Patent Application
20110259761
The invention relates to a method and apparatus for the precipitation of hardness salts in flow back and produced water thereby reducing scaling tendencies.
The invention is related to the pre-treatment of flow back or produced water for the hydraulic fracture treatment of a subterranean formation in a well bore. The water or brine is softened by precipitating hardness salts with electrochemical cells and carbon dioxide gas.
Water is a scarce natural resource around the country. Significant oil and gas development has been curtailed due to the lack of water resources for drilling and oil field development and completion. This scarcity of water supply has resulted in the necessity for design and construction of large ponds to store surface water for oil and gas filed operations thereby increasing the amount of time and money needed for well completion. To mitigate the need for large quantities of water recycling techniques have been developed. With the development of water recycling technologies, oil and gas production companies can recycle the produced and flow back water from their hydro-fracturing operations.
The recycling of produced or flowback water has presented the oil and gas industry with a new set of problems as compared to using potable municipal water. The hardness salts present in recycled water is one of the main challenges which must be overcome when recycling flowback or produced water. These hardness salts can form a scale in the shale formations resulting in the blockage of micro pores thereby resulting in a reduction of potential gas production. A typical method for treating recycled flowback water involves the addition of a mixture of scale inhibiting chemicals to the produced water. The mixture in turn binds the scale causing salts. However, the scale inhibiting chemicals are not only expensive but they also pose a major environmental risk and may plate out on the clay particles in the formation.
The prior art has taken various approaches in softening brine using many varied techniques. One of the first oil field brine softening methods was thermal precipitation of divalent ions with an excess of alkalinity for steam production used in oil recovery operations. U.S. Pat. No. 4,518,505 discloses steam as the heat transfers agent while U.S. Pat. No. 3,731,801 uses hot oil as the heat transfer agent
U.S. Pat. No. 4,444,675 discloses a brine softening method including the step of adding enough soda ash to increase the brine pH to 10.8 11.5 and using seed crystals of calcium carbonate to improve the magnesium hydroxide precipitation. When the brine is heated, it is called “hot lime softening” as shown in U.S. Pat. No. 4,247,371 which is directed to multi-stage flash distillation of brine to fresh water and near saturated brine soluble salts.
U.S. Pat. No. 4,444,675 discloses the use of a chemical anti-scaling agent to tie up divalent ions and carbon dioxide gas injection to lower the pH in the concentrated brine to prevent scaling and fouling heat exchanger surfaces. U.S. Pat. No. 4,472,283 also discloses the concept of injecting carbon dioxide gas to lower the pH in heated brines by adding a quaternary ammonium surfactant to the brine to keep the carbon dioxide in solution at higher temperatures.
U.S. Pat. No. 4,880,057 discloses the use of a reverse osmosis membrane to remove dissolved solids from well water and adding carbon dioxide gas to make carbonic acid. The acidic softened fresh water is then injected back into the well to remove calcium carbonate buildup around the well bore. U.S. Pat. No. 6,096,221 uses the injection of ozone and carbon dioxide into the city water source pipe to remove bio-film and calcium carbonate scale build up in the water piping for hospitals.
U.S. Pat. No. 3,425,925 discloses a galvanic electro-chemical cell that uses magnesium metal as a consumable anode to generate a colloidal suspension of seed crystals of magnesium hydroxide to prevent hard scaling in boiler tubes. The magnesium hydroxide will slightly increase the pH of the brine to encourage precipitation of calcium carbonate on the seed crystal. Copper metal is used for the cathode surface and completes the galvanic circuit. U.S. Pat. No. 4,789,448 discloses a galvanic electro-chemical sell that includes a zinc anode to generate a colloidal suspension of seed crystals. U.S. Pat. No. 4,749,457 also discloses a galvanic electro-chemical sell that includes an aluminum anode to generate a flocculating agent for colloidal suspensions. In this instance dissolved oxygen is used to enhance the corrosion rate of the aluminum anode.
U.S. Pat. No. 3,944,478 discloses a self cleaning electro-chemical cell that has an anode formed from either aluminum or iron that will generate a flocculating agent for colloidal suspension of dye. A very thin gap between the anode and cathode is used to reduce the ohmic voltage drop in the water, increase the wear rate on the aluminum anode, scour scale build up on the cathode and anode surfaces, and increase the amperage loading from 2 mA/sq·cm. to 1 A/sq·cm. The turbulence generates a fine floc that is discharged with a downstream skimmer.
U.S. Pat. No. 4,119,518 is directed to a self cleaning electro-chemical cell that includes a fluidized bed of near spherical particles that scour the surfaces of the cathode and anode. The patent discloses the use of a dimensionally stable anode coating such as platinum and tantalum to generate hypo-chlorous acid, aluminum or iron anodes to create a flocculating agent and a copper or silver anode to generate disinfection metal ions in the treated water. A glass or ceramic spherical particle can be used with the electro-chemical flocculation of waste water. The patent further discloses the use of an ion exchange resin particle that can be used with the fresh water treatment to decrease an ohmic voltage drop in the gap between the electrodes thereby increasing the treatment surface area sued to soften the hard water.
U.S. Pat. No. 6,332,979 discloses a system that includes carbon dioxide gas injection and electro chemical cell treatment for the control of bio-film; corrosion and scale build up on cooling tower heat exchanger surfaces. The pH is maintained between 7.5 and 8.5 with the carbon dioxide gas injection for optimum calcium carbonate scale reduction and bio-film control. U.S. Pat. No. 6,228,249 discloses an electro-chemical cell process to make food grade calcium carbonate from natural sources containing heavy metal contamination. In this patent the electro-chemical cell treatment of the brine precipitates the heavy metals. These precipitates are then removed by filtration. Finally, food grade calcium carbonate is precipitated out of the lime brine by the injection of carbon dioxide gas.
U.S. Pat. No. 5,057,198 discloses a brine softening system that utilizes an electro-chemical cell with a cation exchange membrane separating the anode compartment from the cathode compartment. The cation exchange membrane allows the divalent ions to be transported from the anode compartment to the cathode compartment. The raw brine is introduced into the cathode compartment where the pH is maintained between 10.5 and 11.5 to enhance the precipitation of magnesium hydroxide and the co-adsorption of silicate on magnesium hydroxide precipitate. The brine flow turbulence is used to reduce calcium carbonate scale build up on the cathode surface. The precipitates are filtered from the catholyte and the catholyte is returned to the anode compartment for pH adjustment back to 6-7. The brine Langelier Saturation Index (LSI) should range from −4 to −5. Heating the brine from 10 to 40 degrees C. will decrease the electrical power consumption by 30% and decrease the brine LSI range from −4.5 to −5.5.
U.S. Pat. No. 5,843,291 discloses a system for softening hard water with an electro-chemical cell using a laminar flow of water between the electrodes. The acidic and basic water is collected at the end of the electrode through perforations in the electrode surface. The polarity at the electrode is reversed to remove the calcium carbonate scale buildup on the cathode surface during the cleaning cycle. The polarity reversal will not remove organic gums or iron oxide buildup.
U.S. Pat. No. 3,014,855 discloses how to soften hard water with electro-dialysis. The system includes an electro-chemical cell with both cation and anion exchange membranes. The electrode polarity is reversed to remove the calcium carbonate build up on the cation membrane surface. U.S. Pat. No. 7,329,358 discloses a system that can purify hard water with a continuous electro-deionization for use in the beverage industry. In this disclosure ozone is used to disinfect the water and remove hydrogen sulfide by oxidation to a sulfate and also remove the iron by oxidation to an iron oxide that is subsequently filtered out.
None of the electro-chemical brine softening methods discussed above can be used in an oil field environment because the equipment and methods are unable to handle large fluctuations in temperature, hardness and total dissolved solids (TDS) concentrations, and crude oil, asphaltene, grease, iron and hydrogen sulfide contamination.
The present invention overcomes the shortcomings of the prior systems and methods. It provides an effective and efficient mobile self-cleaning electro-chemical cell that will reduce the LSI of brine in the harsh are difficult environment of oil field development and production.
The present invention is directed to a process and apparatus that provides a solution for oil and gas companies that will recycle the produce brine and flow back water at the production well site. The apparatus is skid mounted and contained within a mobile container module that can be easily transported from well site to well site. It includes an electro-chemical cell that is particularly well suited for oil field applications. The cell uses carbon dioxide for pH adjustment to optimize calcium carbonate precipitation. The anode current is adjusted to produce enough hypo-chlorous acid for sterilization of the brine. The calcium carbonate is precipitated on the heated cathode surface and surface is continuously cleaned with ultrasound.
Accordingly, it is an objective of the instant invention to provide a method and apparatus for effectively and efficiently recycling produce brine and flow back water.
It is a further objective of the instant invention to provide effective electro-chemical brine softening apparatus and method without the use of environmentally dangerous and costly materials.
It is yet another objective of the instant invention to provide a method and apparatus for reducing the scaling tendency of fracture treatment flow back water that is self cleaning and is able to sterilize the brine
It is a still further objective of the invention to provide an apparatus that is compact in size and skid mounted so that it is easily moved from site to site within a transportable container.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with any accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. Any drawings contained herein constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
The present invention provides a solution to oil and gas companies for recycling the produce brine and flow back water at the production well site. Filtered, oxidized, and sterilized flow back water or produced water is brought to the new production well site where it is mixed with fresh water to an appropriate total dissolved solids (TDS) concentration for hydration of the fracture treatment polymer system. The blended water is stored in mobile tanks until pumped away with the fracture treatment of the production well.
As the stored water mixture is pumped to a blender, it is treated with an electro-chemical cell and carbon dioxide is injected into the flow. As the carbonated water passes over heated cathode surfaces, the hardness salts are encouraged to precipitate by super-saturation. The precipitated scale is ground up into a colloidal suspension with the ultrasonic field. The blender takes the treated water and hydrates friction reduction polymer as well as mixing with other chemicals. The polymer blend can also be mixed with proppant before it is pumped down the well bore.
The treated water is softened thus the scaling tendency of the calcium carbonate salt is nullified or reduced and the polymer hydration is complete in the brine. In the process of softening hard water, bicarbonate hardness can be reduced by the application of heat at the surface of the heated cathode, encouraging the carbonate salts to precipitate.
Ca2+CO32−===>CaCO3(s)
2H2O(I)+2e−==>H2(g)+2OH−
The deposition of scale is a difficulty encountered when using water containing ions of sparingly soluble salts and is one of the major obstacles hampering the performance of gas and oil wells. Scale precipitation occurs whenever processing conditions lead to creation of super saturation with respect to one or more of the sparingly soluble salts e.g. CaCO3, CaSO4, BaSO4, etc. The customary method for preventing the formation of these scale deposits is the acidification of this water by means of a mineral acid. The injection of CO2 from an external source helps to reduce the pH of water and prevent scaling by softening water and thus eliminate the use of HCL at the frac job site. The present invention in directed to a skid mounted multi-tube water softening system in which the hard water to be softened is move in one direction through an inlet pipe where the CO2 is introduced into the flow through a manifold containing a plurality of nozzle jets. The hard water is progressively mixed with micro sized bubble of CO2 using hydrodynamic and acoustic cavitation in the treatment conduit and undergoes electro-chemical treatment within the system.
The second plate 52 forms the mirror image of the first plate 40. The second plate 52 is defined also by a first end spaced from a second end by a length (l) which is approximately twice the inner diameter of the segment 24. The second plate 52 has a width (w) which is also approximately the thickness of the cylindrical wall of segment 24. The second plate 52 is further defined by a curved outer edge 54 sized to follow the inner cylindrical wall 48 of segment 24 and also has a straight edge 56 extending from the first end to the second end along the Approximate center line of the segment 24. The second plate 52 has one or more apertures 58 that are positioned in the plate in a predetermined size and position calculated to provide optimum cavitaion with minimal pressure loss. The apertures 51 and 58 are flow thru and each includes a fluid orifice formed by the use of sharp edges so that each aperture is formed perpendicular to the plate and thus positioned at an angle to the fluid flow to create a constriction area. The cross-sectional profile design creates the flow constriction are along the edges 50 and 56 and edges to apertures 51 and 58. The shape edges on the exit side of each edge from vena contract eddys and fluid shearing. A high fluid flow velocity provides for a hydrodynamic cavitaion filed downstream of each baffle unit. The flow velocity in a local constriction is increased while the pressure is decreased, with the result that the cavitaion voids are formed in the fluid flow past the baffle unit to form cavitaion bubbles which create the cavitaion filed. The cavitation bubbles enter into the increased pressure zone resulting from a reduced flow velocity, and collapse. The resulting cavitation exerts a physico-chemical effect on the liquid.
Each aperture is sized to a plate and requires a diameter to match the length, width, and thickness of the plate, all of which are constructed and arranged to induce hydrodynamic cavitaion by implosion if the cavitation induced increase pressure zone where coordinated collapsing occurs. The implosion is accompanied by high local pressure (up to 1500 MPa) and temperature (up to 15,000 degrees K.) as well as by other physico-chemical which initiate the progress of chemical reactions in the fluid that can change the composition of the mixture. Cavitation bubbles generally contain gases and vapors. Collapsing the cavitation bubbles may produce localized high energy conditions like high pressures, high temperatures requiring the baffles to be formed from a corrosive resistant material. When gases are present, high temperatures may occur when the cavitation bubbles collapse and plasmas may be created. The plasmas may emit ultraviolet light to be emitted in pulses. Emission of this ultraviolet light may be called cavitation luminescence. The ultraviolet light may irradiate oxidizing agents contained within and/or associated with the cavitation bubbles. Irradiating oxidizing agents may produce ionization of the oxidizing agents. Irradiating oxidizing agents may produce hydroxyl radicals. The hydroxyl radicals may contact and/or react with organic compounds in a fluid or solution in which the cavitation bubbles are produced. These reactions may destroy or degrade the organic compounds, through the breakage of chemical bonds with the compounds, for example. These reactions may produce partial oxidation of the organic compounds. These reactions may also produce complete oxidation of the organic compounds, to carbon dioxide and water, for example. The fluid or solution that has been treated by the cavitation based method may be called a product of the method.
The treatment process will precipitate hardness salts and reduce scaling tendencies. The treated brine should have a Langelier Saturation Index (LSI) ranging from −1 to −3.
All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference.
It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein.
One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.
