir. The polymer solution is more viscous than the oil within the reservoir and the polymer solution mobilizes the oil towards a production well. At the production well, a mixture of oil and produced water are recovered. The produced water from a polymer flood process can include various contaminants such as oil, grease and other organic materials, as measured by total organic carbon (TOC); dissolved solids, including water hardness contributing ions; and suspended solids.
BRIEF DESCRIPTION

[0007] A method for purifying a hot aqueous stream is disclosed in the detailed disclosure to follow. Methods for purifying an aqueous stream from oil and gas recovery operations, such as SAGD, CSS or polymer flooding are also disclosed in the detailed description.

[0008] One method for purifying an aqueous stream comprising silica of a first concentration, comprises: treating the aqueous stream with an electro-coagulation (EC) process at a temperature optionally in a range of from about 60 C to less than about 100 C to obtain a purified stream comprising silica of a second concentration lower than the first concentration. Optionally, an EC process may be used to treat blow from an evaporator rather than treating the aqueous stream directly.

[0009] Another method for purifying an aqueous stream comprising silica of a first concentration, comprises: treating the aqueous stream with an EC process, optionally at a temperature in a range of from about 60 C to less than about 100 C, to obtain a purified stream comprising silica of a second concentration lower than the first concentration; and evaporating the purified stream to obtain steam and a concentrated solution.

[0010] An oil recovery process described in the detailed description comprises:
recovering an oil/water mixture from an oil well; separating the oil/water mixture to produce an oil product and an aqueous stream comprising silica of a first concentration;
treating the aqueous stream with an electro-coagulation (EC) process at a temperature in a range of from about 60 C to less than about 100 C to obtain a purified stream comprising silica of a second concentration lower than the first concentration;
evaporating the purified stream to obtain steam and a concentrated solution;
injecting the steam, optionally after condensing the steam obtained by the evaporation to form a distillate and heating the distillate to generate steam, into the same or another oil well to recover more oil/water mixture from the oil well.

[0011] A system for enhanced oil recovery has multiple injection wells and at least one production well. Both of these types of wells are in communication with a subterranean oil reservoir. The injection wells are used to introduce a polymer solution or steam into the oil reservoir. The pressure of the polymer solution or the steam mobilizes the oil within the subterranean oil reservoir towards the production well. A mixture of oil and produced water is collected from the production well and brought to the surface. At the surface, the oil and produced water mixture is separated by a separator into an oil stream and an aqueous stream. An electrocoagulation apparatus is used to treat the aqueous stream and produce a waste stream of coagulated solids and a second aqueous stream. The waste stream and the second aqueous stream are separated.

[0012] In one particular system the second aqueous stream is further filtered by a membrane filter and separated into a reject stream and a third aqueous stream.
The water hardness content of the third aqueous stream is reduced by an ion exchanger.
Optionally, a polymer may be added downstream of the ion exchanger to produce a further polymer solution. The further polymer solution is injected into the injection well to mobilize the oil towards the production well.

[0013] A process for recycling polymer flood produced water includes the separation of polymer flood produced water into a hydrocarbon rich stream and a hydrocarbon reduced aqueous stream. The process includes the creation of an electric field in the aqueous stream, optionally in combination with the addition or creation of metallic ions, to destablize at least a portion of a suspended, emulsified or dissolved contaminants and form a solid state of aggregated contaminants in the aqueous stream.
The aggregated contaminants are separated from the aqueous stream. Residual suspended solids that are larger than a size in a range from about mm to about 100nm are rejected from the aqueous stream. Ions that contribute to total water hardness in the aqueous stream are exchanged with ions that do not contribute to total water hardness and a polymer is added to the aqueous stream.
BRIEF DESCRIPTION OF FIGURES

[0014] Figure 1 is a schematic drawing of an oil recovery process.

[0015] Figure 2 is a schematic drawing of a polymer flood system.

[0016] Figure 3 is a schematic drawing of another polymer flood system.

[0017] Figure 4 is a schematic drawing of another polymer flood system.
DETAILED DESCRIPTION

[0018] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about", is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
Moreover, the suffix "(s)" as used herein is usually intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term.

[0019] Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, from

20 to 80, or from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
[0020] The word "purify" and related terms such as "purified" indicate that the concentration of at least one contaminant in a substance being purified has been reduced. It is not necessary for any contaminant of the substance to be completely removed.

[0021] In one embodiment, a method for purifying an aqueous stream comprising silica of a first concentration, comprises: treating the aqueous stream with an electro-coagulation (EC) process at a temperature in a range of from about 60 C to less than about 100 C to obtain a purified stream comprising silica of a second concentration lower than the first concentration.

[0022] Some methods according to embodiments of the present invention may be used to purify aqueous streams originated from waste streams of various industrial processes and/or aqueous streams that have been extracted or collected from the ground, where the aqueous stream is at a high temperature. In some embodiments, the aqueous stream originates from at least one of an oil and gas recovery process, a coal bed methane recovery process, and a geothermal water recovery process.
Examples of the oil and gas recovery processes include, but are not limited to, steam assisted gravity drainage (SAGD), cyclic steam stimulation (CSS) processes and polymer flood processes.

[0023] In some embodiments, the temperature is in a range of from about 60 C
to about 90 C. In some embodiments, the temperature is in a range of from about to about 90 C. In other embodiments, the temperature is less than 60 C, for example in a range from about 15 C to 30 C

[0024] The silica in the aqueous stream and the purified stream may be in various forms, such as dissolved form and colloidal form. Moreover, silica may be in the same or different forms in the aqueous steam flowing into the EC apparatus and the purified stream flowing out from the EC apparatus, considering the possibility of the EC
process changing the form(s) of silica and/or of the EC process preferentially removing certain form(s) of silica. Similarly, silica may be in the same or different forms in water before and after being treated by other processes discussed herein.

[0025] The aqueous stream may comprise at least one of heavy metal, boron, and arsenic. Examples of the heavy metals include but are not limited to aluminum (Al), arsenic (As), beryllium (Be), bismuth (Bi), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), plutonium (Pu), tin (Sn), thorium (Th), thallium (T1), uranium (U), vanadium (V), tungsten (W), zirconium (Zr), and zinc (Zn).

[0026] The aqueous stream may also comprise oil or other organic materials. In some embodiments, the effluent purified stream is lower in at least one of chemical oxygen demand (COD) and total organic carbon (TOC) than the influent aqueous stream.

[0027] Referring to FIG. 1, an oil recovery process 1 in accordance with an embodiment of the present invention comprises: a. recovering an oil/water mixture 2 from an oil well (not shown); b. separating the oil/water mixture 2 to produce an oil product 3 and an aqueous stream 4 comprising silica of a first concentration;
c. treating the aqueous stream 4 with an electro-coagulation (EC) process optionally at a temperature in a range of from about 60 C to less than about 100 C to obtain a purified stream 5 comprising silica of a second concentration lower than the first concentration; d. evaporating the purified stream 5 in an evaporator (not shown) to obtain steam 6 and a concentrated solution 7; e. condensing the steam 6 obtained in evaporating to form a distillate 8; and f. heating the distillate 8 to generate steam 9 injected into the oil well (not shown) to recover the oil/water mixture 2.

[0028] The term "electrocoagulation (EC)" used herein refers to a method or an apparatus in which an electrical potential is applied between a cathode and an anode positioned so as to create an electric field in the aqueous stream, the aqueous stream and dissolved substances therein being an electrolyte. In the electrocoagulation process, the suspended, emulsified or dissolved contaminants in an aqueous stream are destabilized by means of introducing an electrical current which provides the electromotive force to drive the chemical reactions between ions and particles. While reactions are driven or forced, the elements or formed compounds will move toward the most stable state. As a result, this state of stability produces a solid, generally having a propensity to adhere to other solids, colloids, oil (free or emulsified), or non-aqueous phase liquids. This process acts to promote destabilization and removal of these constituents beyond that which would be achieved in the absence of the electrical current. The contaminants are then removed by secondary separation techniques, for example, floatation, sedimentation and filtration.

[0029] If at least one of the cathode and the anode is sacrificial and is made from materials such as iron, steel, aluminum, zinc and magnesium, ions therefrom migrate into the electrolyte and form metal hydroxide species having very low solubility, thus becoming solids. The metal hydroxide species will agglomerate to and bind with other like- and non-like-metal hydroxide species and will also bind with and/or entrap other constituents (such as, but not limited to, oils, colloids, suspended solids).
Under correct operation, these solids will grow to sufficiently large size to be removed by gravity, flotation or filtration. In some embodiments, an electrode used in the EC
process is made of at least one of iron and aluminum and the electrochemical reactions for releasing ions from the electrode are Al A13 + 3e- or Fe Fe2' + 2e-.

[0030] When operating the electrocoagulation apparatus with non-sacrificial electrodes, for example with electrically conductive synthetic graphite electrodes or titanium electrodes, the necessary positively charged ions for maintaining the electrocoagulation process are partially provided by the feed water itself.
The remaining part of the required positively charged ions are added in the form of metallic ions such as salts of aluminum, calcium, iron or magnesium. For an enhanced electron migration, the electrocoagulation process may be operated within the acidic range through chemical dosing with hydrochloric acid (HC1), sulfuric acid (H2SO4) or phosphoric acid (H3PO4), ..., etc. The electrocoagulation process may be operated at neutral and basic conditions too.

[0031] The silica in the aqueous stream and the purified stream may be in various forms, such as dissolved form and colloidal form. Moreover, silica may be in the same or different forms in the aqueous steam flowing into the EC apparatus and the purified stream flowing out from the EC apparatus, considering the possibility of the EC
process changing the form(s) of silica and/or of the EC process preferentially removing certain form(s) of silica. Similarly, silica may be in the same or different forms in water before and after being treated by other processes discussed herein.

[0032] The efficiency of removing silica may be affected by concentrations of metal ions released from the sacrificial electrodes during the EC process. In some embodiments, an electrical current is applied in the EC process so as to release metal ions from the sacrificial electrodes that maintains a molar ratio of the metal ions to silica at about 0.1:1 to about 10:1, or about 0.1:1 to about 8:1.

[0033] The EC process may be operated with more than two electrodes. There may be two EC arrangements when more than two electrodes are used, i.e., monopolar EC

arrangement and bipolar EC arrangement. A monopolar EC arrangement means that each pair of electrodes is internally connected with each other, and has no interconnection with other electrodes. All electrodes are connected directly to the power supply. For example, the arrangement of four electrodes could be described as:
(+ , -, +, -) and for six electrodes as: ( +, -, +, -, +, - ), and so on. This setup may also require a resistance box to regulate the flow current and a multimeter to read the current values.

[0034] A bipolar EC arrangement means that only two monopolar outer electrodes are connected directly to the power supply whereas the other electrodes located between the two monopolar outer electrodes are affected by electrical potential indirectly. The inner electrodes are identified as bipolar electrodes, i.e., the neutral sides of the conductive plate are transformed to charged sides, which have reverse charge compared with the parallel side beside it. For example, the arrangement of four electrodes could be described as: (+ , 0, 0, -) and for six electrodes as: ( +, 0, 0, 0, 0, -) and so on.

[0035] Depending on the ingredients of the aqueous stream to be treated, additives may be used if needed during the electrocoagulation. The additives may be later removed, or involved in the chemical processes to form precipitates. For example, chemical oxidants such as hydrogen peroxide, Fenton's reagent (reaction products of hydrogen peroxide and ferrous iron (Fe2+)), permanganate (added as either potassium permanganate (KMn04) or sodium permanganate (NaMn04)), and ozone (03) may be added if needed. Besides, when non-sacrificial cathodes and anodes are used, the additives may be used to form ions to interact with solutes and particulate matter in coagulating the impurities out of suspension and solution. When sacrificial cathodes and anodes are used, additives may be used to increase the conductivity of the aqueous stream to enhance electrocoagulation processes.

[0036] In some embodiments, an effective amount of ionic flocculant is added in the EC process. In some embodiments, the ionic flocculant comprises at least one of an acrylamide/quaternary ammonium salt copolymer, a copolymer of epichlorohydrin and amine, an acrylamide allyl trialkyl ammonium copolymer, an acrylamide/diallyl dialkyl ammonium copolymer, acrylamide/acrylic acid copolymers and salts thereof, acrylamide/alkylacrylate copolymers, acrylamide/maleic acid copolymers, acrylamide maleic anhydride copolymers, acrylamide/ 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) copolymers, acrylic acid homopolymers and salts thereof, and acrylic acid/AMPS copolymers.

[0037] Exemplary cationic acrylamide/quaternary ammonium salt copolymers may be represented by the following Formula I:

Ri R2 ¨(CH2-0¨x ¨(CH2-0¨y c=o Q
I I

R4¨N--R5 In Formula I, the molar ratio of repeat units x:y may vary from 95:5 to 5:95 with the molar ratio x:y of 60:40 being presently preferred. Rl and R2 may be the same or different and are chosen from H and CH3. Q is -C(0)0-, -0C(0)-, or -C(0)NH-. R3 is branched or linear (C1-C4) alkylene. R4, R5, and R6 are independently chosen from H, C1-C4 linear branched alkyl, and an C5-C8 aromatic or alkylaromatic group. A- is an anion selected from Cl-, Br- , HSO4-, or Me0S03-.

[0038]Exemplary repeat units y are as follows: (AETAC)-2-acryloxyethyltrimethyl ammonium chloride, also referred to as dimethylaminoethylacrylate methyl chloride, in terms of Formula I above, Rl= H, R2= H, Q is -C(0)0-, R3= Et, R4, R5 and R6 are all Me, and A- is Cl-; (MATAC)-3-(meth) acrylamidopropyltrimethyl ammonium chloride, in terms of Formula I above, R1=H, R2=CH3, Q is -C(0)NH-, R3=Pr, R4, and R6 are all Me, and A- is CL; (METAC)-2-methacryloxyethyltrimethyl ammonium chloride, in terms of Formula I above R1=H, R2 =CH3, Q is -C(0)0-, R3 is Et and R4, R5 and R6 are all Me, and A- is CF.

[0039]0ne exemplary cationic flocculant copolymer is a 60:40 mole percent acrylamide/AETAC copolymer. The copolymer may be cross-linked as explained hereinafter. The degree of cross-linking is relatively minor and can amount from about 1 x 10-4% to about 5 x 10% based on 100 molar percent of the repeat units (x) and (y) present. Also, non-cross-linked copolymers may be used. Other acrylamide/AETAC

copolymers that may be mentioned include those in which AETAC is present in a molar amount of about 10%-50%.

[0040] The molecular weight of the copolymer may vary over a wide range, for example, 10,000-20,000,000. Usually, the copolymers will have molecular weights in excess of 1,000,000. The cationic flocculant copolymer should be water soluble or dispersible. It is present practice to employ the cationic flocculant copolymer in the form of a water in oil emulsion. The oil phase may comprise hydrotreated isoparaffins and napthenics with a low level of aromatics.

[0041]Additional cationic flocculants that may be mentioned include polyEPI/DMA (a copolymer of epichlorohydrin and dimethylamine), and acrylamide/allyl trialkyl ammonium copolymer or an acrylamide diallyldialkyl ammonium copolymer. The molecular weights of these cationic flocculants may range, for example, from about 10,000 to 20,000,000.

[0042] The anionic flocculants that may be noted as exemplary are primarily acrylamide copolymers such as acrylamide/acrylic acid copolymers, acrylamide alkylacrylate copolymer, acrylamide/maleic acid, acrylamide maleic anhydride copolymers, and acrylamide/2-acrylamido-2-methyl propane sulfonic acid (AMPS).

Additionally, acrylic acid homopolymers and salt forms, especially sodium salts may be mentioned along with acrylic acid based copolymers such as acrylic acid/AMPS
copolymers. Of specific note are the acrylic acid (AA)/acrylamide copolymers wherein the AA is present in an amount of about 20-50 molar%.

[0043]A temperature at which the EC process is conducted may change according to the temperature of the aqueous stream to be treated. In some embodiments, the temperature is 60 C or above, in a range of from about 80 C to about 95 C.
In some embodiments, the temperature is about 90 C. In other embodiments, the temperature is below 60 C , in a range from about 15 C to 30 C.

[0044]After the EC treatment, solid materials comprising silica are removed by, for example, floatation, sedimentation and filtration, to obtain the purified stream comprising silica of a concentration lower than the concentration of silica in the aqueous stream.

[0045]An evaporative, distillation process performed by an evaporator (not shown) can also be used to treat the aqueous stream, and optionally the purified stream, or both. The evaporator transfers heat to the aqueous or purified stream and separates a portion of the water content, as steam, from a concentrated solution that remains. The steam can be used as a source of high quality steam, including the recycling of some, or all, of the steam to provide heat to the evaporator. Alternatively, the steam can be condensed to produce a purified distillate for further processing, such as steam generation for injection into subterranean oil reservoirs. The concentrated solution is discharged in a blowdown stream as waste that may, or may not, require further processing to meet local regulatory requirements. Alternatively, the concentrated solution, or a part of the concentrated solution, can be recycled back through the evaporator or be processed by an additional evaporator, to extract further water content from the concentrated solution. Various types of evaporators including but not limited to: circulation evaporators; falling film evaporators; plate evaporators;
multiple effect evaporators and the like can be used to treat the aqueous stream, and optionally the purified stream or both.

[0046]Evaporating the purified stream instead of the aqueous stream to obtain steam and a concentrated solution may decrease/eliminate the possibilities of fouling/scaling in the evaporator because the concentration of silica in the purified stream is lower than the concentration of silica in the aqueous stream. In addition, if the EC
process is conducted at a temperature in a range of from about 60 C to less than about 100 C, the energy needed for the evaporation process will be at least reduced.
Through executing the silica removal and evaporation in two separate steps, the feed water quality to the evaporator could be accurately controlled. The evaporator will be protected from scaling/fouling issue from the fluctuation of the feed water.
Even if the produced water is optionally below 60 C, it may be heated to 60 C in treatment by an EC process or an evaporation process, or both. Heat in the product or waste streams or in both may be used to heat the produced water.

[0047]Before flowing into the electrocoagulation apparatus, pretreatments to the aqueous stream may be conducted. In some embodiments, the method further comprises: pretreating the aqueous stream with at least one of evaporation, sedimentation, hydrocyclone, flotation, centrifugation, ceramic or polymeric membrane, skimming, chemical oxidation, electrooxidation (EO), dissolved organic removal process, flocculation, and coalescer at a temperature in the range of from about 15 C to less than about 100 C.

[0048] Optionally, if an evaporation step is used to produce a distillate or steam for re-injection, directly of after an EC process, an EC process can be used to treat the blow down, or waste stream, of the evaporator. Treating the blow down may recover water for re-use or to purify the blow down to meet discharge standards. Further, optionally an EC process may be used to treat condensed stream from an evaporator.

[0049] The term "flotation" used herein refers to a method or an apparatus in which air (or any other suitable gases, such as natural gas, or any suitable mixtures of gases) bubbles released into the feed aqueous stream are attached with suspended particles.
The air-solid mixture rises to the surface of the aqueous stream where it concentrates and is removed. In some embodiments, the flotation may be electroflotation, an electric version of flotation, in which bubbles are generated predominately by the electrolysis of water or brine. Instead of air, hydrogen, oxygen and chlorine bubbles are generated to perform the binding function in the electroflotation.

[0050] The ceramic or polymeric membrane may be at least one of a reverse osmosis (RO) membrane, an ultrafiltration (UF) membrane, a microfiltration (MF) membrane, and a nanofiltration (NF) membrane.

[0051] The term "chemical oxidation" used herein refers to a method or an apparatus in which chemical oxidants react with contaminants in the aqueous stream for purification. Exemplary chemical oxidants include but are not limited to hydrogen peroxide, Fenton's Reagent (reaction products of hydrogen peroxide and ferrous iron (Fe2')), permanganate (added as either potassium permanganate (KMn04) or sodium permanganate (NaMn04)), and ozone (03).

[0052]After electrocoagulation and separation from coagulated materials, the purified stream may be directly used, transported or discharged or may be subjected to further treatment to further purify the water.

[0053]In some embodiments, the method further comprises: treating the purified stream with an electrooxidation (EO) process to obtain an EO treated stream.

[0054] The term "electrooxidation (EO)" used herein refers to a method or an apparatus in which electrooxidation of organic and inorganic impurities (pollutants) takes place via two principle pathways: direct oxidation and indirect oxidation. The direct oxidation occurs at the anode in which the pollutants in the aqueous stream discharge electrons to the anode. The indirect oxidation occurs as a result of the production of powerful oxidizing agents such as chlorine, hydrogen peroxide and ozone in the aqueous stream of an electrical cell.

[0055]In some embodiments, the EO process is at a temperature in a range of from about 60 C to less than about 100 C. In some embodiments, an electrode used in the EO process is made of titanium. In some embodiments, an electrode used in the EO
process is made of coated titanium. In some embodiments, an electrode used in the EO
process is made of Ru0x/IrOx coated titanium.

[0056]In some embodiments, the method further comprises: treating the purified stream with a chemical oxidation process to obtain a chemical oxidation treated stream.

[0057]In some embodiments, the method further comprises: treating the purified stream with at least one of evaporation, dissolved organic removal process, flocculation process, sedimentation process, flotation process, and a ceramic or polymeric membrane treatment process at a temperature in range of from about to about 100 C.

[0058]In embodiments of this invention, electrocoagulation unexpectedly reduces a high percentage of silica to purify an aqueous stream at a temperature in a range of from about 60 C to less than about 100 C. A combination of EC with pretreatment and/or post-treatment technique(s) reduces chemical oxygen demand (COD) and total organic carbon (TOC), besides the silica, to purify oily aqueous streams from, e.g., steam assisted gravity drainage (SAGD) process. Energy consumption in the EC
process unexpectedly decreases with the increase of temperature even with the existence of boron in the aqueous stream to be treated by the EC process.
According to embodiments of the present invention, various water purification processes may be combined with EC in different ways to purify water.

[0059]In an additional feature of this invention, the EC process is used in a system and a further process to treat and recycle the produced water from a polymer flood oil recovery operation.

[0060]Like SAGD and CSS, polymer flooding is a method used in the oil industry to enhance the production of oil from a subterranean reservoir. Polymer flooding is a water intensive process that produces a great deal of produced water, which is often discarded as aqueous waste. Therefore, it is desirable to recycle the produced water to reduce the consumption of local water sources and/or the costs associated with sourcing, transport and storing of water that is suitable for the polymer flood process.
Recycling of the produced water also decreases the costs associated with processing the aqueous waste to meet any local regulatory requirements. Polymer flooding may be used to recover heavy oil or bitumen, for example from the oil sands of Alberta, Canada. In particular, polymer flooding may be used to for oil deposits that are too deep for strip mining but not deep enough for steam driven methods.

[0061] Figure 2 depicts a polymer flood system 100 that includes a number of treatment units. The treatment units reduce or remove various contaminants from polymer flood produced water 10, the contaminants include: total organic carbon, including oil and grease; dissolved solids, including water hardness contributing ions;
and suspended solids. The treated polymer flood produced water 10 provides a suitable solvent for the production of a polymer solution 150 and a further polymer solution 152. A suitable solvent for producing the polymer solution 150 can include polymer flood produced water 10 that has been processed by the polymer flood system 100 so that the polymer flood produced water 10 has little to no oil or grease; a total water hardness content of at least less than 1 Oppm (as CaCO3); the total suspended solid content is at least less than 100ppm; the alkalinity is at least less than 1000ppm;
and the size of any remaining suspended solids is at least less than 100nm.

[0062] The polymer flood system 100 involves the injection of a polymer solution 150 into a subterranean reservoir 104 to increase the mobility of the oil within the subterranean reservoir 104. The polymer flood system 100 includes multiple injection wells 102 that are designed to introduce the polymer solution 150 into the subterranean reservoir 104 to increase the mobility of the oil towards a production well 106.

[0063]During polymer flooding, solutions of polyacrylamide, polysaccharide, xanthan or other polymers, or combination of polymers that have viscosifying properties can be added to a suitable solvent, typically water, to produce the polymer solution 150.

[0064] The addition of the polymer to the suitable solvent produces the polymer solution 150 with a viscosity that can be equal to or greater than the viscosity of the oil within in the subterranean reservoir 104. Injection of the polymer solution 150 into the injection wells 102 creates a flood front of the polymer solution 150 that physically mobilizes the oil towards the production well 106.

[0065]At the production well 106 a mixture of oil and produced water 108 is collected and brought to the surface. This is referred to as production. Following production, the mixture of oil and produced water 108 is separated into an oil stream 112 and a first aqueous stream 114 by a separator 110. The separator 110 can be various apparatuses, including horizontal or vertical, two and three phase separator vessels, and the like.

[0066] Following the separator 110, the first aqueous stream 114 contains a portion of the polymer solution, and a variety of other contaminants, such as: total organic carbon (TOC), which includes suspended or emulsified oil and grease; dissolved solids; and suspended solids. The dissolved solids include water hardness contributing ions which can chemically interfere with the viscosifying properties of the polymer.
Further, the suspended solids can physically interfere with the viscosifying properties of the polymer. To remove the suspended and dissolved solids, the first aqueous stream 114 is first treated to decrease the TOC to decrease the fouling of down stream filters.

[0067] The first aqueous stream 114 is directed to an EC process 116, for example as described above. The EC process 116 decreases the amount of TOC and produces a waste stream 118 of aggregated contaminants and a second aqueous stream 120.
Following the EC process 116, the second aqueous stream 120 contains amounts of dissolved and suspended solids that are not suitable for producing a further polymer solution 152. The decrease in the TOC by the EC process 116 makes the second aqueous stream 120 suitable for a membrane filter 122.

[0068] The membrane filter 122 is a ceramic or polymeric membrane filter that separates the second aqueous stream 120 into a reject stream 124 and a third aqueous stream 126. The ceramic or polymeric membrane filter can be a spiral wound, tubular or hollow fiber ultrafiltration membrane filter with membrane pores that are at least mm in size, or sized in the range of about mm to about 100nm. Suspended solids within the second aqueous stream 120 that are larger than the membrane pores, or do not fit through the pores due the shape of the suspended solids, are rejected by the ultrafiltration membrane filter and form the reject stream 124. The third aqueous stream 126 is directed to a ion exchanger 128.

[0069] The ion exchanger 128 is a cation exchanger, such as a weak acid cation exchange resin, zeolite or the like. The ion exchanger 128 exchanges water cations that increase water hardness with cations that do not increase water hardness.
For example, the ion exchanger 128 can remove Ca ' ', Mg ' ', Ba '' and Sr '' out of the third aqueous stream 126 and replace them with either or both of Na ' or H. The exchange of water hardness contributing cations for water hardness non-contributing cations produces a fourth aqueous stream 130 that is suitable for the addition of polymer to produce the further polymer solution 152.

[0070] The further polymer solution 152 can be injected into the subterranean reservoir 104 through the injection wells 102.

[0071] In an additional optional feature of the polymer flood system 100, a precipitation softener 160 is located upstream of the membrane filter 122 (as shown in Figure 4). The precipitation softener 160 softens the second aqueous stream 120 by reducing the total dissolved solids and total hardness of the second aqueous stream 120.
The precipitation softener 160 can be a cold, warm or hot lime precipitation softener.

[0072] In an additional optional feature of the polymer flood system 100, a decarbonator 162 is located upstream of the ion exchanger 128 to reduce the levels of gases, such as carbon dioxide, within the third aqueous stream 126 (as shown in Figure 4).

[0073] Optionally, the decarbonator 162 can be preceded by an upstream acidification step (not shown), such as the addition of H2SO4 that converts carbonates and bicarbonate alkalinity present in the third aqueous stream 126 to carbon dioxide, which is removed by the decarbonator 162.

[0074] The volume of the polymer flood produced water 10 can be supplemented by alternative sources of water. The alternative source of water can have a contaminant content that differs from the contaminant content of the polymer flood produced water 10. The difference between the two contaminant contents can be the type of contaminants present or the amounts of contaminants present, or both.
Depending on the specific contaminant content of the alternative source of water, it can be blended with the polymer flood produced water 10 before any one, or more, of the treatment units described above.

[0075]. Figure 3 depicts the additional optional feature of the polymer flood system 100, wherein a secondary source of water 180 may be blended with the polymer flood produced water 10. The secondary source of water 180 can be blended to increase the volume of suitable water available to produce further polymer solvent 152. The secondary source of water 180 can be brackish water, saline water or fresh water. The contaminant content of the secondary source of water 180 can determine at which point the secondary source of water 180 will be introduced into the polymer flood system 100.

[0076]For example, if the TOC content of the secondary source of water 180 is unsuitably high for the membrane filter 122, the secondary source of water 180 can be blended with the first aqueous stream 114 and enter the EC process 116.

[0077] If the secondary source of water 180 contains unsuitably high amounts of hard water ions and the amount of TOC is suitable for the membrane filter 122, then the secondary source of water 180 can be blended with the second aqueous stream upstream of the membrane filter 122 and the ion exchanger 128.

[0078] If the secondary source of water 180 contains unsuitably high amounts of water hard water ions and unsuitably high amounts of TOC then the secondary source of water 180 can be introduced into the polymer flood system 100 upstream of the optional precipitation softener 160.

[0079] If the secondary source of water 180 contains unsuitably high levels of suspended solids, the secondary source of water 180 can be blended with the second aqueous stream 120, upstream of the membrane filter 122.

[0080] If the secondary source of water 180 contains suitable levels of TOC
and suspended solids, then the secondary source of water 180 can be blended with the third aqueous stream 126, upstream of the ion exchanger 128.

[0081] However, the secondary source of water 180 may be suitable for blending directly into the fourth aqueous stream 130. For example, the secondary source of water 180 may be inherently suitable or it may be treated by other processes that remove or reduce the TOC, the dissolved solids and suspended solids to levels suitable for blending with the fourth aqueous stream 130.

[0082]In an additional optional feature of the polymer flood system 100, the ion exchange process 128 can include a slipstream 129 that allows a portion of the third aqueous stream 126 to by-pass the ion exchange process 128 (as shown in Figure 4).
For example, it may be desirable for the further polymer solution 152 to have some total water hardness content. However, the ion exchange process 120 removes substantially all of the total water hardness content. In this instance, the operator may direct some of the third aqueous stream 126 into the slip stream 129 and then blend the third aqueous stream 126 with the fourth aqueous stream 130 to provide a source of total water hardness for the further polymer solution 152.

[0083]In an additional optional feature of the polymer flood system 100, the EC
process 116, the membrane filter 122, the ion exchanger 128, the precipitation softener 160 and the decarbonator 162 are all modular treatment apparatuses that are transportable within a self-contained structure, such as a trailer or an intermodal carrier (not shown). In this feature, the operator may determine which of the various modular treatment apparatuses of the polymer flood system 100 is required, in addition to the EC process 116 and the membrane filter 122, for a given polymer flood operation.
The operator's determination can be guided by the contents of the mixture of oil and produced water 108 and the contents of the secondary source of water 180, if utilized.
Further, throughout the production life of a given subterranean reservoir 104, the contamination content of the mixture of oil and produced water 108 can change.
Such a change could necessitate the incorporation of one or more modular treatment apparatuses, or the exchange of one modular treatment apparatuses for another in the polymer flood system 100.

[0084] In an alternative option of membrane filter 122, the ceramic or polymeric membrane filter can be a spiral wound, tubular or hollow fiber reverse osmosis membrane filter that separates the second aqueous stream 120 into a reject stream 124 and a third aqueous stream 126. The reject stream 124 contains the dissolved and suspended solids of the second aqueous stream 120.

[0085]Alternatively, the membrane filter 122 can be an spiral wound, tubular or hollow fiber ultrafiltration membrane with the third aqueous stream 126 being further filtered by a spiral wound, tubular or hollow fiber reverse osmosis membrane filter.

[0086] In one option of the polymer flood system 100, the first aqueous stream can polymer flood produced water that followed a SAGD or CSS process.
EXAMPLES

[0087] The following examples are included to provide additional guidance to those of ordinary skill in the art in practicing the claimed invention. Accordingly, these examples do not limit the invention as defined in the appended claims.

[0088]Dissolved silica solution was prepared as follows: Na2SiO3 (0.203 g) and 0.6 g of NaC1 were dissolved in 1 L of deionized water followed by 0.1 M HC1 solution being added to adjust the pH to 7.5. The obtained silica solution (120 ml) was placed in a plastic beaker, and heated to and maintained at 80 C. In a parallel experiment, the silica solution (120 ml) in another plastic beaker was maintained at room temperature (23 C) for comparison.

[0089] Two symmetric iron plate electrodes (3.2 cm x 4 cm) were immersed partly in the solutions of each beaker. There was a direct current supplier (Land 2000, DC
voltage range: 0-25 V, Maximum current: 5 A, Wuhan Landian electronics Co., Ltd., Wuhan, China) connected with the two electrodes. Constant current (200 mA) was charged into the iron electrodes for 4 minutes to conduct electrocoagulation (EC).

[0090]In each of another two plastic beakers, two symmetric aluminum plate electrodes of the same size (3.2 cm x 4 cm) were used. Constant currents (300 mA) were charged to the electrodes in the two plastic beakers for 4 minutes to conduct electrocoagulation (EC), one beaker at 23 C and the other beaker at 80 C.

[0091]After EC process, centrifugation was used to separate wastes coagulated and suspended in the water to obtain treated solution.

[0092]Ammonium molybdate method was used to measure the silica concentration executed on a LaMotte colorimeter at room temperature. The silica concentrations of the original silica solution and the EC treated solutions respectively with iron and aluminum electrodes, at room temperature or 80 C are shown in table 1 below.
The related energy consumptions of EC process at different conditions are also shown in Table 1.

[0093] The removal percentage in table 1 and following tables was calculated by using the following formula: (value of raw water or solution-value of treated water or solution)/ value of raw water or solution x 100%.
Table 1 Si02 Energy consumption mg/L Removal % (kWh/m3) Original silica solution 103.9 / /
EC treated solution (Al electrode, 23 C) 13.0 87.5 3.9 EC treated solution (Al electrode, 80 C) 2.0 98.1 2.2 EC treated solution (Fe electrode, 23 C) 36.7 64.7 2.1 EC treated solution (Fe electrode, 80 C) 31.7 69.5 1.1

[0094]It can be seen from table 1, when using EC to remove dissolved silica, higher removal percentage will be reached at higher temperature (80 C in the experiment).
Meanwhile, the energy consumption of the electrocoagulation process was lower at high temperature. The energy consumption of 80 C operation was around half of that at room temperature.

[0095]Raw water (collected from a sampling point immediately downstream of a skim tank in a SAGD operation of Canada and comprising 7.5 ppm of boron) was placed in four glass beakers. Electrocoagulation experiments were conducted in the four glass beakers at room temperature (23 C), 40 C, 60 C and 85 C, respectively, with iron plate electrodes (3.2 cm x 4 cm) charged with a constant current (100 mA) for minutes. Centrifugation was used to separate wastes coagulated and suspended in the water to obtain treated water.

[0096]A total organic carbon (TOC) analyzer (SIEVERS 900 TOC analyzer, General Electric Company, New York, US) and a HACH 5000 (DR/5000, HACH
Company, Loveland, Colorado, USA) were used to measure the TOC and the chemical oxygen demand (COD) of the raw water as received and the EC treated water at the room temperature. Inductively coupled plasma (ICP) was used to measure the silica concentrations in the raw water and the treated water. CODs, TOCs and silica concentrations of the raw water and the EC treated water at different temperatures are shown in table 2 below, as well as the energy consumption of EC process at different temperatures.
Table 2 Energy Si02 TOC COD
consumption Removal Removal Removal mg/L mg/L mg/L kWh/m3 % % %
Raw water 73.1 / 179.8 / 787 / /
Treated water, 20.5 72 146.9 18.3 589 25 0.75 Treated water, 20.7 72 151.4 15.8 588 25 0.58 Treated water, 17.0 77 149.7 16.7 574 27 0.44 Treated water, 14.2 81 145.4 19.1 529 32 0.35

[0097]It can be seen from table 2 that the silica and COD removal percentages increased with the increase of temperature, especially since 60 C. As to the organic material removal, which is characterized by TOC, highest removal percentage was reached at 85 C. The energy consumption decreased with the increase of the temperature. At 85 C, the energy consumption was only 46.7% of that at room temperature.

[0098]Titanium cathode and Ru0x/IrOx coated titanium anode were used in the electrochemical oxidation (EO) cell. The distance between the pair of electrodes was 1 mm and the electrode size was 4 cm*10 cm. The water treated using EC at 85 C
in example 2 was heated to 85 C again before being pumped through the EO cell at the flow rate of 6 ml/min. There was a direct current supplier (Land 2000, DC
voltage range: 0-25 V, Maximum current: 5 A, Wuhan Landian electronics Co., Ltd., Wuhan, China) connected with the two electrodes. A constant current (600 mA) was charged into the electrodes for 30 minutes for conducting electrochemical oxidation.
The effluent of the EO cell was collected as EO treated water. The COD and TOC of the EO treated water were measured. For comparison, a similar EO experiment was conducted on another sample of water treated using EC at 85 C in example 2, but at room temperature without reheating.

[0099] CODs and TOCs of the EC treated water (at 85 C of example 2), and the EO
treated water at different temperatures are shown in table 3 below, as well as the energy consumption of EO process at different temperature.
Table 3 Energy TOC COD
consumption Removal Removal mg/L mg/L kWh/m3 % %
EC treated water 145.4 / 529 / /
EO treated water, 119.1 18.0 379 28.3 63 EO treated water, 103.9 28.5 310 41.4 54

[00100] It can be seen from table 3, after being further treated by EO, the organic materials as indicated by TOC values were further removed from the EC treated water.
With the temperature increased, the organic material removal percentage increased.
From room temperature to 85 C, the organic material (characterized by TOC) removal percentage was increased by about 10% while the energy consumption of EO
process was reduced by 14%. A combination of EC and EO reduced significantly both silica and organic materials from the raw water.

[00101] Raw water (collected from a sampling point immediately downstream of a skim tank in an SAGD operation of Canada and comprising 7.5 ppm of boron) was filtered by a multichannel ceramic membrane element (pore size: 200 nm, purchased from Inopor GmbH, Hermsdorf, Germany) at 85 C. The filtered water was stored after filtration and before EC treatment. The filtered water was placed in a plastic beaker, measured about the concentration of silica and TOC thereof, and heated to and maintained at 80 C. Two symmetric iron plate electrodes (3.2 cm x 4 cm) were immersed partly in the water. There was a direct current supplier connected with the two electrodes. Constant current (200 mA) was charged into the iron electrodes for 10 minutes to conduct electrocoagulation (EC).

[00102] In another experiment two symmetric aluminum plate electrodes of the same sizes were used. Constant current (300 mA) was charged to the electrodes for 10 minutes to conduct electrocoagulation (EC).

[00103] Centrifugation was used to separate wastes coagulated and suspended in the water to obtain EC treated water (purified stream). A total organic carbon (TOC) analyzer (SIEVERS 900 TOC analyzer, General Electric Company, New York, US) was used to measure the TOC of the raw water, the filtered water, the filtered water before EC and the EC treated water at the room temperature. Inductively coupled plasma (ICP) was used to measure the silica concentration in the filtered water before EC and the EC treated water. TOCs and silica concentrations of the filtered water before EC and the EC treated water are shown in table 4 below. Silica concentrations of water before and after filtration were not tested during experiment, so values thereabout are not shown in table 4 below.

Table 4 Si02 TOC
Removal mg/L mg/L Removal %
%
Raw water / / 233 /
Ceramic membrane filtered water / / 140 39.9 Ceramic membrane filtered water 130 0 124.3 /
(before EC) EC treated water (Al electrode) 11.1 91.4 95.2 23.4 EC treated water (Fe electrode) 11.2 91.4 98.9 20.4

[00104] It can be seen from table 4, TOC of filtered water decreased to some extent during the storage period and when using EC to treat the ceramic membrane filtered water, the silica in the filtered water was further removed by 91.4%. The residual organic material in the filtered water, as indicated by TOC, was further removed by around 20%. A combination of the membrane filtration and the EC process removed most of the silica and the organic materials from the raw water.

[00105] NaC1 (1219.9 g), 16.6 g of CaC12, 96.4 g of Na2B407, 83.3 ml of 98%
H2SO4, 167.9 g of NaHCO3 and 354.8 g of Na2SiO3 were dissolved in deionized water to prepare 500 L of simulation aqueous stream for silica removal evaluation.
The total silica concentration of the simulation aqueous stream was measured by inductively coupled plasma (ICP) analysis to be 142 ppm.

[00106] The simulation aqueous stream was pumped through an electrocoagulation chamber comprising aluminum or iron electrodes at 90 C at a flow rate of 1 L/min.
DC electrical currents of 1-8A were constantly applied to the electrodes. The effluent from the EC chamber was collected and cooled down to room temperature before filtering through a 0.8 micron microfiltration membrane to produce a purified stream.

[00107] The total silica concentrations of the purified stream (residual silica) were also measured. The aluminum or iron consumption amount (dissolved electrode material concentration) was calculated based on the weight loss of the electrodes. The results are shown in Table 5.
Table 5 dissolved electrode Electrical Residual silica electrode material current (A) (PPm) material concentration (ppm) 4 Aluminum 60 33 Iron 148 86

[00108] As can be seen from table 5, with the increase of electrical currents, more aluminum or iron were dissolved and more silica was removed. The silica removal percentage could be adjusted by electrical current applied in electrocoagulation to meet the downstream influent requirement.

[00109] NaC1 (1219.9 g), 16.6 g of CaC12, 96.4 g of Na2B407, 83.3 ml of 98%
H2SO4, 167.9 g of NaHCO3 and 354.8 g of Na2SiO3 were dissolved in deionized water to prepare 500 L of simulation aqueous stream for silica removal evaluation.
The total silica concentration of the simulation aqueous stream was measured by ICP to be 142 PPm=

[00110] The simulation aqueous stream was pumped through an electrocoagulation chamber comprising aluminum electrodes at 90 C at a flow rate of 1 L/min. DC
electrical currents of 8A was constantly applied to the electrodes. The effluent from the EC chamber was collected and cooled down to room temperature before filtering through a 0.8 micron microfiltration membrane, producing a purified stream.

[00111] Another sample of simulation aqueous stream (700 g) was placed in a stainless steel beaker, and heated under ambient condition to evaporate in open air to get 35 g of concentrated solution. During the evaporation process, white solids kept precipitating out and the simulation aqueous stream turned cloudy. After cooling down the concentrated solution to room temperature, 0.717 g of the while solids were obtained by centrifugation.

[00112] The same evaporation process was also executed on the purified stream obtained in example 1 with a total silica concentration (residual silica) of 5 ppm. The purified stream was clear and no precipitation was observed during the evaporation.
After cooling down the 35 g of concentrated solution to room temperature, 0.08 g of white solids precipitated out and was separated by centrifugation.

[00113] The white solids were washed three times with deionized water and then dried at 90 C. The compositions of the white solids were characterized by an energy dispersive spectrometer (Quanta FEG250 from FEI company, USA) and results are shown in table 7.
Table 7 analyte White solids from evaporation White solids from of simulation aqueous stream evaporation of purified stream Element Weight% Atomic%
Weight% Atomic%
0 56.92 69.91 50.75 63.64 Na 2.90 2.48 12.26 10.70 Al ND ND 13.93 10.36 Si 37.79 26.44 16.20 11.58 Cl ND ND 4.49 2.54 Ca 2.39 1.17 2.37 1.19

[00114] "ND" in table 2 means "not detected". As is shown in table 7 that the major component in the white solids is 5i02 and the concentration of 5i02 in white solids from evaporation of the purified stream is lower than the concentration of 5i02 in white solids from evaporation of the simulation aqueous stream, indicating less possibility of scaling/fouling when using effluent from the EC process than when using directly the aqueous stream without treatment.

[00115] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art.
It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMS:

1. A method for purifying an aqueous stream comprising silica of a first concentration, comprising: treating the aqueous stream with an electro-coagulation (EC) process at a temperature in a range of from about 60 °C to less than about 100 °C
to obtain a purified stream comprising silica of a second concentration lower than the first concentration.

2. The method of claim 1, wherein the temperature is in a range of from about 60 °C
to about 90 °C.

3. The method of claim 1, wherein the temperature is in a range of from about 80 °C
to about 90 °C.

4. The method of claim 1, wherein the purified stream is lower in at least one of chemical oxygen demand (COD) and total organic carbon (TOC) than the aqueous stream.

5. The method of claim 1, wherein the aqueous stream comprises at least one of heavy metal, boron, and arsenic.

6. The method of claim 1, wherein the aqueous stream is originated from at least one of a geothermal water stream, a coal bed methane water stream, and a wastewater stream from an oil and gas recovery process.

7. The method of claim 1, wherein an electrode used in the EC process is made of iron.

8. The method of claim 1, wherein an electrode used in the EC process is made of aluminum.

9. The method of claim 1, wherein an effective amount of ionic flocculant is added in the EC process.

10. The method of claim 9, wherein the ionic flocculant comprises at least one of an acrylamide/quaternary ammonium salt copolymer, a copolymer of epichlorohydrin and amine, an acrylamide allyl trialkyl ammonium copolymer, acrylamide/diallyl dialkyl ammonium copolymer, acrylamide/acrylic acid copolymers and salts thereof, acrylamide/alkylacrylate copolymers, acrylamide/maleic acid copolymers, acrylamide maleic anhydride copolymers, acrylamide/ 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) copolymers, acrylic acid homopolymers and salts thereof, and acrylic acid/AMPS copolymers.

11. The method of claim 1, further comprising: treating the purified stream with an electrooxidation (EO) process to obtain an EO treated stream.

12. The method of claim 11, wherein the EO process is at a temperature in a range of from about 60 °C to less than about 100 °C.

13. The method of claim 11, wherein the EO process is at a temperature about 85 °C.

14. The method of claim 11, wherein an electrode used in the EO process is made of titanium.

15. The method of claim 11, wherein an electrode used in the EO process is made of RuOx/IrOx coated titanium.

16. The method of claim 1, further comprising: treating the purified stream with a chemical oxidation process to obtain a chemical oxidation treated stream.

17. The method of claim 16, wherein at least one of hydrogen peroxide, fenton's reagent, permanganate and ozone is used in the chemical oxidation process.

18. The method of claim 1, further comprising: treating the purified stream with at least one of dissolved organic removal process, flocculation process, sedimentation process, flotation process, and a ceramic or polymeric membrane treatment process at a temperature in range of from about 15 °C to less than about 100 °C.

19. The method of claim 18, wherein the ceramic or polymeric membrane treatment process comprises at least one of a reverse osmosis (RO) treatment process, a ultrafiltration (UF) treatment process, a microfiltration (MF) treatment process, and a nanofiltration (NF) treatment process.

20. The method of claim 1, further comprising: pretreating the aqueous stream with at least one of sedimentation, hydrocyclone, flotation, centrifugation, ceramic or polymeric membrane, skimming, chemical oxidation, and coalescer before the EC
process.

21. A method for purifying an aqueous stream from comprising contaminants of a first concentration, the method comprising: treating the aqueous stream with an electro-coagulation (EC) process to obtain a purified stream comprising contaminants of a second concentration lower than the first concentration, wherein the aqueous stream is originated from at least one of a geothermal water stream, a coal bed methane water stream, and a wastewater stream from an oil and gas recovery process.

22. The method of claim 22, wherein the temperature of the aqueous stream in a range of from about 60 °C to less than about 100 °C.

23. The method of claim 21, further comprising evaporating the purified stream to obtain steam and conecentrated solution.

24. The method of claim 21, further comprising evaporating the aqueous stream to obtain steam and a concentrated solution wherein the EC process treats either the steam after it is condense, or the concentrated solution.

25. A system for enhanced oil recovery, comprising:
a. at least one injection well and at least one production well, the wells in communication with a subterranean oil reservoir, wherein the at least one injection well receives a first polymer solution from an injection pump and directs the first polymer solution into the subterranean oil reservoir to produce an oil and water mixture from the production well;
b. a separator to separate the oil and water mixture into an oil stream and a first aqueous stream;
c. an electrocoagulation apparatus to treat the first aqueous stream and produce a waste stream and a second aqueous stream;
d. a membrane filter to separate the second aqueous stream into a reject stream and a third aqueous stream;
e. an ion exchanger to produce a fourth aqueous stream that has a lower total hardness than the third aqueous stream; and f. a polymer to add to the fourth aqueous stream to produce a second polymer solution that is injected into the at least one injection well by the injection pump.

26. The system of claim 22, further comprising a precipitation softener that is upstream of the membrane filter

27. The system of claim 22, wherein the membrane filter is selected from the group consisting of a polymeric ultrafiltration membrane, a polymeric reverse osmosis membrane, a ceramic ultrafiltration membrane and a ceramic reverse osmosis membrane.

28. The system of claim 22, further comprising a decarbonation process that is upstream of the ion exchange process.

29. The system of claim 22, further comprising directing at least a portion of the third aqueous stream into a slip stream prior to the ion exchanger.

30. The system of claim 26, further comprising blending the at least a portion of the third aqueous stream from the slip stream with the fourth aqueous stream or the second polymer solution.

31. The system of claim 22, wherein the ion exchange process is a weak acid cation exchanger.

32. The system of claim 22, further comprising a second membrane filter to produce a second reject stream and a second permeate stream and directing the second permeate stream to the ion exchange process.

33. The system of claim 9, wherein the second membrane process is a reverse osmosis membrane step.

34. The system of claim 22, further comprising blending a secondary aqueous stream with the the second aqueous stream.

35. The system of claim 22, wherein at least one of the electrocoagulation apparatus, the membrane filter and the ion exchanger are a modular treatment apparatus.

36. The system of claim 32, wherein the modular treatment apparatus are housed in intermodal carriers.

37. A process of recycling polymer flood produced water, comprising:
a. separate the polymer flood produced water into an aqueous stream and a hydrocarbon stream;
b. create an electric field in the aqueous stream to form a solid within in the aqueous stream stream;
c. separate the solid from the aquous stream;
d. reject suspended solids that are substantially larger than 0.1µm to 2nm from the aqueous stream;
e. exchange contributing water hardness cations in the aqueous stream with non-contributing water hardness cations; and f. add a viscosifying polymer to the aqueous stream.

38. A method for purifying an aqueous stream comprising silica of a first concentration, comprising:

treating the aqueous stream with an electro-coagulation (EC) process to obtain a purified stream comprising silica of a second concentration lower than the first concentration; and evaporating the purified stream to obtain steam and a concentrated solution.

39. The method of claim 38, wherein the temperature in a range of from about 60 °C
to less than about 100°C

40. The method of claim 38, wherein the temperature is in a range of from about 80 °C to about 95 °C.

41. The method of claim 38, wherein the temperature is about 90 °C.

42. The method of claim 38, wherein in the EC process metal ions released from at least one of electrodes has a molar ratio to silica of about 0.1:1 to about 10:1.

43. The method of claim 38, wherein an electrode used in the EC process is made of iron.

44. The method of claim 38, wherein an electrode used in the EC process is made of aluminum.

45. The method of claim 38, wherein an effective amount of ionic flocculant is added in the EC process.

46. The method of claim 45, wherein the ionic flocculant comprises at least one of an acrylamide/quaternary ammonium salt copolymer, a copolymer of epichlorohydrin and amine, an acrylamide allyl trialkyl ammonium copolymer, acrylamide/diallyl dialkyl ammonium copolymer, acrylamide/acrylic acid copolymers and salts thereof, acrylamide/alkylacrylate copolymers, acrylamide/maleic acid copolymers, acrylamide maleic anhydride copolymers, acrylamide/ 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) copolymers, acrylic acid homopolymers and salts thereof, and acrylic acid/AMPS copolymers.

47. The method of claim 38, wherein the purified stream is obtained by filtration after the EC process.

48. The method of claim 38, wherein in the EC process metal ions released from at least one of electrodes has a molar ratio to silica of about 0.1:1 to about 8:1.

49. An oil recovery process comprising:
recovering an oil/water mixture from an oil well;
separating the oil/water mixture to produce an oil product and an aqueous stream comprising silica of a first concentration;
treating the aqueous stream with an electro-coagulation (EC) process to obtain a purified stream comprising silica of a second concentration lower than the first concentration;
evaporating the purified stream to obtain steam and a concentrated solution;
condensing the steam obtained in evaporating to form a distillate; and heating the distillate to generate steam injected into the oil well to recover the oil/water mixture.

50. The oil recovery process of claim 49, wherein the EC process is at a temperature in a range of from about 60 °C to less than about 100 °C.

51. The oil recovery process of claim 49, wherein the temperature is in a range of from about 80°C to about 95°C.

52. The oil recovery process of claim 49, wherein the temperature is about 90 °C.

53. The oil recovery process of claim 49, wherein an electrical current is applied in the EC process so as to release metal ions from the electrode that maintains a molar ratio of the metal ions to silica at about 0.1:1 to about 10:1.

54. The oil recovery process of claim 49, wherein an electrode used in the EC
process is made of iron.

55. The oil recovery process of claim 49, wherein an electrode used in the EC
process is made of aluminum.

56. The oil recovery process of claim 49, wherein an effective amount of ionic flocculant is added in the EC process.

57. The oil recovery process of claim 56, wherein the ionic flocculant comprises at least one of an acrylamide/quaternary ammonium salt copolymer, a copolymer of epichlorohydrin and amine, an acrylamide allyl trialkyl ammonium copolymer, acrylamide/diallyl dialkyl ammonium copolymer, acrylamide/acrylic acid copolymers and salts thereof, acrylamide/alkylacrylate copolymers, acrylamide/maleic acid copolymers, acrylamide maleic anhydride copolymers, acrylamide/ 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) copolymers, acrylic acid homopolymers and salts thereof, and acrylic acid/AMPS copolymers.

58. The oil recovery process of claim 49, wherein the purified stream is obtained by filtration after the EC process.

59. The oil recovery process of claim 49, wherein in the EC process metal ions released from at least one of electrodes has a molar ratio to silica of about 0.1:1 to about 8:1.