RU2110489C1 - Method for elimination of deposits of sulfates of alkaline-earth metals - Google Patents

Abstract

FIELD: elimination of deposits of sulfates of alkaline-earth metals from the surface of underground wells and gasoline engines. SUBSTANCE: low frequent sound energy is proposed to improve solubility of sulfate deposits alkaline-earth metals. Deposit is brought into contact with aqueous solution having pH 11-14, said solution comprises polyaminopolycarboxylic acid (its concentration being 0.1-1.0 M) or its salt and synergist (its concentration being 0.1-1.0 M). Sound energy having frequency 1.5-6.5 kHz is passed through solution. EFFECT: improved efficiency of the method. 12 cl, 8 dwg

Description

 The invention relates to the use of low-frequency sound energy to increase the dissolution of scale of alkaline earth metals, in particular scale of barium and strontium sulfates, from surfaces with scale deposits on them using a descaling solvent. The invention is particularly useful for removing such scale from oil working equipment, including downhole pipes, piping and casing, as well as underground parts of the equipment. The invention is also suitable for removing these deposits from other types of equipment, such as boilers, evaporators and heat exchangers.

 Water contains cations of alkaline earth metals such as barium, strontium, calcium, magnesium and anions such as sulfate, bicarbonate, carbonate, phosphate and fluoride. When combinations of these anions and cateons are present in concentrations exceeding the solubility of products of various kinds that can be formed, precipitation occurs until the corresponding solubilities of the products are exceeded for a long time.

 For example, when the concentrations of barium and sulfate ions exceed the solubility of the barium sulfate product, a precipitate will form. The solubility of the products is exceeded for various reasons, such as evaporation of the aqueous phase, changes in pH, pressure or temperature and the introduction of additional ions, which can form insoluble compounds with ions already present in the solution.

 When the products of these reactions precipitate on the surface, they form adherent deposits or scale. Deposits can interfere with efficient heat transfer, the formation of a fluid stream, contribute to the corrosion process, or be a place of bacteria accumulation. Deposits are a costly problem for any industrial water system, gas and oil refining systems, pulp and paper mill systems and other systems, causing slowdowns and shutdowns for cleaning and disposal.

 US Pat. Nos. 4,908,077, 4,990,718, 5,049,297, and 5,084,105 disclose a method for removing barium sulfate and other sulfate deposits using a solution comprising a combination of a chelating agent containing a catalyst or synergist containing a polyaminopolycarboxylic acid, such as EDTA or DTPA, together with (1) monocarboxylic anions acids such as acetic acid, hydroxy acetic acid, mercaptoacetic acid or salicylic acid; (2) oxalates; (3) thiosulfates; or (4) nitriloacetic acid.

 Deposits are removed under alkaline conditions, preferably at pHs from about 8.0 to about 14.0, best results are achieved at pHs about 12. When the solution becomes saturated with cations of the metal deposits, the spent solution is removed by reintroduction into the subsurface formation or by regeneration.

 In normal practice, to remove deposits and scale, a predetermined volume of solvent is supplied to the tank and left in a static state for a long period of time. This is very inefficient from an economic point of view, because the tank must be shut down from the process for a long period of time, as a result of which productivity is lost.

 Exposure at a certain temperature is also an ineffective method in terms of reaction rate. In addition, the circulating solvent for deposits in the openings of the tank is too expensive due to the large volume of solvent required to fill the pipelines and circulate.

 The invention provides an effective method of removing deposits of alkaline earth metals by contacting deposits with a solvent that removes deposits, while low-frequency sound energy is passed through the solvent at the same time to more efficiently dissolve the deposits.

 A method for removing the deposition of alkaline earth metal sulfates involves contacting the deposits with an aqueous solution having a pH of from about 8 to about 14 and containing a chelating agent comprising polyaminopolycarboxylic acid present in a concentration of from 0.1 to 1.0 M, or a salt of such an acid and synergist or the catalyst while passing through the solvent low-frequency sound energy, from 1.5 to 6.5 kHz, preferably 1.5 kHz. The preferred synergist or catalyst is an oxalate anion, but other synergists, including monocarboxylates, thiosulfates or nitriloacetic acid, can be used. The concentration of the synergist or catalyst is from 0.1 to 1.0 M.

In FIG. 1 - 4 shows the dissolution rate of barium sulfate when using a solvent containing 0.5 M DTPA and 0.5 M oxalic acid (0.4 g / l BaO ₄ dispersion, 25 ^o C) at a pH of 12.2 s KOH, while time as sound energy of various low frequency and power level 6 (60% of power) is simultaneously passed through the solvent; in FIG. 5 - the dissolution rate of barium sulfate in a solvent containing 0.5 M DTPA and 0.5 M salicylic acid (0.4 g / l BaO ₄ dispersion, 25 ^o C) at a pH of 12.2 with KOH, while at the same time sound energy is passed through the solvent at a frequency of 1.5 kHz and a power level of 6 (60% power); in FIG. 6 - the rate of dissolution of barium sulfate in the piping system when using the DTPA / oxalic acid solvent while passing through the solvent the sound energy of a frequency of 1.5 kHz and a power level of 6 (60% power); in FIG. 7 - the rate of dissolution of strontium sulfate in the piping system when using a DTPA / oxalic acid solvent while transmitting sound energy of a frequency of 1.5 kHz and a power level of 6 (60% power) through the solvent; in FIG. 8 - the dissolution rate of calcium sulfate in the piping system when using the DTPA / oxalic acid solvent, while at the same time sound energy of a frequency of 1.5 kHz and a power level of 6 (60% power) are passed through the solvent. In FIG. 6-8 - 0.5 M DTPA, 0.5 M oxalic acid; the area of the pipeline with deposits, increased sound frequency, 50 ^o C, pH 12.2 with KOH.

 According to the invention, deposits of alkaline earth metal sulfates, especially barium sulfate, calcium sulfate and strontium sulfate, are removed using chemical deposition removing agents, subject to low frequency sound energy.

 The method is particularly suitable for removing such deposits from the surfaces of oil production equipment used to deliver oil and / or water from underground formations to the surface. The method, however, can also be used to remove deposits from the formations themselves, especially in areas surrounding equipment and input tanks.

 Deposits and sediments can form to such an extent that the permeability of the formation is disturbed as a result of a lower volumetric flow rate, a higher pump pressure, and eventually the formation is left. The method is also used to remove deposits from equipment and from oil producing, located on the surface, and from another, for example, from the surface of boilers and heat exchangers and from other equipment located in the conditions of formation of deposits.

 The deposits themselves are usually an adherent sediment of the resulting mineral deposits on metal surfaces exposed to water containing deposits forming components. These components include alkaline earth metals, including calcium, strontium and barium, together with varying amounts of radium depending on the origin of the water. Barium sulfate deposits are particularly difficult to remove by existing chemical methods due to their very low solubility.

 The invention allows deposits to be removed using an aqueous solution containing a chelating agent and a catalyst or synergist to accelerate the dissolution of deposits, as described in US patent 4980077, 1990, while low frequency sound energy is passed through the solution. This patent is incorporated herein by reference.

 The pH of the solution is maintained at a pH of from about 8.0 to about 14.0, preferably about 11-13, preferably about 12. Suitable chelating agents include polyaminopolycarboxylic acid, such as EDTA (ethylenediaminetetraacetic acid) or DTPA (diethylenetriaminopentaacetic acid), which tend to form a stable complex with an alkaline earth metal cation from the resulting deposition.

 The chelant may be added to the solvent in the form of an acid or alternatively as an acid salt, preferably a potassium salt. The concentration of the chelant in the aqueous solution should usually be from 0.1 to 1.0 M. The concentration of the catalyst or synergist in the aqueous solution should also be from 0.1 to 1.0 M. In any case, the alkaline conditions used in the deposition process, will convert free acid to salt.

 A preferred synergist or catalyst is an oxalate anion (US Pat. No. 4,980,077). Oxalate is preferably used in an amount of from about 0.1 to 1.0 M, more preferably from about 0.5 M, at a pH of 8.0-14.0, preferably 11-13, and usually about 12.

 The desired pH is obtained by adding a base, preferably a potassium base, such as potassium hydroxide, potassium hydroxide. An alternative synergist or catalyst is a monocarboxylic acid anion, preferably salicylate, as described in US Pat. No. 5,084,105, 1992. This patent is incorporated herein by reference.

 Thiosulfate synergists or synergists of nitriloacetic acid may also be used, as described in US Pat. No. 5,049,297. The patent is incorporated herein by reference. The amounts of chelant used with monocarboxylic acid or other synergists are comparable to the amounts used with oxalate synergists, the pH values used are also comparable, i.e. the concentration of the chelant and synergist is from 0.1 to 1.0 M, usually about 0.5 M, the pH of the solution is from 8 to 14, usually 11-13 and the best results for about pH 12.

 Preferred solutions include, as a chelating agent, about 0.1 to about 1.0 M ethylenediaminoacetic acid (EDTA) and / or diethylenetriaminopentaacetic acid (DTPA), or salts of these acids. In addition, preferably an oxalate catalyst of about 0.1 to about 1.0, preferably up to about 0.5 M, is added to the aqueous solution. The pH of the solution is then adjusted by adding the base to the desired value, preferably to about 12.

 It has been found that it is important to avoid the use of sodium cations when operating at high pH, approximately pH 8, and instead use potassium cation or alternatively cesium cation as the cation removing agent. From an economic point of view, potassium is preferable because of its availability.

 Thus, the usual way to obtain a solvent is to dissolve the chelant and oxalic acid (potassium oxalate) in water to the appropriate concentration, after which the potassium base, usually potassium hydroxide, is added to bring the pH to the desired value, approximately 12. This aqueous composition can be used for removal of deposits from equipment, or alternatively, it can be pumped into an underground formation when it is a formation from which deposits are removed, while in both cases it is simultaneous through a solution They pass sound energy of low frequency.

 The mode of action of the synergist or catalyst is not explained here. Although no special theory is required regarding the actual mechanism of its activity in the conversion or dissolution of deposits, it is believed that the adsorption of a synergist or catalyst on the surface of barium sulfate can modify the surface crystal structure so that barium in the modified crystal is easily removed using a chelating agent.

An aqueous solution containing the composition may be directed down the well to remove barium sulfate deposits that clog pipe equipment, such as piping, casing, etc., and passage paths. Before being directed down the well, the composition may be heated to a temperature of from about 25 ^° C. to about 100 ^° C., although the temperature existing in the downhole may not need to be preheated.

 Acoustic vibrations with a low frequency of from 1.5 to 6.5 kHz and preferably 1.5 kHz are passed through the solution inside the pipe equipment and passageways requiring processing. Low-frequency sound energy is generated by a suitable source containing a vibrator or transducer powered by electrical energy, which is lowered downhole into the solvent.

A suitable sound energy source is marketed under the trade name "T" - ^MotorTM by Sonic Research Corporation, which manufactures sound vibrators with frequencies from 1.5 to 6.5 kHz. The excitation of low-frequency sound energy removing deposits of solvent allows the solvent to more efficiently dissolve deposits.

 Although this does not explain the mechanism by which low-frequency sound energy makes it possible to more efficiently dissolve deposits, it is believed that sound energy destroys deposits on small particles and also mixes the solvent to create a flushing action by the solvent in connection with the deposits.

 As long as the solvent remains in contact with the equipment for the required time, sound energy is switched on intermittently, and a solvent containing dissolved deposits forms on the surface, it can be removed, if necessary, by reintroduction into the subsurface formation. This cycle can be repeated at the frequency required to remove deposits from the equipment.

 In order to show the use of low-frequency sound energy to enhance the ability of the solvent removing sediment to dissolve deposits in the laboratory, various aqueous solutions were tested, the test results are given below. The experiments described below were performed in cylindrical glass vessels.

 Barium sulfate or, when used, other sulfates or solid sediment components, were mixed with the selected solvents while passing through the solvent an acoustic energy of a frequency of 1.5 to 6.5 kHz and the dissolution rate and final concentration of the solute were determined. These tests were repeated with the same solvents without the use of sound energy. The results are shown graphically in the drawings.

As shown in FIG. 1-4, the dissolution rate of barium sulfate when using an aqueous solution containing 0.5 M DTPA and 0.5 M oxalic acid at pH 12.2 and a temperature of 25 ^o C, while at the same time low-frequency sound energy is passed through the solution with a level power 6 (60% power), compared with the dissolution rate when using the same solvent without the use of sound energy (control).

 The dissolution rate of barium sulfate in solution is measured by the light transmittance (%) of the dispersed deposition of barium sulfate contained in the solution. The transmittance (%) of light increases in proportion to the amount of barium sulfate dissolved in the solvent.

 As shown in FIG. 1 and 4, in the initial stage, the transmittance (%) decreases (the number of particles and / or surface area increases) for a short period of time and then increases at high speed. The decrease in the transmittance (%), it is believed, is the result of the destruction of separate agglomerates of barium sulfate crystals.

 Lower transmittance values (%) are not observed for barium sulfate dispersions in the absence of sound energy. The results show that when sound energy is passed through the solution, a significant increase in the dissolution rate of barium sulfate and the amount of dissolved barium sulfate is observed.

 FIG. 5 shows the dissolution rate of barium sulfate when using an aqueous solution of DTPA / salicylic acid with and without the use of low-frequency sound energy. The results show a significant increase in the dissolution rate of barium sulfate and an increase in the amount of dissolved barium sulfate.

The dissolution rate of barium sulfate, strontium sulfate and calcium sulfate in the pipeline was also evaluated using sound energy of frequency 1.5 kHz at power level 6 (60% power) using a DTPA / oxalic acid solvent at 50 ^° C and pH 12.2. Heavy deposits and tarry sediments are completely removed in a period of 2 to 3 hours with sound amplification and at 50 ^o C. Most of the deposits and tarry residues remain after 6 hours with stirring only at 50 ^o C.

 As shown in FIG. 6 and 7, low-frequency sound energy improves the dissolution of deposits of barium sulfate and strontium sulfate (in the pipeline) twice.

 As shown in FIG. 8, low-frequency sound energy improves the dissolution of calcium sulfate deposits in the pipeline by 1.75 times. These results show that the use of a solvent enhanced by exposure to low-frequency sound energy significantly increases the dissolution rate of deposits in the pipeline compared to using a solvent without sound energy.

The sonic energy for the above tests is generated by converter "T" - Motor ^TM, manufactured Sonic Research Corporation, as shown above. "T" - ^MotorTM consists of rods of magnetostrictive material, compressed together and enclosed by a wire coil. The rods contain 90% iron, 5% terbium and 5% solid dysprosium under the trade name "Terfenol D" Edge Technologies, Inc.

 The "Terfenol D" stem is an exceptional material known that can produce a variable frequency and withstand high temperatures and pressures. The rods vibrate in length when a direct current flows through the coil. The induced magnetic field causes the rods to expand, i.e. magnetostrictive displacement.

This motion generates vibration or acoustic waves or sonic energy having a frequency of 0-50 kHz which extends forward from the "T" - Motor ^TM for some distance and the acoustic pressure wave is estimated at a value of 3000 lb / ⁱⁿ² (217.45 kg / cm ^2. “T” ^—MotorTM or converter is driven by a standard frequency generator and power amplifier.

For all tests, the power level is set at 6 (60% power). The frequency of vibrations transmitted through the sediment solution to dissolve the alkaline earth metal sulfate deposits in the above tests is from 1.5 to 6.5 kHz, preferably 1.5 kHz. The “T” - ^MotorTM is only about 60 cm long and 5 cm in diameter and can easily be lowered down the conduit to pass sound energy through the sediment removal solution contained in that conduit.

Claims (12)

 1. A method of removing deposits of alkaline earth metal sulfates from the surface of underground wells, comprising contacting the deposits with an aqueous solution having a pH of 11-14 and containing a chelating agent, which is used polyaminopolycarboxylic acid with a concentration of 0.1 to 1.0 M or a salt of this acid and a synergist with a concentration of 0.1 - 1.0 M, characterized in that sound energy is passed through the solution with a frequency of 1.5 - 6.5 kHz.  2. The method according to claim 1, characterized in that diethylene triaminopentaacetic acid is used as the polyaminopolycarboxylic acid.  3. The method according to claim 1, characterized in that ethylene diaminotetraacetic acid is used as the polyaminopolycarboxylic acid.  4. The method according to claim 1, characterized in that remove deposits consisting of barium sulfate, strontium, calcium and mixtures thereof, as well as radioactive material, mainly radium 226 and radium 228.  5. The method according to claim 1, characterized in that they use a synergist, which includes an anion of monocarboxylic acid.  6. The method according to claim 5, characterized in that as monocarboxylic acid using salicylic acid or substituted acetic acid.  7. The method according to claim 1, characterized in that they use a synergist that includes an oxalate anion.  8. The method according to claim 1, characterized in that the synergist is selected from anions of thiosulfate and nitriloacetate.  9. The method according to claim 1, characterized in that the frequency of sound energy is maintained at 1.5 kHz.  10. The method according to claim 1, characterized in that they use a solution whose pH is approximately 12.  11. The method according to claim 1, characterized in that the solution is brought to the specified pH value by adding potassium base. 12. The method according to p. 1, characterized in that the contacting of the deposits with the solution is provided at 25 - 100 ^o C.

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