Fracturing flow-back fluid treatment method and system

Abstract

The invention belongs to the technical field of fracturing flow-back fluid treatment, and discloses a fracturing flow-back fluid treatment method and system. The system comprises a fracturing flow-back fluid inlet pipeline, a pretreatment pool, a micron inflation water pump device, a gas storage tank, an air flotation cyclone, a metal film electric flocculation device, a vacuum water storage tank and a two-stage DTL film treatment device. The fracturing flow-back fluid is treated and recycled through a combined process of pretreatment, air flotation rotational flow treatment, metal film electric flocculation treatment and DTL membrane method treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of fracturing flowback fluid treatment, and more specifically, relates to a fracturing flowback fluid treatment method and system. Background Art

[0002] At present, most oil fields have been mined for many years. Due to the gradual decline in the production capacity and permeability of oil wells, the oil production has begun to show a downward trend. In order to increase the production of oil fields, more and more oil fields have begun to use fracturing technology for exploitation. At present, the most widely used fracturing technology is hydraulic fracturing. In the production process, the production of fracturing flowback fluid is inevitable. The fracturing fluid of hydraulic fracturing is a mixture of water, additives, sand and stone. Therefore, the fracturing flowback fluid has the characteristics of high oil, high SS, high salt, high COD, etc. The treatment and reuse of fracturing flowback fluid has a great impact on the production of oil fields.

[0003] The most commonly used processes for treating fracturing flowback fluid are combined processes such as flocculation sedimentation, flotation, biochemical, advanced oxidation, and membrane. Among them, flocculation sedimentation mainly removes some oils, SS, COD, etc. from pollutants in water through bridging adsorption and other effects by adding PAC, PAM and other agents. Flocculation sedimentation is often used as a pretreatment unit. Flotation equipment mainly uses a large number of bubbles to adsorb and capture some fine particles such as oils and other pollutants during the floating process to achieve solid-liquid separation, thereby removing SS, oils, COD and other substances in water. The biochemical pool mainly uses the activated sludge method to remove easily treated organic matter in water and reduce COD in water. Advanced oxidation mainly uses ozone catalytic oxidation process to deeply remove COD in water. The ozone introduced into the water is catalyzed by the catalyst to decompose and generate hydroxyl radicals. Hydroxyl radicals are a substance with strong oxidizing ability. Hydroxyl radicals can break the chain of large molecular organic matter into small molecular organic matter, and can even oxidize organic matter into carbon dioxide and water. Most pollutants in water can be removed by ozone catalytic oxidation, thereby meeting the discharge and reuse standards of flowback fluid. The membrane process mainly uses membrane separation technology to remove pollutants from water. In order to meet the reuse standards, a double membrane method (ultrafiltration + reverse osmosis) is generally used for treatment. However, in order to reuse the return fluid, reverse osmosis technology is often required for the final step of deep treatment. The large amount of additives, sand, oil and other substances in the return fluid will cause huge pollution to the RO membrane, which greatly affects the flux permeability and even the service life of the membrane. In addition, silicon substances have a great impact on the membrane. Reverse osmosis has strict restrictions on silicon. In order to prevent the formation of silicon scale, the silicon content in the concentrated water is generally required to be less than 200mg / L.

[0004] Moreover, the fracturing flowback fluid treatment process currently mainly used in engineering includes a multi-stage pretreatment + deep treatment combination process. This process has high energy consumption, large mud production, large footprint, serious membrane pollution, and many problems in actual operation.

[0005] Therefore, in summary, a new method and system for treating fracturing flowback fluid is urgently needed. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies of the prior art and propose a method and system for treating fracturing flowback fluid. The present invention realizes the treatment and reuse of fracturing flowback fluid through a combined process of pretreatment + air flotation cyclone treatment + metal membrane electrocoagulation treatment + DTL membrane treatment.

[0007] In order to achieve the above-mentioned object, the present invention provides a fracturing flowback fluid treatment system on one hand, the system comprising a fracturing flowback fluid inlet pipeline, a pretreatment tank, a micron aerated water pump device, an air storage tank, an air flotation cyclone, a metal membrane electrocoagulation device, a vacuum water storage tank and a two-stage DTL membrane treatment device;

[0008] The micron aerated water pump device comprises a centrifugal pump and a gas-liquid mixing nozzle;

[0009] The gas outlet of the gas storage tank is connected to a first exhaust pipeline and a second exhaust pipeline;

[0010] The fracturing flowback fluid water inlet pipeline is connected to the upper water inlet of the pretreatment tank; the desiliconizing agent pipeline is connected to the top drug inlet of the pretreatment tank; the lower water outlet of the pretreatment tank is connected to the water inlet of the centrifugal pump; the water outlet of the centrifugal pump is connected to the water inlet of the gas-liquid mixing nozzle, and the first exhaust pipeline is connected to the air inlet of the gas-liquid mixing nozzle; the outlet of the gas-liquid mixing nozzle is connected to the tangential water inlet of the air flotation cyclone; the lower water outlet of the air flotation cyclone is connected to the upper water inlet of the metal membrane electroflocculation device;

[0011] The metal film electro-flocculation device is provided with a titanium metal mesh membrane, a metal film water collecting pipe and a pulse aeration device. The titanium metal mesh membrane is used as the cathode of the metal film electro-flocculation device and is used to realize the suction filtration separation of the mud-water mixture in the metal film electro-flocculation device; the metal film water collecting pipe is used to allow the reaction liquid obtained by suction filtration separation to enter the vacuum water storage tank; the anode of the metal film electro-flocculation device is an aluminum electrode; the pulse aeration device is arranged at the bottom of the metal film electro-flocculation device and is connected to the second exhaust pipeline;

[0012] The vacuum water storage tank is connected to a vacuum pump and a chlorine removal agent addition pipeline; the lower water outlet of the vacuum water storage tank is connected to the water inlet of the two-stage DTL membrane treatment device; the qualified reuse water outlet of the two-stage DTL membrane treatment device is connected to the outside.

[0013] According to the present invention, preferably, a stirring device is provided in the pretreatment tank.

[0014] According to the present invention, preferably, the desiliconizing agent pipeline includes a sodium aluminate agent dosing pipeline and a PAC agent dosing pipeline.

[0015] According to the present invention, preferably, the air flotation cyclone is a monopolar air flotation cyclone.

[0016] According to the present invention, preferably, the pore size of the titanium metal mesh membrane is 0.3-0.8 μm.

[0017] According to the present invention, preferably, the titanium metal mesh membrane is also equipped with a backflush pipeline; the gas outlet of the gas storage tank is also connected to a third exhaust pipeline; the third exhaust pipeline is connected to the backflush pipeline.

[0018] According to the present invention, preferably, there are multiple vacuum water storage tanks; each vacuum water storage tank is provided with a stirring device and an ORP probe.

[0019] In the present invention, as a preferred solution, there are two vacuum water storage tanks, one for operation and one for standby.

[0020] According to the present invention, preferably, the pretreatment tank is provided with a first bottom mud discharge port;

[0021] The air flotation cyclone is provided with a top oil discharge port and a bottom slag discharge port;

[0022] The metal membrane electroflocculation device is provided with a second bottom mud discharge port;

[0023] The first bottom mud discharge port, the top oil discharge port, the bottom slag discharge port and the second bottom mud discharge port are all connected to the sludge tank.

[0024] According to the present invention, preferably, the lower water outlet of the vacuum water storage tank is connected to the water inlet of the first-stage DTL membrane treatment device in the two-stage DTL membrane treatment device;

[0025] The first-stage DTL membrane treatment equipment is provided with a primary water production port and a primary concentrated water discharge port, and the primary water production port is connected to the water inlet of the second-stage DTL membrane treatment equipment;

[0026] The second-stage DTL membrane treatment equipment is provided with a secondary water outlet and a secondary concentrated water discharge outlet, wherein the secondary water outlet is a qualified reuse water outlet of the two-stage DTL membrane treatment device;

[0027] The primary concentrated water discharge port and the secondary concentrated water discharge port are connected to the sludge tank.

[0028] Another aspect of the present invention provides a method for treating fracturing flowback fluid, the method using the above system comprising the following steps:

[0029] S1: The fracturing flowback fluid and the silicon removal agent are sent to the pretreatment tank to obtain sludge precipitation and pretreatment clear liquid after reaction;

[0030] S2: the pre-treated clear liquid is pressurized by the centrifugal pump and sent to the gas-liquid mixing nozzle to be mixed with the gas sent to the gas-liquid mixing nozzle from the first exhaust pipeline to obtain a water-gas-solid three-phase mixture;

[0031] S3: sending the water-gas-solid three-phase mixture into the flotation cyclone along the tangential direction, and separating by cyclone to obtain the bubble-oil droplet adherence body, the mud and sand mixture and the flotation cyclone clear liquid;

[0032] S4: sending the clear liquid from the air flotation cyclone into the metal membrane electrocoagulation device, performing electrolysis under pulse aeration conditions, and performing flocculation adsorption to obtain adsorption precipitate and reaction liquid; driving the reaction liquid through the titanium metal mesh membrane under the negative pressure of the vacuum pump, and filtering the reaction liquid into a vacuum water storage tank;

[0033] S5: In the vacuum water storage tank, the reaction liquid is mixed with a residual chlorine removal agent and reacted to obtain a reduction reaction liquid; the reduction reaction liquid is sent to the two-stage DTL membrane treatment device to obtain qualified reused produced water and secondary concentrated water.

[0034] According to the present invention, preferably, in step S1:

[0035] The silicon removal agent includes sodium aluminate agent and PAC agent, and the ratio of the mass concentration of the sodium aluminate agent in the pretreatment tank to the mass concentration of silicon in the fracturing flowback fluid in the pretreatment tank is (0.8-1.2): (0.8-1.2); the mass concentration of the PAC agent in the pretreatment tank is 30-50 mg / L;

[0036] The hydraulic retention time of the pretreatment tank is 15-30min;

[0037] The method further comprises discharging the sludge precipitate into a sludge pond.

[0038] According to the present invention, preferably, in step S2: in the gas-liquid mixing nozzle, the pretreated clear liquid is mixed with the gas sent into the gas-liquid mixing nozzle from the first exhaust pipeline to produce bubbles with a diameter of 100-200 μm, thereby obtaining a water-gas-solid three-phase mixture.

[0039] In the present invention, a large amount of pre-treated clear liquid directly enters the centrifugal pump, and after being pressurized by the pump, enters the gas-liquid mixing nozzle at a high flow rate. Due to its high flow rate, a high vacuum area (about -0.08Mpa) is formed inside the nozzle; the pre-treated clear liquid in the gas-liquid mixing nozzle is fully mixed with the gas in the gas storage tank sucked in, and tiny bubbles with a diameter of 100-200μm are produced, generating a water-gas-solid three-phase mixture. The water-gas-solid three-phase mixture enters the air flotation cyclone at a high flow rate along the tangential direction. During the cyclone separation process, the bubbles collide and adsorb with the oil droplets in the water to form a bubble-oil droplet adhesion body. According to the density difference, under the centrifugal action, the bubble-oil droplet adhesion body is discharged from the oil discharge port at the top of the air flotation cyclone into the sludge pool. The sand particles in the water and a large amount of mud form a high-density mud-sand mixture. Under the action of centrifugal force, the mud-sand mixture will flow on the inner wall of the air flotation cyclone, and finally be discharged to the sludge pool at the bottom of the air flotation cyclone. The clear liquid of the flotation cyclone separated by the flotation cyclone is discharged from the water outlet at the bottom of the flotation cyclone. In the present invention, a large amount of silicon scum, sand and oil substances in the fracturing return fluid can be removed after being treated in the pretreatment tank and the flotation cyclone.

[0040] According to the present invention, preferably, in step S3: the method further comprises discharging the bubble-oil droplet adhered body into the sludge pool from the top oil discharge port, and discharging the mud-sand mixture into the sludge pool from the bottom slag discharge port.

[0041] According to the present invention, preferably, in step S4:

[0042] The pulse aeration conditions include: aeration for 10 seconds and then stopping aeration for 50 seconds;

[0043] The current density of the electrolysis is determined according to the water quality of the fracturing flowback fluid, preferably 5-50 mA / m 2 ;

[0044] The negative pressure of the negative pressure drive is -50kpa to -25kpa;

[0045] The method further comprises discharging the adsorbed precipitate into a sludge pond;

[0046] In the present invention, the clear liquid from the air flotation cyclone enters the metal membrane electrocoagulation device:

[0047] The metal membrane electrocoagulation device uses aluminum plates as anodes for electrolysis. Aluminum plates are used to electrolyze aluminum ions, which are then converted into polynuclear hydroxyl complexes after a series of hydrolysis and polymerization reactions. The polynuclear hydroxyl complexes can react with silicon, fluorine, calcium, magnesium and other ions remaining in the clear liquid of the air flotation cyclone to form adsorption precipitation for deep removal. At the same time, the polynuclear hydroxyl complexes can also adsorb large molecular organic matter in the water to achieve the effect of removing part of the COD.

[0048] The cathode of the metal membrane electroflocculation device adopts a titanium metal mesh membrane with a pore size of 0.5 microns. The titanium metal mesh membrane serves as both the cathode of the metal membrane electroflocculation device and as a membrane for suction filtration and separation. The mud-water mixture in the metal membrane electroflocculation device is filtered in the form of immersion ultrafiltration by external pressure suction filtration. Under the negative pressure drive of the vacuum water storage tank (-50kpa), the titanium metal mesh membrane performs suction filtration and separation on the mud-water mixture in the metal membrane electroflocculation device, and the separated reaction liquid is pumped into the vacuum water storage tank.

[0049] A pulse aeration device is installed at the bottom of the metal membrane electroflocculation device, and the pulse time is 10 seconds of aeration followed by 50 seconds of aeration stop. Under the action of pulse aeration, the mass transfer effect in the metal membrane electroflocculation device is guaranteed. At the same time, pulse aeration will generate large bubbles with high flow rate to flush the surface of the titanium metal mesh membrane and maintain the flux of the titanium metal mesh membrane.

[0050] As a preferred solution, the method further comprises backflushing the titanium metal mesh membrane using a backflushing pipeline; the backflushing pressure is 0.8-1.2 bar and the time is 2.5-3.5 min.

[0051] According to the present invention, preferably, the metal membrane electrocoagulation device is operated in a batch mode, and the steps included in the operation cycle are: simultaneous electrolysis and filtration separation, stopping electrolysis and filtration separation, backflushing the titanium metal mesh membrane - stopping backflushing, static sedimentation, and sludge discharge.

[0052] According to the present invention, preferably, the electrolysis time is 40-50 min.

[0053] According to the present invention, preferably, the backflushing treatment time is 2.5-3.5 min.

[0054] According to the present invention, preferably, the static sedimentation time is 8-12 minutes.

[0055] According to the present invention, preferably, the sludge discharge time is 1.5-2.5 minutes.

[0056] According to the present invention, preferably, in step S5:

[0057] The vacuum water storage tank in operation is acted upon by a vacuum pump, and the vacuum degree in the vacuum water storage tank is -55kpa to -45kpa;

[0058] The residual chlorine removal agent is sodium bisulfite;

[0059] In the present invention, during the electrolysis process, the chloride ions in the water will inevitably produce residual chlorine and other substances at the anode oxidation. The residual chlorine has strong oxidizing properties and will damage the subsequent DTL membrane. Sodium bisulfite is added to the vacuum water storage tank according to the value of the ORP probe in the vacuum water storage tank. The added agent is stirred and mixed with the residual chlorine in the water to react, thereby reducing the residual chlorine in the water.

[0060] The dosage of the residual chlorine removal agent is determined according to the ORP value in the vacuum water storage tank measured by the ORP probe; the ORP value in the vacuum water storage tank is controlled at 100-150mv;

[0061] The reduction reaction liquid is sent to the first-stage DTL membrane treatment device of the two-stage DTL membrane treatment device to obtain primary produced water and primary concentrated water; the primary produced water is sent to the second-stage DTL membrane treatment device to obtain the qualified recycled produced water and secondary concentrated water; the primary concentrated water and the secondary concentrated water are discharged into the sludge tank;

[0062] The recovery rate of the first-stage DTL membrane treatment equipment is controlled at 75-85%;

[0063] The recovery rate of the second-stage DTL membrane treatment equipment is controlled at 90-95%. In the present invention, the total recovery rate of the two-stage DTL membrane treatment device is controlled at 75%.

[0064] The beneficial effects of the technical solution of the present invention are as follows:

[0065] The present invention uses a pretreatment tank as the main silicon removal unit to pretreat water before the membrane. In the pretreatment tank, silicon is mainly removed by adding sodium aluminate; flocculant PAC is added in the pretreatment tank to remove a large amount of silicon and SS in the water. At the same time, a part of the oil in the fracturing return fluid will be removed after flocculation and precipitation, thereby reducing the viscosity of the return fluid. The present invention does not set a mud-water separation zone in the pretreatment tank. The pretreatment clear liquid produced by adding drugs and mixing evenly directly enters the flotation cyclone for mud-water separation. Compared with conventional coagulation sedimentation tanks, the residence time is reduced, the tank body is reduced, land is saved, and construction costs are reduced.

[0066] The pre-treated clear liquid of the present invention is inflated by a micron aeration water pump device and then treated by a flotation cyclone. In the flow field of the cyclone, oil droplets collide and adsorb with bubbles to form bubble-oil droplet adhesion bodies, which are affected by centrifugal and flotation effects, so that oil, water and slag are efficiently separated. After being treated by the flotation cyclone, most of the oil and SS in the water are removed. The present invention uses a micron aeration water pump device to perform aeration and liquid fusion on the pre-treated clear liquid. The bubbles mixed in the pre-treated clear liquid are of micron level, with an average diameter of about 100-200 μm and a rising speed of about 150 s / m. The smaller the bubble diameter, the longer its action time, about 3 minutes, which is similar to the hydraulic retention time of the flotation cyclone, ensuring the effect of centrifugal oil-water separation. In the flotation cyclone, its characteristics are used to achieve efficient separation of water-oil sludge.

[0067] The metal membrane electro-flocculation device of the present invention uses a titanium metal mesh as a cathode, integrating electro-flocculation and membrane separation, ensuring the electro-flocculation removal effect while achieving in-situ solid-liquid separation, compressing the process unit, and saving space. The present invention selects a titanium metal mesh with a pore size of 0.5 microns, which can intercept suspended matter generated during the electrolysis process, ensuring the SDI and other index requirements before entering the membrane. With aluminum as the anode, the aluminum salt produced by electrolysis will generate a multi-nuclear hydroxyl complex after hydrolysis and polymerization, which can have an enhanced removal effect on calcium, magnesium, silicon, fluorine and other ions in water. Under the influence of the electric field, the titanium metal mesh acts as a cathode to reduce the impact of the membrane being blocked by negatively charged groups.

[0068] During the electrolysis process, the anode will also have a side reaction of chlorine ion oxidation, generating chlorine gas. Some of the chlorine gas dissolves in water to produce residual chlorine. Residual chlorine has a certain oxidizing property and can cause certain damage to the membrane. Sodium bisulfite is added to the vacuum water storage tank to remove the residual chlorine in the water and avoid damage to the membrane by residual chlorine.

[0069] The present invention performs a series of pretreatments for substances that cause serious membrane pollution, ensuring the efficient operation of the two-stage DTL membrane treatment device. After being treated by a series of process units including a pretreatment tank, an air flotation cyclone, and a metal membrane electrocoagulation device, the return liquid enters the two-stage DTL membrane treatment device. The DTL membrane has a high flux, and the unique mesh design avoids concentration polarization in the channel, while taking into account the water quality and energy consumption of the produced water.

[0070] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0072] Figure 1A structural schematic diagram of a fracturing flowback fluid processing system provided in Example 1 of the present invention is shown.

[0073] The following are the descriptions of the reference numerals:

[0074] 1. Fracturing flowback fluid inlet pipeline, 2. pretreatment tank, 3. centrifugal pump, 4. gas-liquid mixing nozzle, 5. gas storage tank, 6. air flotation cyclone, 7. metal membrane electroflocculation device, 8. vacuum water storage tank, 9. two-stage DTL membrane treatment device, 10. sludge tank, 11. vacuum pump, 12. qualified recycled produced water, 13. exhaust, 14. first exhaust pipeline, 15. second exhaust pipeline, 16. third exhaust pipeline. DETAILED DESCRIPTION

[0075] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0076] In the following embodiments:

[0077] The two-stage DTL membrane treatment device was purchased from Luxin Tiandiren Environmental Technology (Anhui) Group Co., Ltd. Special concentrated water grid: open N-type flow channel; effective membrane area 29.5m 2 ; Pressure level: 75bar / 90bar.

[0078] Example 1

[0079] This embodiment provides a fracturing flowback fluid processing system, such as Figure 1 As shown, the system includes a fracturing flowback fluid inlet pipeline 1, a pretreatment tank 2, a micron aerated water pump device, an air storage tank 5, an air flotation cyclone 6, a metal membrane electrocoagulation device 7, a vacuum water storage tank 8 and a two-stage DTL membrane treatment device 9;

[0080] The pretreatment tank 1 is provided with a stirring device;

[0081] The micron aeration water pump device comprises a centrifugal pump 3 and a gas-liquid mixing nozzle 4;

[0082] The gas outlet of the gas storage tank 5 is connected to a first exhaust pipeline 14, a second exhaust pipeline 15, and a third exhaust pipeline 16;

[0083] The air flotation cyclone 6 is a single-pole air flotation cyclone;

[0084] The fracturing flowback fluid water inlet pipeline 1 is connected to the upper water inlet of the pretreatment tank 2; the desiliconization agent pipeline (not shown) is connected to the top drug inlet of the pretreatment tank 2, and the desiliconization agent pipeline includes a sodium aluminate agent addition pipeline and a PAC agent addition pipeline; the lower water outlet of the pretreatment tank 2 is connected to the water inlet of the centrifugal pump 3; the water outlet of the centrifugal pump 3 is connected to the water inlet of the gas-liquid mixing nozzle 4, and the first exhaust pipeline 14 is connected to the air inlet of the gas-liquid mixing nozzle 4; the outlet of the gas-liquid mixing nozzle 4 is connected to the tangential water inlet of the air flotation cyclone 6; the lower water outlet of the air flotation cyclone 6 is connected to the upper water inlet of the metal membrane electroflocculation device 7;

[0085] The metal film electro-flocculation device 7 is provided with a titanium metal mesh, a metal film water collecting pipe and a pulse aeration device; the pore size of the titanium metal mesh is 0.5 μm, and the titanium metal mesh is used as the cathode of the metal film electro-flocculation device 7 and is used to realize the suction filtration separation of the mud-water mixture in the metal film electro-flocculation device 7; the titanium metal mesh is also equipped with a backflush pipeline, and the third exhaust pipeline 16 is connected to the backflush pipeline; the metal film water collecting pipe is used to allow the reaction liquid obtained by suction filtration separation to enter the vacuum water storage tank; the anode of the metal film electro-flocculation device is an aluminum electrode; the pulse aeration device is arranged at the bottom of the metal film electro-flocculation device and is connected to the second exhaust pipeline 15;

[0086] There are two vacuum water storage tanks 8, one for operation and one for standby; each vacuum water storage tank 8 is connected to a vacuum pump 11 and a chlorine removal agent dosing pipeline, and each vacuum water storage tank 8 is provided with a stirring device and an ORP probe; the lower water outlet of the vacuum water storage tank 8 is connected to the water inlet of the first-stage DTL membrane treatment device in the two-stage DTL membrane treatment device 9; the first-stage DTL membrane treatment device is provided with a primary water production port and a primary concentrated water discharge port, and the primary water production port is connected to the water inlet of the second-stage DTL membrane treatment device; the second-stage DTL membrane treatment device is provided with a secondary water production port and a secondary concentrated water discharge port, and the secondary water production port is the qualified reuse water production port of the two-stage DTL membrane treatment device;

[0087] The pretreatment tank 2 is provided with a first bottom mud discharge port; the flotation cyclone 6 is provided with a top oil discharge port and a bottom slag discharge port; the metal membrane electrocoagulation device 7 is provided with a second bottom mud discharge port; the first bottom mud discharge port, the top oil discharge port, the bottom slag discharge port, the second bottom mud discharge port, the first concentrated water discharge port and the second concentrated water discharge port are all connected to the sludge tank 10.

[0088] This embodiment also provides a method for treating fracturing flowback fluid. The fracturing flowback fluid is fracturing flowback fluid from an oil field in Heilongjiang. The water quality before and after treatment by this embodiment is shown in Table 1.

[0089] Table 1

[0090]

[0091] The method adopts the above system and comprises the following steps:

[0092] S1: The fracturing flowback fluid and the silicon removal agent are sent into the pretreatment tank 2, and are quickly stirred and mixed by the stirring equipment in the pretreatment tank 2, and sludge precipitate (a small amount of large precipitate) and pretreatment clear liquid are obtained after the reaction; the sludge precipitate is regularly discharged into the sludge tank 10;

[0093] The ratio of the mass concentration of the sodium aluminate agent in the pretreatment tank 2 to the mass concentration of silicon in the fracturing flowback fluid in the pretreatment tank 2 is 1:1; the mass concentration of the PAC agent in the pretreatment tank 2 is 30-50 mg / L;

[0094] The hydraulic retention time of the pretreatment tank 2 is 15-30min;

[0095] S2: The pre-treated clear liquid is pressurized by the centrifugal pump 3 and sent to the gas-liquid mixing nozzle 4, and mixed with the gas sent to the gas-liquid mixing nozzle 4 from the first exhaust pipeline 14, to produce bubbles with a diameter of 100 μm, and obtain a water-gas-solid three-phase mixture;

[0096] S3: sending the water-gas-solid three-phase mixture into the flotation cyclone 6 along the tangential direction, and separating by cyclone to obtain the bubble-oil droplet adherence body, the mud and sand mixture and the flotation cyclone clear liquid;

[0097] Discharge the bubble-oil droplet adhered body into the sludge tank 10 from the top oil discharge port, and discharge the mud-sand mixture into the sludge tank 10 from the bottom slag discharge port;

[0098] S4: The clear liquid of the air flotation cyclone is sent to the metal membrane electrocoagulation device 7. The metal membrane electrocoagulation device 7 is operated in a batch mode. The steps in the operation cycle are as follows: electrolysis (current density is 20 mA / m2) is carried out simultaneously under pulse aeration conditions (aeration for 10 seconds and then aeration for 50 seconds). 2 , 45min) and suction filtration separation, stop electrolysis and suction filtration separation, backflush the titanium metal mesh membrane at a pressure of 1 bar for 3min-stop backflush, let it stand for 10min, drain the mud for 2min, one cycle is 1h, and obtain adsorption precipitate and reaction solution;

[0099] The reaction liquid is pumped into the vacuum water storage tank 8 under the negative pressure drive (-50 kPa) of the vacuum pump 11; the adsorbed precipitate is discharged into the sludge tank 10;

[0100] S5: In the vacuum water storage tank 8 (vacuum degree is -50kpa), the reaction liquid is mixed with sodium bisulfite and reacted to obtain a reduction reaction liquid; the reduction reaction liquid is sent to the first-stage DTL membrane treatment device of the two-stage DTL membrane treatment device 9 to obtain primary produced water and primary concentrated water; the primary produced water is sent to the second-stage DTL membrane treatment device to obtain the qualified reuse produced water and secondary concentrated water; the primary concentrated water and the secondary concentrated water are discharged into the sludge tank;

[0101] The dosage of the sodium bisulfite is determined according to the ORP value in the vacuum water storage tank 8 measured by the ORP probe; the ORP value in the vacuum water storage tank 8 is controlled at 100-150mv;

[0102] The recovery rate of the first-stage DTL membrane treatment equipment is controlled at 80%; the recovery rate of the second-stage DTL membrane treatment equipment is controlled at 95%, and the total recovery rate of the two-stage DTL membrane treatment device 9 is controlled at 75%.

[0103] The fracturing flowback fluid (i.e., the produced water that meets the standards for reuse) treated by the system and method of the present invention can meet the "General Technical Conditions for Fracturing Fluids" SY / T, and the fracturing fluid can be reused.

[0104] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A fracturing flowback fluid treatment system, characterized in that: The system includes a fracturing flowback fluid inlet pipeline, a pretreatment tank, a micron aerated water pump device, an air storage tank, an air flotation cyclone, a metal membrane electrocoagulation device, a vacuum water storage tank and a two-stage DTL membrane treatment device; The micron aerated water pump device comprises a centrifugal pump and a gas-liquid mixing nozzle; The gas outlet of the gas storage tank is connected to a first exhaust pipeline and a second exhaust pipeline; The fracturing flowback fluid water inlet pipeline is connected to the upper water inlet of the pretreatment tank; the desiliconizing agent pipeline is connected to the top drug inlet of the pretreatment tank; the lower water outlet of the pretreatment tank is connected to the water inlet of the centrifugal pump; the water outlet of the centrifugal pump is connected to the water inlet of the gas-liquid mixing nozzle, and the first exhaust pipeline is connected to the air inlet of the gas-liquid mixing nozzle; the outlet of the gas-liquid mixing nozzle is connected to the tangential water inlet of the air flotation cyclone; the lower water outlet of the air flotation cyclone is connected to the upper water inlet of the metal membrane electroflocculation device; The metal film electro-flocculation device is provided with a titanium metal mesh membrane, a metal film water collecting pipe and a pulse aeration device. The titanium metal mesh membrane is used as the cathode of the metal film electro-flocculation device and is used to realize the suction filtration separation of the mud-water mixture in the metal film electro-flocculation device; the metal film water collecting pipe is used to allow the reaction liquid obtained by suction filtration separation to enter the vacuum water storage tank; the anode of the metal film electro-flocculation device is an aluminum electrode; the pulse aeration device is arranged at the bottom of the metal film electro-flocculation device and is connected to the second exhaust pipeline; The vacuum water storage tank is connected to a vacuum pump and a chlorine removal agent addition pipeline; the lower water outlet of the vacuum water storage tank is connected to the water inlet of the two-stage DTL membrane treatment device; the qualified reuse water outlet of the two-stage DTL membrane treatment device is connected to the outside.

2. The fracturing flowback fluid processing system according to claim 1, wherein: A stirring device is provided in the pretreatment tank; The desiliconizing agent pipeline includes a sodium aluminate agent dosing pipeline and a PAC agent dosing pipeline; The air floating cyclone is a single-pole air floating cyclone; The pore size of the titanium metal mesh membrane is 0.3-0.8 μm; The titanium metal mesh is also equipped with a backflush pipeline; the gas outlet of the gas storage tank is also connected to a third exhaust pipeline; the third exhaust pipeline is connected to the backflush pipeline; There are multiple vacuum water storage tanks; each vacuum water storage tank is provided with a stirring device and an ORP probe; The pretreatment tank is provided with a first bottom mud discharge port; The air flotation cyclone is provided with a top oil discharge port and a bottom slag discharge port; The metal membrane electroflocculation device is provided with a second bottom mud discharge port; The first bottom mud discharge port, the top oil discharge port, the bottom slag discharge port and the second bottom mud discharge port are all connected to the sludge tank.

3. The fracturing flowback fluid processing system according to claim 1, wherein: The lower water outlet of the vacuum water storage tank is connected to the water inlet of the first-stage DTL membrane treatment device in the two-stage DTL membrane treatment device; The first-stage DTL membrane treatment equipment is provided with a primary water production port and a primary concentrated water discharge port, and the primary water production port is connected to the water inlet of the second-stage DTL membrane treatment equipment; The second-stage DTL membrane treatment equipment is provided with a secondary water outlet and a secondary concentrated water discharge outlet, wherein the secondary water outlet is a qualified reuse water outlet of the two-stage DTL membrane treatment device; The primary concentrated water discharge port and the secondary concentrated water discharge port are connected to the sludge tank.

4. A method for treating fracturing flowback fluid, characterized in that: The method adopts the system described in any one of claims 1 to 3, comprising the following steps: S1: The fracturing flowback fluid and the silicon removal agent are sent to the pretreatment tank to obtain sludge precipitation and pretreatment clear liquid after reaction; S2: the pre-treated clear liquid is pressurized by the centrifugal pump and sent to the gas-liquid mixing nozzle to be mixed with the gas sent to the gas-liquid mixing nozzle from the first exhaust pipeline to obtain a water-gas-solid three-phase mixture; S3: sending the water-gas-solid three-phase mixture into the flotation cyclone along the tangential direction, and separating by cyclone to obtain the bubble-oil droplet adherence body, the mud and sand mixture and the flotation cyclone clear liquid; S4: sending the clear liquid from the air flotation cyclone into the metal membrane electrocoagulation device, performing electrolysis under pulse aeration conditions, and performing flocculation adsorption to obtain adsorption precipitate and reaction liquid; driving the reaction liquid through the titanium metal mesh membrane under the negative pressure of the vacuum pump, and filtering the reaction liquid into a vacuum water storage tank; S5: In the vacuum water storage tank, the reaction liquid is mixed with a residual chlorine removal agent and reacted to obtain a reduction reaction liquid; the reduction reaction liquid is sent to the two-stage DTL membrane treatment device to obtain qualified reused produced water and secondary concentrated water.

5. The method for treating fracturing flowback fluid according to claim 4, wherein: In step S1: The silicon removal agent includes sodium aluminate agent and PAC agent, and the ratio of the mass concentration of the sodium aluminate agent in the pretreatment tank to the mass concentration of silicon in the fracturing flowback fluid in the pretreatment tank is (0.8-1.2): (0.8-1.2); the mass concentration of the PAC agent in the pretreatment tank is 30-50 mg / L; The hydraulic retention time of the pretreatment tank is 15-30min; The method further comprises discharging the sludge precipitate into a sludge pond.

6. The method for treating fracturing flowback fluid according to claim 4, wherein: In the step S2: in the gas-liquid mixing nozzle, the pretreated clear liquid is mixed with the gas sent into the gas-liquid mixing nozzle from the first exhaust pipeline to produce bubbles with a diameter of 100-200 μm, thereby obtaining a water-gas-solid three-phase mixture.

7. The method for treating fracturing flowback fluid according to claim 4, wherein: In the step S3: the method further comprises discharging the air bubble-oil droplet adhered body into the sludge pool from the top oil discharge port, and discharging the mud-sand mixture into the sludge pool from the bottom slag discharge port.

8. The method for treating fracturing flowback fluid according to claim 4, wherein: In step S4: The pulse aeration conditions include: aeration for 10 seconds and then stopping aeration for 50 seconds; The current density of the electrolysis is 5-50ma / m 2 ; The negative pressure of the negative pressure drive is -50kpa to -25kpa; The method further comprises discharging the adsorbed precipitate into a sludge pond; The method further comprises backflushing the titanium metal mesh membrane using a backflushing pipeline; the backflushing pressure is 0.8-1.2 bar and the time is 2.5-3.5 minutes.

9. The method for treating fracturing flowback fluid according to claim 8, wherein: The metal membrane electroflocculation device is operated in a batch mode, and the steps in the operation cycle are: simultaneous electrolysis and suction filtration separation, stopping electrolysis and suction filtration separation, back-flushing the titanium metal mesh membrane - stopping back-flushing, static sedimentation, and mud discharge; Preferably, the electrolysis time is 40-50 min; Preferably, the backflushing treatment time is 2.5-3.5 min; Preferably, the static sedimentation time is 8-12 minutes; Preferably, the sludge discharge time is 1.5-2.5 min.

10. The method for treating fracturing flowback fluid according to claim 4, wherein: In step S5: The vacuum degree in the vacuum water storage tank is -55kpa to -45kpa; The residual chlorine removal agent is sodium bisulfite; The dosage of the residual chlorine removal agent is determined according to the ORP value in the vacuum water storage tank measured by the ORP probe; the ORP value in the vacuum water storage tank is controlled at 100-150mv; The reduction reaction liquid is sent to the first-stage DTL membrane treatment device of the two-stage DTL membrane treatment device to obtain primary produced water and primary concentrated water; the primary produced water is sent to the second-stage DTL membrane treatment device to obtain the qualified recycled produced water and secondary concentrated water; the primary concentrated water and the secondary concentrated water are discharged into the sludge tank; The recovery rate of the first-stage DTL membrane treatment equipment is controlled at 75-85%; The recovery rate of the second-stage DTL membrane treatment equipment is controlled at 90-95%.

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