CN-122010336-A - Treatment system and treatment method for fracturing flowback fluid

CN122010336ACN 122010336 ACN122010336 ACN 122010336ACN-122010336-A

Abstract

The invention relates to a treatment system and a treatment method of fracturing flowback fluid, wherein the treatment system comprises an adjusting precipitation unit, a dissolved air flotation unit, a direct filtration membrane filtration unit, a reverse osmosis membrane concentration unit, an MVR evaporation crystallization unit and an electrochemical oxidation unit which are sequentially connected along a treatment flow. The MVR evaporation crystallization unit comprises a vapor-water separator, a vacuum device communicated with a vapor outlet of the vapor-water separator and a condensate pipeline communicated with a condensate outlet of the vapor-water separator, wherein the vapor-water separator is provided with a sodium sulfate feeding device, and the vacuum device is used for controlling the vapor pressure in the vapor-water separator. The water inlet end of the electrochemical oxidation unit is connected with a condensate pipeline of the MVR evaporation crystallization unit. The method has the beneficial effects that a plurality of processing units are sequentially connected, suspended matters, colloid, oil, hardness, silicon, high-concentration salt and refractory organic matters in the flowback fluid can be systematically removed, and finally purified water meeting the discharge or reuse standard is produced, so that the recycling and near-zero discharge targets of the waste water are achieved.

Inventors

WANG XU
LI TING
WANG YANBING
ZHANG WEI
WANG YUCHEN

Assignees

中煤(北京)环保股份有限公司

Dates

Publication Date: 20260512
Application Date: 20260227

Claims (10)

1. The treatment system for the fracturing flow-back fluid is characterized by comprising an adjusting and precipitating unit, a dissolved air flotation unit, a direct filtration membrane filtering unit, a reverse osmosis membrane concentration unit, an MVR evaporation crystallization unit and an electrochemical oxidation unit which are sequentially connected along a treatment flow; The MVR evaporation crystallization unit comprises a vapor-water separator, a vacuum device communicated with a vapor outlet of the vapor-water separator and a condensate pipeline communicated with a condensate outlet of the vapor-water separator, wherein the vapor-water separator is provided with a sodium sulfate adding device for adding sodium sulfate into evaporation stock solution in the vapor-water separator, the vacuum device is used for controlling the vapor pressure in the vapor-water separator, and the condensate outlet is used for discharging condensate water; and the water inlet end of the electrochemical oxidation unit is connected with a condensate pipeline of the MVR evaporation crystallization unit.
2. The treatment system for frac flowback fluid of claim 1, wherein: The direct filtration membrane filtration unit comprises a primary dealkalization reaction tank (31), a secondary dealkalization reaction tank (32) and a direct filtration membrane component (36) which are connected in sequence; The first-stage dealkalization reaction tank (31) is provided with a first lime adding device for adding lime to remove bicarbonate alkalinity of the liquid to be treated in the first-stage dealkalization reaction tank (31); the second-stage dealkalization reaction tank (32) is provided with a second lime feeding device which is used for continuously feeding lime so as to enable the solution to be treated in the second-stage dealkalization reaction tank (32) to generate magnesium hydroxide sediment and remove silicon; The filtering membrane adopted by the straight filtering membrane component (36) is a hybrid membrane formed by compounding inorganic materials and PTFE, and the filtering pore diameter of the hybrid membrane is 0.01-0.5 mu m.
3. The treatment system for frac flowback fluid of claim 2, wherein: a silicon removal agent adding device is further arranged in the secondary dealkalization reaction tank (32), an on-line silicon content monitor is arranged on a water inlet pipe of the secondary dealkalization reaction tank (32), and the silicon removal agent adding device is in signal connection with the on-line silicon content monitor; When the on-line silicon content monitor detects that the silicon content in the inlet water is greater than 50mg/L, the silicon removing agent adding device is started to add the silicon removing agent, and when the silicon content in the inlet water is detected to be less than 50mg/L, the silicon removing agent adding device is closed.
4. The treatment system for frac flowback fluid of claim 1, wherein: the steam-water separator is also provided with a calcium sulfate adding device; And the method is used for adding calcium sulfate into the evaporation stock solution in the steam-water separator.
5. The treatment system for frac flowback fluid of claim 1, wherein: the reverse osmosis membrane concentration unit is provided with a concentrated water circulation mechanism, and the concentrated water circulation mechanism is provided with a variable-frequency high-pressure pump, a TDS on-line monitor and a controller; The TDS on-line monitor is arranged on a concentrated water pipeline of the reverse osmosis membrane concentration unit and is used for detecting the TDS concentration of a concentrated water side in real time, the TDS on-line monitor is in signal connection with the input end of the controller, and the output end of the controller is in signal connection with the variable-frequency high-pressure pump; The controller can adjust the operating frequency of the variable-frequency high-pressure pump according to the detection signal of the TDS on-line monitor so as to control the TDS concentration of the concentrate side to be in the range of 75000mg/L to 100000 mg/L; the RO membrane component (43) of the reverse osmosis membrane concentration unit is a coiled pipe type reverse osmosis membrane component with the pressure resistance of more than or equal to 90 bar.
6. The treatment system for frac flowback fluid of claim 1, wherein: the dissolved air flotation unit comprises a gel breaking reaction tank (21) and a dissolved air flotation device which are connected in sequence; The gel breaking reaction tank (21) is provided with a gel breaker adding device which is used for adding the gel breaker to reduce the viscosity of the fracturing flowback fluid, and the gel breaker adding device can adjust the adding amount of the gel breaker according to the viscosity of the effluent and/or the concentration of the soluble organic matters; the dissolved air flotation device comprises an air flotation tank, a dissolved air water pump (24) and a dissolved air water tank (25), wherein an inlet of the dissolved air water pump (24) is communicated with a clear water area of the air flotation tank, an outlet of the dissolved air water pump (24) is communicated with a water inlet of the dissolved air water tank (25), and a water outlet of the dissolved air water tank (25) is communicated with a water inlet area of the air flotation tank through a releaser to form a water outlet backflow dissolved air path; The reflux ratio of the dissolved air flotation device is more than or equal to 50%, and the dissolved air pressure is more than or equal to 0.5MPa.
7. The treatment system for frac flowback fluid of claim 1, wherein: The electrochemical oxidation unit comprises an electrochemical catalytic oxidation device (61) for performing advanced oxidation treatment on condensate from the MVR evaporation crystallization unit so as to remove organic matters and ammonia nitrogen in the condensate.
8. The treatment system for frac flowback fluid of claim 1, wherein: the device also comprises a sludge collecting and discharging unit; the sludge collecting and discharging unit is connected with the sludge discharging ports of the regulating and precipitating unit, the dissolved air floatation unit and the direct filtration membrane filtering unit and is used for collecting and discharging sludge and waste residues generated by the units.
9. A method of treating a frac flowback fluid, using the treatment system of any one of claims 1-8, comprising the steps of: s1, introducing the fracturing flowback fluid into the regulating and precipitating unit to perform water quality and water quantity homogenization and preliminary sedimentation treatment; S2, introducing the effluent of the S1 into the dissolved air flotation unit for gel breaking and air flotation separation treatment, and removing suspended matters, colloid and partial organic matters; S3, introducing the effluent of the S2 into the straight filter membrane filtration unit for dealkalization and desilication and membrane filtration treatment to remove residual impurities; s4, introducing the effluent of the S3 into the reverse osmosis membrane concentration unit for concentration to obtain concentrated solution and produced water; S5, introducing the concentrated solution obtained in the step S4 into the MVR evaporation crystallization unit, adding sodium sulfate in the evaporation process, controlling the evaporation temperature to be not higher than 60 ℃, and obtaining solid salt and condensate through evaporation crystallization; And S6, introducing the condensate generated by the MVR evaporation crystallization unit in the S5 into the electrochemical oxidation unit for deep oxidation treatment to obtain produced water.
10. The method for treating a frac flowback fluid according to claim 9, wherein: in the step S3, the dealkalization and desilication treatment comprises the steps of introducing water discharged from the step S2 into a primary dealkalization reaction tank, adding lime and controlling the pH value of a reaction system to be 8.0-9.0 so as to remove bicarbonate alkalinity, then introducing the water discharged into a secondary dealkalization reaction tank, adding lime again and controlling the pH value of the reaction system to be 9.0-10.0, desilication is carried out by utilizing the generated magnesium hydroxide precipitate, and selectively adding a desilication agent according to the content of the silicon in the water, so that the content of the silicon in the water is reduced to be below 50 mg/L; In the step S4, the TDS concentration of the concentrated solution is controlled in the range of 75000mg/L to 100000mg/L by controlling the concentrated water circulation and the variable-frequency high-pressure pump of the reverse osmosis membrane concentration unit; In the step S5, the molar quantity of sodium sulfate added is not less than the total molar quantity of calcium ions and magnesium ions in the concentrated solution entering the MVR evaporation crystallization unit.

Description

Treatment system and treatment method for fracturing flowback fluid Technical Field The invention relates to the technical field of oil and gas field wastewater treatment, in particular to a treatment system and a treatment method of fracturing flowback fluid. Background The fracturing technology is a key technology for improving the yield of an oil and gas well in petroleum and natural gas exploitation, and a high-pressure fracturing fluid is injected into a stratum to enable the stratum to generate cracks, so that an oil and gas seepage channel is increased. The water-based fracturing fluid is widely applied because of low cost and controllable performance, and is usually based on clear water or thickened water, and various chemical auxiliary agents such as a thickening agent (e.g. vegetable gum), a cross-linking agent, a gel breaker, a bactericide and the like are added. After the fracturing operation is finished, part of the fracturing fluid can carry rock scraps, crude oil, dissolved salts and other substances in the stratum to return to the ground, so that a fracturing flowback fluid is formed. The liquid mainly originates from well flushing wastewater, gel breaking flowback fluid and unused fracturing base fluid, the production amount of the liquid can reach 20% -80% of the total amount of injected fracturing fluid, and the liquid has the characteristics of intermittent discharge, complex components, high pollutant concentration and the like. The fracturing flowback fluid has remarkable water quality difference due to the influence of the formula of the fracturing fluid, flowback period and stratum condition, and is generally characterized by high turbidity, complex composition, high viscosity, serious emulsification, difficult solid-liquid separation, high Chemical Oxygen Demand (COD) mainly from a thickener (such as hydroxypropyl guanidine gum) and a surfactant which are difficult to degrade, high Total Dissolved Solids (TDS) content, high hardness, outstanding chloride ion concentration, and a certain amount of heavy metals, fluoride and the like, and also carries suspended matters, petroleum, salts, microorganisms and the like in the stratum besides various chemical additives in the original fracturing fluid. According to the current industry standard, the disposal mode of the fracturing flowback fluid mainly comprises recycling, reinjection and discharge. With the increasingly strict environmental protection requirements, the reinjection treatment is limited by the increasingly strict formation compatibility and environmental risk management and control, and the recycling can not completely absorb the generated flowback fluid, and particularly during the non-fracturing operation period, a large amount of flowback fluid needs to seek the drainage or other recycling ways. At present, the discharge or surface reuse (such as farm irrigation, urban miscellaneous use and the like) needs to meet the wastewater comprehensive discharge standard (GB 8978) or stricter recycling water quality standard, wherein the indexes such as COD, ammonia nitrogen, salt, chloride ions, hardness and the like have higher requirements, and the COD removal rate is less than 50 percent in the traditional oil separation-coagulation-filtration process, so that the treatment requirements can not be met. In order to achieve high standard emission or recycling, the prior art generally adopts multistage advanced treatment processes including units of air floatation, catalytic oxidation, softening and precipitation, biochemical treatment, membrane concentration, evaporation and crystallization and the like. For example, some projects employ a combined flow of air flotation, advanced oxidation, multi-stage membrane concentration, MVR evaporation, deep oxidation. However, the following prominent problems still exist in practical applications of this type of process: (1) The process adaptability is weak, the water quality of the fracturing flowback fluid is affected by multiple factors such as the fracturing fluid formula, the formation lithology, the flowback stage and the like, the interwell difference is large, and the time sequence fluctuation is severe. The immobilized process flow is difficult to dynamically respond to water quality change, and is easy to cause membrane system fouling, evaporation unit scaling or biochemical system failure, and the operation stability is poor; (2) The pretreatment requirements are harsh, an evaporation crystallization unit (represented by MVR technology of a main stream of well sites in particular) is limited by the temperature rising capability of a compressor (usually only 20-24 ℃), the hardness of the inlet water is required to be almost completely removed, the process of deep softening (such as high-density precipitation and ion exchange) is long, the medicament dependence is strong, the regulation difficulty is high when the water quality fluctuates, and the residual hardness is easy to cau