Efficient short-distance unconventional oilfield wastewater mixed layer reinjection water treatment device

Abstract

The utility model belongs to the field of oil and gas field wastewater treatment, and particularly relates to an efficient short-distance unconventional oil field wastewater mixed layer reinjection water treatment device. An efficient short-distance unconventional oilfield wastewater mixed-layer reinjection water treatment device comprises an oil removal tank, a softening sedimentation tank, an ultrafiltration membrane group, a water purification tank and a water distribution pipe network which are connected in sequence, the oil removal tank is connected to external oilfield wastewater, and is also connected with a flocculant dosing tank, a coagulant aid dosing tank and a pH regulator dosing tank; the softening and precipitating tank is connected with a pH regulator dosing tank and a softening and precipitating agent dosing tank. The treated water quality meets the water injection quality index of the clastic rock reservoir, and the damage rate of the treated reinjection water to the reservoir is reduced by more than 30%.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the field of oil and gas field wastewater treatment, concretely relates to a kind of high-efficiency short-range unconventional oilfield wastewater mixed layer reinjection water treatment device. BACKGROUND

[0002] In recent years, with the domestic main oil field entering production decline period successively, unconventional oil and gas resource potential is huge, and it will be important field to obtain stable oil and gas production for quite a long period in future.Unconventional oil well oil production increases year by year, but a large amount of wastewater is also generated.However, part of oil and gas enterprises does not equip water injection well of same formation before unconventional oil exploitation, so the produced wastewater of this part of unconventional oil well can only rely on mixed layer reinjection of other conventional oil layer water injection well in the area.Due to the different water types of different horizons, they may contain calcium, magnesium and other scale-forming cations and carbonate, sulfate and other scale-forming anions, so mixed layer reinjection may have the risk of incompatibility between injection water source and reinjection formation water, and incompatibility between water sources may lead to scaling, thereby blocking the risk of surface water treatment equipment, pipeline and formation, affecting safe reinjection.

[0003] At present, the most common reinjection water treatment system of oil field generally adopts "oil removal-coagulation air flotation-multistage filtration" three-stage process, and the scale prevention method of system and pipeline is to add chemical scale inhibitor in water body.The process flow is long, and sludge amount is high, and effluent water quality is unstable;in addition, although the scale prevention mode of adding chemical scale inhibitor has the characteristics of simple construction and wide use range, but the dosage of reagent is high, scale prevention effect is limited, sludge production amount is large, and scale-forming ions cannot be completely removed from water body, and these scale-forming ions still have the risk of scaling in equipment, pipeline, downhole pipe wall and formation under the change of different temperature, pressure, flow rate and other conditions.Although calcium, magnesium and other scale-forming cations can be converted into insoluble precipitate by adding chemical precipitant, but the initial generated precipitate floc is small, and a large amount of it is suspended in water, so the water retention time of precipitation process is long, the volume requirement of softening precipitation equipment is large, and the precipitation efficiency is low.

[0004] Therefore, a kind of unconventional oilfield wastewater mixed layer reinjection water treatment device with short process, good effluent effect and scale-forming ions can be directly captured and removed from water body is developed, the device has short reaction time, can greatly reduce sludge amount, equipment occupies small area, can realize low-cost, short-process and high-efficiency control of scale-forming ions, thereby effectively solving the scaling problem of wastewater in water injection station treatment and reinjection process, improving water treatment efficiency, reducing scale removal cost, prolonging the service life of equipment and pipeline, ensuring safe reinjection of unconventional oilfield wastewater, and reducing reservoir damage. SUMMARY

[0005] The utility model provides a kind of unconventional oilfield wastewater mixed layer reinjection water treatment device with short process flow, stable water quality, can directly capture and remove scale-forming ions from water system, so that the quality of reinjection water meets the index of water quality of fractured rock reservoir, and the damage rate of reservoir after treatment is reduced by more than 30%.

[0006] The technical scheme of the utility model lies in:

[0007] A kind of unconventional oilfield wastewater mixed layer reinjection water treatment device with high efficiency short range, including the oil removal tank, softening precipitation tank, ultrafiltration membrane group, water tank and distribution pipe network connected in sequence;The oil removal tank is connected to external oilfield wastewater, and the oil removal tank is also connected with flocculant dosing tank, coagulant dosing tank and pH regulator dosing tank, and the flocculant dosing tank and the coagulant dosing tank are connected to the top of the oil removal tank by a dosing pump;The softening precipitation tank is connected with pH regulator dosing tank and softening precipitant dosing tank, and the pH regulator dosing tank is connected to the top of the oil removal tank and the softening precipitation tank by a dosing pump.

[0008] The softening precipitation tank is also connected with carbon dioxide aeration pipe.

[0009] It also includes ion online monitoring unit, the ion online monitoring unit includes scale-forming ion measuring sensor in softening precipitation tank and external computer outside softening precipitation tank, and scale-forming ion measuring sensor is electrically connected with external computer.

[0010] The scale-forming ion measuring sensor includes but is not limited to calcium ion sensor and magnesium ion sensor, and calcium ion sensor and magnesium ion sensor are electrically connected with external computer.

[0011] The softening precipitation tank is provided with softening precipitation water outlet and sludge outlet;Softening precipitation water outlet is connected with the water inlet of ultrafiltration membrane group;Sludge outlet is exported by a sewage pipeline.

[0012] The ultrafiltration membrane group is provided with ultrafiltration membrane group water outlet and concentrated water outlet, and the ultrafiltration membrane group water outlet is connected to the purification tank, and the concentrated water outlet is connected to the softening precipitation tank.

[0013] The ultrafiltration membrane group is provided with water inlet pipeline and water outlet pipeline;The water inlet pipeline is communicated with softening precipitation water outlet and the water inlet of ultrafiltration membrane group, and water inlet pump and flowmeter are arranged on the water inlet pipeline;Water outlet pipeline is communicated with ultrafiltration membrane group water outlet and the water inlet of purification tank.

[0014] The distribution pipe network includes several parallelly arranged injection pipelines;First-stage booster pump and second-stage booster pump are sequentially arranged between water tank and injection pipeline.

[0015] The external oilfield wastewater is connected to the oil removal tank by a buffer tank, and a raw water pump is further arranged between the external oilfield wastewater and the buffer tank.

[0016] The filter press is arranged on the blowdown pipeline.

[0017] The technical effect of the utility model lies in:

[0018] (1) The softening-filtration process is adopted to remove the scale-forming cations such as calcium and magnesium from water, compared with the traditional addition of chemical scale inhibitors, the process has good scale inhibition effect, small sludge content, and can completely eliminate the hidden danger of scale formation in equipment, pipelines, downhole pipe wall and formation under the condition of different temperature, pressure, flow rate and other conditions;

[0019] (2) Compared with the traditional oilfield water treatment of adding only chemical precipitants to remove scale-forming cations, the ultrafiltration membrane group is connected after the softening precipitation tank, which can filter the suspension liquid containing a large amount of initial precipitates through the ultrafiltration membrane group, on the one hand, the water quality after softening and precipitation can be quickly purified, on the other hand, because the ultrafiltration membrane group concentrates the insoluble precipitates at the concentrated water outlet, therefore, the suspension liquid of the concentrated precipitates returns to the softening precipitation tank due to the increase of concentration, which can greatly shorten the precipitation hydraulic retention time of carbonate insoluble substances in the softening precipitation tank, improve the treatment efficiency, and reduce the equipment volume of the precipitation tank;

[0020] (3) High degree of automation, online monitoring of calcium ions and magnesium ions can be realized, so as to adjust the aeration amount of the precipitant and carbon dioxide in real time;

[0021] (4) The process is short and efficient, which can make the water quality after treatment meet the water quality index of the fractured rock reservoir water injection, and the reservoir damage rate of the reinjection water after treatment is reduced by more than 30%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a structural schematic view of the utility model.

[0023] Fig. 1 is a structural schematic view of the utility model. DETAILED DESCRIPTION

[0024] Example 1

[0025] The application discloses a high-efficiency short-range unconventional oilfield wastewater mixed-layer reinjection water treatment device, which comprises, in sequence, an oil removal tank 2, a softening and precipitation tank 3, an ultrafiltration membrane group 4, a clean water tank 5 and a water distribution pipe network 6; the oil removal tank 2 is connected to external oilfield wastewater; the oil removal tank 2 is further connected with a flocculant dosing tank 8, a coagulant aid dosing tank 9 and a pH regulator dosing tank 10; the flocculant dosing tank 8 and the coagulant aid dosing tank 9 are both connected to the top of the oil removal tank 2 through a dosing pump; the softening and precipitation tank 3 is connected with the pH regulator dosing tank 10 and a softening and precipitation agent dosing tank 11; the pH regulator dosing tank 10 is connected to the top of the oil removal tank 2 and the softening and precipitation tank 3 through a dosing pump;

[0026] The softening and precipitation agent in the softening and precipitation agent dosing tank 11 is a sodium carbonate or potassium carbonate aqueous solution, and the molar amount of the softening and precipitation agent is 1-1.5 times the sum of the molar amounts of the precipitated cations. The flocculant is a polyaluminum chloride or polyferric sulfate aqueous solution, and the amount of the flocculant is 500-2000 ppm. The coagulant aid is a polyacrylamide aqueous solution, and the amount of the coagulant aid is 50-500 ppm.

[0027] The specific implementation process of the embodiment is as follows:

[0028] In the first step, external oilfield wastewater (unconventional oilfield wastewater) enters the oil removal tank 2 for pretreatment; a pH regulator is pumped in to adjust the pH to 7-8, then a flocculant and a coagulant aid are pumped in; after the wastewater is reacted in the oil removal tank 2 for a certain period of time, the floating oil and most of the suspended solids are removed, and the supernatant flows into the softening and precipitation tank 3;

[0029] In the second step, a pH regulator is added into the softening and precipitation tank 3 to adjust the pH to 9-11, and a certain amount of softening and precipitation agent is added; after the wastewater is reacted in the softening and precipitation tank 3, the soluble scale-forming cations (calcium ions, magnesium ions and the like) in the wastewater can be converted into carbonate insoluble substances; since the initial precipitates are mostly in an amorphous state, the particle size is small, and there is not enough time for aggregation and precipitation, therefore the effluent from the softening and precipitation tank 3 is a suspension liquid containing a large amount of carbonate insoluble substances;

[0030] In the third step, the suspension liquid enters the ultrafiltration membrane group 4 for rapid filtration; the ultrafiltration membrane in the ultrafiltration membrane group 4 can effectively filter the remaining small amount of suspended solids in the raw wastewater and the carbonate insoluble substances in the suspension liquid; the clean water filtered by the ultrafiltration membrane group 4 then enters the clean water tank;

[0031] In the fourth step, the permeate water at the effluent port of the ultrafiltration membrane group 4 is pumped into the clean water tank 5;

[0032] In the fifth step, the reinjection water in the clean water tank 5 is injected into corresponding injection wells through the water distribution pipe network 6.

[0033] Embodiment 2

[0034] On the basis of embodiment 1, further comprising that the softening and precipitation tank 3 is also connected with a carbon dioxide aeration pipe 19, and in addition to adding softening and precipitation reagent, a certain amount of carbon dioxide can also be introduced into the softening and precipitation tank 3 through the carbon dioxide aeration pipe 19, and the carbon dioxide is partially dissolved in water under alkaline condition to generate carbonate, so as to capture scale-forming ions, and scale-forming cations exist in the wastewater in the form of carbonate insoluble substance; the carbonate insoluble substance is partially precipitated at the bottom of the softening and precipitation tank 3 in the initial stage of formation, and most of it is still suspended in the wastewater in the form of micro-floc, so that the effluent of the softening and precipitation tank 3 is a suspension liquid containing a large amount of carbonate insoluble substance.

[0035] Embodiment 3

[0036] On the basis of embodiment 2, further comprising an ion online monitoring unit, the ion online monitoring unit comprises a scale-forming ion measuring sensor 12 located in the softening and precipitation tank 3 and an external computer 13 located outside the softening and precipitation tank 3, and the scale-forming ion measuring sensor 12 is electrically connected with the external computer 13; the scale-forming ion measuring sensor 12 includes but is not limited to a calcium ion sensor and a magnesium ion sensor, and both the calcium ion sensor and the magnesium ion sensor are electrically connected with the external computer 13.

[0037] Embodiment 4

[0038] On the basis of embodiment 3, further comprising that the softening and precipitation tank 3 is provided with a softening and precipitation effluent outlet and a sludge outlet; the softening and precipitation effluent outlet is connected with the water inlet of the ultrafiltration membrane group 4, and the sludge outlet is externally discharged through a sludge discharge pipeline, and a filter press 7 is arranged on the sludge discharge pipeline; the ultrafiltration membrane group 4 is provided with an ultrafiltration membrane group 4 effluent outlet and a concentrated water outlet, the ultrafiltration membrane group 4 effluent outlet is connected to a purification tank, and the concentrated water outlet is connected to the softening and precipitation tank 3, and the concentrated water containing a high concentration of carbonate insoluble substance is returned to the softening and precipitation tank 3, so that calcium, magnesium and other scale-forming cations are captured and removed from the water body through the softening and filtration process; the carbonate insoluble substance in the softening and precipitation tank 3 will quickly settle at the bottom to produce precipitation sludge as the concentration increases and the settling time increases, and the precipitation sludge is regularly discharged from the bottom of the softening and precipitation tank 3 and externally transported after being compressed and reduced in volume by the filter press 7.

[0039] Embodiment 5

[0040] On the basis of embodiment 4, further comprising that the ultrafiltration membrane group 4 is provided with a water inlet pipeline and a water outlet pipeline; the water inlet pipeline communicates the softening and precipitation effluent outlet and the water inlet of the ultrafiltration membrane group 4, and a water inlet pump 15 and a flow meter 16 are arranged on the water inlet pipeline; the water outlet pipeline communicates the ultrafiltration membrane group 4 effluent outlet and the water inlet of the purification tank. The water distribution pipe network 6 comprises a plurality of parallelly arranged water injection pipelines; a first booster pump 17 and a second booster pump 18 are sequentially arranged between the water injection pipeline and the water tank 5. The external oilfield wastewater is connected to the oil removal tank 2 through a buffer tank 1, and a raw water pump 14 is further arranged between the external oilfield wastewater and the buffer tank 1.

[0041] The specific implementation process of the embodiment is as follows:

[0042] In the first step, the external oilfield wastewater (non-conventional oilfield wastewater) is pumped into the buffer tank 1 by the raw water pump 14 to keep the water quality stable, so that the wastewater with stable flow is obtained, and the influence of flow or pressure fluctuation on the subsequent water treatment equipment is reduced.

[0043] In the second step, the wastewater with stable flow enters the oil removal tank 2 for pretreatment, a pH regulator is pumped in to adjust the pH to 7-8, and then a flocculant and a coagulant aid are pumped in. After the wastewater is reacted in the oil removal tank 2 for a certain period of time, the floating oil and most of the suspended solids are removed, and the supernatant flows into the softening and precipitation tank 3.

[0044] In the third step, a pH regulator is added to the softening and precipitation tank 3 to adjust the pH to 9-11, and a certain amount of softening and precipitation agent is added. After the wastewater is reacted in the softening and precipitation tank 3, the soluble scale-forming cations (calcium ions, magnesium ions, etc.) in the wastewater can be converted into carbonate insoluble substances. At the same time, a certain amount of carbon dioxide can be introduced into the softening and precipitation tank 3 through the carbon dioxide aeration pipe 19. Under alkaline conditions, the carbon dioxide is partially dissolved in water and generates carbonate, thereby capturing scale-forming ions, so that the scale-forming cations exist in the wastewater in the form of carbonate insoluble substances. A small part of the carbonate insoluble substances is precipitated at the bottom of the softening and precipitation tank 3 in the initial stage of formation, and most of them are still suspended in the wastewater in the form of micro-flocs. Therefore, the effluent from the softening and precipitation tank 3 is a suspension containing a large amount of carbonate insoluble substances.

[0045] In the fourth step, the suspension is pressurized by the water inlet pump 15 and then enters the ultrafiltration membrane group 4 for filtration. The ultrafiltration membrane in the ultrafiltration membrane group 4 can effectively filter the remaining small part of the suspended solids in the raw water of the wastewater and the carbonate insoluble substances in the suspension. The clear water filtered by the ultrafiltration membrane group 4 then enters the clear water tank, and the concentrated water containing high-concentration carbonate insoluble substances is returned to the softening and precipitation tank 3, so that the scale-forming cations such as calcium and magnesium are captured and removed from the water body through the softening and filtration process.

[0046] In the fifth step, as the concentration of carbonate insoluble substances in the softening and precipitation tank 3 increases and the settling time increases, the carbonate insoluble substances will gradually settle at the bottom to form a precipitate. The sludge is periodically discharged from the bottom of the softening and precipitation tank 3 and then transported out after being compressed by the filter press 7.

[0047] In the sixth step, the effluent from the outlet of the ultrafiltration membrane group 4 is pumped into the clean water tank 5.

[0048] In the seventh step, the reinjection water in the clean water tank 5 is pressurized by the primary booster pump 17 and then pressurized by the secondary booster pump 18, and then injected into the corresponding injection well along the injection pipeline.

[0049] Specific experimental case

[0050] In a shale oil horizontal well exploitation site in northern Shaanxi, the main layer for shale oil exploitation is Chang 7 layer. It is planned to reinject the treated produced water of the horizontal well into Chang 2 layer, a conventional layer in the block. According to the water quality analysis results, the Chang 2 formation water belongs to NaHCO3 water type and contains a certain amount of SO4 2- , CO3 2- , etc. The produced water of Chang 7 belongs to CaCl2 water type and contains a considerable amount of Ca 2+ , Mg 2+ , etc. Therefore, when the produced water of Chang 7 is mixed and reinjected into Chang 2 layer, insoluble carbonates such as calcium carbonate and magnesium carbonate are generated, which poses a serious scaling risk. Therefore, the produced water of Chang 7 needs to be treated, especially to remove Ca and Mg, so as to realize the safe reinjection of the produced water of Chang 7 into Chang 2 layer. The specific treatment method is as follows:

[0051] The produced water is first pumped into the buffer tank 1 by the raw water pump 14 for water quality homogenization and stabilization, and then enters the oil removal tank 2 at a certain flow rate. The pH regulator is pumped into the oil removal tank 2 to maintain the pH at 7-8, and then the PAC solution and PAM solution are pumped into the oil removal tank 2 for coagulation reaction to remove most of the oil and suspended solids in the water. Then the effluent from the oil removal tank 2 enters the softening and precipitation tank 3, and the pH regulator is added to maintain the pH at 9-9.5. Then sodium carbonate solution is pumped into the softening and precipitation tank 3. The carbonate in sodium carbonate can react with the dissolved calcium and magnesium ions in the wastewater to form calcium carbonate and magnesium carbonate micro-floc suspended in the water. The effluent from the softening and precipitation tank 3 is pressurized by the water inlet pump 15 and enters the ultrafiltration membrane group 4. The ultrafiltration membrane group 4 can quickly filter the calcium carbonate, magnesium carbonate and other small precipitate flocs in the influent, and further filter the suspended solids in the produced wastewater. The permeate water produced by ultrafiltration is discharged into the clean water tank 5, and the concentrated water is returned to the softening and precipitation tank 3. With the continuous return of the ultrafiltration concentrated water, the concentration of carbonate insoluble substances in the softening and precipitation tank 3 increases, thereby accelerating the sedimentation of carbonate insoluble substances in the softening and precipitation tank 3. The bottom of the softening and precipitation tank 3 is funnel-shaped and is regularly discharged. The sludge is pressed by the filter press 7 to produce mud cake with low water content, which is then transported out. The permeate water in the clean water tank 5 is the reinjection water, and its water quality meets the water quality index of clastic rock oil reservoir. Compared with the untreated produced wastewater, the reinjection water reduces the reservoir damage rate by 35.2%. The reinjection water in the clean water tank 5 is pressurized by the primary booster pump 17 and the secondary booster pump 18 and then reinjected into different injection wells according to the water demand on site.

Claims

1. A high-efficiency short-range unconventional oilfield wastewater mixed layer reinjection water treatment device, characterized in that: It comprises sequentially connected oil removal tank (2), softening sedimentation tank (3), ultrafiltration membrane group (4), purified water tank (5) and water distribution pipe network (6); the oil removal tank (2) is connected to external oilfield wastewater, and the oil removal tank (2) is also connected with flocculant dosing tank (8), coagulant aid dosing tank (9) and pH regulator dosing tank (10), the flocculant dosing tank (8) and the coagulant aid dosing tank (9) are connected to the top of the oil removal tank (2) through a dosing pump; the softening sedimentation tank (3) is connected with the pH regulator dosing tank (10) and the softening sedimentation agent dosing tank (11), and the pH regulator dosing tank (10) is connected to the top of the oil removal tank (2) and the softening sedimentation tank (3) through a dosing pump.

2. The efficient short-range unconventional oilfield wastewater mixed layer reinjection water treatment device according to claim 1, characterized in that: The softening sedimentation tank (3) is also connected with a carbon dioxide aeration pipe (19).

3. The apparatus for treating short-range unconventional oilfield wastewater according to claim 1, wherein: It also comprises an ion online monitoring unit, which comprises a scale-forming ion measuring sensor (12) located in the softening sedimentation tank (3) and an external computer (13) located outside the softening sedimentation tank (3), and the scale-forming ion measuring sensor (12) is electrically connected with the external computer (13).

4. The apparatus for treating short-range unconventional oilfield wastewater according to claim 3, wherein: The scale-forming ion measuring sensor (12) comprises but is not limited to a calcium ion sensor and a magnesium ion sensor, and both the calcium ion sensor and the magnesium ion sensor are electrically connected with the external computer (13).

5. The apparatus for treating short-range unconventional oilfield wastewater according to claim 3, wherein: The softening sedimentation tank (3) is provided with a softening sedimentation effluent outlet and a sludge outlet; the softening sedimentation effluent outlet is connected with the water inlet of the ultrafiltration membrane group (4); and the sludge outlet is externally discharged through a sludge discharge pipeline.

6. The apparatus for treating short-range unconventional oilfield wastewater according to claim 5, wherein: The ultrafiltration membrane group (4) is provided with an ultrafiltration membrane group (4) effluent outlet and a concentrated water outlet, the ultrafiltration membrane group (4) effluent outlet is connected to the purification tank, and the concentrated water outlet is connected to the softening sedimentation tank (3).

7. The apparatus for treatment of short-range unconventional oilfield wastewater of claim 6, wherein: The ultrafiltration membrane group (4) is provided with a water inlet pipeline and a water outlet pipeline; the water inlet pipeline communicates the softening sedimentation effluent outlet and the water inlet of the ultrafiltration membrane group (4), and the water inlet pipeline is provided with a water inlet pump (15) and a flow meter (16); and the water outlet pipeline communicates the ultrafiltration membrane group (4) effluent outlet and the water inlet of the purification tank.

8. The apparatus for treating short-range unconventional oilfield wastewater according to claim 7, wherein: The water distribution pipe network (6) comprises a plurality of parallelly arranged water injection pipelines; a first booster pump (17) and a second booster pump (18) are sequentially arranged between the purified water tank (5) and the water injection pipelines.

9. The apparatus for treating short-range unconventional oilfield wastewater of claim 1, wherein: The external oilfield wastewater is connected to the oil removal tank (2) through a buffer tank (1), and a raw water pump (14) is further arranged between the external oilfield wastewater and the buffer tank (1).

10. The apparatus for treating short-range unconventional oilfield wastewater according to claim 5, wherein: A filter press (7) is arranged on the sludge discharge pipeline.

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