Process and equipment for efficiently treating and recycling fracturing wastewater

Abstract

The invention belongs to the technical field of oilfield wastewater treatment, and discloses a process and equipment for efficiently treating and recycling fracturing wastewater. The process comprises the steps of coagulation, chemical precipitation, sterilization and pH regulation. Firstly, polyaluminum chloride is added into the fracturing wastewater through a pipeline mixer; then the wastewater enters a two-stage modified sedimentation tank for coagulation and chemical precipitation reaction to remove pollutants such as organic matters, suspended matters, calcium, magnesium and total iron, floc densification is completed under the action of adding polyacrylamide along with a paddle to achieve the effect of strengthening solid-liquid separation, and coagulated floc and chemical precipitates are settled to a sludge hopper to be discharged respectively; water discharging is completed in a clear water area with small disturbance; finally, effluent enters a sterilization system and is adjusted by a pH adjusting system to be discharged. The process flow is simple, the labor cost is low, the fracturing wastewater can be deeply treated and reaches the standard for reuse, the sludge is reduced, and the sediment is recycled.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield wastewater treatment, and in particular relates to a process and equipment for efficiently treating and reusing fracturing wastewater. Background Art

[0002] Fracturing refers to the process of oil or gas production, which uses hydraulic force to artificially create cracks in the formation, improve the flow environment of oil underground, and increase the production of oil and gas wells. Fracturing waste fluid is an environmental pollutant produced by the fracturing process in oil and gas fields. The high concentration of suspended solids (SS), salts and dissolved organic matter contained in it is harmful to the environment and public health, so direct discharge is strictly prohibited. Generally, it is directly discharged after simple treatment, and the residual organic matter causes pollution to the surrounding ecological environment. Therefore, it is of great significance to develop efficient treatment and reuse processes for fracturing wastewater and improve the reuse rate of fracturing wastewater.

[0003] Most of the existing fracturing wastewater treatment processes use the treatment method of "flocculation + multi-stage oxidation + filtration and sedimentation". The patent with application number CN110294550A discloses a reuse and compound treatment method and device for fracturing flowback fluid. The treatment process adopted by this patent is mainly the treatment process of "flotation + catalytic oxidation + filtration". However, the catalyst required for the catalytic oxidation method is expensive and difficult to recycle. The impact of the catalyst component on the subsequent reuse of water quality is unknown. The patent with application number CN201610242734.X discloses a method for deep treatment of fracturing flowback fluid in oil and gas fields to meet the discharge standards. This patent adopts a combination of coagulation and pretreatment, followed by a three-stage oxidation treatment process. The process flow is relatively complicated, the treatment cost is high, and it occupies a large area. Summary of the invention

[0004] The purpose of the present invention is to propose a highly efficient treatment and reuse process and equipment for fracturing wastewater, which is used to treat wastewater generated in the fracturing process of unconventional and low-permeability oil and gas fields, and solve the problem of environmental pollution caused by residual organic matter in the wastewater. It mainly targets the problem that the traditional treatment method has a complex process flow and high treatment cost, resulting in the inability to efficiently treat and meet emission standards.

[0005] In order to overcome the shortcomings of the prior art, the present invention provides the following solutions:

[0006] A highly efficient treatment and reuse process equipment for fracturing wastewater comprises an inlet tank, which is connected with a first-stage modified sedimentation tank. A pipeline mixer is arranged on the pipeline between the inlet tank and the first-stage modified sedimentation tank. A first stirring paddle is arranged in the center of the first-stage modified sedimentation tank. A first paddle-following drug-adding pipeline is arranged on the first stirring paddle. A first single-bucket mud discharge pipeline is arranged at the bottom of the first-stage modified sedimentation tank. The first-stage modified sedimentation tank is connected with a second-stage modified sedimentation tank. A second stirring paddle is arranged in the center of the second-stage modified sedimentation tank. A second paddle-following drug-adding pipeline is arranged on the second stirring paddle. A second single-bucket mud discharge pipeline is arranged at the bottom of the second-stage modified sedimentation tank. The second-stage modified sedimentation tank is connected with a sterilization system and a pH adjustment system in sequence. The pH adjustment system is connected to an outlet tank. The pH adjustment system is connected with an acid-base agent storage tank. The acid-base agent storage tank is also connected with the second-stage modified sedimentation tank at the same time.

[0007] The first single-bucket mud discharge pipeline and the second single-bucket mud discharge pipeline are both connected to the filter press device, and the filter press device is connected to the water outlet of the water inlet pool.

[0008] The acid-base agent storage tank is connected to the pH adjustment system through the second acid-base dosing system, and the acid-base agent storage tank is connected to the secondary modified sedimentation tank through the first acid-base dosing system.

[0009] The water depth of the clear water area of ​​the first-stage modified sedimentation tank and the second-stage modified sedimentation tank is 0.7-1.0 meters, and the pool diameter or pool depth below the clear water area is 2.0-2.5 meters.

[0010] The first-stage modified sedimentation tank and the second-stage modified sedimentation tank are both vertical flow sedimentation tanks, and the water inlet faces the stirring area.

[0011] A highly efficient treatment and reuse process for fracturing wastewater comprises the following steps:

[0012] Coagulation and sedimentation: the wastewater is mixed with the coagulant in the pipeline mixer. The coagulated wastewater enters the first-stage modified sedimentation tank. Flocculants are added to the first-stage modified sedimentation tank to remove organic matter and suspended solids to complete coagulation and sedimentation.

[0013] Chemical precipitation: the effluent from the first modified sedimentation tank enters the second modified sedimentation tank, and the reagent and flocculant for reducing the total hardness of calcium ions, magnesium ions and iron ions are added to the second modified sedimentation tank to complete the chemical precipitation;

[0014] Sterilization and pH adjustment: The effluent from the secondary modified sedimentation tank is sterilized. After sterilization, the effluent enters the pH adjustment system. Acidic agents are added to the pH adjustment system to adjust the pH value to neutral before effluent.

[0015] The coagulated flocs produced by the first-stage modified sedimentation tank and the precipitates produced by the second-stage modified sedimentation tank enter the filter press device, and the filtrate produced by the filter press device flows back to the wastewater before coagulation, and the filter residue produced is collected through slag discharge for solid waste treatment.

[0016] The secondary modified sedimentation tank is added with a reagent and a flocculant for reducing the total hardness of calcium ions, magnesium ions and iron ions to complete chemical precipitation, specifically:

[0017] First, Na2CO3 was added to the secondary modified sedimentation tank to adjust the pH value to 10.50; then NaOH was added to adjust the pH value to 12.50; finally, polyacrylamide was added at a dosage of 10 mg / L and the reaction time was 10 min.

[0018] The pipeline mixer controls the zeta potential to be in a slightly destabilized state of ±10 mV.

[0019] The water produced after adjusting the pH to neutral is used to prepare EM50 / EM50S / EM60 / VS fracturing fluid or guar gum fracturing fluid after water quality testing.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The equipment proposed by the present invention is to add two paddle-type dosing pipes on the basis of a conventional sedimentation tank, so that the coagulation treatment process can be combined with the secondary sedimentation. The paddle-type dosing pipes can deliver the added agent to the place with greater stirring intensity, thereby improving the mass transfer efficiency of the agent, completing the floc densification and achieving the effect of strengthening solid-liquid separation; the secondary modified sedimentation tank solves the problem of removing high-valent ions in the configuration of fracturing fluid; the pH adjustment system is connected to the back-end equipment so that the final effluent can be recycled. The equipment of the present invention has a high degree of automation, low labor cost, and a simple process flow, and plays a significant role in solving the problem of reuse of fracturing wastewater at a low cost. The equipment of the present invention is of great significance in solving the problem of environmental pollution caused by discharge after traditional fracturing wastewater treatment, and realizes the efficient treatment of fracturing wastewater, while ensuring that the effluent meets the reuse requirements.

[0022] The modified sedimentation tank deepens the reactor tank, creating a fluid state with less interference to facilitate sludge sedimentation and water clarification; the water inlet faces the stirring area, forming a local high G value area to facilitate the completion of coagulation.

[0023] The process method of the present invention combines the processes of coagulation treatment and chemical precipitation deep treatment to treat fracturing wastewater. Coagulation can significantly reduce organic matter and suspended solids. Chemical precipitation deep treatment has high removal efficiency for the total hardness of calcium ions, magnesium ions and iron ions, thereby completing the treatment of fracturing wastewater up to standard. While effectively removing organic matter and suspended solids in the wastewater, the indicators of calcium, magnesium, total iron and the like in the effluent also meet the reuse requirements.

[0024] The sludge and sediment discharged from the two-stage sedimentation tank are treated by a filter press, and the obtained filtrate is returned to the water inlet for further treatment. The sludge is treated as solid waste and the sediment is recycled, which has certain economic benefits.

[0025] At the same time, the final effluent can be reused in the preparation of fracturing fluid, realizing the resource application of fracturing wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for use in the embodiment:

[0027] Figure 1 This is a schematic diagram of a process equipment for efficiently treating and reusing fracturing wastewater according to the present invention;

[0028] In the figure: 1. water inlet tank; 2. pipeline mixer; 3. first paddle-type dosing pipe; 4. first motor; 5. first stirring paddle; 6. first single-bucket mud discharge pipe; 7. filter press; 8. first water outlet; 9. second paddle-type dosing pipe; 10. second motor; 11. second stirring paddle; 12. second single-bucket mud discharge pipe; 13. second water outlet; 14. pH real-time detection device; 15. first acid-base dosing system; 16. acid-base agent storage tank; 17. sterilization system; 18. pH adjustment system; 19. second acid-base dosing system; 20. water outlet tank; 21. first-level modified sedimentation tank; 22. second-level modified sedimentation tank. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings:

[0030] The invention proposes a highly efficient treatment and reuse process for fracturing wastewater. Two paddle-fed dosing pipes are added to the conventional sedimentation tank, so that the coagulation treatment process can be combined with the secondary sedimentation. The subsequent pH adjustment tank solves the problem of removing high-valent ions in the fracturing fluid. The process has the advantages of high automation, low labor cost and simple process, and plays a significant role in solving the problem of reuse of fracturing return fluid at low cost.

[0031] A highly efficient treatment and reuse process equipment for fracturing wastewater comprises an inlet tank 1, the inlet tank 1 is connected with a first-stage modified sedimentation tank 21, a pipeline mixer 2 is arranged in the pipeline between the inlet tank 1 and the first-stage modified sedimentation tank 21, a first stirring paddle 5 is arranged in the center of the first-stage modified sedimentation tank 21, a first paddle-following drug-adding pipeline 3 is arranged on the first stirring paddle 5, a first single-bucket mud discharge pipeline 6 is arranged at the bottom of the first-stage modified sedimentation tank 21, the first-stage modified sedimentation tank 21 is connected with a second-stage modified sedimentation tank 22; a second stirring paddle 11 is arranged in the center of the second-stage modified sedimentation tank 22, a second paddle-following drug-adding pipeline 9 is arranged on the second stirring paddle 11, a second single-bucket mud discharge pipeline 12 is arranged at the bottom of the second-stage modified sedimentation tank 22, the second-stage modified sedimentation tank 22 is connected with a sterilization system 17 and a pH adjustment system 18 in sequence, the pH adjustment system 18 is connected to an outlet tank 20, the pH adjustment system 18 is connected with an acid-base agent storage tank 16, and the acid-base agent storage tank 16 is also connected with the second-stage modified sedimentation tank 22 at the same time.

[0032] The water depth of the clear water area of ​​the first-stage modified sedimentation tank 21 and the second-stage modified sedimentation tank 22 is 0.7-1.0 meters, and the pool diameter / pool depth below the clear water area is maintained at 2.0-2.5 meters, which deepens the reactor pool depth and creates a fluid state with less interference to facilitate sludge sedimentation and water clarification.

[0033] The water inlets of the first modified sedimentation tank 21 and the second modified sedimentation tank 22 face the stirring area, forming a local high G value area to facilitate the completion of coagulation.

[0034] The first paddle dosing pipe 3 in the first-stage modified sedimentation tank 21 and the second paddle dosing pipe 9 in the second-stage modified sedimentation tank 22 are flocculant dosing pipes. The flocculant is added to the place with higher stirring intensity through the paddle dosing pipes, thereby improving the mass transfer efficiency of the flocculant liquid.

[0035] The first single-bucket mud discharge pipe 6 at the bottom of the first-stage modified sedimentation tank 21 and the second single-bucket mud discharge pipe 12 at the bottom of the second-stage modified sedimentation tank 22 are connected to a filter press device 7, and the filter press device 7 is connected to the water inlet tank 1. The filtrate produced by the filter press device 7 flows back to the water inlet tank 1, and the filter residue is treated as a solid waste through the residue discharge.

[0036] The first modified sedimentation tank 21 and the second modified sedimentation tank 22 are vertical flow sedimentation tanks, wherein the second modified sedimentation tank 22 is provided with a pH real-time detection device 14 .

[0037] The acid-base agent storage tank 16 is connected to the pH adjustment system 18 through the second acid-base dosing system 19 , and the acid-base agent storage tank 16 is connected to the secondary modified sedimentation tank 22 through the first acid-base dosing system 15 .

[0038] The first stirring paddle 5 is controlled by a first motor 4 with a gearbox; the second stirring paddle 11 is controlled by a second motor 10 with a gearbox.

[0039] A highly efficient treatment and reuse process for fracturing wastewater comprises the following steps:

[0040] Coagulation and sedimentation, the wastewater is mixed with the coagulant in the pipeline mixer 2, and the coagulated wastewater enters the first modified sedimentation tank 21, and flocculants are added to the first modified sedimentation tank 21 to remove organic matter and suspended matter, completing coagulation and sedimentation

[0041] Chemical precipitation, the effluent of the first modified sedimentation tank 21 enters the second modified sedimentation tank 22, and the agent and flocculant for reducing the total hardness of calcium ions, magnesium ions and iron ions are added to the second modified sedimentation tank 22 to complete the chemical precipitation;

[0042] Sterilization and pH adjustment: The effluent from the secondary modified sedimentation tank 22 is sterilized, and the effluent after sterilization enters the pH adjustment system 18, into which an acidic agent is added to adjust the pH value to neutral before effluent.

[0043] Example

[0044] A highly efficient treatment and reuse process for fracturing wastewater is carried out using the above equipment, comprising the following steps:

[0045] Coagulation and sedimentation, the wastewater from the water inlet pool 1 enters the pipeline mixer 2, polyaluminium chloride (PAC) is added to the pipeline mixer 2 for mixing, and stays for about 30 seconds to fully mix with PAC, and the ζ potential is controlled to be in a slightly destabilised state of ±10mV to complete the coagulation process of organic matter; the wastewater flowing out of the pipeline mixer 2 enters the first-stage modified sedimentation tank 21 from the bottom, and the speed of the first stirring paddle 5 is controlled at 100r / min by adjusting the first motor 4 with a gearbox, and polyacrylamide (PAM) is added to the first-stage modified sedimentation tank 21 through the first paddle dosing pipeline 3. The mass transfer efficiency of the PAM solution is improved to ensure the effective removal of organic matter, and the coagulated flocs enter the filter press 7 through the first single-bucket mud discharge pipeline 6. The filtrate produced by the filter press 7 flows back to the water inlet pool 1, and the produced filter residue is collected for solid waste treatment through the slag discharge.

[0046] Chemical precipitation, the first modified sedimentation tank 21 discharges water from the upper first water outlet 8, and the discharged water enters the second modified sedimentation tank 22 from the bottom. The speed of the second stirring paddle 11 is controlled at 100r / min by adjusting the second motor 10 with a gearbox. The acid-base agent storage tank 16 first adds Na2CO3 to the secondary modified sedimentation tank 22 through the first acid-base dosing system 15 to adjust the pH value to 10.50; then NaOH is added to adjust the pH value to 12.50; finally PAM is added, the PAM dosage is 10 mg / L, and the reaction time is 10 min; the pH real-time detection device 14 detects the pH value change in real time, and PAM is added to the position of the secondary modified sedimentation tank 22 with greater stirring intensity through the second paddle dosing pipeline 9, so as to improve the mass transfer efficiency of the PAM solution, further promote the removal of calcium ions, magnesium ions and iron ions, and reduce the total hardness of the wastewater; the precipitate enters the filter press 7 through the second single-bucket mud discharge pipeline 12, and the filtrate produced by the filter press 7 is refluxed to the water inlet pool 1, and the produced filter residue is collected for solid waste treatment through slag discharge.

[0047] Sterilization and pH adjustment: the secondary modified sedimentation tank 22 discharges water from the second water outlet 13 at the top, and the effluent enters the sterilization system 17 for sterilization treatment. After sterilization, the effluent enters the pH adjustment system 18, and the acid-base agent storage tank 16 adds acidic agent to the pH adjustment system 18 through the second acid-base dosing system 19, and the water is discharged after the pH is adjusted to neutral.

[0048] The effluent from the pH adjustment system 18 enters the effluent pool 20, and after water quality testing, the effluent can be used to prepare EM50 / EM50S / EM60 / VS fracturing fluid or guar gum fracturing fluid.

[0049] In summary, the present invention combines the processes of coagulation, chemical precipitation, sterilization and pH adjustment to achieve standard treatment and reuse of fracturing wastewater. First, polyaluminium chloride is added to the fracturing wastewater through the pipeline mixer 2 to control the ζ potential to be in a slightly destabilized state of ±10mV. Then, it enters the high G value reaction zone of the two-stage modified sedimentation tank tangentially for coagulation and chemical precipitation reaction to remove pollutants such as organic matter, suspended matter, calcium, magnesium and total iron. Under the action of polyacrylamide added with the paddle, the flocs are densified to achieve the effect of strengthening solid-liquid separation. The coagulated flocs and chemical precipitates are settled to the sludge hopper and discharged separately, and the water is discharged in the clear water area with less disturbance. Finally, the effluent enters the sterilization system, and the effluent is used for reuse to prepare EM50 / EM50S / EM60 / VS or guar gum fracturing fluid after the pH is adjusted to about 7.00 by the pH adjustment system. The sludge and sediment discharged from the two-stage sedimentation tank are treated by a filter press, and the obtained filtrate is returned to the water inlet for further treatment, and the sludge solid waste is treated and the sediment is recycled. The present invention can deeply treat fracturing wastewater and achieve standard reuse, reduce sludge, and recycle sediments.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art can still modify or make equivalent substitutions to the specific implementations of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A highly efficient treatment and reuse process equipment for fracturing wastewater, characterized in that: The invention comprises a water inlet tank (1), the water inlet tank (1) is connected to a first modified sedimentation tank (21), a pipeline mixer (2) is arranged in the pipeline between the water inlet tank (1) and the first modified sedimentation tank (21), a first stirring paddle (5) is arranged in the center of the first modified sedimentation tank (21), a first paddle-following drug-adding pipeline (3) is arranged on the first stirring paddle (5), a first single-bucket mud discharge pipeline (6) is arranged at the bottom of the first modified sedimentation tank (21), the first modified sedimentation tank (21) is connected to a second modified sedimentation tank (22); the second modified sedimentation tank (22) ) A second stirring paddle (11) is arranged at the center, a second paddle-following drug-adding pipeline (9) is arranged on the second stirring paddle (11), a second single-bucket mud discharge pipeline (12) is arranged at the bottom of the secondary modified sedimentation tank (22), the secondary modified sedimentation tank (22) is connected with the sterilization system (17) and the pH adjustment system (18) in sequence, the pH adjustment system (18) is connected to the water outlet tank (20), the pH adjustment system (18) is connected with the acid-base agent storage tank (16), and the acid-base agent storage tank (16) is also connected with the secondary modified sedimentation tank (22) at the same time.

2. The highly efficient treatment and reuse process equipment for fracturing wastewater according to claim 1, characterized in that: The first single-bucket mud discharge pipeline (6) and the second single-bucket mud discharge pipeline (12) are both in communication with the filter press device (7), and the filter press device (7) is connected to the water outlet of the water inlet pool (1).

3. The highly efficient treatment and reuse process equipment for fracturing wastewater according to claim 1 is characterized in that: The acid-base agent storage tank (16) is connected to the pH adjustment system (18) through the second acid-base dosing system (19), and the acid-base agent storage tank (16) is connected to the secondary modified sedimentation tank (22) through the first acid-base dosing system (15).

4. The highly efficient treatment and reuse process equipment for fracturing wastewater according to claim 1, characterized in that: The water depth of the clear water area of ​​the first modified sedimentation tank (21) and the second modified sedimentation tank (22) is 0.7-1.0 m, and the pool diameter or pool depth below the clear water area is 2.0-2.5 m.

5. The highly efficient treatment and reuse process equipment for fracturing wastewater according to claim 1, characterized in that: The first modified sedimentation tank (21) and the second modified sedimentation tank (22) are both vertical flow sedimentation tanks, and the water inlets face the stirring area.

6. A highly efficient treatment and reuse process for fracturing wastewater, characterized in that: The following steps are involved: Coagulation and sedimentation, mixing the wastewater with the coagulant in the pipeline mixer (2), the coagulated wastewater enters the first modified sedimentation tank (21), and a flocculant is added to the first modified sedimentation tank (21) to remove organic matter and suspended matter, thereby completing coagulation and sedimentation; Chemical precipitation, the effluent from the first modified sedimentation tank (21) enters the second modified sedimentation tank (22), and a reagent and a flocculant for reducing the total hardness of calcium ions, magnesium ions and iron ions are added to the second modified sedimentation tank (22) to complete the chemical precipitation; Sterilization and pH adjustment: the effluent from the secondary modified sedimentation tank (22) is sterilized, and the effluent after sterilization enters the pH adjustment system (18), an acidic agent is added to the pH adjustment system (18), and the pH value is adjusted to neutral before the effluent is discharged.

7. A process for efficiently treating and reusing fracturing wastewater according to claim 6, characterized in that: The coagulated flocs produced by the first modified sedimentation tank (21) and the precipitates produced by the second modified sedimentation tank (22) enter the filter press device (7), the filtrate produced by the filter press device (7) flows back to the wastewater before coagulation, and the filter residue produced is collected by slag discharge for solid waste treatment.

8. A process for efficiently treating and reusing fracturing wastewater according to claim 6, characterized in that: The secondary modified sedimentation tank (22) is added with a reagent and a flocculant for reducing the total hardness of calcium ions, magnesium ions and iron ions to complete chemical precipitation, specifically: First, Na2CO3 was added to the secondary modified sedimentation tank (22) to adjust the pH value to 10.50; then, NaOH was added to adjust the pH value to 12.50; finally, polyacrylamide was added in an amount of 10 mg / L and the reaction time was 10 min.

9. A process for efficiently treating and reusing fracturing wastewater according to claim 6, characterized in that: The pipeline mixer (2) controls the zeta potential to be in a slightly destabilized state of ±10 mV.

10. A process for efficiently treating and reusing fracturing wastewater according to claim 6, characterized in that: The water produced after adjusting the pH to neutral is used to prepare EM50 / EM50S / EM60 / VS fracturing fluid or guar gum fracturing fluid after water quality testing.

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