CN111453873B

CN111453873B - Treatment method of fracturing flowback fluid

Info

Publication number: CN111453873B
Application number: CN201910048170.XA
Authority: CN
Inventors: 陈天欣; 王兴睿; 胡金燕; 朱进; 雷宇; 易畅; 银小兵; 向启贵
Original assignee: Petrochina Co Ltd
Current assignee: Petrochina Co Ltd
Priority date: 2019-01-18
Filing date: 2019-01-18
Publication date: 2022-10-04
Anticipated expiration: 2039-01-18
Also published as: CN111453873A

Abstract

The invention discloses a method for treating fracturing flow-back fluid, and belongs to the technical field of water treatment. The method is applied to a treatment system which comprises a lift pump, a first reaction tank, a second reaction tank, a concentration tank, a tubular microfiltration unit and a reverse osmosis unit. In the embodiment of the invention, for the fracturing flow-back fluid collected in the flow-back tank, the detection result of the fracturing flow-back fluid can be obtained firstly, and then the specific treatment is carried out based on the detection result. When the total iron concentration is less than the first concentration threshold value, the petroleum pollutant concentration is less than the second concentration threshold value, and the COD concentration is less than the third concentration threshold value, the chemical dosing treatment of the fracturing flow-back fluid can be realized through the first reaction tank and the second reaction tank. And then, the buffer precipitation is carried out through the concentration tank, the microfiltration of the tubular microfiltration unit and the desalination treatment of the reverse osmosis unit realize the treatment of the fracturing flow-back fluid, so that the limitation of the external environment is avoided, and the treatment cost of the fracturing flow-back fluid is reduced.

Description

Treatment method of fracturing flowback fluid

Technical Field

The invention relates to the technical field of water treatment, in particular to a method for treating fracturing flow-back fluid.

Background

Shale gas refers to unconventional natural gas which is added into shale rich in organic matters and interlayers thereof and mainly exists in an adsorption state and a free state. Because the shale gas is a clean and efficient energy resource and chemical raw material, the shale gas becomes a widely applied gas source. However, in the process of exploiting the shale gas, especially when the fracturing fluid is used for fracturing exploitation of the shale gas, about 15% -75% of the fracturing fluid returns along with the shale gas to form fracturing flow-back fluid, also called flow-back wastewater. Because the fracturing flow-back fluid comprises formation underground water, fracturing fluid, drill cuttings and the like, the fracturing flow-back fluid has the characteristics of high salinity, high chroma, poor biodegradability, difficult treatment and the like, if the fracturing flow-back fluid is directly discharged, the dissolved oxygen content in the water body is easily reduced, and destructive influence is caused on the ecological environment of the water body.

In the related technology, the fracturing flow-back fluid can be treated in the modes of natural evaporation treatment, freeze thawing treatment, filtration treatment, distillation treatment and the like, so that the direct discharge of the fracturing flow-back fluid is avoided, and the destructive influence on the ecological environment of a water body is avoided. Wherein, the natural evaporation treatment refers to that the flowback liquid is naturally evaporated by sunlight to remove water, and the residual salts and sludge are solidified. The freeze-thaw treatment is to freeze the fracturing flow-back fluid below the freezing point to freeze, precipitate salt due to the reduction of solubility, reduce the salt concentration of ice, and heat and melt the ice to obtain low-concentration brine, thereby realizing the separation of salt and water. The filtration treatment means removal of mechanical impurities/suspended matters and the like by a filter and/or activated carbon. The distillation treatment refers to heating the fracturing flow-back fluid by utilizing different boiling points of solid-liquid components so as to evaporate water and realize solid-liquid separation.

The designer finds that the related art has at least the following technical problems:

the natural evaporation treatment has small treatment capacity and long treatment period, and is greatly limited by temperature and land; the freezing and thawing treatment is limited by geographical climate, and needs enough freezing weather, which is not beneficial to industrialized treatment; the filtration treatment is limited by the aperture of the filter pores of the filter, and bacteria in the fracturing flow-back fluid can generate turbid liquid, so that the filter is easily blocked; the distillation treatment requires condensation and recycling of distilled water, thereby increasing economic cost.

Disclosure of Invention

The invention provides a method for treating fracturing flowback fluid, which can solve the problem of environmental limitation during treatment of the fracturing flowback fluid. The technical scheme is as follows:

in a first aspect, a method for treating a fracturing flow-back fluid is provided, the method is applied to a treatment system, the treatment system comprises a lift pump, a first reaction tank, a second reaction tank, a concentration tank, a tubular microfiltration unit and a reverse osmosis unit, and the method comprises the following steps:

obtaining a detection result of the fracturing flow-back fluid in the flow-back tank, wherein the detection result comprises total iron concentration, petroleum pollutant concentration and COD (Chemical Oxygen Demand) concentration;

when the total iron concentration is less than a first concentration threshold value and the petroleum pollutant concentration is less than a second concentration threshold value, the lift pump conveys the fracturing flow-back fluid to the first reaction tank;

adding a coagulant and sodium hydroxide into the fracturing flow-back fluid collected by the first reaction tank to obtain a first reaction liquid, and conveying the first reaction liquid to the second reaction tank;

when the COD concentration is less than a third concentration threshold value, adding sodium carbonate into the first reaction liquid collected by the second reaction tank to obtain a second reaction liquid, and conveying the second reaction liquid to the concentration tank;

the concentration tank is used for carrying out buffer precipitation on the second reaction liquid, and concentrated clear liquid at the upper part in the concentration tank after buffer precipitation is conveyed to the tubular microfiltration unit;

the tubular microfiltration unit is used for performing microfiltration on the concentrated clear liquid, conveying the microfiltration clear liquid obtained after microfiltration to the reverse osmosis unit, and refluxing the microfiltration turbid liquid obtained after microfiltration to the concentration tank;

and the reverse osmosis unit is used for desalting the microfiltration clear liquid after microfiltration.

Optionally, after the delivering the first reaction liquid to the second reaction tank, the method further includes:

when the COD concentration is greater than the third concentration threshold value, adding sodium carbonate and sodium hypochlorite into the first reaction liquid collected by the second reaction tank to obtain a third reaction liquid, and conveying the third reaction liquid to the concentration tank;

the concentration tank is used for carrying out buffer precipitation on the third reaction liquid, and concentrated clear liquid at the upper part in the concentration tank after buffer precipitation is conveyed to the tubular microfiltration unit;

adding sodium sulfite into the microfiltration clear liquid collected by the reverse osmosis unit to neutralize the sodium hypochlorite in the microfiltration clear liquid;

and the reverse osmosis unit is used for desalting the micro-filtered clear liquid after neutralization according to a mode of desalting the micro-filtered clear liquid after micro-filtration.

Optionally, the processing system further includes an aeration tank, and after obtaining the detection result of the fracturing flow-back fluid in the flow-back tank, the processing system further includes:

when the total iron concentration is greater than the first concentration threshold value and/or the petroleum pollutant concentration is greater than the second concentration threshold value, the lift pump conveys the fracturing flow-back fluid to the aeration tank, the aeration tank is aerated, and the aerated fracturing flow-back fluid is conveyed to the first reaction tank;

adding the coagulant and sodium hydroxide into the fracturing flow-back fluid collected by the first reaction tank to obtain a fourth reaction liquid, and conveying the fourth reaction liquid to the second reaction tank;

when the COD concentration is smaller than the third concentration threshold value, adding sodium carbonate into a fourth reaction liquid collected by the second reaction tank to obtain a fifth reaction liquid, and conveying the fifth reaction liquid to the concentration tank;

the concentration tank is used for carrying out buffer precipitation on the fifth reaction liquid, and concentrated clear liquid at the upper part in the concentration tank after buffer precipitation is conveyed to the tubular microfiltration unit;

and the reverse osmosis unit is used for desalting the microfiltration clear liquid obtained after microfiltration.

Optionally, after the delivering the fourth reaction liquid to the second reaction tank, the method further includes:

when the COD concentration is greater than the third concentration threshold value, adding sodium carbonate and sodium hypochlorite into a fourth reaction liquid collected by the second reaction tank to obtain a sixth reaction liquid, and conveying the sixth reaction liquid to the concentration tank;

the concentration tank is used for carrying out buffer precipitation on the sixth reaction liquid, and concentrated clear liquid at the upper part in the concentration tank after buffer precipitation is conveyed to the tubular microfiltration unit;

and the reverse osmosis unit is used for desalting the micro-filtered clear liquid after neutralization in a manner of desalting the micro-filtered clear liquid after micro-filtration.

Optionally, the tubular microfiltration unit comprises a first high pressure pump and a tubular microfiltration membrane;

the tubular microfiltration unit is right concentrate clear solution micro filtration to carry the microfiltration clear solution that obtains after will micro filtration to reverse osmosis unit, the dirty liquid of micro filtration that obtains after will micro filtration flows back to concentrate the jar, include:

the first high-pressure pump conveys the concentrated clear liquid in the concentration tank to the tubular microfiltration membrane;

and (3) conveying the microfiltration clear liquid obtained after microfiltration by the tubular microfiltration membrane to the reverse osmosis unit, and refluxing the microfiltration turbid liquid obtained after microfiltration to the concentration tank.

Optionally, the tubular microfiltration unit further comprises a water storage tank;

the microfiltration clear liquid obtained after the microfiltration of the tubular microfiltration membrane is conveyed to the reverse osmosis unit and comprises the following components:

the microfiltration clear liquid obtained after microfiltration by the tubular microfiltration membrane is conveyed to the water storage tank for storage;

and when the liquid level of the microfiltration clear liquid stored in the water storage tank is greater than a liquid level threshold value, conveying the microfiltration clear liquid obtained after the microfiltration of the tubular microfiltration membrane to the reverse osmosis unit.

Optionally, the reverse osmosis unit comprises a buffer tank, a second high pressure pump, a cartridge filter, and a reverse osmosis tank;

the reverse osmosis unit carries out desalination treatment on the microfiltration clear liquid and comprises:

adding a chemical agent into the microfiltration clear liquid collected in the buffer tank to adjust the pH value of the microfiltration clear liquid, wherein the pH value of the adjusted microfiltration clear liquid is more than or equal to 7 and less than or equal to 8;

the second high-pressure pump conveys the micro-filtration clear liquid adjusted in the buffer tank to the cartridge filter for filtration;

and conveying the filtered filtrate to the reverse osmosis tank, and separating by using a reverse osmosis membrane arranged in the reverse osmosis tank.

Optionally, the treatment system further comprises a sludge thickening tank and a plate and frame filter press, and the method further comprises:

conveying concentrated turbid liquid at the lower part in the concentration tank to the sludge concentration tank;

adding a flocculating agent into the concentrated turbid liquid collected by the sludge concentration tank to obtain a flocculated turbid liquid, and conveying the flocculated turbid liquid to the plate-and-frame filter press;

and the plate-and-frame filter press is used for carrying out solid-liquid separation on the flocculated turbid liquid, and refluxing the separated turbid liquid to the concentration tank.

Optionally, the flocculant is polyacrylamide, and the addition amount of the flocculant in each liter of concentrated turbid liquid in the sludge concentration tank is 1-3 mg.

In a second aspect, a method for treating a fracturing flow-back fluid is provided, and the method is applied to a treatment system, wherein the treatment system comprises a lift pump, a first reaction tank, a first dosing tank, a second reaction tank, a third dosing tank, a concentration tank, a tubular microfiltration unit, a reverse osmosis unit and a processor, and the method comprises the following steps:

the processor acquires the detection result of the fracturing flow-back fluid in the flow-back tank, wherein the detection result comprises the total iron concentration, the petroleum pollutant concentration and the COD concentration;

when the processor determines that the total iron concentration is less than a first concentration threshold and the petroleum-based pollutant concentration is less than a second concentration threshold, controlling the lift pump to convey the fracturing flow-back fluid to the first reaction tank;

the processor respectively controls the first dosing tank and the second dosing tank to add coagulant and sodium hydroxide into the fracturing flow-back liquid collected by the first reaction tank, and when the reaction duration in the first reaction tank is equal to a first time domain value, the first reaction tank is controlled to convey the first reaction liquid obtained after the reaction to the second reaction tank;

when the processor determines that the COD concentration is smaller than a third concentration threshold value, controlling the third dosing box to add sodium carbonate into the first reaction liquid collected by the second reaction tank, and when the reaction time length in the second reaction tank is equal to the first time threshold value, controlling the second reaction tank to convey the second reaction liquid obtained after the reaction to the concentration tank;

when the processor detects that the time of the second reaction liquid buffered precipitation performed by the concentration tank is equal to a second time threshold value, the concentrated clear liquid at the upper part in the concentration tank after buffered precipitation is controlled to be conveyed to the tubular microfiltration unit;

the processor controls the tubular microfiltration unit to carry out microfiltration on the concentrated clear liquid, and conveys the microfiltration clear liquid obtained after microfiltration to the reverse osmosis unit, and reflows the microfiltration turbid liquid obtained after microfiltration to the concentration tank;

and the processor controls the reverse osmosis unit to carry out desalination treatment on the microfiltration clear liquid after microfiltration.

The technical scheme provided by the invention has the beneficial effects that at least:

in the embodiment of the invention, for the fracturing flow-back fluid collected in the flow-back tank, the detection result of the fracturing flow-back fluid can be obtained firstly, and then the specific treatment is carried out based on the detection result. When the total iron concentration is less than the first concentration threshold value, the petroleum pollutant concentration is less than the second concentration threshold value, and the COD concentration is less than the third concentration threshold value, the chemical dosing treatment of the fracturing flow-back fluid can be realized through the first reaction tank and the second reaction tank. And then, the buffer precipitation is carried out through the concentration tank, the microfiltration of the tubular microfiltration unit and the desalination treatment of the reverse osmosis unit realize the treatment of the fracturing flow-back fluid, so that the limitation of the external environment is avoided, and the treatment cost of the fracturing flow-back fluid is reduced.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic flow chart of a method for treating a fracturing flow-back fluid according to an embodiment of the present invention;

fig. 2 is a schematic flow chart of another method for treating a fracturing flow-back fluid according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a schematic flow chart of a method for treating a fracturing flow-back fluid according to an embodiment of the present invention. The method is applied to a treatment system which comprises a lift pump, a first reaction tank, a second reaction tank, a concentration tank, a tubular microfiltration unit and a reverse osmosis unit. As shown in fig. 1, the method includes the following steps.

Step 101: and obtaining a detection result of the fracturing flow-back fluid in the flow-back tank.

To the fracturing flow-back fluid of collecting in the flow-back pond, can be detected the quality of water of fracturing flow-back fluid by the operating personnel to obtain the testing result of fracturing flow-back fluid, and then can carry out pertinence processing based on the testing result, with the treatment effect that improves fracturing flow-back fluid.

The detection result can comprise total iron concentration, petroleum pollutant concentration and COD concentration, wherein the total iron concentration is the sum of ferrous ion concentration and ferric ion concentration, and the petroleum pollutant concentration refers to the concentration of oil pollutants contained in drilling fluid leaked in the fracturing flow-back fluid in the exploitation process of an oil-gas well.

Step 102: and when the total iron concentration is less than a first concentration threshold value and the petroleum pollutant concentration is less than a second concentration threshold value, the fracturing flow-back fluid is conveyed to the first reaction tank by the lifting pump.

When total iron concentration is less than the first concentration threshold value, and petroleum class pollutant concentration is less than the second concentration threshold value, it all is less to show that the fracturing returns the communicating pipe way between export and the first retort of elevator pump and start the elevator pump this moment to return the flowing back liquid with the fracturing and carry to first retort.

Wherein the first concentration threshold may be 1.2 mg/l and the second concentration threshold may be 10 mg/l.

It should be noted that, when the total iron concentration is greater than the first concentration threshold value, and/or the petroleum pollutant concentration is greater than the second concentration threshold value, it indicates that the concentration of the iron-containing pollutant and/or the petroleum pollutant in the fracturing flow-back fluid is greater, at this time, the treatment system may further include an aeration tank, so that the lift pump may first convey the fracturing flow-back fluid to the aeration tank, perform aeration in the aeration tank, and convey the aerated fracturing flow-back fluid to the first reaction tank, so as to promote the ferrous ions and ferric ions in the fracturing flow-back fluid, and the petroleum pollutant to perform preliminary oxidation through the aeration of the fracturing flow-back fluid, and then convey the fracturing flow-back fluid to the first reaction tank, so as to facilitate subsequent treatment of the fracturing flow-back fluid. When the fracturing flow-back fluid is aerated in the aeration tank, pure oxygen or air can be used as an air source, which is not limited in the embodiment of the invention.

Step 103: adding a coagulant and sodium hydroxide into the fracturing flow-back fluid collected by the first reaction tank to obtain a first reaction liquid, and conveying the first reaction liquid to the second reaction tank.

Specifically, a communication pipeline between the first dosing tank and the first reaction tank and a communication pipeline between the second dosing tank and the second reaction tank may be conducted, and then coagulant and sodium hydroxide may be added to the fracturing flow-back fluid collected in the first reaction tank according to the set coagulant addition amount and sodium hydroxide addition amount. When the reaction duration in the first reaction tank is not less than the first time threshold value, a communicating pipeline between the first reaction tank and the second reaction tank is conducted so as to convey the first reaction liquid obtained in the first reaction tank to the second reaction tank.

Wherein, the first time threshold may be 3 minutes or 5 minutes, etc. The coagulant can be ferric chloride or other chemical substances, the addition amount of the ferric chloride can be 1-20 mg and the addition amount of the sodium hydroxide can be 50-800 mg in each liter of fracturing flow-back fluid, and the pH value of the obtained first reaction liquid is not less than 10, so that the effect of softening the water quality is achieved. In the embodiment of the invention, the stirring mechanism can be arranged in the first reaction tank, so that after the coagulant and the sodium hydroxide are added into the first reaction tank, the sufficiency of the reaction of the fracturing flow-back fluid, the coagulant and the sodium hydroxide and the generation rate of the first reaction liquid can be ensured under the stirring action of the stirring mechanism.

A booster pump can be arranged between the first reaction tank and the second reaction tank so as to convey the first reaction liquid obtained in the first reaction tank to the second reaction tank. Of course, the first reaction solution obtained in the first reaction tank may also flow to the second reaction tank by itself, which is not limited in the embodiment of the present invention.

For example, after a fracturing flow-back fluid formed after flow-back of a certain oil and gas well is conveyed to a first reaction tank through a lift pump, 15 milligrams of ferric chloride and 200 milligrams of sodium hydroxide can be added into each liter of fracturing flow-back fluid, ferric chloride and sodium hydroxide are added into the fracturing flow-back fluid collected by the first reaction tank, and after the reaction time is 2 minutes, a first reaction liquid with a pH value of 10.3 is obtained, and then the first reaction liquid is conveyed to a second reaction tank.

It should be noted that, after the fracturing flow-back fluid is aerated in the aeration tank and the aerated fracturing flow-back fluid is delivered to the fracturing flow-back fluid after the first reaction tank, a coagulant and sodium hydroxide are added to the aerated fracturing flow-back fluid collected in the first reaction tank to obtain a fourth reaction fluid, and the fourth reaction fluid is delivered to the second reaction tank.

Step 104: and when the COD concentration is less than a third concentration threshold value, adding sodium carbonate into the first reaction liquid collected by the second reaction tank to obtain a second reaction liquid, and conveying the second reaction liquid to the concentration tank.

When the COD concentration is smaller than a third concentration threshold value, the COD concentration in the fracturing flow-back fluid is smaller, at the moment, a communication pipeline between the third dosing tank and the second reaction tank can be conducted, and then sodium carbonate is added into the first reaction liquid collected by the second reaction tank according to the set sodium carbonate addition amount. When the reaction duration in the second reaction tank is not less than the first time threshold value, the communication pipeline between the second reaction tank and the concentration tank is conducted so as to convey the second reaction liquid obtained in the second reaction tank to the concentration tank.

Wherein, the adding amount of the sodium carbonate in each liter of the first reaction liquid can be 50-3000 mg. In the embodiment of the invention, the stirring mechanism can be arranged in the second reaction tank, so that after the sodium carbonate is added into the second reaction tank, the sufficiency of the reaction between the first reaction liquid and the sodium carbonate and the generation rate of the second reaction liquid can be ensured under the stirring action of the stirring mechanism.

A booster pump can be arranged between the second reaction tank and the concentration tank to convey the second reaction liquid obtained in the second reaction tank into the concentration tank. Of course, the second reaction solution obtained in the second reaction tank may also flow to the concentration tank by itself, which is not limited in the embodiment of the present invention.

Continuing the above example, in the second reaction tank, sodium carbonate may be added to the first reaction solution collected in the second reaction tank in an amount of 1500 mg of sodium carbonate per liter of the first reaction solution, and after a reaction time of 2 minutes, the second reaction solution is obtained, and then the second reaction solution is transferred to the concentration tank.

When the COD concentration is less than the third concentration threshold, if the first reaction tank transfers the fourth reaction solution to the second reaction tank, sodium carbonate is added to the fourth reaction solution collected by the second reaction tank to obtain a fifth reaction solution, and the fifth reaction solution is transferred to the concentration tank for buffer precipitation.

In addition, when the detection result of the fracturing flow-back fluid includes a COD concentration greater than a third concentration threshold value, which indicates that the COD concentration in the fracturing flow-back fluid is relatively high, and at this time, in order to avoid the COD concentration from affecting the treatment effect of the fracturing flow-back fluid, when the first reaction tank conveys the first reaction liquid to the second reaction tank, sodium carbonate and sodium hypochlorite may be added to the first reaction liquid collected by the second reaction tank, so as to obtain a third reaction liquid, and the third reaction liquid is conveyed to the concentration tank for buffer precipitation. When the first reaction tank conveys the fourth reaction liquid to the second reaction tank, sodium carbonate and sodium hypochlorite can be added into the fourth reaction liquid collected by the second reaction tank to obtain a sixth reaction liquid, and the sixth reaction liquid is conveyed to the concentration tank for buffer precipitation.

Step 105: and the concentration tank carries out buffer precipitation on the second reaction liquid, and concentrated clear liquid at the upper part in the concentration tank after buffer precipitation is conveyed to the tubular microfiltration unit.

Specifically, deposit to the second reaction liquid buffering of collecting in the concentrator tank, and after long not less than second time threshold when buffering the sediment, can obtain concentrated clear liquid in the middle and upper portion in the concentrator tank, and then can switch on the intercommunication pipeline between the clear liquid export of concentrator tank and the water inlet of tubular microfiltration unit to carry the concentrated clear liquid of middle and upper portion in the concentrator tank to tubular microfiltration unit.

The concentrated clear liquid can be clear liquid with the height of more than 1/2 of the height of the second reaction liquid collected in the concentration tank after the time of the buffer precipitation is not less than a second time threshold. The second preset time period may be 10 minutes or 15 minutes, etc. The clear liquid delivery port of concentration jar can be located the high 2/3 eminence of concentration jar to guarantee through the sedimentation of concentration jar after, the concentrated clear liquid in the concentration jar is carried to tubular microfiltration unit.

Further, the treatment system can also comprise a sludge concentration tank and a plate-and-frame filter press, and correspondingly, the treatment method can also comprise the following steps: and conveying the concentrated turbid solution at the lower part of the concentration tank to a sludge concentration tank, adding a flocculating agent into the concentrated turbid solution collected by the sludge concentration tank to obtain a flocculated turbid solution, conveying the flocculated turbid solution to a plate-and-frame filter press, carrying out solid-liquid separation on the flocculated turbid solution by the plate-and-frame filter press, and refluxing the separated turbid solution to the concentration tank.

Based on the treatment method, the concentrated turbid liquid formed after the second reaction liquid in the concentration tank is buffered and precipitated can be treated by the sludge concentration tank and the plate-and-frame filter press, so that the pollution to the environment caused by direct discharge of the concentrated turbid liquid is avoided. The concentrated turbid liquid can be turbid liquid with the height of 1/2 or less in the concentration tank after the buffering and precipitation time of the second reaction liquid collected in the concentration tank is not less than the second time threshold.

Wherein, concentrated jar can be the round platform column structure of handstand, and after the second reaction liquid of collecting is carried out the buffering through concentrated jar like this, the concentration of the concentrated turbid liquid in the concentrated jar increases along with the increase of the degree of depth of concentrated jar to improve the concentration of the concentrated turbid liquid of bottom in the concentrated jar. In addition, because the sectional area of the bottom of the concentration tank is small, concentrated turbid liquid is not promoted to shake when being conveyed to the sludge concentration tank. Then adding a flocculating agent into the concentrated turbid liquid collected by the sludge concentration tank to obtain flocculated turbid liquid under the flocculation action of the flocculating agent, and then conveying the obtained flocculated turbid liquid to a plate-and-frame filter press to perform solid-liquid separation on the flocculated turbid liquid through the plate-and-frame filter press to obtain separated sludge cakes and separated water. The separated water can continuously flow back to the concentration tank along the water outlet of the plate-and-frame filter press to be subjected to circulating treatment, so that the treatment effect of the fracturing flow-back fluid is improved.

Wherein, the concentrate delivery port of concentrated jar can be located the bottommost of concentrated jar to avoid when carrying concentrated turbid liquid to the concentrated jar of mud, the disturbance that causes concentrated clear liquid. The flocculant added into the sludge concentration tank can be polyacrylamide, and the addition amount of the flocculant in each liter of concentrated turbid liquid in the sludge concentration tank can be 1-3 mg. In the embodiment of the invention, the stirring mechanism can be arranged in the sludge concentration tank, so that after the flocculating agent is added into the concentrated turbid liquid collected in the sludge concentration tank, the concentrated turbid liquid can be stirred by the stirring mechanism to accelerate the flocculation of the concentrated turbid liquid, and the stirring power gradient can be controlled to be 20-60 per second.

It should be noted that, when the concentrated clear liquid and the concentrated turbid liquid in the concentration tank are respectively conveyed to the tubular microfiltration unit and the sludge concentration tank, the ratio between the flow rate of the concentrated clear liquid and the flow rate of the concentrated turbid liquid can be controlled within a range of 6 to 1, so as to avoid that the flow rate of the concentrated clear liquid is too large, the load of the tubular microfiltration unit is increased, or the flow rate of the concentrated clear liquid is small, and the treatment efficiency of the fracturing flowback liquid is reduced.

Step 106: and the tubular microfiltration unit is used for performing microfiltration on the concentrated clear liquid, conveying the microfiltration clear liquid obtained after microfiltration to the reverse osmosis unit, and refluxing the microfiltration turbid liquid obtained after microfiltration to the concentration tank.

Specifically, switch on the communicating pipe between the clear solution delivery port of tubular microfiltration unit and the water inlet of reverse osmosis unit, switch on the communicating pipe between the turbid liquid delivery port of tubular microfiltration unit and the backward flow mouth of concentrated jar simultaneously and switch on, later start tubular microfiltration unit to carry out the micro filtration to the concentrated clear solution that carries to the concentrated jar, and carry the microfiltration clear solution that obtains after will micro filtration to reverse osmosis unit, can flow back the microfiltration turbid liquid that obtains after the micro filtration to the concentrated jar.

The tubular microfiltration unit may include a first high-pressure pump and a tubular microfiltration membrane, and accordingly, a specific treatment method for performing microfiltration by the tubular microfiltration unit may be that the first high-pressure pump is started to deliver concentrated clear liquid in the concentration tank to the tubular microfiltration membrane, the microfiltration clear liquid obtained after the tubular microfiltration membrane is subjected to microfiltration is delivered to the reverse osmosis unit, and the microfiltration turbid liquid obtained after the microfiltration flows back to the concentration tank.

Wherein, when carrying out the microfiltration to concentrated clear solution through tubular microfiltration membrane, because tubular microfiltration membrane's the aperture of damming is less, can reach the micron order, consequently, in order to guarantee the microfiltration effect, can be through the concentrated clear solution of first high-pressure pump suction concentration jar in to carry to tubular microfiltration membrane, thereby can improve the pressure of tubular microfiltration membrane's water inlet, and then realize the microfiltration to concentrated clear solution under the high pressure effect. Wherein the cut-off pore size of the tubular microfiltration membrane can be not more than 0.15 micron.

When the microfiltration turbid liquid obtained after tubular microfiltration is used for the microfiltration of the filter membrane flows back to the concentration tank, the backflow port of the concentration tank can be positioned at the lower part so as to avoid the disturbance generated by the microfiltration turbid liquid flowing back to the concentration tank and then on the concentrated clear liquid in the concentration tank.

Furthermore, after the concentrated clear liquid in the concentration tank is subjected to microfiltration through the tubular microfiltration membrane, pollutants are bound to the tubular microfiltration membrane, and the tubular microfiltration membrane can be backwashed in order to avoid the bound pollutants from reducing the microfiltration effect of the tubular microfiltration membrane. In order to avoid waste of water resources, the tubular microfiltration membrane can be backwashed by microfiltration clear liquid obtained after microfiltration in the embodiment of the invention, so that the tubular microfiltration unit can also comprise a water storage tank. The microfiltration clear liquid obtained after the tubular microfiltration membrane microfiltration can be conveyed to a water storage tank for storage, and when the liquid level of the microfiltration clear liquid stored in the water storage tank is greater than a liquid level threshold value, the microfiltration clear liquid obtained after the tubular microfiltration membrane microfiltration is conveyed to a reverse osmosis unit.

When the tubular microfiltration membrane is backwashed, the tubular microfiltration unit can comprise an automatic control system, so that corresponding valves on a clear liquid outlet and a clear liquid inlet of the tubular microfiltration membrane are controlled to be opened or closed through the automatic control system, a backwashing pipeline of the tubular microfiltration membrane is conducted, and then the tubular microfiltration membrane is backwashed through the microfiltration clear liquid stored in the water storage tank.

Step 107: and the reverse osmosis unit is used for desalting the microfiltration clear liquid after microfiltration.

Specifically, the reverse osmosis unit is started to realize the desalination treatment of the microfiltration clear liquid conveyed by the tubular microfiltration unit.

The reverse osmosis unit can comprise a buffer tank, a second high-pressure pump, a security filter and a reverse osmosis tank, correspondingly, a specific treatment method for desalting treatment through the reverse osmosis unit can be that a chemical agent is added into the microfiltration clear liquid collected in the buffer tank to adjust the pH value of the microfiltration clear liquid, the pH value of the adjusted microfiltration clear liquid is greater than or equal to 7 and less than or equal to 8, the second high-pressure pump is started to convey the adjusted microfiltration clear liquid in the buffer tank to the security filter for filtration, the filtrate obtained after filtration is conveyed to the reverse osmosis tank, and the reverse osmosis membrane arranged inside the reverse osmosis tank separates the filtrate obtained after filtration.

Wherein, in order to improve the desalination effect of microfiltration clear liquid to and the inside reverse osmosis membrane that sets up of microfiltration clear liquid to reverse osmosis tank causes destruction when avoiding desalination, can adjust the pH value of microfiltration clear liquid earlier, for example can add sodium hydroxide solution, dilute hydrochloric acid solution, reductant or antisludging agent etc. in the microfiltration clear liquid. And then filtering fine particles with turbidity of more than 1 degree in the microfiltration clear liquid through a cartridge filter so as to avoid scratching the reverse osmosis membrane. The reverse osmosis membrane that sets up in the reverse osmosis jar can be followed the horizontal direction installation, and the filtrating that obtains after the cartridge filter filtration this moment can realize the separation processing under self action of gravity, also is the desalination of realization microfiltration clear liquid promptly.

It should be noted that, when the COD concentration is greater than the third concentration threshold, sodium hypochlorite is added to the first reaction solution collected by the second reaction tank, so that sodium hypochlorite may be remained in the reaction solution generated by the second reaction tank, in order to avoid the remaining sodium hypochlorite to reduce the treatment effect of the fracturing flow-back fluid, after the microfiltration clear liquid obtained by microfiltration of the tubular microfiltration unit is conveyed to the reverse osmosis unit, sodium sulfite may be added to the microfiltration clear liquid collected by the reverse osmosis unit, so as to neutralize the sodium hypochlorite in the microfiltration clear liquid, and the reverse osmosis unit desalinizes the neutralized microfiltration clear liquid in a manner of desalting the microfiltration clear liquid after microfiltration. That is, after the clear liquid of microfiltration that reverse osmosis unit collection tubular micro filtration unit carried, can now add sodium sulfite in the clear liquid of microfiltration to carry out the neutralization to sodium hypochlorite through sodium sulfite, thereby realize the processing to remaining sodium hypochlorite. Then, the microfiltration clear liquid after the microfiltration is desalted according to the above-mentioned method for desalting the microfiltration clear liquid after the microfiltration.

In the embodiment of the invention, for the fracturing flow-back fluid collected in the flow-back tank, the detection result of the fracturing flow-back fluid can be obtained firstly, and then the specific treatment is carried out based on the detection result. When the total iron concentration is less than a first concentration threshold value and the concentration of petroleum pollutants is less than a second concentration threshold value, the fracturing flow-back fluid is conveyed into a first reaction tank by a lifting pump, and coagulant and sodium hydroxide are added into the fracturing flow-back fluid collected by the first reaction tank to obtain a first reaction liquid and conveyed to a second reaction tank. And when the COD concentration is less than a third concentration threshold value, adding sodium carbonate into the first reaction liquid collected by the second reaction tank to obtain a second reaction liquid and conveying the second reaction liquid to the concentration tank. And then, buffer precipitation is performed sequentially through the concentration tank, the concentrated clear liquid after buffer precipitation is subjected to microfiltration through the tubular microfiltration membrane, and the microfiltration clear liquid obtained after microfiltration is subjected to desalination treatment through the reverse osmosis unit, so that the fracturing flow-back fluid is treated, the limitation of the external environment is avoided, and the treatment cost of the fracturing flow-back fluid is reduced. And (3) conveying the concentrated turbid liquid in the concentration tank to a sludge concentration tank, adding a flocculating agent into the concentrated turbid liquid collected by the sludge concentration tank for flocculation treatment, and conveying the concentrated turbid liquid to a plate and frame filter press for solid-liquid separation through the plate and frame filter press, so that the concentration of the concentrated turbid liquid in the concentration tank is reduced. The microfiltration turbid liquid obtained after microfiltration is carried out through the tubular microfiltration membrane can flow back to the concentration tank to be circularly treated, so that the treatment effect of the fracturing flow-back fluid is improved, and the damage to the external environment in the treatment process of the fracturing flow-back fluid is avoided.

Fig. 2 is a schematic flow chart of a method for treating a fracturing flow-back fluid according to an embodiment of the present invention. The method is applied to a treatment system, and the treatment system comprises a lift pump, a first reaction tank, a first dosing tank, a second reaction tank, a third dosing tank, a concentration tank, a tubular microfiltration unit, a reverse osmosis unit and a processor. As shown in fig. 2, the method includes the following steps.

Step 201: the processor obtains the detection result of the fracturing flow-back fluid in the flow-back tank.

After the operator detects the quality of the fracturing flow-back fluid and obtains the detection result of the fracturing flow-back fluid, the data acquisition table is displayed in the display interface controlled by the processor, so that the operator can fill the detection result in the displayed data acquisition table to realize the acquisition of the detection result by the processor.

Certainly, the processor may also obtain the detection result of the fracturing flow-back fluid in other manners, for example, after the detection instrument detects the fracturing flow-back fluid, the detection instrument may directly upload the detection result obtained by the detection to the processor, so as to achieve the obtaining of the detection result by the processor, which is not limited in the embodiment of the present invention.

The detection result comprises total iron concentration, petroleum pollutant concentration and COD concentration, and the total iron concentration is the sum of ferrous ion concentration and ferric ion concentration.

Step 202: and when the processor determines that the total iron concentration is less than a first concentration threshold value and the petroleum pollutant concentration is less than a second concentration threshold value, controlling the lift pump to convey the fracturing flow-back fluid to the first reaction tank.

Specifically, the process implemented in step 202 is controlled by the processor, which is the same as or similar to the implementation process in step 102, and is not repeated herein in the embodiment of the present invention.

Step 203: and when the reaction duration in the first reaction tank is equal to a first time threshold value, the first reaction tank is controlled to convey the first reaction liquid obtained after the reaction to the second reaction tank.

Specifically, the process implemented in step 203 is controlled by the processor, which is the same as or similar to the implementation process in step 103, and is not repeated herein in the embodiment of the present invention.

Step 204: and when the processor determines that the COD concentration is less than a third concentration threshold value, controlling a third dosing tank to add sodium carbonate into the first reaction liquid collected by the second reaction tank, and when the reaction duration in the second reaction tank is equal to a first time domain value, controlling the second reaction tank to convey the second reaction liquid obtained after the reaction to a concentration tank.

Specifically, the process implemented in step 204 is controlled by the processor, which is the same as or similar to the implementation process in step 104, and is not repeated herein in the embodiment of the present invention.

Step 205: and when the processor detects that the time length of the second reaction liquid buffered precipitation of the concentration tank is equal to a second time threshold value, controlling to convey the concentrated clear liquid at the upper part in the concentration tank after the buffered precipitation to the tubular microfiltration unit.

Specifically, the process implemented in step 205 is controlled by the processor, which is the same as or similar to the implementation process in step 105, and is not repeated herein in this embodiment of the present invention.

Step 206: the processor controls the tubular microfiltration unit to carry out microfiltration on the concentrated clear liquid, the microfiltration clear liquid obtained after microfiltration is conveyed to the reverse osmosis unit, and the microfiltration turbid liquid obtained after microfiltration is refluxed to the concentration tank.

Specifically, the process implemented in step 206 is controlled by the processor, which is the same as or similar to the implementation process in step 106, and is not repeated herein in the embodiment of the present invention.

Step 207: the reverse osmosis unit is controlled by the processor to carry out desalination treatment on the microfiltration clear liquid after microfiltration.

Specifically, the process implemented in step 207 is controlled by the processor, and is the same as or similar to the implementation process in step 107, and is not repeated herein in the embodiment of the present invention.

In the embodiment of the invention, for the fracturing flow-back fluid collected in the flow-back tank, the processor firstly obtains the detection result of the fracturing flow-back fluid and then carries out targeted treatment based on the detection result. When the total iron concentration obtained by the processor is smaller than a first concentration threshold value and the concentration of the obtained petroleum pollutants is smaller than a second concentration threshold value, controlling the lift pump to convey the fracturing flow-back fluid into the first reaction tank, and controlling the first dosing tank and the second dosing tank to respectively add coagulant and sodium hydroxide into the fracturing flow-back fluid collected by the first reaction tank so as to obtain a first reaction liquid, and conveying the first reaction liquid to the second reaction tank. And when the COD concentration acquired by the processor is less than a third concentration threshold value, controlling a third dosing box to add sodium carbonate into the first reaction liquid collected by the second reaction tank to obtain a second reaction liquid, and conveying the second reaction liquid to a concentration tank. And then, buffer precipitation is performed sequentially through the concentration tank, the concentrated clear liquid after buffer precipitation is subjected to microfiltration through the tubular microfiltration membrane, and the microfiltration clear liquid obtained after microfiltration is subjected to desalination treatment through the reverse osmosis unit, so that the fracturing flow-back fluid is treated, the limitation of the external environment is avoided, and the treatment cost of the fracturing flow-back fluid is reduced.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A treatment method of fracturing flow-back fluid is applied to a treatment system, the treatment system comprises a lift pump, a first reaction tank, a second reaction tank, a concentration tank, a tubular microfiltration unit and a reverse osmosis unit, and the method comprises the following steps:

obtaining a detection result of the fracturing flow-back fluid in the flow-back tank, wherein the detection result comprises total iron concentration, petroleum pollutant concentration and Chemical Oxygen Demand (COD) concentration;

when the total iron concentration is less than a first concentration threshold value and the petroleum pollutant concentration is less than a second concentration threshold value, the lift pump conveys the fracturing flow-back fluid to the first reaction tank, wherein the first concentration threshold value is 1.2 mg/L, and the second concentration threshold value is 10 mg/L;

the reverse osmosis unit is used for desalting the microfiltration clear liquid after microfiltration;

after the first reaction liquid is conveyed to the second reaction tank, the method further comprises the following steps:

2. The treatment method of claim 1, wherein the treatment system further comprises an aeration tank, and the obtaining the detection result of the fracturing flow-back fluid in the flow-back tank further comprises:

3. The treatment method according to claim 2, wherein after said delivering said fourth reaction solution to said second reaction tank, further comprising:

4. The process of any one of claims 1 to 3, wherein the tubular microfiltration unit comprises a first high pressure pump and a tubular microfiltration membrane;

the tubular microfiltration unit is to concentrated clear liquid micro-filtration to the clear liquid of microfiltration that obtains after will micro-filtering carries to reverse osmosis unit, the dirty liquid of microfiltration that obtains after will micro-filtering flows back to the concentration jar includes:

and conveying the microfiltration clear liquid obtained after the microfiltration of the tubular microfiltration membrane to the reverse osmosis unit, and refluxing the microfiltration turbid liquid obtained after the microfiltration to the concentration tank.

5. The process of claim 4, wherein the tubular microfiltration unit further comprises a water storage tank;

6. The process of any one of claims 1 to 3, wherein the reverse osmosis unit comprises a surge tank, a second high pressure pump, a cartridge filter and a reverse osmosis tank;

adding a chemical agent into the microfiltration clear liquid collected in the buffer tank to adjust the pH value of the microfiltration clear liquid, wherein the pH value of the microfiltration clear liquid after adjustment is more than or equal to 7 and less than or equal to 8;

the second high-pressure pump conveys the micro-filtration clear liquid adjusted in the buffer tank to the cartridge filter for filtration, and conveys the filtrate obtained after filtration to the reverse osmosis tank;

and a reverse osmosis membrane arranged in the reverse osmosis tank separates filtrate obtained after filtration.

7. The process of any one of claims 1 to 3, wherein the process system further comprises a sludge thickening tank and a plate and frame filter press, the process further comprising:

8. The process according to claim 7, wherein the flocculant is polyacrylamide, and the amount of the flocculant added to each liter of the concentrated sludge solution in the sludge concentrating tank is in the range of 1 to 3 mg.

9. A method for treating a fracturing flow-back fluid, wherein the method is applied to a treatment system, the treatment system comprises a lift pump, a first reaction tank, a first dosing tank, a second reaction tank, a third dosing tank, a concentration tank, a tubular microfiltration unit, a reverse osmosis unit and a processor, and the method comprises the following steps:

the processor obtains a detection result of the fracturing flow-back fluid in the flow-back tank, wherein the detection result comprises total iron concentration, petroleum pollutant concentration and COD concentration;

when the processor detects that the time length of the second reaction liquid buffered and precipitated by the concentration tank is equal to a second time threshold value, controlling to convey the concentrated clear liquid at the upper part in the concentration tank after the buffered and precipitated to the tubular microfiltration unit;

the processor controls the tubular microfiltration unit to carry out microfiltration on the concentrated clear liquid, and conveys the microfiltration clear liquid obtained after microfiltration to the reverse osmosis unit, and the microfiltration turbid liquid obtained after microfiltration is refluxed to the concentration tank;