System and method for in-situ formation of barrier coating on metallic article in contact with or exposed to water within a water system

Abstract

The present invention provides a system for in-situ formation of a barrier coating on a metallic article in contact with or exposed to water within a water system, comprising: a generator connected to a power supply unit for generating electromagnetic wave having a time varying frequency, and one or more treatment assemblies each comprising two treatment units electrically coupled to the generator and positioned in a spaced-apart fashion to come into contact with the water. Each of the treatment units comprises an inductor coil load and a capacitive load connected in series, and the time-varying frequency electromagnetic wave is applied across the two treatment units to produce a synergistic effect of inductance field, capacitance electric field and a flow of ionic wave current in the water, whereby the water is energized in an oxidizing state having an oxidizing potential sufficient to induce precursor ions of the metal which are reactive with hydroxyl groups in the water for in-situ formation of a passivating metal oxide or salt as the barrier coating on a surface of the metallic article. The invention also provides a method for in-situ formation of a barrier coating on a metallic article.

Description

FIELD OF THE INVENTION

[0001] This invention relates generally to the improvement of the oil field production / productivity by minimizing the corrosion issues that lead to oil production down time, high maintenance cost including the replacement of expensive equipment and chemical treatment, in particular the oil field equipment of metallic articles in contact with re-circulating injection water used in water injection oil well, shale and sand oil production. More particularly, the invention relates to systems and methods for in-situ formation of a barrier coating on a metallic article such as pipelines, water tanks in contact with or exposed to water within a water system to prevent corrosion issues, including microbially-induced corrosion for example sulphate reducing bacteria (SRB) corrosion.BACKGROUND OF THE INVENTION

[0002] Water injection is widely used for depleting oil reservoir / well, shale oil and sand oil for extracting the residual oil trapped between the soil / shale / sand particles. While water is the most viable media used for such applications, many associated corrosion issues do occur due to the metallic structures are in contact with water in the water circulation system. Of which, the most common and most severe corrosion failures of steel and metallic structures are due to the sulphate reducing bacteria (SRB) in soil / shale / sand that can cause oil production shut down / loss, also incurring high replacement / maintenance cost. The high SRB steel corrosion rates lead to frequent and prolonged oil production shut down especially when metallic articles are located at the explosion proof area. The replacement cost of the corroded pipes / tank / equipment are very expensive too. More importantly, some catastrophic structural failure due to the MIC can lead to disastrous environmental pollutions and destructive consequences such as oil leakages or fire hazards.

[0003] In water injection oil production, water flows through the SRB highly populated and colonized soil / shale / sand strata due to the conducive underground environment. These SRB bacteria acquire their metabolic energy through effectively using iron as an electron donor to fuel their sulphate to sulphide reduction metabolism.(4⁢Fe0→4⁢Fe2++8⁢e-)⁢(8⁢e+SO42-+9⁢H+→HS-+4⁢H2⁢O)

[0004] While SRB metabolism requires electron donors to prime the reactions, there are many possible electron donor sources from the environment but the most abundant electron donor element in the water injection wells system is the Iron. Iron is one of the most important REDOX metals. It has the Fe0, Fe++, and Fe+++ oxidation / reduction states. This makes it the most abundant electron donor source for SRB to utilize it for its metabolism process. However, when Iron is being used as electron donor by SRB, bare steel is dissolved as Fe++ ions hence corrosion is taking place. Making the situation worst is the large amount of SRB is being picked up from the underground strata when the injection water passes through underground.

[0005] While chemical treatment is the common standard practice in treating the injection water, there are several issues that still persistently exist in the water injection well oil extraction,

[0006] corrosion issues, including general corrosions and microbially-induced corrosion such as SRB corrosion, and

[0007] high chemical treatment cost and environment issues.

[0008] Steel surfaces in contact with the injection well water, such as internal surfaces and bottom of water holding tanks as well as internal surfaces of water pipes all have different degrees of corrosion damages.

[0009] For general corrosion issues such as oxygen corrosions, chemical treatment in the prior art uses either anodic or cathodic inhibitors to solve this type of corrosion issues, but most inhibitors such as phosphate inhibitors are either bacteria promoting, or they are having a negative environment impact. For SRB corrosion control, the chemical treatment generally is to use strong oxidizing biocide chemicals to kill the SRB in the water, but the performance is unsatisfactory.

[0010] Corrosion inhibition chemicals and strong oxidizing biocides chemicals or toxic chemicals are commonly combined and used for inhibiting steel corrosion and mitigating the SRB corrosion. However, the chemical consumption cost is very high, and there are limitations on performance.

[0011] In general, in addition to the dissolved oxygen, the high chloride ions level in the water can induce pitting and localized corrosion. H2S which is commonly produced when SRB reduced the sulphates in water / soil, is also an add-on problem to the severity of corrosion in water injection well structures.

[0012] Presently, these corrosion problems are generally solved by using chemicals in the art. However, when oxygen corrosion and bacteria corrosion are both present in a closed loop system, the chemical treatment solutions can become self-conflicting. Corrosion inhibitors especially phosphate inhibitors have conflicting effect with oxidizing biocides. Phosphate is known as a good nutrient to bacteria and promotes bacterial growth. Whereas the purpose of biocides is to kill the bacteria. When the strong oxidizing biocides are applied, they also oxidize and corrode the steel pipes and structures. When more corrosions occur, more phosphate nutrient inhibitors are therefore added for corrosion control, which however results in more bacteria growth and hence more biocides need to be added to control the bacteria. This becomes a vicious cycle.

[0013] The effectiveness of chemical corrosion inhibitors is largely controlled by the dosing concentration and method. The operating principle of cathodic or anodic inhibitors is to produce a corrosion protective film on the anodic or cathodic steel corrosion cell surface in the water. However, the formation and thickness of the protective film rely on control of the dosing concentration, and the protective film can be damaged by silt, sand or other aggressive particles carried by the water especially the injection well water. These damages on the protective film can cause even more severe localized corrosion.

[0014] Unlike the common bacteria in the water system which are mostly aerobic bacteria, SRB is anaerobic bacteria. They colonize on the immersed steel structure where oxygen is scarce, such as crevices, inside the pits, beneath coating, inhibitor films, joints, biofilms, stagnant flow dead ends and the like. These are areas where SRB colonize and which are hard to reach by the biocides. While hypochlorite can create the strong oxidizing environment in the water, it has limited penetration into the biofilms to kill the SRB hiding in the biofilms. The efficacy of the biocide treatment on controlling SRB corrosion is therefore compromised.

[0015] Even though SRB shows a low count in the water, severe microbial induced corrosion is found to take place due to the presence of SRB in biofilms, crevices, pits and the like, where SRB are populated. The situation of low SRB count in the water yet with high steel SRB corrosion in the water system is therefore commonly encountered in the water system.

[0016] Besides the method of using chemicals, there are other physical corrosion control methods, but they are not adopted in water injection wells due to many technology limitations. These physical methods include impressed current cathodic protection (CP) method and sacrificial anode system. The CP method has many limitations and shortcomings specially when it is used for pipeline internal protection because the coverage for each anode is very short and thus it is not suitable for long pipeline internal work. It is also ineffective in solving crevice / pitting, and SRB corrosion control. Hence the CP method is not adopted in the applications of water injection.

[0017] There are also other corrosion protection methods, for example known from Singaporean patent application no. SG148149A1 which uses AC time varying wave electromagnetic wave produced by inductor coils to treat the water so as to produce magnetite on steel surfaces in contact with the treated water for protection of the steel, but the magnetite formation is sporadic and uneven. This method of using time varying wave water treatment cannot solve the SRB corrosion problem and is not effective for the water injection well application.

[0018] The corrosion control working principle of inductor coil-induced time varying electromagnetic wave treatment is to increase the energy of the water environment which the steel is exposing to. To form magnetite under such a circumstance, the following reaction and condition must take place in sequential order.

[0019] Firstly, steel (Fe) must be oxidised into Fe2+, that is,Fe→Fe2++2⁢e-(1)

[0020] (Fe loses two electron is oxidation, and when Fe is dissolved as Fe2+, it is metal loss or corrosion is taking place at the steel surface)

[0021] Fe2+ ions can be free flowing in the water or remain on the steel surface or be attracted to the adjacent negative cathode surface. When Fe2+ ions encounter OH− ions in the water or on the steel surface, they would form into hydroxide according to the following reaction.Fe2++2⁢OH-→Fe(OH)2(2)

[0022] Then the product Fe(OH)2 subsequently forms into magnetite Fe3O4 at room temperature in the elevated energy water environment energized by the time varying electromagnetic wave.3⁢Fe(OH)2→2⁢H2⁢O+H2+Fe3⁢O4(3)

[0023] Based on the above sequential reactions, formation of magnetite must have Fe2+ ions as a precursor first, followed by reaction with the hydroxyl ions in the water before it can proceed to the magnetite formation. Hydroxyl ions are readily available in the water, but the majority of the steel surface in the injection well water system is bare steel where it is Feº instead of Fe2+ ions that exists. If the surface is Feº-based surface without the Fe2+ ions precursor, there will be no formation of magnetite even the time varying electromagnetic wave is constantly energizing the water. This bare Feº surface is however very susceptible and most vulnerable to SRB corrosion in the presence of SRB.

[0024] For this reason, when the water environment is in the mild oxidation state which has an oxidation-reduction potential (ORP) in the range from +200 to 350 mV vs Ag / AgCl reference electrode, it is difficult for the above reaction (1) to take place and most steel surface will remain as Feº instead of Fe2+ and therefore magnetite cannot be formed evenly on all the steel surfaces. In this case, the water treated by the time varying electromagnetic wave cannot reduce the SRB steel corrosion rate for mild oxidative state water. It is used only when there is no SRB present in the water system.

[0025] Under the SRB present condition, the bare uncorroded Feº surface is even more vulnerable to SRB attack, but undergoes a different set of corrosion reactions. SRB would first convert the sulphate into H2S which is known to rapidly react with metallic iron to corrode iron (uncorroded Feº) to form FeS which is the SRB corrosion (see FIG. 1). This SRB corrosion rate is very much higher than the general corrosion.H2⁢S+Fe0→FeS+H2(4)

[0026] Yet there is another prior art U.S. Pat. No. 10,807,886B2 which also uses time varying electromagnetic wave, but it adopts the CP principle for steel corrosion by replacing the DC current in the CP method with DC biased time varying electromagnetic wave. The arrangement of this prior art is to connect the positive terminal of the DC imposed time varying wave to the emitter, and the negative terminal is connected to the structure to be protected. This prior art uses DC to direct the time varying wave to travel from the emitter / anode and impress directly onto the desired steel structure surface which is acting as the cathode. The DC biased current in prior art is used as a directional guide and the water is used as a path for the electromagnetic wave to travel. This prior art is silent on the use of DC component for hypochlorite generation from chloride content in water and for SRB corrosion control. Because this prior art is of the same CP working principle, the DC superimposed time varying wave has the difficulty in applying to internal surfaces of long distance pipelines as in the case of injection well water pipes. The CP method can be effective for open environment protection, but not suitable for closed loop protection especially for internal protection of long distance injection well steel pipes. For example, a typical 12 inch diameter pipe, the maximum effective coverage for internal surface of pipeline by an emitter source is only approximately 2 to 3 meters comparing with kilo meters of the injection water pipeline length, this requires thousands of emitters to give full coverage and thus is impractical. This prior art is therefore not suitable to apply in injection well water although it is using DC imposed time varying electromagnetic wave. Moreover, it is ineffective in SRB corrosion protection and has no effect in improving the oil extraction. Yet another issue with the prior art is the limitation in protecting the crevices or pits due to the DC component in the time varying wave cannot reach the deep pit to stop the corrosion.

[0027] Therefore, there exists a need for new system and method that are capable of creating a long-lasting barrier coating on the surface of a metallic article at low cost to allow an efficient control and prevention of the general and SRB corrosions of the article, thereby providing the desirable beneficial effects including elimination or mitigation of using chemicals to avoid more damages to the environment, improved oil recovery performance and solving the corrosion and SRB corrosion problems all in one go yet having the ability of helping to improve oil production rate.SUMMARY OF THE INVENTION

[0028] The present invention has been developed to fulfill the needs noted above and therefore has a principal object of the provision of a system for providing general and SRB corrosion protection of a metallic article by treating the water to a higher oxidizing state (i.e. more positive ORP water) in combined use of energizing the water by the time varying frequency electromagnetic wave to spontaneously form a strong adhering magnetite coating layer evenly over the entire metallic article. With the magnetite coating layer formed, the metallic article is fully protected against oxygen corrosion under the elevated oxidizing state of water environment. This minimizes the bare Feº surface which is vulnerable to SRB attack.

[0029] Another object of the invention is to provide a system for providing general and SRB corrosion protection of a metallic article, which takes the advantage of high chloride content in the water to produce a synergistic effect with the time varying electromagnetic wave to overcome the shortcomings of the physical and chemical corrosion methods while exhibiting the excellent SRB corrosion performance. The chloride content is converted into oxidizing precursors in the invention by using the DC components of the DC biased time varying electromagnetic wave to initiate and promote the even formation of protective dense magnetite covering all the steel structure surface in contact with the injection water.

[0030] A further object of the invention is to provide a system for providing general and SRB corrosion protection of a metallic article at low cost, which does not require any continuous chemical dosing and hence saves the expensive chemical dosing recurring cost, yet is able to overcome the inefficacy of chemical treatment and physical corrosion protection methods available in the prior art.

[0031] These and other objects and advantages of the invention are satisfied by providing system for in-situ formation of a barrier coating on a metallic article in contact with or exposed to water within a water system, comprising:

[0032] a generator for generating electromagnetic wave having a time varying frequency;

[0033] a power supply unit connected to the generator for applying a driving voltage to the generator to drive the generation of the electromagnetic wave; and

[0034] one or more treatment assemblies each comprising two treatment units positioned in a spaced-apart fashion to come into contact with the water, wherein each of the treatment units comprises an inductor coil load and a capacitive load connected in series, and the two treatment units are electrically coupled respectively to first and second terminals of the generator to apply the time-varying frequency electromagnetic wave generated by the generator across the two treatment units to produce a synergistic effect of one or more of the following:

[0035] a time varying inductance field in and around the respective coil load,

[0036] a capacitance electric field across the capacitive loads of the two treatment units, and

[0037] a flow of ionic wave current travelling in a pulsating and time-varying manner in the water between the two treatment units,

[0038] whereby the water is energized in an oxidizing state having an oxidizing potential sufficient to induce precursor ions of the metal which are reactive with hydroxyl groups in the water for in-situ formation of a passivating metal oxide or salt as the barrier coating on a surface of the metallic article.

[0039] The term “metallic article” used herein includes the elemental metal article and the metal alloy article.

[0040] Preferably, a bypass switch may be provided to create a bypass path between the two treatment units so as to short circuit the capacitive loads of the two treatment units.

[0041] In some cases, the two treatment units of the system according to the invention may be spaced at a distance in the range 2 to 20 mm, preferably 2 to 10 mm, to produce a capacitive close field. Advantageously, a plurality of treatment assemblies may be assembled together in a treatment chamber to enhance the capacitive close field.

[0042] In some cases, the two treatment units of the system according to the invention may be spaced far apart from each other to produce a resistive far field.

[0043] In one embodiment of the invention, the water in the oxidizing state may be achieved by producing a positive oxidation reduction potential (ORP) shift in the water. The positive ORP may be preferably shifted to more than +200 mV (e.g. more than +350 mV) vs Ag / AgCl reference electrode. The positive ORP shift may be caused by a method selected from the group consisting of DC electrolysis, ozonation, hydrogen peroxide, and oxidant dosing.

[0044] According to the invention, the capacitive load may be provided in the form of plate, rod, tube or mesh.

[0045] In one specific embodiment of the invention, the generator may be configured to generate a direct current (DC) biased time-varying frequency pulsating electromagnetic wave comprising an alternating current (AC) and a biased DC component. The frequency of the electromagnetic wave may range from about 500 Hz to about 1,000,000 Hz, preferably from about 200 Hz to about 5,000 Hz, and the electromagnetic field has a sweeping frequency of 10 to 100 Hz.

[0046] In one specific embodiment of the invention, the system of the invention may be used to provide corrosion protection for iron-based articles, more particularly, for steel structures. In some cases, the induced precursor ions are Fe2+ ions which react with the hydroxyl groups to form passivating magnetite as the barrier coating on the surface of the iron-based article. The iron-based article may be selected from well servicing equipment of oil production field. One example of the well servicing equipment is the equipment associated with the injection well water.

[0047] In another specific embodiment of the invention, the system of the invention may be used to provide corrosion protection for copper-based articles, more particularly, for copper alloy structures. In some cases, the induced precursor ions are Cu+ ions which react with the hydroxyl groups to form passivating cuprous oxide as the barrier coating on the surface of the copper-based article. Preferably, the induced precursor Cu+ ions react with the hydroxyl groups to form a composite coating consisting of an inner layer of passivating cuprous oxide (Cu2O) on the surface of the copper-based article and an outer layer of passivating cupric oxide (CuO) on the inner layer.

[0048] Preferably, the frequency of the electromagnetic wave may be selected to excite the metallic article so that a skin effect may be created on the surface of the metallic article to allow the electromagnetic wave to travel on said surface.

[0049] The system of the invention is applicable to the metallic article, no matter whether it is placed in open loop or closed loop system.

[0050] Another aspect of the invention is to provide a method for in-situ formation of a barrier coating on a metallic article in contact with or exposed to water within a water system, comprising the steps of:

[0051] generating electromagnetic wave having a time varying frequency; and

[0052] applying the time-varying frequency electromagnetic wave to one or more treatment assemblies each comprising two treatment units positioned in a spaced-apart fashion to come into contact with the water, wherein each of the treatment units comprises an inductor coil load and a capacitive load connected in series so that the application of the time-varying frequency electromagnetic wave across the two treatment units produces a synergistic effect of one or more of the following:

[0053] a time varying inductance field in and around the respective coil load,

[0054] a capacitance electric field across the capacitive loads of the two treatment units, and

[0055] a flow of ionic wave current travelling in a pulsating and time-varying manner in the water between the two treatment units,

[0056] subjecting the water to the synergistic effect, whereby to energize the water in an oxidizing state having an oxidizing potential sufficient to induce precursor ions of the metal which are reactive with hydroxyl groups in the water for in-situ formation of a passivating metal oxide or salt as the barrier coating on a surface of the metallic article. Preferably, the water in the oxidizing state may be achieved by producing a positive oxidation reduction potential (ORP) shift in the water.

[0057] In one specific embodiment of the invention, the generating step may comprise configuring the time-varying frequency electromagnetic wave to have a DC biased component, having the frequency in the range from about 500 Hz to about 1,000,000 Hz, preferably from about 200 Hz to about 5,000 Hz, and the electromagnetic field may have a sweeping frequency of 10 to 100 Hz.

[0058] Unlike the conventional CP systems or methods which use the electromagnetic wave to treat the water for corrosion protection of the structure in a closed loop water system, the essence of the invention is to treat the water to a higher oxidizing state (namely more positive ORP water) in combination with using the time varying pulsating electromagnetic wave to energize the water so that the water is subject to the effects of inductive field, capacitive field and ionic wave current to induce precursor ions of the metal, enabling formation in-situ of a passivating and stable metal oxide or salt on the surface of the metallic article, which causes no further corrosion. The passivating and stable metal oxide or salt forms and acts as a barrier coating on the article surface, and this barrier coating has advantages of self repairing and low maintenance and would last through the service life of the metallic article as long as it is subject to the treatment according to the invention. This on-site produced and active barrier coating against the general and SRB corrosions is not known nor suggested from the prior art.

[0059] To have a better understanding of the invention reference is made to the following detailed description of the invention and embodiments thereof in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIG. 1 is a schematic view of bare uncorroded Fe0 surface is vulnerable to SRB attach to form SRB corrosion.

[0061] FIG. 2 is the Pourbaix Diagram for iron at 25° C.

[0062] FIGS. 3A and 3B are schematic views of SRB colonies on the base steel treated by the prior art technologies and by the invention, respectively.

[0063] FIG. 4 is schematic view of a system for in-situ formation of magnetite constructed consistent with a preferred embodiment of the invention.

[0064] FIG. 5 is an exemplary arrangement of treatment assembly according to the invention.

[0065] FIG. 6 is a schematic view of a chamber in which multiple pairs of treatment assemblies are installed according to one embodiment of the invention.

[0066] FIG. 7 shows some examples of PWM adapted for the invention.

[0067] FIG. 8 is an exemplary DC biased AC time varying frequency electromagnetic wave useful in the invention.

[0068] FIG. 9 is a schematic layout of an exemplary injection water piping system.

[0069] FIG. 10 is an exemplary in-tank treatment system constructed consistent with a preferred embodiment of the invention.

[0070] FIG. 11 is an exemplary in-line treatment system constructed consistent with a preferred embodiment of the invention.

[0071] FIGS. 12A and 12B show alternative arrangements of the treatment assemblies placed inside the inline treatment chamber 150.

[0072] FIGS. 13A and 13B show the surface tension of the water before and after the treatment by the system of the invention.

[0073] FIGS. 14A and 14B show FTIR spectra of the injection water before and after the treatment by the invention.

[0074] FIG. 15 shows viscosity reduction rate for the same energy input, wherein curve 1 represents the viscosity reduction rate achieved by thermal heating and curve 2 represents the viscosity reduction rate achieved by the treatment of the invention.

[0075] FIG. 16A and 16B are boiling point distribution plot of untreated hydrocarbon and treated hydrocarbon by the invention, respectively.

[0076] FIG. 17 is an image of the treated steel plate after immersion in the treated water and the control steel plate after immersion in the untreated water for 3 hours.

[0077] FIG. 18 is a SEM image of magnetite coating formed on the steel surface.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0078] While this invention is illustrated and described in preferred embodiments, the system for in-situ formation of a barrier coating on a metallic article in contact with or exposed to water within a water system may be produced in many different configurations, sizes, forms and materials.

[0079] For the sake of clarity and convenience, “steel or iron” is taken herein as one example of the metallic articles. It would be appreciated that any other metallic articles that have the tendency to corrode are applicable.

[0080] When steel or iron is exposing to a strong oxidizing water which has a very positive ORP reading, such as chlorinated or ozonated water, metals corrosion rate will be increased and usually this is not a desirable water environment condition for steel corrosion control. However, the invention adopts a completely opposite concept and corrosion control principle that utilizes the oxidizing effect of hypochlorite as an advantage to produce the synergistic effect with time varying electromagnetic pulsating wave to control SRB corrosion and general corrosion in the water system. In particular, the invention purposely proposes to form a very even and dense magnetite coating over the entire steel surface that is in contact with water using the oxidizing water environment whose ORP is in the range of +200 to +700 mV and preferably in the range of +350 to +700 mV. Compared with the conventional time varying electromagnetic wave treated water system, if the water ORP is in the range of +100 to +350 mV (the ORP readings are vs Ag / AgCl reference cell), then only the isolated spots or localized corroded area can be covered by magnetite.

[0081] FIG. 2 shows a Pourbaix diagram which illustrates the principle of formation of Fe3O4 according to the invention. When the steel is exposing to an untreated water system, the Fe3O4 magnetite formation zone can only take place in a very small range of pH and steel to water potential. After receiving the treatment of the invention, the water is excited to have an elevated entropy energy and the higher oxidizing ORP, the Fe3O4 zone in the Pourbaix diagram is enlarged, which allows the formation of Fe3O4 to take place at a much broader pH range to the acidic environment and more positive steel to water potential. This is an important feature of the invention which is different from the prior art. On the contrary, the CP working principle is to move the steel potential to very negative such that the steel is constantly in the Fe immunity zone in the Pourbaix diagram.

[0082] According to the method of the invention, the Fe3O4 magnetite forms on the steel / water interface at the outermost bare steel surface material and grows outward to the water side. This magnetite formed is a part of the steel base material instead of an added-on coating layer. Therefore there is no gap between the magnetite and the base steel. The magnetite coating is stable and adheres strongly to the base steel with thickness generally in the range of 15 μm up to maximum of about 80 μm. This magnetite coating acts as an intermediate barrier between the base steel surface and the SRB to prevent the SRB from living on the Fe0 bare steel for their metabolism. As the magnetite coating layer grows in thickness, the SRB will be pushed outward and unable to contact the bare base steel directly. This means that the SRB becomes isolated from the base bare steel surface, thereby blocking the SRB corrosion formed on the steel surface.

[0083] FIGS. 3A and 3B respectively illustrate schematic diagrams of SRB on the base steel treated using the prior art method and the base steel treated using the method of the invention. As illustrated in FIG. 3A, a coating 1 is applied onto the surface of the base steel 2 and the SRB hides under the coating 1 or the porous Fe2O3 rust layer and is in direct contact with the base steel 2, leading to Fe2S corrosion crater 3. In contrast, FIG. 3B shows the magnetite 4 grows from the surface of the base steel 2 as a barrier to the SRB so as to isolate the SRB from the base steel. In this case, the SRB corrosion cannot proceed.

[0084] The magnetite coating is a very stable, electrically conductive oxide similar as iridium oxides, ruthenium oxides. Without these oxides, when an electric current or a corrosion current leaves a metal surface, the metal would dissolve as ions and hence the corrosion takes place. Magnetite is so stable that even when the current leaves the metal surface, it does not dissolve as ions hence no corrosion would occur. For this reason, magnetite is also used as inert anode in the cathodic protection method and as anodic corrosion protection for mild steel in acid.

[0085] In addition to isolating the SRB from the base steel, the invention also has the advantage that the water is excited to be in the higher oxidative state, which provides the disinfection effect like a biocide in killing SRB and other organisms in the water system. This helps to improve the bacteria control performance. Furthermore, the high electromagnetic inductive and capacitive fields generated can kill and control the bacteria multiplication when the water passes therethrough.

[0086] Another major advantage of the invention is the water is energized to have a higher energy level and therefore can transfer the energy to the untreated water in a lower energy level. This allows the water not passing through the treatment system of the invention is still able to receive the energization. With this energy transfer, the magnetite is able to form in crevices, pits or other hard-to-reach areas.

[0087] Referring now to FIG. 4 which provides a system 100 constructed consistent with a preferred embodiment of the present invention. In this embodiment, the system 100 comprises a generator 110 for generating electromagnetic wave having a time varying frequency; a power supply unit (not shown) connected to the generator 110 for applying a driving voltage to the generator 110 to drive the generation of the electromagnetic wave; a treatment chamber 120 in which a plurality of treatment assemblies 121 are connected in parallel with the generator 110, and a steel pipe 130 through which the water or the water system comprising a mixture of water and oil flows, and the treatment chamber is mounted across a diameter of the steel pipe 130 to allow the water or the water and oil mixture to pass through the treatment chamber 120 in this embodiment.

[0088] The power supply unit is electrically connected to the generator 110. AC power supply is used in the power supply unit. The power supply unit supplies a desired AC driving voltage to the generator 110 and further comprises a direct current (DC) biasing unit to provides a DC current to a wave signal producing printing circuit board (PCB) in the generator 110 enabling the generation of the DC-biased time varying pulsating electromagnetic wave operating at a selected frequency. It is possible that the power supply unit takes the AC power, and rectifies it into a lower voltage DC current generally less than 60V DC for safety reason. On the other hand, with the advancement in lithium battery, the DC current can also come from the lithium battery or other DC sources.

[0089] The generator 110 can be of any type of means known in the art that is able to generate the time varying frequency electromagnetic wave. For example, the generator may include the PCB to which the DC current from the power supply unit is fed to produce the time varying electromagnetic pulsating wave comprising the DC component. The generator 110 has a positive terminal 111 and a negative terminal 112. Preferably the following time varying electromagnetic wave specification is needed:

[0090] the output waveform from the PCB may be square wave, sine wave, triangular wave. preferably square wave;

[0091] the time varying frequency ranges from 100 to 1 million hertz, preferably in the range of 500 to 50,000 Hz; the frequency range may be segmented and have different sweeping frequency to suit the application needs; for example, lower frequency range of less than 1000 Hz is more effective in producing the magnetite, and high frequency has better disinfection effect; and

[0092] the sweeping frequency of the time electromagnetic varying wave is between 10 to 100 Hz.

[0093] The wave frequency is known to be inversely proportionate to the output wave current. Yet the output current density determines the efficacy of the disinfection and rate of magnetite formation. For the bacteria disinfection, higher voltage generally produces better kill efficacy. Therefore, there is a situation requiring jumps in frequency range segments from low range to higher range skipping the midrange to improve the overall treatment efficacy.

[0094] In some situations, due to the high conductivity of water, high voltage will produce high current and may exceed the current capacity of the PCB. In this case, Pulse Width Modulation (PWM) may be used to control the current output yet maintaining the required voltage. FIG. 7 shows some examples of PWM adapted for the invention.

[0095] The plurality of treatment assemblies 121 are housed in the treatment chamber 120 and are connected in parallel with the generator 110. FIG. 5 shows an exemplary arrangement of the treatment assembly. In this embodiment, each of the assemblies 121 preferably comprises two treatment units 122A, 122B. Each of the treatment units 122A, 122B comprises an inductor coil 123A, 123B and a capacitive plate 124A, 124B in series connection. The capacitive plate 124A, 124B may be made of, for example, a semi-consumable material, for example conductive flexible or rigid graphite or graphene, if the semi-consumable material does not affect the final extracted oil quality.

[0096] The treatment units 122A, 122B are placed in the water system with the inductor coils 123A, 123B being electrically coupled with the two terminals 111, 112 of the generator 110, respectively, so that the DC biased time varying electromagnetic wave is applied across the treatment units 122A, 122B to generate a time varying electromagnetic pulsating field in the vicinity of the coils 123A, 123B and the plates 124A, 124B. The generated time varying electromagnetic pulsating field is dominated by a time varying inductance field in and around the coils 123A, 123B and a capacitance electric field across the capacitive plates 124A, 124B. In the meantime, because the time varying electromagnetic wave comprises the biased DC component which travels in a pulsating and time-varying manner, there will be a pulsing ionic wave current produced in the water or the water and oil mixture, i.e. there are physical ions or charges flowing in the water or the water and oil mixture, which is an important and distinguishing feature of the invention. After being subject to such an ionic wave current, the internal energy including the vibrational and rotational energy of the water or the water and oil mixture is changed, which results in the water molecule clusters carrying electrons. This can change the clustering arrangement of the water molecule, and more importantly, the energy can be stored in the water or the water and oil mixture for a period of time before it is completely dissipated to the surroundings.

[0097] In other words, when the DC-biased time varying electromagnetic wave is applied through the treatment assemblies 121, there is a synergistic effect of the time varying inductance field in and around the coils 123A, 123B, the capacitance electric field across the capacitive plates 124A, 124B, and a flow of ionic wave current produced in the water. When the water flow passes through the treatment chamber 120 and thus is subjects to the synergistic treatment, water molecules, charged molecules, ions, hydrogen bonds, polar bonds, and Van Der Waals force in the water will vibrate in response to this treatment. Such a vibration state leads to elevated water energy which is stored in the treated water, and it takes as much as 48 hours to completely dissipate the elevated energy. The energized state of the treated water results in re-arrangement of water clusters, bond attraction forces and the like, and is reflected in the larger fluctuation in surface tensions, bond absorbance peaks in FTIR (Fourier Transform InfraRed spectrographs) curves, as well as changes in the ORP of the water, viscosity of water / oil and many other properties. Accordingly, the advantages include but not limited to:

[0098] The more active fluctuation in surface tension of the water, the better capillary penetration effect the water has. This can help in oil extraction in water injection well.

[0099] High energy state of the water promotes the formation of high energy reaction end products such as high energy iron oxide magnetite Fe3O4 instead of lower energy state hematite Fe2O3. This can greatly benefit control of both the general corrosion and the SRB corrosion.

[0100] The SRB corrosion is a reductive reaction. With the more oxidizing state water environment, it is less conducive to the SRB reductive reaction.

[0101] With the time varying frequency electromagnetic wave transmitting between the two treatment units 122A, 122B in the oil and water mixture, the current and voltage gradient between the two treatment units 122A, 122B can be varied according to the following factors:

[0102] distance or gap between pair of signal assemblies,

[0103] spacing between the two treatment units,

[0104] surface area and / or geometry of the capacitive load,

[0105] fluid electrical conductivity of the water or the water and oil mixture oil / water mixture,

[0106] the externally applied wave voltage, the frequency, the time varying sweeping frequency, and the wave form which can all be varied to produce the desirable current strength and voltage,

[0107] the wave between the two treatment units 122A, 122B which can be programmed to comprise the pure AC component or comprise both of the AC and DC components, and

[0108] materials selected for making the treatment units 122A, 122B to control the generation or prevent the generation of the undesirable type of end-product when the DC component is present in the time varying wave form.

[0109] The spacing between the two treatment units 122A, 122B is important and adjustable to suit the different on-site treatment requirements. When the voltage / current is applied to the treatment assembly, a potential field is generated in the vicinity of the treatment assembly. This potential gradient near the assembly potential field is the highest and gradually reduces along with increase in the spacing between the two treatment units 122A, 122B.

[0110] Referring now to FIG. 5 again, when the two treatment units 122A, 122B are spaced closely to bring their potential fields overlapping with each other, the behavior between the two treatment units 122A, 122B is capacitive, which is called herein “capacitive close field”. When the two treatment units 122A, 122B are spaced far apart from each other so that the potential gradient between the two treatment units 122A, 122B is negligible, the behavior between the two treatment units 122A, 122B is resistive, which is called herein “resistive far field”.

[0111] If the invention is utilized for bacteria / micro-organisms killing and control of multiplication, the capacitive close field is adopted, where the spacing between the two assemblies shall be very close and typically between 2 to 10 mm depending on the voltage applied and the water / oil mixture conductivities.

[0112] FIG. 5 shows an arrangement of the invention for producing a DC pulsing ionic wave current. In the capacitive close field, the two plates 124A, 124B form “transmit and receiving” a signal terminal pair, not only the time varying capacitance electric field is generated, but also there is a flow of ionic current is generated inside the water between the two plates 124A, 124B. This ionic current can be alternating or single directional depending on whether DC biased wave is required in the application. The ionic current generated consists of both the charge ions and the free electrons. The combined effect of the inductance field, the capacitive field, the ionic wave current in this treatment assembly produces a high intensity fast-changing voltage and current gradient between the two treatment units 122A, 122B, and the ionic wave current disrupts the metabolism process of the micro-organisms when they pass through the gap or the vicinity of the two treatment units.

[0113] All catabolic and anabolic metabolism processes of living micro-organisms' rely on REDOX (reduction and oxidation) and enzymatic reactions, regardless of whether the micro-organisms are bacteria, animals, or plants. Electron transport takes place in all these REDOX cell metabolisms reactions / processes including in Krebs cycle, Mitochondria oxidative phosphorylation, Calvin cycle, Respiration or Photosynthesis. When the organisms are exposed to the high intensity fast changing voltage and current gradient field, the transport of all the electrons of the REDOX reaction metabolisms will be disrupted. This results in killing the organisms and disrupting their multiplication. The hydrogen bonds (polar bonds) between the DNA protein helix threads are particularly sensitive to this external electromagnetic wave change, which greatly affects the DNA unzipping and re-pairing assembling of DNA in a new cell division process. This is important for ensuring the effective control of bacteria growth which greatly relies on the bacteria's ability to multiplicate instead of just the direct kill rate.

[0114] When the water or the oil and water mixture flows in the pipe and is subject to the effect of the capacitive field generated by the system 100 of the invention, either the micro-organism in the water or the oil and water mixture is killed, or more importantly the micro-organism reproduction is disrupted. This advantageously results in effective control of bacteria / micro-organism growth in the water or the water system.

[0115] To further amplify the effect of the capacitive close field, multiple pairs of treatment assemblies 121 are assembled closely together in a chamber 120′ preferably lined with a non-conductive electrical isolation material 126, as shown in FIG. 6. The chamber 120′ has an inlet 127 through which the untreated water or the untreated water and oil mixture flows into the chamber 120′, and an outlet 128 through which the treated water or the treated water and oil mixture flows out of the chamber 120′. A wet plasma 129 can be generated within the chamber 120′, and this wet plasmatic effect would amplify the bacteria kill efficacy and provide the better disinfection of the multiplication of the bacteria in the water or the water system. In this regard, the distance between adjacent two pairs of treatment assemblies is preferably between 2 and 20 mm, preferably 2 and 10 mm.

[0116] In some cases, an extremely low conductive fluid flows through the pipe, the loop impedance of the treatment assembly is so high that there is little current flow between the two treatment units, then a bypass switch 125 is provided to create a bypass path between the two treatment units 122A, 122B so as to short circuit the capacitive plates 124A, 124B, as best shown in FIG. 5. Alternatively, if the conductivity of the water is predetermined, then the capacitive loads may be eliminated. Similarly, if the oxidizing (ORP) state of the water and the magnetite formation can be achieved very quickly, the coils in the treatment unit may not be required.

[0117] As discussed above, the bacteria kill mechanism according to the invention is through disruption of the electrons in the metabolism process. A part of the bacteria or micro-organisms may be killed immediately, and some of them may be killed after a time lag of up to hours or day. Depending on the electrical conductivity of the water or the water and oil mixture, the loop resistance of the treatment assembly increases or decreases when the conductivity is low or high. In order for the effective bacteria control, the voltage and current of the treatment assembly must be sufficiently high to an extent that is able to create the disruption effect on the organism metabolism. One approach is to shape and size the surface area of the capacitive loads e.g. the capacitive plates 124A, 124B so as to either increase or reduce the current flow between the two capacitive plates 124A, 124B and maintain the correct voltage.

[0118] The DC component added into the time varying frequency electromagnetic wave to produce an effective wave form is preferred in some cases, for example when the water or the water system has a high chloride content. FIG. 8 shows an exemplary wave form of the time-varying AC pulsating electromagnetic wave comprising the biased DC component. With this DC component, the high chloride content in the water or in the water and oil mixture can be converted into hypochlorite which can enhance the bacteria kill effect on the water or the water and oil mixture. Adjusting the DC component magnitude may vary the amount of hypochlorite generation to the desirable level.

[0119] One important feature of the invention is that the invention takes advantage of the high chloride content in the water system, which is converted into hypochlorite to produce a sufficient amount of the precursors Fe2+ ions in order for magnetite formation. High chloride content is typically present in the injection well water, but generally regarded as an undesirable factor from conventional corrosion point of view. In the invention, the chloride content present in the water may be converted into the final products of hypochlorite or hypochlorous acid by using the DC electrolysis method, or the DC component in the DC biased superimposed time varying electromagnetic wave generated by the generator 110, this will increase the ORP of the water to a high positive oxidizing ORP reading up to +900 mV. When the water is excited to have such a higher oxidative state, the bare steel surface Fe in contact with the higher oxidative state water can react quickly to form the Fe2+ ions, and simultaneously with the presence of time varying electromagnetic wave, or the energy stored the exited water is transferred to the steel surface, enabling formation of magnetite Fe3O4 quickly, evenly and densely over the entire steel surface in contact with the water. The formation of magnetite Fe3O4 in this high oxidation environment is found to take place within an hour, and the growth of the magnetite layer can separate the SRB from the bare steel-based article, as shown in FIG. 3B.

[0120] There are other approaches to make the ORP of the water goes more oxidizing, namely have a higher positive ORP reading, including using sodium hypochlorite dosing to achieve the desirable positive ORP, in situ generation or dosing of hydrogen peroxide H2O2, direct injection of ozone or in situ production method. However, the oxidizing water used alone cannot produce the magnetite Fe3O4, and it accelerates the corrosions instead, and also cannot stop the SRB corrosion. The oxidizing water needs to be used in conjunction with the specified time varying frequency wave treatment applied by the system of the invention herein.

[0121] When the chloride content in the water is low, it is advantageous to provide an ozone or hydrogen peroxide generator as a supplementary device to enhance the oxidizing potential of the water so as to improve formation of the precursors Fe2+ ions to form the magnetite Fe3O4. In the situation where the generation of hypochlorite is undesirable yet it is required to have the DC component in the water or the water system to produce the negative ORP shift, then boron doped diamond material can be used to prevent chlorine / hypochlorite generation. If the hypochlorite generation is not a problem, then mixed metal oxides of ruthenium and iridium coated titanium or niobium substrates can be used in the water with high or low chloride content. By adjusting the ratio of ruthenium and iridium oxide, it will change the amount of chlorine / hypochlorite generation. Platinum coating or cladding on the titanium or tantalum substrate can also be used.

[0122] In addition to facilitate producing the precursors Fe2+ ions for the magnetite formation, the water is excited to have the increased vibration entropy energy, thereby to enable the water surface tension become more active. The high energy state of the water can be detected by the large fluctuation of FTIR O—H peak absorbance curves, and the changes in surface tension can be detected by the surface tension tensiometer. As shown in FIGS. 14A and 14B, the consecutive tests were carried out, revealing that the surface tension before receiving the treatment by the system of the invention shows a smaller deviation in both O-H bond stretching absorbance peak and O—H bond scissor mode absorbance peak, and thus in the surface tension, which implies less active interaction between the water molecules. After the water is subjecting to the time varying electromagnetic wave treatment of the invention, a larger deviation in the surface tension is detected, which signifies the water has become more active after the treatment, and this helps in pushing the oil out from the geoformation.

[0123] In order to further enhance the formation of magnetite Fe3O4 on the steel surface for the SRB corrosion control, a skin effect on the steel surface is created by the system of the invention simultaneously. When the time varying frequency electromagnetic wave having a high frequency range in the order of 104 to 105 Hz travels directly on the steel pipe, the wave will travel on the steel skin surface to create the skin effect which brings about the following functions:

[0124] accelerate the generation of Fe into the precursor Fe2+ ions and electrons,

[0125] retard adhesion of bacteria or organism onto the steel surface, and

[0126] interfere electron transport in bacteria cell metabolism process / reaction.

[0127] When the skin effect takes place on the untreated steel surface, the acceleration of iron dissolution into the Fe2+ ions would increase the steel corrosion rate which is an undesirable reaction for steel corrosion usually. However, in this invention, this skin reaction is advantageously used to promote the formation of the magnetite in the condition that the time varying frequency electromagnetic wave is in combined use with the oxidizing environment in the water. As mentioned above, the Fe2+ ions are essential and acting as the precursor for formation of the magnetite Fe3O4 while the water is energized to have a higher entropy energy together with the more oxidizing ORP, which promote to form the magnetite Fe3O4 for protection of the base bare steel. Once the magnetite is formed, the iron dissolution into the Fe2+ ions will not proceed.

[0128] With the higher frequency of the time varying frequency wave skin effect on the metal surface, the wave would travel on the metal surface including the crevices, pits, and boundary layer beneath the coating where SRB colonized, and hence makes a direct impact on the adhering SRB cells and its metabolism, thereby reducing the SRB population. This further enhances the SRB control by reaching out to the SRB that cannot be killed in the water. The metabolism of SRB can be disrupted by the skin effect applied on the steel surface. The SRB metabolism includes ions exchange / electron transportation REDOX reactions, with the result of the SRB steel corrosion. When the synergistic effect of strong inductive field and capacitive field in combination with ionic wave current is imposing on the SRB colonies, their metabolic REDOX reactions would be disrupted or greatly affected. Hence this kind of skin effect further enhances the SRB corrosion.

[0129] The skin effect may be realized by the direct excitation of the steel through connection of the output terminal of the wave generator with the steel. In this case, the frequency of the generated wave is higher enough to enable the wave to travel on the steel skin where the SRB are located instead of internal mass of the steel. The frequency used in the invention is sufficient to create the skin effect. Another approach to realize the skin effect is to excite the steel by the pure DC current or the fixed frequency AC power supply together with an inductor coil load or a capacitive load mounted on either the output or input terminal of the wave generator. The inductor coil load or the capacitive load is provided to suppress the potential avalanche current produced by the time varying frequency electromagnetic wave and to prevent the short circuit. A constant current power supply can also be used in this excitation circuit to control the avalanche output current.

[0130] The well servicing equipment of oil production field may include at least one of an oilfield structure, a vessel, a pipeline, a storage tank, a buffer tank and a subterranean formation. The system of the invention may be adapted to suit different well servicing equipment, including in-tank treatment system and in-pipeline treatment system. FIG. 9 is a schematic layout of an exemplary injection water piping system comprising the in-tank treatment system and in-pipeline treatment system. As illustrated, in the injection water piping system, the water is subject to the treatment applied by the system of the invention, and the treated water 200 flows down to the oil reservoir 210, the water, oil and / or gas mixture 220 after extracted from the oil reservoir 210 is delivered to the separator 230 to separate the oil / gas out from the water. The separated water is then pumped to and stored at a buffer tank for further distribution and injected into the various injection wells.

[0131] For the in-tank treatment system, the majority of the water is in stationary state, and some new makeup water may also be introduced into the tank. In this situation, to ensure all the water in the tank could receive the time varying frequency electromagnetic wave treatment of the invention, the resistive far field is preferred for the in-tank treatment system. In particular, the treatment units 122A, 122B shown in FIG. 5 are placed remote from the tank wall, such that the time varying electromagnetic field and the ionic current in the water can be evenly distributed to treat the in-tank water. The distance between the adjacent treatment assemblies 121 and the spacing between the treatment units 122A, 122B shall be defined so as to ensure the potential distributions are as even as possible. One or more treatment assemblies may be utilized depending on the size of the tank. Typically, the capacitive load useful for the in-tank treatment system is preferably in the form of rod or tube type probe for the purpose of easy installation. It would be appreciated that other geometrical shapes or constructions are possible for the in-tank treatment system. FIG. 10 shows an exemplary layout of the in-tank treatment system of the invention. As illustrated in FIG. 10, two treatment assemblies 121 are deployed in a water tank 140 in a manner that the adjacent treatment assemblies 121 and the treatment units 122A, 122B of each treatment assembly are spaced sufficiently apart. The distance D between the adjacent treatment assemblies 121 and the spacing d between the treatment units 122A, 122B are sufficient to generate the resistive far field inside the tank water.

[0132] There is illustrated in FIG. 11 an in-line treatment system, in which an inline treatment chamber 150 is installed on the pipe 130 having an inlet 131 and an outlet 132. The plurality of treatment assemblies 121 are housed in the treatment chamber 150, and the capacitive close field is adopted for the in-line treatment system. Generally the distance D between the adjacent treatment assemblies 121 and the spacing d between the treatment units 122A, 122B are very short, for instance in the order of 2 to 10 mm so that the strong capacitive field is generated for the treatment of the water following through the treatment chamber 150 to provide the maximum bacteria and organism disinfection effects as well as the maximum energization of the water.

[0133] FIGS. 12A and 12B show alternative arrangements of the treatment assemblies placed inside the inline treatment chamber 150. In the arrangement shown in FIG. 12A, the treatment units 122A, 122B provided in pair are connected in parallel with the wave generator 110 and immersed in the water contained in the treatment chamber 150. Similarly, the treatment units 122A, 122B and the capacitive plates 124A, 124B are spaced closely to generate a high voltage gradient time varying frequency electromagnetic wave field across the treatment units122A, 122B and induce a flow of ionic wave current in the water for treatment of the water. Depending on the length of pipeline, the inline treatment chamber 150 may be installed on the pipe at an interval of typically every 2 to 3 km.

[0134] An alternative arrangement of the treatment assemblies is illustrated in FIG. 12B. As illustrated, the plurality of treatment units 122A, 122B in pair are arranged in rows in parallel to each other in the treatment chamber 150. Each of the capacitive plates 124A, 124B of the treatment units 122A, 122B has a part of its surface covered by a conductive coating, and the coated surfaces 125 being oriented in one direction and arranged between non-coated emitter surfaces 126. The coated emitter surface 125 may only account for a half or any suitable length of the entire emitter surface. In the array configuration of FIG. 12B, the capacitive plates 124A, 124B are not wire connected. Due to the lower energy required to discharge, the wave preferentially discharges only on the coated surface 125. Such a capacitive load array configuration allows to increase by many times the wave discharging and re-entering the capacitive loads, unlike the small spacing configuration where the wave current can only discharge once between the capacitor load pair. Therefore, to produce the same treatment effect, the amount of energy input is drastically reduced in this configuration.

[0135] The system and method of the invention find a wide range of applications where corrosion control in the water or the water system is required, especially for the general and SRB corrosion control in the water injection well of oilfield. The water after being injected into the well passes through the oil reservoir and pushes out the oil as the oil / water mixture to reach the ground for separation. The separated water is then recycled into the injection well for repeated oil extraction.

[0136] In the prior art, surfactant chemicals are added to boost the oil production by activating the water surface tension in contact with the oil and soil / porous rock / sand. Hydrocarbon crude oil consists mainly the paraffin alkane group and the asphaltene group. These crude oil hydrocarbons are very large, long chain hydrocarbon molecules. Correspondingly, the intermolecular attraction force between these large molecules contribute to the high viscosity of the crude oil, also the adhesion of oil to the other substrate surface are strong. High viscosity and adhesion to the strata surface slow down the oil production rate. To improve the oil production rate, it is often that chemical treatment is adopted to improve the oil production.

[0137] Surfactant (surface activation) chemicals added into the injection water lower the water surface tension or improve the water activeness in contact with the oil and soil / porous rock / sand. The lowered interfacial tension or improved wettability allows the water to become easier to flow therethrough, displacing more oil to increase the oil recovery. There are also chemical methods using alkaline agent to react with the oil forming surfactants to serve the same oil recovery improvement purpose. While surfactant can help to improve oil production, most surfactant chemicals are environmentally unfriendly.

[0138] This invention makes use of the same time varying frequency electromagnetic wave to improve the water activity instead of using surfactants. FIGS. 13A and 13B show the surface tension of the water (the region encircled in the figures) tested by a tensiometer before and after the treatment by the system of the invention. It is clear that there is a greater fluctuation in the encircled region of FIG. 13B in the surface tension after the treatment, indicating the high activation energy of water. Further, the treated injection water is energized to alter the water property and has increased water capillary migration / wettability property in the oil / sand / rock crevices to improve the ability to push out the oil from the crevices without using any surfactants.

[0139] FIGS. 14A and 14B respectively show FTIR analysis of the injection water before the treatment and after the treatment for a few minutes to 1.5 hours, for example for about 15 minutes in certain cases or for 1 hour in certain cases. Five random samples were taken respectively from the untreated water and the treated water at different points of positions for the FTIR analysis. There is clearly illustrated that the injection water after the treatment is highly energized, with the deviation Δstre of O—H bond stretching absorbance peak being larger than that of the untreated water as well as the deviation Δscis of O—H bond scissor mode absorbance peak being larger than that of the untreated water. The water was treated to be highly energized to render the greater O—H bond stretching and the greater O—H bond scissor vibration, so the FTIR absorbance peaks for O—H bond stretching and for O—H bond scissor vibration showed a larger fluctuation at different positions taken from the untreated water and the treated water. The deviation Astre after the treatment increases from 0.556 (FIG. 14A) to 0.944 (FIG. 14B). This highly energized water when passing through the oil reservoir not only can transfer the energy to the hydrocarbon too, but also helps to reduce the high viscosity of heavy oil including its adhesion to the soil / rocks, making it easier to be pushed out from the porous geoformation by the injection water. This is because hydrocarbon is very sensitive to the time varying frequency electromagnetic wave. The high energy of the treated water can be transmitted to the lower energy state oil underground to excite the hydrocarbon oil which may not be directly treated by the system of the invention, which definitely helps to reduce the oil viscosity and oil adhesion, thereby yielding some improvements in oil production rate. FIG. 15 is a diagram showing the viscosity reduction of heavy oil when treated directly by the system of the invention (curve 20) and by thermal heating (curve 10). As shown in FIG. 15, the viscosity reduction rate of the oil treated by the time varying frequency electromagnetic wave treatment of the invention is faster than the viscosity reduction rate of the oil treated by thermal heating method, and therefore the time required is much shorter. If heavy hydrocarbon is treated directly, the viscosity and oil fractional boiling point distribution property would shift from heavy hydrocarbon (untreated hydrocarbon, see FIG. 16A) to the lighter hydrocarbon behaviour (treated hydrocarbon, see FIG. 16B).

[0140] The magnetite acts as a good barrier coating and has the advantages of self-repairing and low maintenance. The self-repairing property of the magnetite layer is unique. When the magnetite coating is damaged during service, a new magnetite layer will re-form on the freshly exposed bare steel surface. As a result, the maintenance of the steel structure is low. Another feature of the electromagnetic wave system of the invention is that the wave has the tendency to travel on the steel surface throughout the entire cross section of the steel via the skin effect. Under this skin effect, the magnetite layer not only forms on the steel's general outer surfaces, but also forms within the steel's pits, cracks and crevices that are hard to be reachable. This makes it an excellent corrosion protection method for applications where conventional DC cathodic protection current and conventional coating materials cannot normally reach.

[0141] The system and method of the invention are applicable to other metallic articles than iron-based articles. For example, when a copper alloy article is subjected to the same time varying pulsating electromagnetic wave treatment, an evenly dense barrier composite coating (Cu2O / CuO) of passivating cuprous oxide (Cu2O) formed on the surface of the copper alloy article and passivating cupric oxide (CuO) formed on the cuprous oxide layer, which has an excellent corrosion protection property, would well adhere to the surface of the copper alloy article. Likewise, this passivating composite coating is a very effective corrosion protection coating to prevent the copper alloy article from corrosion.Assays

[0142] Assays were carried out to verify the corrosion control effects after the time varying frequency electromagnetic field treatment. Specifically, one piece of mild steel plate was cut into two, and the first half was immersed in the treated water for 3 hours, and the second half was used as a control and immersed for 3 hours in the water which was not treated. FIG. 17 is a photo of the first half of steel plate 310 and the second half of control steel plate 320. It can be seen that a full black magnetite coating was formed on the first half of steel plate 310, and no magnetite formation was found on the second half of control steel plate 320. The black magnetite thickness was measured and is about from 15 to 80 μm (see FIG. 18).

[0143] Other assays were carried out to confirm the beneficial effect achieved by the invention. For example, a mild steel test plate was installed on a pipe at a position 4 km downstream of the treatment chamber, and it showed the black magnetite formation as well. A saw blade was immersed in the in treated injection water drained off from the filter for 30 minutes and also showed the full magnetite formation.

[0144] It was surprisingly found that the average corrosion rate in the test site of the injection well oilfield after formation of the magnetite is about 0.006 mm / year, which is far below the good control requirement standard of 0.076 mm / year and much better than the chemically treated water where an average of corrosion rate is 4 times higher than the control requirement standard.

[0145] Further, onsite SRB kill efficacy was analyzed. The amount of SRB detected at the inlet of the treatment chamber was 2,500 cfu / ml (colony forming unit per millilitre water), and the amount of SRB detected at the outlet of the treatment chamber was only 25 cfu / ml. Also, the on-site findings showed that the SRB count at the inlet of the treatment chamber for storing the injection water returned from ground soil reduced greatly from 2,500 cfu / ml to less than 200 cfu / ml after the injection water was being subject to the treatment of the invention for 3 months. This indicates the SRB kill effect attained by the system of the invention is significant and has propagated to the whole soil strata.

[0146] The invention thus provides a system and a method for providing corrosion protection of a metallic article in contact with or exposed to the water through in-situ formation of a barrier coating thereon, which is very simple and energy-saving and which is effective in providing various treatments in one go. In this invention, the DC biased AC time varying frequency electromagnetic wave is used to excite the water but not the metallic article itself, so no impressed current on the metallic article takes place. The high chloride content in the water is purposedly used to create the oxidizing environment so that the water is excited to a higher oxidizing state to become the more positive ORP water to promote creation of the precursor Fe2+ ions for spontaneously forming the strong adhering magnetite coating evenly over the entire injection water steel system, which provides an efficient general and SRB corrosion protection for the metallic article. This is the most distinguishing and unique feature of the invention from the prior art technologies.

[0147] While the embodiments described herein are intended as exemplary corrosion protection system and method, it will be appreciated by those skilled in the art that the present invention is not limited to the embodiments illustrated. Those skilled in the art will envision many other possible variations and modifications by means of the skilled person's common knowledge without departing from the scope of the invention, however, such variations and modifications should fall into the scope of this invention.

Claims

1. A system for in-situ formation of a barrier coating on a metallic article in contact with or exposed to water within a water system, comprising:a generator for generating electromagnetic wave having a time varying frequency;a power supply unit connected to the generator for applying a driving voltage to the generator to drive the generation of the electromagnetic wave; andone or more treatment assemblies each comprising two treatment units positioned in a spaced-apart fashion to come into contact with the water, wherein each of the treatment units comprises an inductor coil load and a capacitive load connected in series, and the two treatment units are electrically coupled respectively to first and second terminals of the generator to apply the time-varying frequency electromagnetic wave generated by the generator across the two treatment units to produce a synergistic effect of one or more of the following:a time varying inductance field in and around the respective coil load,a capacitance electric field across the capacitive loads of the two treatment units, anda flow of ionic wave current travelling in a pulsating and time-varying manner in the water between the two treatment units,whereby the water is energized in an oxidizing state having an oxidizing potential sufficient to induce precursor ions of the metal which are reactive with hydroxyl groups in the water for in-situ formation of a passivating metal oxide or salt as the barrier coating on a surface of the metallic article.

2. The system as claimed in claim 1, wherein:a bypass switch is provided to create a bypass path between the two treatment units so as to short circuit the capacitive loads of the two treatment units; orthe two treatment units are spaced at a distance in the range 2 to 20 mm, preferably 2 to 10 mm, to produce a capacitive close field, preferably a plurality of treatment assemblies are assembled together in a treatment chamber to enhance the capacitive close field; orany combination thereof.

3. (canceled)4. (canceled)5. The system as claimed in claim 1, wherein the two treatment units are spaced far apart from each other to produce a resistive far field.

6. The system as claimed in claim 1, wherein the water in the oxidizing state is achieved by producing a positive oxidation reduction potential (ORP) shift in the water, preferably the positive ORP is shifted to more than +200 mV vs Ag / AgCl.

7. (canceled)8. The system as claimed in claim 1, wherein the capacitive load is provided in the form of plate, rod, tube or mesh.

9. The system as claimed in claim 1, wherein the generator is configured to generate a direct current (DC) biased time-varying frequency pulsating electromagnetic wave comprising an alternating current (AC) and a biased DC component.

10. The system as claimed in claim 1, wherein the frequency of the electromagnetic wave ranges from about 500 Hz to about 1,000,000 Hz, preferably from about 200 Hz to about 5,000 Hz, and the electromagnetic field has a sweeping frequency of 10 to 100 Hz.

11. The system as claimed in claim 1, the metallic article is iron-based, and the induced precursor ions are Fe2+ ions which react with the hydroxyl groups to form passivating magnetite as the barrier coating on the surface of the iron-based article, preferably the iron-based article is well servicing equipment of oil production field.

12. (canceled)13. The system as claimed in claim 1, wherein the metallic article is copper-based, and the induced precursor ions are Cu+ ions which react with the hydroxyl groups to form passivating cuprous oxide as the barrier coating on the surface of the copper-based article, preferably the induced precursor Cu+ ions react with the hydroxyl groups to form a composite coating consisting of an inner layer of the passivating cuprous oxide on the surface of the copper-based article and an outer layer of passivating cupric oxide on the inner layer.

14. (canceled)15. The system as claimed in claim 1, wherein the frequency of the electromagnetic wave is selected to excite the metallic article so that a skin effect is created on the surface of the metallic article to allow the electromagnetic wave to travel on said surface.

16. The system as claimed in claim 1, further comprising means for enhancing the oxidizing potential of the water to facilitate formation of the precursor ions.

17. A method for in-situ formation of a barrier coating on a metallic article in contact with or exposed to water within a water system, comprising the steps of:generating electromagnetic wave having a time varying frequency; andapplying the time-varying frequency electromagnetic wave to one or more treatment assemblies each comprising two treatment units positioned in a spaced-apart fashion to come into contact with the water, wherein each of the treatment units comprises an inductor coil load and a capacitive load connected in series so that the application of the time-varying frequency electromagnetic wave across the two treatment units produces a synergistic effect of one or more of the following:a time varying inductance field in and around the respective coil load,a capacitance electric field across the capacitive loads of the two treatment units, anda flow of ionic wave current travelling in a pulsating and time-varying manner in the water between the two treatment units,subjecting the water to the synergistic effect, whereby to energize the water in an oxidizing state having an oxidizing potential sufficient to induce precursor ions of the metal which are reactive with hydroxyl groups in the water for in-situ formation of a passivating metal oxide or salt as the barrier coating on a surface of the metallic article.

18. The method as claimed in claim 17, wherein the water in the oxidizing state is achieved by producing a positive oxidation reduction potential (ORP) shift in the water.

19. The method as claimed in claim 17, comprising shifting the positive ORP to more than +200 mV vs Ag / AgCl.

20. The method as claimed in claim 17, wherein:the water in the oxidizing state is achieved by producing a positive oxidation reduction potential (ORP) shift in the water, and wherein the positive ORP shift is caused by a method selected from the group consisting of DC electrolysis, ozonation, hydrogen peroxide, and oxidant dosing; orcomprising shifting the positive ORP to more than +200 mV vs Ag / AgCl, and wherein the positive ORP shift is caused by a method selected from the group consisting of DC electrolysis, ozonation, hydrogen peroxide, and oxidant dosing.

21. The method as claimed in claim 17, comprising providing a bypass switch to create a bypass path between the two treatment units so as to short circuit the capacitive loads of the two treatment units.

22. The method as claimed in claim 17, wherein the two treatment units are spaced at a distance in the range 2 to 20 mm, preferably 2 to 10 mm, to produce a capacitive close field, preferably assembling a plurality of treatment assemblies together to enhance the capacitive close field.

23. (canceled)24. The method as claimed in claim 17, wherein the two treatment units are spaced far apart from each other to produce a resistive far field.

25. The method as claimed in claim 17, wherein the generating step comprises configuring the time-varying frequency electromagnetic wave to have a DC biased component.

26. The method as claimed in claim 17, wherein the frequency of the electromagnetic wave ranges from about 500 Hz to about 1,000,000 Hz, preferably from about 200 Hz to about 5,000 Hz, and the electromagnetic field has a sweeping frequency of 10 to 100 Hz.

27. The method as claimed in claim 17, the metallic article is iron-based, and the induced precursor ions are Fe2+ ions which react with the hydroxyl groups to form passivating magnetite as the barrier coating on the surface of the iron-based article, preferably the iron-based article is well servicing equipment of oil production field.

28. (canceled)29. The method as claimed in claim 17, wherein the metallic article is copper-based, and the induced precursor ions are Cu+ ions which react with the hydroxyl groups to form passivating cuprous oxide as the barrier coating on the surface of the copper-based article, preferably the induced precursor Cu+ ions react with the hydroxyl groups to form a composite coating consisting of an inner layer of the passivating cuprous oxide on the surface of the copper-based article and an outer layer of passivating cupric oxide on the inner layer.

30. (canceled)31. The method as claimed in claim 17, wherein the frequency of the electromagnetic wave is selected to excite the metallic article so that a skin effect is created on the surface of the metallic article to allow the electromagnetic wave to travel on said surface.

32. (canceled)33. The system as claimed in claim 2, wherein:the two treatment units are spaced far apart from each other to produce a resistive far field; orthe water in the oxidizing state is achieved by producing a positive oxidation reduction potential (ORP) shift in the water, preferably the positive ORP is shifted to more than +200 mV vs Ag / AgCl; orthe capacitive load is provided in the form of plate, rod, tube or mesh; orthe generator is configured to generate a direct current (DC) biased time-varying frequency pulsating electromagnetic wave comprising an alternating current (AC) and a biased DC component; orthe frequency of the electromagnetic wave ranges from about 500 Hz to about 1,000,000 Hz, preferably from about 200 Hz to about 5,000 Hz, and the electromagnetic field has a sweeping frequency of 10 to 100 Hz; orthe metallic article is iron-based, and the induced precursor ions are Fe2+ ions which react with the hydroxyl groups to form passivating magnetite as the barrier coating on the surface of the iron-based article, preferably the iron-based article is well servicing equipment of oil production field; orthe metallic article is copper-based, and the induced precursor ions are Cu+ ions which react with the hydroxyl groups to form passivating cuprous oxide as the barrier coating on the surface of the copper-based article, preferably the induced precursor Cu+ ions react with the hydroxyl groups to form a composite coating consisting of an inner layer of the passivating cuprous oxide on the surface of the copper-based article and an outer layer of passivating cupric oxide on the inner layer; orthe frequency of the electromagnetic wave is selected to excite the metallic article so that a skin effect is created on the surface of the metallic article to allow the electromagnetic wave to travel on said surface; orfurther comprising means for enhancing the oxidizing potential of the water to facilitate formation of the precursor ions; orany combination thereof.

34. The method as claimed in claim 20, wherein:comprising providing a bypass switch to create a bypass path between the two treatment units so as to short circuit the capacitive loads of the two treatment units; orthe two treatment units are spaced at a distance in the range 2 to 20 mm, preferably 2 to 10 mm, to produce a capacitive close field, preferably assembling a plurality of treatment assemblies together to enhance the capacitive close field; orthe two treatment units are spaced far apart from each other to produce a resistive far field; orthe generating step comprises configuring the time-varying frequency electromagnetic wave to have a DC biased component; orthe frequency of the electromagnetic wave ranges from about 500 Hz to about 1,000,000 Hz, preferably from about 200 Hz to about 5,000 Hz, and the electromagnetic field has a sweeping frequency of 10 to 100 Hz; orthe metallic article is iron-based, and the induced precursor ions are Fe2+ ions which react with the hydroxyl groups to form passivating magnetite as the barrier coating on the surface of the iron-based article, preferably the iron-based article is well servicing equipment of oil production field; orthe metallic article is copper-based, and the induced precursor ions are Cu+ ions which react with the hydroxyl groups to form passivating cuprous oxide as the barrier coating on the surface of the copper-based article, preferably the induced precursor Cu+ ions react with the hydroxyl groups to form a composite coating consisting of an inner layer of the passivating cuprous oxide on the surface of the copper-based article and an outer layer of passivating cupric oxide on the inner layer; orthe frequency of the electromagnetic wave is selected to excite the metallic article so that a skin effect is created on the surface of the metallic article to allow the electromagnetic wave to travel on said surface; orany combination thereof.

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