CN112794501A - Method for removing boron ions in fracturing flow-back fluid - Google Patents
Method for removing boron ions in fracturing flow-back fluid Download PDFInfo
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Abstract
The invention belongs to the technical field of oil and gas field wastewater treatment, and particularly relates to a method for removing boron ions in fracturing flow-back fluid. Adopting a chemical agent-coupling ion exchange technology, namely firstly adding an oxidant into the flowback liquid, then adding a metal ion precipitator, adjusting the pH value of the flowback liquid to be alkaline, and reacting for a period of time; adding an inorganic flocculant, then adding a compounded boron remover, reacting for a period of time, finally adjusting the pH value to be slightly acidic, and finally settling boron ions, the boron remover and colloidal particles together through a net catching effect; and then combining an ion exchange treatment technology, the final boron removal rate can reach about 88%, the content of the treated suspended matters is reduced to be below 20mg/L, the content of calcium and magnesium ions is reduced to be below 300mg/L, and the treated flowback liquid meets the requirement of secondary liquid preparation.
Description
Technical Field
The invention belongs to the technical field of oil and gas field wastewater treatment, and particularly relates to a method for removing boron ions in fracturing flow-back fluid.
Background
The fracturing technology is an important technology for increasing the yield of oil and gas fields at present. The fracturing fluid is a transmission medium in the fracturing process, can transmit power required in the fracturing process, and has the functions of crack formation and sand carrying, so that the quality of the fracturing fluid plays a decisive role in fracturing. Usually, 30 to 50 percent of fracturing fluid is returned to the ground after the fracturing process is finished, so that fracturing flow-back fluid is formed.
The components of the fracturing flowback fluid are very complex, and the fracturing flowback fluid contains thickening agents, cross-linking agents, cleanup additives, clay stabilizers, bactericides, pH regulators and other regulators which are added during the preparation of the fracturing fluid, and also contains crude oil generated in the fracturing process and various substances mixed in by contacting with the stratum.
The current treatment method of the fracturing flow-back fluid mainly comprises the following steps:
and (6) discharging. The fracturing flow-back fluid is treated to reach the national emission standard, and the method has high treatment difficulty and high cost.
And ② reinjection. The method is that the flow-back fluid is treated to reach the water injection standard of oil and gas field, the standard of the method is only 7 items, and the flow-back fluid can be injected into a reservoir stratum after the treatment reaches the standard for gas production or oil production.
And thirdly, recharging. The recharge and the reinjection are the same during treatment, and are not different, the only difference is that the recharge is to inject the treated water into a non-oil gas reservoir, is not used for gas production or oil production, and is to find a stratum with strong water absorption capacity to treat sewage.
And fourthly, recycling. The recycling is to use the fracturing flow-back fluid after a series of treatments for the preparation of the next flow-back fluid, the method is an ideal treatment mode of the flow-back fluid, the flow-back fluid is widely used in recent years and is a development trend in the future, and the flow-back fluid can be prepared after the treated flow-back fluid meets 16 indexes of certain temperature resistance, viscosity, shearing resistance, gel breaking performance and the like.
The factors influencing the re-preparation of the fracturing flowback fluid are various, and the fracturing flowback fluid comprises oil content, organic impurity content, acidity and alkalinity, calcium ions, magnesium ions, iron ions and residual boron crosslinking agents, wherein the oil content and the organic impurity content can meet the recycling index through flocculation precipitation, and the calcium ions, the magnesium ions, the iron ions and the like can be removed through a chemical precipitation method. The residual cross-linking agent in the fracturing flowback fluid isAn organoboron crosslinker that ionizes out [ B (OH) ] as the pH of the flowback fluid increases4]-The cross-linking agent can be cross-linked with the guanidine gum in the flowback liquid, so that the viscosity of the base liquid is increased, and the recycling of the flowback liquid is further influenced. Therefore, the increase of the viscosity of the base fluid caused by crosslinking can be avoided only by reducing the content of boron ions in the flowback fluid, and by looking up relevant standards, when the content of boron in the flowback fluid is reduced to be below 3mg/L, the requirement of secondary fluid preparation of the flowback fluid can be met, and the removal of the boron ions is also a difficulty in recycling the fracturing flowback fluid.
At present, the main methods for removing boron are as follows:
an extraction method. Boric acid can generate a chelate with an organic matter containing ortho-dihydroxy, the chelate brings the boric acid into an organic phase to achieve the purpose of separating from a solution, and finally a back-extraction agent is added to extract boron from the organic phase, and finally the boron is extracted from the solution. The method has the advantages of wide application range, good selectivity, high removal rate which can reach more than 90 percent, but the extraction method is too complex in experiment, has more influence factors, is expensive in extractant price, is not environment-friendly, and causes pollution to the environment, so that the boron removal by the extraction method is still not largely adopted for many years.
② oxide adsorption method. Boron is located in the second period and third main group of the periodic table of elements, and determines the electron-deficient characteristics of boron, while metal oxides generally have the property of losing electrons, i.e., providing lone-pair electrons, such as calcium oxide, magnesium oxide, and the like. The metal oxide is usually in the form of positive ion in the solution, and the boron atom is in the form of borate negative ion, so that both of them directly produce adsorption, thereby removing boron from the solution. Although the oxide adsorption method has a large adsorption capacity, good selectivity and good regenerability, it is not suitable for a solution having a low boron content, and thus has a certain limitation.
③ chemical precipitation method. Since borate is a sparingly soluble salt, the chemical precipitation method utilizes this property of boric acid to adjust the acidity or basicity of the solution and convert the boric acid in the solution into a sparingly soluble salt, thereby removing boron. The acid precipitation method is a method in which boron is changed to boric acid by adding sulfuric acid or the like to the solution, and the boric acid is separated because of its low solubility in the solution. Since the acid precipitation method consumes a large amount of precipitant during the precipitation process and requires a certain treatment of the precipitate after the precipitation, it is relatively complicated and the removal rate is not high, so that the method is not used as a main method for removing boron in view of economy and ease of treatment.
Fourthly, reverse osmosis method. The principle of the reverse osmosis method is to remove boron from a solution by using the selective permeability of a membrane because the concentration of both sides of the membrane has a certain concentration difference. The effect of pH on boron removal was studied by pator et al and the results showed 100% removal when pH 9.5. The reason is that when the pH value in the solution reaches 9.5, borate ions are generated, and borate has negative charges and can repel the surface of the membrane to cause that the reverse osmosis membrane cannot be penetrated, so that boron is intercepted, and the aim of removing boron is fulfilled. The reverse osmosis is simple to operate, the removal rate is high, the method is suitable for the solution with a high pH value, if the pH value is low, the solution is acidic, the boron removal is not facilitated, and the removal rate is low.
Resin method. The principle of boron removal by the resin method is that the resin contains hydroxyl functional groups which can generate complex reaction with borate ions, so that boron is absorbed from the solution and removed. The resin method for removing boron is suitable for the solution with small boron content, has good selective adsorption, can not be influenced by other ions, and can also be used for treating and recycling the treated resin without polluting the environment.
Therefore, how to reduce the boron content in the flowback fluid to be below 3mg/L has important application value under the conditions of low cost and simple operation.
Disclosure of Invention
The invention aims to provide a method for removing boron ions in fracturing flowback fluid, which solves the engineering problem that secondary fluid preparation of the flowback fluid is influenced due to the fact that crosslinking is carried out in advance caused by boron in the flowback fluid by using a method of combining a boron removal agent with ion exchange.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
according to the method for removing boron ions in the fracturing flow-back fluid, an oxidant and a calcium-magnesium ion precipitator are added into a guanidine gum fracturing flow-back fluid, the pH is adjusted to 9.5-10, the reaction is carried out until calcium-magnesium ions are completely precipitated, an inorganic flocculant and a boron removal agent are added, the reaction is carried out for 10-15 min, the pH is adjusted to 6-7, and the mixture is kept stand and filtered to obtain a liquid, so that the purpose of removing boron ions in the fracturing flow-back fluid is achieved.
The further improvement of the invention is that the amount of boron in every 1L of guanidine gum fracturing flow-back fluid is less than or equal to 20 mg.
The further improvement of the invention is that when the amount of boron in each 1L of the guanidine gum fracturing flow-back fluid is more than 8mg and less than or equal to 20mg, the boron in the fracturing flow-back fluid is removed by the boron removal device, so that the aim of removing boron ions in the fracturing flow-back fluid is fulfilled.
The invention has the further improvement that the oxidant is hydrogen peroxide or sodium hypochlorite, and the mass concentration of the hydrogen peroxide in the hydrogen peroxide is 0.1 percent; the amount of the oxidant is 0.08-0.15% of the mass of the guanidine gum fracturing flow-back fluid.
The invention further improves that the calcium-magnesium ion precipitator is sodium carbonate or sodium sulfate, and the molar ratio of the usage amount of the precipitator to the total substance amount of calcium-magnesium ions in the guanidine gum fracturing flow-back fluid is 1: 1-2.
The method is further improved in that a sodium hydroxide aqueous solution with the mass concentration of 4% is adopted to adjust the pH value to 9.5-10.
The invention has the further improvement that the inorganic flocculant is an aqueous solution of polyaluminium chloride, and the addition amount of the inorganic flocculant in every 1L of the guanidine gum fracturing flow-back fluid is 500-800 mg/L.
The further improvement of the invention is that the boron removing agent is a mixture of polyvinyl alcohol with the molecular weight of 5-7: 1 and 1400 ten thousand polyacrylamide.
The further improvement of the invention is that the molar ratio of the boron removing agent to the boron in the guanidine gum fracturing flow-back fluid is (1-15) to 20.
The method is further improved in that a citric acid solution with the concentration of 100-300 mg/L is adopted to adjust the pH value to 6-7; the standing time is 30-35 min.
Compared with the prior art, the invention has the following beneficial effects:
1. the oxidant added in the invention can not only decolorize the flowback liquid to ensure that the treated flowback liquid has high transparency, but also oxidize the residual cross-linking agent in the flowback liquid, and the cross-linking mechanism of the cross-linking agent is that the organic boron complex generates multi-stage ionization and slowly ionizes to form [ B (OH)]4]-Then [ B (OH)4]-And the product undergoes a complex reaction with ortho-cis hydroxyl in the guar gum to form jelly with higher viscosity. When oxidizing by adding an oxidizing agent, the organoboron complex can be completely oxidized to give [ B (OH) ]4]-And basically all boron ions are ionized, so that residual boron in the backflow liquid can be removed more completely, and basically no residue exists.
2. The traditional treatment method has a certain effect of removing boron in the flowback fluid, but the removal rate is low, and the requirement of secondary liquid preparation of the fracturing flowback fluid cannot be met. The mechanism of the removal is that polyacrylamide flocculates and precipitates guar splits, and simultaneously polyvinyl alcohol and ortho-cis hydroxyl in the guar undergo a complex reaction to generate a complex which precipitates together with the guar splits, so that boron ions are masked in the solution, and the stability is good through experimental verification.
3. For the fracturing flow-back fluid with the boron content of 8-20 mg/L, firstly, the boron removing agent is utilized to remove about 50% of boron ions, and then the ion exchange method is combined to finally reduce the boron content to be below 3mg/L, so that the requirement of secondary liquid preparation is met.
The reaction formula is as follows:
drawings
FIG. 1 is a schematic diagram of the mechanism of boron removal by chemical agents.
FIG. 2 is a process flow diagram of chemical boron removal.
FIG. 3 is a process flow diagram of a treatment with a boron removal apparatus.
Detailed Description
The present invention will be described in detail below with reference to examples.
The method comprises the following steps: firstly, adding an oxidant and a calcium-magnesium ion precipitator into fracturing flow-back fluid, then adjusting the pH of the flow-back fluid to 9.5-10 with alkali, reacting for about 8-12 min, then adding an inorganic flocculant and a boron removal agent, reacting for about 8-15 min, adjusting the pH of the flow-back fluid to 6-7 with acid, standing for a period of time, and filtering with a solvent filter to obtain liquid, namely finally obtaining water meeting secondary liquid preparation.
The used flowback fluid is guanidine gum fracturing flowback fluid, wherein the boron content is less than or equal to 20mg/L, namely the boron content in 1L of guanidine gum fracturing flowback fluid is less than or equal to 20 mg.
When the amount of boron in every 1L of guanidine gum fracturing flow-back fluid is more than 8mg and less than or equal to 20mg, boron in the liquid is removed through a boron removal device (specifically, the liquid is filtered by utilizing a resin column, the resin used in the resin column is LSC-800 boron selective chelating resin, and the airspeed in the resin column is 10h-1I.e. when the volume of the resin treatment flowback fluid is less than 320 times of the volume of the resin treatment flowback fluid), the aim of removing boron ions in the fracturing flowback fluid is fulfilled.
The oxidant is hydrogen peroxide or sodium hypochlorite solution, wherein the mass concentration of the hydrogen peroxide in the hydrogen peroxide is 0.1%. The mass concentration of the sodium hypochlorite solution is 0.1 percent, and the addition amount of the oxidant is 0.08 to 0.15 percent of the mass of the fracturing flow-back fluid.
The calcium and magnesium ion precipitator is sodium carbonate or sodium sulfate, and the molar ratio of the amount of the precipitator to the total amount of calcium and magnesium ions in the guanidine gum fracturing flow-back fluid is 1: 1-2.
The alkali used is an aqueous solution of sodium hydroxide, and the mass concentration of the aqueous solution of sodium hydroxide is 4%.
The used inorganic flocculant is an aqueous solution of polyaluminium chloride, and the addition amount of the inorganic flocculant is 500-800 mg/L.
The boron removing agent is obtained by mixing polyacrylamide with the molecular weight of 1400 million and imported polyvinyl alcohol according to the mass ratio of 1: 5-7, the molar ratio of boron in the boron removing agent and the guanidine gum fracturing flow-back fluid is (1-15) to 20, and the reaction time is about 10-15 min.
The used acid is citric acid, and the concentration of the citric acid is about 100-300 mg/L.
The standing time is about 30-35 min.
Referring to fig. 1, the mechanism of boron removal by chemical agents is: boric acid can be hydrolyzed in the solution to generate boron ions, which is beneficial to the generation of the boron ions under the alkaline condition, so that the pH value of the flowback liquid is adjusted to be alkaline, then a well-compounded boron remover is added, polyacrylamide is used for flocculating and precipitating guar splits, meanwhile, polyvinyl alcohol and ortho-cis hydroxyl in the guar undergo a complex reaction to generate a complex, the complex can form a net with the guar splits through the net catching effect, and the precipitate can be formed under the action of gravity after the net grows to a certain volume, thereby achieving the effect of removing the boron ions in the solution.
The boron removing device adopts an ion exchange method to remove boron, and the mechanism of boron removal by the ion exchange method is as follows: the LSC-800 boron selective chelating resin is a styrene series macroporous chelating resin with an N-methyl glucose amino structure. The polyvalent alcohol group part in the chemical structure can generate complex anions with boron, and the amine group part of the chemical structure is used as an anion exchange group to capture the generated complex anions, so that boron is selectively adsorbed.
For the flowback liquid with the boron content of 8-20 mg/L, a chemical agent-coupled ion exchange technology is adopted; for the flowback fluid with the boron content lower than 8mg/L, only chemical agents are needed for treatment.
The following are specific examples.
Example 1
The test is carried out in an oil field of Ordos and the treatment capacity of the equipment is 20m3H is used as the reference value. Chemical agentThe process flow for boron removal is shown in figure 2.
The clear water after the above process flow is treated by a boron removal device, and the specific process flow is shown in fig. 3.
Referring to fig. 2 and 3, the specific process flow is as follows: raw water firstly enters a coalescence degreaser, the coalescence degreaser performs coarse graining degreasing, and oil-containing waste water flows through the coalescence filler, under the dual functions of wetting coalescence and collision coalescence, oil drops are made to float to the water surface from small to large, and are discharged into an oil collecting tank through an oil discharge pipe.
The water from the coalescence degreaser automatically flows into a micro-electrolysis oxidation device, and the generated nascent state [ H ] is utilized through the electrochemical reaction generated by the potential difference of the electrolysis filler]And Fe2+The oxidation-reduction reaction is carried out with the waste liquid component, so that high molecular organic matters such as guanidine gum and the like in the oil field fracturing waste water can be subjected to chain scission and gel breaking to achieve the effects of removing emulsified oil, reducing viscosity, decoloring and removing heavy metals, meanwhile, the agents prepared by the NaOH dosing tank and the PAC dosing tank are added into the box, the opening degree of each dosing pump is controlled, and the prepared agents are guaranteed to be added in about 5 hours.
And (3) water flowing out of the micro-electrolysis oxidation box enters a fast and slow stirring tank, and a medicament prepared by the PAM medicament adding tank is added into the tank, so that the prepared medicament is ensured to be added in about 5 hours.
The water flowing out of the fast and slow stirring tank flows into a separation unit, and the main equipment is an inclined tube sedimentation tank. The method is mainly based on the shallow layer sedimentation theory, suspended impurities in water are precipitated in the inclined tube, sludge slides downwards to the bottom of the tank along the inclined tube under the action of gravity, and then is discharged to a sludge tank in a centralized manner.
The water flowing out of the inclined tube sedimentation tank automatically flows into a water tank and enters a filtering unit through a water pump, the core of the filtering unit comprises a peach shell filter, a multi-media filter and a flat membrane filter which are sequentially connected, and clear water is obtained after filtering.
The clear water is used for secondary liquid preparation after reaching the standard after being adsorbed by resin, and the adsorption device adopts a vehicle-mounted device and returns to the base for regeneration after being adsorbed and saturated. And (3) regenerating by passing hydrochloric acid with the mass concentration of 5% through a column, washing with water, and adjusting the pH value of the effluent of the resin column to be neutral. Adding lime into the regenerated liquid to precipitate calcium borate, filtering out the calcium borate precipitate, and discharging the clear liquid after resin adsorption.
The specific test is as follows: 500mL of guanidine gum fracturing flow-back fluid taken from an on-site well-1 is measured and put in a beaker, and the boron ion concentration of raw water is 18.95mg/L through determination of curcumin spectrophotometry. The calcium ion concentration is 365.5mg/L and the suspended matter content is 120.9 mg/L. The dosage of each agent is determined based on the concentration of the measured ions.
Firstly, adding an oxidant hydrogen peroxide (with the mass concentration of 0.1%) into a sodium hydroxide dosing tank, wherein the addition amount of the oxidant hydrogen peroxide is 0.1% of the mass of the guanidine gum fracturing flow-back fluid, then adding a calcium-magnesium ion precipitator sodium carbonate, the addition amount of the calcium-magnesium ion precipitator sodium carbonate is carried out according to the molar ratio of 1: 1 to calcium-magnesium ions in the flow-back fluid, adjusting the pH value of the solution to 10 by using a sodium hydroxide aqueous solution with the mass concentration of 4%, and reacting for 10min at room temperature. And then adding a prepared inorganic flocculant polyaluminum chloride solution into a PAC dosing tank, wherein the addition amount of the inorganic flocculant in each 1L of guanidine gum fracturing flow-back fluid is 800 mg/L. And finally, adding a boron removing agent into the PAM dosing tank, wherein the adding amount of the boron removing agent is 1: 20 of the molar ratio of the boron removing agent to boron in the flowback fluid, and adding an antifoaming agent which is 0.1% of the mass of the guanidine gum fracturing flowback fluid (the antifoaming agent is not added, and the antifoaming agent is preferably added). And finally, regulating the pH value of the solution to 7 by using a 300mg/L citric acid solution, standing for 30min, taking the treated supernatant for measurement, and measuring to obtain the product with the boron content reduced to 9.56mg/L, the calcium ion reduced to 65.80mg/L and the suspended matter reduced to 16.5 mg/L. And then, a boron removal device is used for processing, and finally the boron content is measured to be 2.85mg/L, namely the requirement of secondary liquid preparation is met.
Example 2
500mL of fracturing flow-back fluid taken from an on-site well-2 is measured and put in a beaker, the boron content is 17.36mg/L measured by a curcumin spectrophotometry, the calcium ion content is 310.23mg/L measured by a titration method, and the content of suspended matters is 170.66 mg/L. The dosage of each agent is determined according to the measured ion content.
Firstly, adding an oxidant sodium hypochlorite solution (with the mass concentration of 0.1%) into a sodium hydroxide dosing tank, wherein the addition amount of the oxidant sodium hypochlorite solution is 0.08% of the mass of the guanidine gum fracturing flow-back fluid, then adding a calcium magnesium ion precipitator sodium carbonate, the addition amount of the calcium magnesium ion precipitator sodium carbonate is performed according to the molar ratio of 1: 1 to calcium magnesium ions in the flow-back fluid, adjusting the pH value of the solution to 9.5 by using a sodium hydroxide aqueous solution with the mass concentration of 4%, and reacting for 12min at room temperature. And then adding a prepared inorganic flocculant polyaluminum chloride solution into a PAC dosing tank, wherein the addition amount of the inorganic flocculant in each 1L of guanidine gum fracturing flow-back fluid is 800 mg/L. And finally, adding a boron remover (the boron remover is a mixture of polyvinyl alcohol with the molecular weight of 7: 1 and 1400 ten thousand polyacrylamide) into the PAM dosing tank, wherein the molar ratio of the boron remover to boron in the flowback fluid is 15: 20, and adding an antifoaming agent which is 0.1% of the mass of the guanidine gum fracturing flowback fluid (the antifoaming agent is not added, and the antifoaming agent is preferably added). And finally, regulating the pH value of the solution to 6 by using a 300mg/L citric acid solution, standing for 35min, taking the treated supernatant for measurement, and measuring to obtain the product with the boron content reduced to 9.56mg/L, the calcium ion reduced to 65.80mg/L and the suspended matter reduced to 16.5 mg/L. And then, a boron removal device is used for processing, and finally the boron content is measured to be 2.85mg/L, namely the requirement of secondary liquid preparation is met.
The experiment is carried out in a laboratory, and after treatment of chemical agents, the boron content is measured to be 8.69mg/L, the calcium ion content is reduced to 58.93mg/L, and the suspended matters are reduced to 17.9 mg/L. Then, a boron removal device is used for processing, the finally measured boron content is 1.96mg/L, and the requirement of secondary liquid preparation is also met.
Example 3
500mL of fracturing flowback fluid retrieved from the in-situ well-3 was measured in a beaker, and the boron content was 19.65mg/L as measured by curcumin spectrophotometry, the calcium ion content was 1000.5mg/L as measured by titration, and the suspended matter content was 230.6 mg/L. The dosage of each agent is determined according to the measured ion content.
Firstly, adding an oxidant hydrogen peroxide (with the mass concentration of 0.1%) into a sodium hydroxide dosing tank, wherein the addition amount of the oxidant hydrogen peroxide is 0.1% of the mass of the guanidine gum fracturing flow-back fluid, then adding a calcium-magnesium ion precipitator sodium sulfate, the addition amount of the calcium-magnesium ion precipitator sodium sulfate is carried out according to the molar ratio of the calcium-magnesium ion precipitator sodium sulfate to the calcium-magnesium ion in the flow-back fluid of 1: 1, adjusting the pH value of the solution to 10 by using a sodium hydroxide aqueous solution with the mass concentration of 4%, and reacting for 8min at room temperature. And then adding a prepared inorganic flocculant polyaluminum chloride solution into a PAC dosing tank, wherein the addition amount of the inorganic flocculant in each 1L of the guanidine gum fracturing flow-back fluid is 500 mg/L. And finally, adding a boron remover into a PAM dosing box, wherein the boron remover is a mixture of polyvinyl alcohol with the molecular weight of 5: 1 and 1400 ten thousand polyacrylamide, the molar ratio of the boron remover to boron in the return liquid is 5: 20, finally, adjusting the pH of the solution to 7 by using a 300mg/L citric acid solution, standing for 30min, taking the treated supernatant for determination, and determining that the boron content is reduced to 9.56mg/L, the calcium ion is reduced to 65.80mg/L, and the suspended matter is reduced to 16.5 mg/L. And then, a boron removal device is used for processing, and finally the boron content is measured to be 2.85mg/L, namely the requirement of secondary liquid preparation is met.
The experiment is carried out in a laboratory, and after treatment by chemical agents, the boron content is measured to be 9.36mg/L, the calcium ion content is reduced to 108.16mg/L, and the suspended matter content is reduced to 17.9 mg/L. Then, a boron removal device is used for processing, the finally measured boron content is 2.85mg/L, and the requirement of secondary liquid preparation is also met.
Example 4
500mL of fracturing flow-back fluid taken from an on-site well-4 is measured and put in a beaker, the boron content is 18.21mg/L as measured by a curcumin spectrophotometry, the calcium ion content is 439.65mg/L as measured by a titration method, the suspended matter content is 198.76mg/L, and the addition of each medicament is determined according to the measured ion content.
Firstly, adding an oxidant hydrogen peroxide (with the mass concentration of 0.1%) into a sodium hydroxide dosing tank, wherein the addition amount of the oxidant hydrogen peroxide is 0.15% of the mass of the guanidine gum fracturing flow-back fluid, then adding a calcium-magnesium ion precipitator sodium carbonate, the addition amount of the calcium-magnesium ion precipitator sodium carbonate is performed according to the molar ratio of 1: 2 to calcium-magnesium ions in the flow-back fluid, adjusting the pH value of the solution to 10 by using a sodium hydroxide aqueous solution with the mass concentration of 4%, and reacting for 10min at room temperature. And then adding a prepared inorganic flocculant polyaluminum chloride solution into a PAC dosing tank, wherein the addition amount of the inorganic flocculant in each 1L of guanidine gum fracturing flow-back fluid is 600 mg/L. And finally, adding a boron remover into a PAM dosing box, wherein the boron remover is a mixture of polyvinyl alcohol with the molecular weight of 6: 1 and 1400 ten thousand polyacrylamide, the molar ratio of the boron remover to boron in the return liquid is 10: 20, finally, adjusting the pH of the solution to 7 by using a 300mg/L citric acid solution, standing for 32min, taking the treated supernatant for determination, and determining that the boron content is reduced to 9.56mg/L, the calcium ion is reduced to 65.80mg/L, and the suspended matter is reduced to 16.5 mg/L. And then, a boron removal device is used for processing, and finally the boron content is measured to be 2.85mg/L, namely the requirement of secondary liquid preparation is met.
The experiment is carried out in a laboratory, and after treatment by chemical agents, the boron content is measured to be 8.46mg/L, the calcium ion content is reduced to 78.16mg/L, and the suspended matter content is reduced to 14.3 mg/L. Then, a boron removal device is used for processing, the finally measured boron content is 2.62mg/L, and the requirement of secondary liquid preparation is also met.
Example 5
500mL of fracturing flow-back fluid taken from an on-site well-5 is measured and put in a beaker, the boron content is 7.13mg/L measured by a curcumin spectrophotometry, the calcium ion content is 190.38mg/L measured by a titration method, the content of suspended matters is 108.82mg/L, and the addition of each medicament is determined according to the measured ion content.
Firstly, adding an oxidant hydrogen peroxide (with the mass concentration of 0.1%) into a sodium hydroxide dosing tank, wherein the addition amount of the oxidant hydrogen peroxide is 0.1% of the mass of the guanidine gum fracturing flow-back fluid, then adding a calcium-magnesium ion precipitator sodium carbonate, the addition amount of the calcium-magnesium ion precipitator sodium carbonate is carried out according to the molar ratio of 1: 1 to calcium-magnesium ions in the flow-back fluid, adjusting the pH value of the solution to 10 by using a sodium hydroxide aqueous solution with the mass concentration of 4%, and reacting for 10min at room temperature. And then adding a prepared inorganic flocculant polyaluminum chloride solution into a PAC dosing tank, wherein the addition amount of the inorganic flocculant in each 1L of guanidine gum fracturing flow-back fluid is 700 mg/L. And finally, adding a boron removing agent into a PAM dosing box, wherein the adding amount of the boron removing agent is 1: 20 according to the molar ratio of the boron in the flowback liquid, finally, adjusting the pH value of the solution to 6.5 by using a 300mg/L citric acid solution, standing for 30min, taking the treated supernatant for measurement, and measuring to obtain the product with the boron content reduced to 9.56mg/L, the calcium ion reduced to 65.80mg/L and the suspended matter reduced to 16.5 mg/L. And then, a boron removal device is used for processing, and finally the boron content is measured to be 2.85mg/L, namely the requirement of secondary liquid preparation is met.
The experiment is carried out in a laboratory, after the treatment of chemical agents, the boron content is measured to be 2.86mg/L, the calcium ion content is reduced to 28.18mg/L, the suspended matters are reduced to 13.3mg/L, and the requirement of secondary liquid preparation is also met.
The fracturing flow-back fluid of five wells is treated by the method, and a chemical agent-coupled ion exchange technology is adopted for the flow-back fluid with the boron content of 8-20 mg/L; for the flowback fluid with the boron content lower than 8mg/L, only chemical agents are needed for treatment. The treated flow-back liquid finally meets the requirement of secondary liquid preparation, which shows that the invention has universal applicability.
Claims (10)
1. The method for removing boron ions in fracturing flow-back fluid is characterized by adding an oxidant and a calcium-magnesium ion precipitator into guanidine gum fracturing flow-back fluid, adjusting the pH to 9.5-10, reacting until calcium-magnesium ions are completely precipitated, adding an inorganic flocculant and a boron removal agent, reacting for 10-15 min, adjusting the pH to 6-7, standing, filtering to obtain liquid, and finishing the purpose of removing boron ions in the fracturing flow-back fluid.
2. The method for removing boron ions in the fracturing flow-back fluid as claimed in claim 1, wherein the amount of boron in the fracturing flow-back fluid is less than or equal to 20mg per 1L of guar gum.
3. The method for removing boron ions in fracturing flow-back fluid according to claim 1, wherein when the amount of boron in 1L of guar gum fracturing flow-back fluid is more than 8mg and less than or equal to 20mg, boron in the fracturing flow-back fluid is removed by the boron removal device, so that the purpose of removing boron ions in the fracturing flow-back fluid is achieved.
4. The method for removing boron ions in the fracturing flow-back fluid according to claim 1, wherein the oxidant is hydrogen peroxide or sodium hypochlorite, and the mass concentration of the hydrogen peroxide in the hydrogen peroxide is 0.1%; the amount of the oxidant is 0.08-0.15% of the mass of the guanidine gum fracturing flow-back fluid.
5. The method for removing boron ions in the fracturing flow-back fluid as claimed in claim 1, wherein the calcium-magnesium ion precipitator is sodium carbonate or sodium sulfate, and the molar ratio of the amount of the precipitator to the total amount of calcium-magnesium ions in the guargum fracturing flow-back fluid is 1: 1-2.
6. The method for removing boron ions in the fracturing flow-back fluid as claimed in claim 1, wherein the pH is adjusted to 9.5-10 by using a sodium hydroxide aqueous solution with a mass concentration of 4%.
7. The method for removing boron ions in the fracturing flow-back fluid according to claim 1, wherein the inorganic flocculant is an aqueous solution of polyaluminum chloride, and the addition amount of the inorganic flocculant in each 1L of the guar gum fracturing flow-back fluid is 500-800 mg/L.
8. The method for removing boron ions in the fracturing flow-back fluid as claimed in claim 1, wherein the boron remover is a mixture of polyvinyl alcohol with a molecular weight ratio of (5-7): 1 and 1400 ten thousand of polyacrylamide.
9. The method for removing boron ions in the fracturing flow-back fluid as claimed in claim 1, wherein the molar ratio of the boron remover to the boron in the guargum fracturing flow-back fluid is (1-15) to 20.
10. The method for removing boron ions in the fracturing flow-back fluid as claimed in claim 1, wherein the pH is adjusted to 6-7 by using a citric acid solution with a concentration of 100-300 mg/L; the standing time is 30-35 min.
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