Short-process high-salinity fracturing flow-back fluid treatment process

Abstract

The invention relates to the technical field of fracturing flow-back fluid treatment, and discloses a short-process hypersalinity fracturing flow-back fluid treatment process which comprises the following steps: S1, conveying hypersalinity fracturing flow-back fluid from a stock solution water tank to a ceramic ultrafiltration system through a water inlet pump, and filtering the hypersalinity fracturing flow-back fluid through a self-cleaning filter before the hypersalinity fracturing flow-back fluid enters a ceramic membrane to remove large-particle suspended solids; according to the method, the high-salinity fracturing flow-back fluid is treated by using a ceramic ultrafiltration and immersion combustion evaporation process, so that the treatment efficiency can be kept stable, and the final produced water can reach the emission standard; according to the process, the dosage of chemicals is small, generated solid products are few, and the treatment cost of the solid products is low; the process can be continuously operated, and the system does not need to be frequently started and stopped; the process flow is short, the occupied area is small, the number of operators is small, the operation cost is reduced, and finally the purposes of high treatment efficiency, short process flow, low treatment cost and the like for treating the high-salinity fracturing flow-back fluid wastewater are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of fracturing flowback fluid treatment, in particular to a short-flow process for treating high-mineralization fracturing flowback fluid. Background Art

[0002] Shale gas is a strategically important resource, typically stored in difficult-to-extract sedimentary rocks. Recovering economically viable hydrocarbons requires specialized processes. Traditional oil and gas field extraction methods are unable to unlock the potential of low-permeability fields, making hydraulic fracturing a key tool for increasing production. Hydraulic fracturing utilizes hydraulic pressure to inject fracturing fluid, applying pressure to the oil layer, disrupting the reservoir and enhancing the hydraulic fracturing process, ultimately increasing permeability and boosting oil and gas field production. This fracturing fluid, known as "fracturing flowback," flows back from the oil field during extraction and transportation.

[0003] To improve fracturing effectiveness and fluid properties, fracturing fluids are often added with various chemical additives, such as thickeners, pH adjusters, surfactants, crosslinkers, clay stabilizers, and breakers. This complicates the handling of fracturing flowback fluids. Furthermore, upon entering the formation, the fracturing fluid mixes with formation water, carrying with it large quantities of clay minerals, heavy metal ions, and bacteria from deep within the formation during its return flow. Consequently, fracturing flowback fluids are characterized by high mineralization, high viscosity, high suspended solids content, and high COD values. Direct discharge to the surface can cause severe environmental pollution. Furthermore, shale gas production is often carried out in remote, arid, and water-scarce regions, and the fracturing process requires significant amounts of freshwater, exacerbating water resource imbalances. Therefore, effectively handling fracturing flowback fluids, recycling and reusing them, or performing harmless treatment to reduce pollutant emissions, is not only a requirement for environmental protection in development areas but also a key technical component of clean and sustainable shale gas development.

[0004] Currently, there are three main methods for disposing fracturing flowback fluid both domestically and internationally: first, discharge in compliance with the first-level standard of the national "Comprehensive Wastewater Discharge Standard" (GB8978-1996); second, reinjection into the formation after treatment to meet the standards in accordance with the "Recommended Indicators and Analysis Methods for Water Quality in Clastic Reservoirs"; and third, reuse as drilling fluid or fracturing fluid, prepared in accordance with energy industry standards (NB / T14002.3-2022). Deep well reinjection is limited by regional geology and external environmental conditions and carries certain geophysical and environmental risks, resulting in fewer applications. The requirements for reused fluids are extremely high, requiring stable water quality, no scaling tendency, and good compatibility with chemical additives. Currently, the primary method for disposing fracturing flowback fluid is discharge in compliance with standards.

[0005] Considering the water quality characteristics of fracturing flowback fluid, treatment that meets discharge standards requires the removal of suspended solids, reduction of hardness, mineralization, COD, etc. The traditional treatment process is "turbidity removal, softening pretreatment (flotation, high-density tanks, softening membranes, etc.) + organic matter treatment (mostly advanced oxidation or combined advanced oxidation processes) + concentration treatment (mostly high-pressure reverse osmosis and electrodialysis depending on the influent water quality) + partition evaporation (MVC, MVR)". This conventional process is suitable for treating fracturing flowback fluid with low mineralization. When the mineralization of the flowback fluid is high, using this treatment process will result in equipment scaling, frequent shutdowns for cleaning, and inability to operate continuously; high chemical consumption, high sludge production, and high operating costs; cumbersome process flow, large equipment footprint, and high investment costs. Therefore, a short-process high-mineralization fracturing flowback fluid treatment process is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a short-flow process for treating high-mineralization fracturing flowback fluid to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a short-flow high-mineralization fracturing flowback fluid treatment process, comprising the following steps:

[0008] S1. High-mineralization fracturing flowback fluid is transported from the raw liquid tank to the ceramic ultrafiltration system through the water inlet pump. Before entering the ceramic membrane, it is filtered through a self-cleaning filter to remove large suspended particles;

[0009] S2. The pre-treated return liquid enters the ceramic ultrafiltration system. Under the interception effect of the ceramic membrane, the produced water is discharged into the produced water tank through the water outlet, and the concentrated water returns to the raw liquid tank for cyclic treatment;

[0010] S3, backwashing and chemical cleaning, using the produced water in the produced water tank to backwash the ceramic membrane;

[0011] S4. The water produced by the ceramic ultrafiltration system is transported to the submerged combustion evaporation system through an evaporation feed pump. Landfill gas, anaerobic biogas or natural gas is used as energy to heat, evaporate, concentrate and crystallize the produced water. The steam and non-condensable gas generated by evaporation are removed from the mist droplets through a separation tower. The steam enters the condensation system for condensation and discharge after meeting the standards. The non-condensable gas enters the non-condensable gas treatment system.

[0012] S5. The non-condensable gas passes through the acid spray tower and the alkali spray tower in sequence. The alkaline substances in the gas phase react with the acidic substances in the liquid phase to form soluble salts. The acidic substances in the gas phase react with the alkaline substances in the liquid phase to form soluble salts. The treated non-condensable gas is discharged through the exhaust pipe in accordance with regulations. The soluble salts at the bottom of the tower are returned to the submerged combustion evaporation system.

[0013] S6. The saturated residual liquid produced by evaporation is transported to the salt mud dehydration system through a lifting pump. The dehydrated salt mud is packaged and centrally processed, and the supernatant is returned to the submerged combustion evaporation system.

[0014] Preferably, in the above-mentioned step S1, the filtering accuracy is 50 to 500 μm.

[0015] Preferably, in the above: in S2, the ceramic ultrafiltration system comprises a ceramic membrane;

[0016] The single membrane area of ​​the ceramic membrane is 10 to 25 m 2 , the operating flux is 20~150LMH, the operating pH range is 1~13.5, the operating temperature range is 15~40℃, and the operating pressure range is 0.1~0.6MPa.

[0017] Preferably, in the above-mentioned step S3, the ceramic ultrafiltration system is backwashed once with produced water every 30 to 60 minutes of operation, the backwash time is 30 to 120 seconds, the backwash flux is 40 to 240 LMH, the backwash pH range is 1 to 13.5, and the backwash water enters the raw water tank.

[0018] Preferably, the ceramic ultrafiltration system is chemically cleaned after running for 3 to 4 months, using sodium hydroxide, citric acid and hydrochloric acid to remove residual organic matter, colloids and microorganisms;

[0019] The concentration of sodium hydroxide is 0.1-1.0%, the concentration of citric acid is 5-20%, and the concentration of hydrochloric acid is 0.1-0.4%. The cleaning agent enters the ceramic ultrafiltration system through the chemical cleaning system, and the cleaned sewage flows back to the chemical cleaning system.

[0020] Preferably, in the above step S6, the moisture content of the dehydrated salt mud is 40-70%.

[0021] The present invention also provides a short-process system for treating high-mineralization fracturing flowback fluid, comprising a raw liquid water tank, a ceramic ultrafiltration system, a produced water tank, a backwash system, a chemical cleaning system, an immersion combustion evaporation system, a steam condensation system, a non-condensable gas system, a salt mud dehydration system, a condensate water tank, and a dosing system;

[0022] The raw liquid water tank is used to temporarily store the high-mineralization fracturing flowback fluid to be processed;

[0023] The ceramic ultrafiltration system is used to pre-treat fracturing flowback fluid, remove silica, suspended matter and organic matter in the water, and reduce the viscosity and turbidity of the water;

[0024] The produced water tank is used to store the produced water treated by the ceramic ultrafiltration system, providing a stable water source for the subsequent submerged combustion evaporation system;

[0025] The backwash system is used to regularly backwash the ceramic membrane using produced water to prevent clogging of the membrane surface;

[0026] The chemical cleaning system is used to regularly perform chemical cleaning on the ceramic membrane;

[0027] The submerged combustion evaporation system is used to deeply treat the water produced by the ceramic ultrafiltration system, removing TDS, COD, ammonia nitrogen, calcium, magnesium ions and salt ions in the water through heating, evaporation, concentration and crystallization;

[0028] The steam condensation system is used to condense the steam generated by evaporation into liquid water;

[0029] The non-condensable gas system is used to purify the non-condensable gas generated during the evaporation process;

[0030] The salt mud dehydration system is used to dehydrate the saturated evaporation residue produced by evaporation to reduce the volume of waste residue;

[0031] The condensed water tank is used to store the condensed water generated by the steam condensation system as a treated clean water resource;

[0032] The dosing system is used to add reagents to the submerged combustion evaporation system.

[0033] Preferably, the above: the water outlet of the raw liquid water tank is connected to the water inlet of the ceramic ultrafiltration system, the water outlet of the ceramic ultrafiltration system is connected to the water inlet of the water production tank, the water inlet of the ceramic ultrafiltration system is connected to the outlet of the backwash system, the water inlet of the ceramic ultrafiltration system is connected to the water outlet of the chemical cleaning system, the water outlet of the water production tank is connected to the water inlet of the submerged combustion evaporation system, the dosing system is connected to the inlet pipe of the submerged combustion evaporation system, the steam and non-condensable gas outlet of the submerged combustion evaporation system is connected to the inlet of the steam condensation system, the steam condensation system outlet is connected to the inlet of the condensation water tank, the non-condensable gas outlet of the steam condensation system is connected to the inlet of the non-condensable gas system, and the residual liquid outlet of the submerged combustion evaporation system is connected to the inlet of the salt mud dehydration system.

[0034] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0035] 1. The present invention provides a short-process high-mineralization fracturing flowback fluid treatment process and system, which treats high-mineralization fracturing flowback fluid through a combination of ceramic ultrafiltration and submerged combustion evaporation. First, the high-mineralization fracturing flowback fluid is pretreated by the interception effect of the ceramic ultrafiltration system, mainly removing silica, viscosity and suspended matter in the water body. Then, the submerged combustion evaporation system is used to evaporate and crystallize the fracturing flowback fluid containing high concentrations of TDS, COD, ammonia nitrogen, calcium, magnesium ions and other pollutants, ultimately producing condensed water, non-condensable gas and salt mud. Since more than 90% of the salt is discharged in the form of crystalline salt, the condensed water can meet the first-level standard in the "Integrated Sewage Discharge Standard" (GB8978-1996). After the non-condensable gas is deeply treated by acid and alkali spraying, all indicators also meet the standards.

[0036] 2. The invention uses a ceramic ultrafiltration system to pre-treat high-mineralization fracturing flowback fluid to remove silica, viscosity and suspended matter, thereby improving the treatment efficiency of the subsequent submerged combustion evaporation system. The system only requires a small amount of membrane cleaning agent and does not produce additional sludge.

[0037] 3. The present invention utilizes gas fuel to perform pressurized submerged combustion on the subsurface of the liquid through an immersion combustion evaporation system, and forms ultrafine bubbles through a special structure. The ultrafine bubbles are in direct contact with the high-mineralization fracturing return fluid for heat exchange, and the mass transfer and heat transfer efficiency is high. Moreover, because there is no partition for heat exchange, scaling and coking will not occur inside the evaporation system. While maintaining efficient processing capacity, the evaporation system can operate continuously and stably without the need for frequent shutdowns to clean equipment for coke and scale.

[0038] 4. The present invention combines ceramic ultrafiltration and submerged combustion evaporation systems to treat high-mineralization fracturing flowback fluid, which has a short process flow, reduces costs and energy consumption, reduces floor space, simplifies operation and maintenance, and enhances adaptability and flexibility to adapt to situations where land resources are scarce, costs are sensitive, and environmental requirements are high. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0040] Figure 1 is a process flow chart of the present invention;

[0041] Figure 2 This is a diagram showing the effect of direct evaporation of the fracturing flowback fluid on pollutant removal;

[0042] Figure 3This is a diagram showing the effect of pollutant removal on the fracturing flowback fluid after ceramic ultrafiltration treatment of the present invention;

[0043] Figure 4 This is a diagram showing the effect of the ceramic ultrafiltration + submerged combustion evaporation process of the present invention on pollutant removal;

[0044] Figure 5 The membrane flux diagram of the effect of temperature on silica rejection of the present invention;

[0045] Figure 6 is a viscosity removal rate graph showing the effect of temperature on silica retention rate according to the present invention;

[0046] Figure 7 The membrane flux diagram of the effect of operating pressure on silica rejection of the present invention;

[0047] Figure 8 is a viscosity removal rate diagram showing the effect of operating pressure on silica rejection rate of the present invention;

[0048] Figure 9 This is a comparison chart of the treatment effects of the submerged combustion evaporation of the present invention and ceramic ultrafiltration + submerged combustion evaporation. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which this application can be implemented. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in this application without affecting the efficacy and purpose that can be achieved by this application.

[0051] Example

[0052] See also Figure 1 The present invention provides a technical solution: a short-process high-mineralization fracturing flowback fluid treatment process, comprising the following steps:

[0053] S1. High-mineralization fracturing flowback fluid is transported from the raw liquid tank to the ceramic ultrafiltration system through the water inlet pump. Before entering the ceramic membrane, it is filtered through a self-cleaning filter to remove large suspended particles; the filtration accuracy is 50-500μm.

[0054] S2. The pre-treated return liquid enters the ceramic ultrafiltration system. Under the interception effect of the ceramic membrane, the produced water is discharged into the produced water tank through the water outlet, and the concentrated water returns to the raw liquid tank for cyclic treatment;

[0055] The ceramic ultrafiltration system includes a ceramic membrane; the material of the ceramic membrane can be TiN, and the single membrane area of ​​the ceramic membrane is 10 to 25m 2 , the operating flux is 20~150LMH, the operating pH range is 1~13.5, the operating temperature range is 15~40℃, and the operating pressure range is 0.1~0.6MPa.

[0056] The optimal operating conditions of the porcelain ultrafiltration system are: operating temperature 25-30℃, operating pressure 0.1-0.4MPa.

[0057] S3, backwashing and chemical cleaning, using the produced water in the produced water tank to backwash the ceramic membrane;

[0058] The ceramic ultrafiltration system uses produced water for backwashing every 30 to 60 minutes of operation. The backwash time is 30 to 120 seconds, the backwash flux is 40 to 240 LMH, the backwash pH range is 1 to 13.5, and the backwash water enters the raw water tank.

[0059] The ceramic ultrafiltration system is chemically cleaned after 3 to 4 months of operation, using sodium hydroxide, citric acid and hydrochloric acid to remove residual organic matter, colloids and microorganisms;

[0060] The concentration of sodium hydroxide is 0.1-1.0%, the concentration of citric acid is 5-20%, and the concentration of hydrochloric acid is 0.1-0.4%. The cleaning agent enters the ceramic ultrafiltration system through the chemical cleaning system. The cleaned sewage flows back to the chemical cleaning system to remove the residual pollutants on the surface of the ceramic membrane through impact and friction.

[0061] S4. The water produced by the ceramic ultrafiltration system is transported to the submerged combustion evaporation system through an evaporation feed pump. Landfill gas, anaerobic biogas or natural gas is used as energy to heat, evaporate, concentrate and crystallize the produced water. The steam and non-condensable gas generated by evaporation are removed from the mist droplets through a separation tower. The steam enters the condensation system for condensation and discharge after meeting the standards. The non-condensable gas enters the non-condensable gas treatment system.

[0062] S5. The non-condensable gas passes through the acid spray tower and the alkali spray tower in sequence. The alkaline substances in the gas phase react with the acidic substances in the liquid phase to form soluble salts. The acidic substances in the gas phase react with the alkaline substances in the liquid phase to form soluble salts. The treated non-condensable gas is discharged through the exhaust pipe in accordance with regulations. The soluble salts at the bottom of the tower are returned to the submerged combustion evaporation system.

[0063] S6. The saturated residual liquid produced by evaporation is transported to the salt mud dehydration system through a lifting pump. The dehydrated salt mud is packaged and centrally processed, and the supernatant is returned to the submerged combustion evaporation system. The moisture content of the salt mud after dehydration is 40-70%.

[0064] The present invention also provides a short-process system for treating high-mineralization fracturing flowback fluid, comprising a raw liquid water tank, a ceramic ultrafiltration system, a produced water tank, a backwash system, a chemical cleaning system, an immersion combustion evaporation system, a steam condensation system, a non-condensable gas system, a salt mud dehydration system, a condensate water tank, and a dosing system;

[0065] The outlet of the raw liquid water tank is connected to the water inlet of the ceramic ultrafiltration system, the outlet of the ceramic ultrafiltration system is connected to the water inlet of the production water tank, the water inlet of the ceramic ultrafiltration system is connected to the outlet of the backwash system, the water inlet of the ceramic ultrafiltration system is connected to the water outlet of the chemical cleaning system, the outlet of the production water tank is connected to the water inlet of the submerged combustion evaporation system, the dosing system is connected to the inlet pipe of the submerged combustion evaporation system, the steam and non-condensable gas outlet of the submerged combustion evaporation system is connected to the inlet of the steam condensation system, the outlet of the steam condensation system is connected to the inlet of the condensation water tank, the non-condensable gas outlet of the steam condensation system is connected to the inlet of the non-condensable gas system, and the residual liquid outlet of the submerged combustion evaporation system is connected to the inlet of the salt mud dehydration system.

[0066] Raw liquid water tank, used to temporarily store high-mineralization fracturing flowback fluid to be processed;

[0067] Ceramic ultrafiltration system, used to pre-treat fracturing flowback fluid, remove silica, suspended solids and organic matter from the water, and reduce water viscosity and turbidity;

[0068] The produced water tank is used to store the produced water treated by the ceramic ultrafiltration system, providing a stable water source for the subsequent submerged combustion evaporation system;

[0069] Backwash system, used to regularly backwash the ceramic membrane with produced water to prevent clogging of the membrane surface;

[0070] Chemical cleaning system, used for regular chemical cleaning of ceramic membranes;

[0071] The submerged combustion evaporation system is used to deeply treat the water produced by the ceramic ultrafiltration system. It removes TDS, COD, ammonia nitrogen, calcium, magnesium ions and salt ions in the water through heating, evaporation, concentration and crystallization.

[0072] Steam condensation system, used to condense the steam generated by evaporation into liquid water;

[0073] Non-condensable gas system, used to purify the non-condensable gas generated during the evaporation process;

[0074] Salt mud dehydration system is used to dehydrate the saturated residual liquid produced by evaporation to reduce the volume of waste residue;

[0075] Condensate tank, used to store condensed water generated by the steam condensation system as a treated clean water resource;

[0076] Dosing system is used to add reagents to the submerged combustion evaporation system.

[0077] The water produced by the ceramic ultrafiltration system enters the submerged combustion evaporation system to remove TDS, COD, ammonia nitrogen, calcium, magnesium ions and other salt ions in the water. The water produced by the ceramic ultrafiltration system is transported to the submerged combustion evaporation system by the evaporation feed pump. The landfill gas, anaerobic biogas or natural gas and other combustible gases are used as energy to heat, evaporate, concentrate and crystallize the water produced by the ceramic ultrafiltration system. The steam and non-condensable gas generated in the evaporation process pass through the separation tower to remove the droplets entrained by the mist, and then enter the steam condensation system through the pipeline. The condensed water produced after condensation is discharged in compliance with the standards, and the non-condensable gas that cannot be condensed enters the non-condensable gas system for treatment. The non-condensable gas first enters the acid spray tower through the induced draft fan, quickly fills the air intake section space under the negative pressure of the induced draft fan, and then rises evenly through the equalizing section. In the filler absorption section, the alkaline substances in the gas phase react chemically with the acidic substances in the liquid phase to generate soluble salts, which are discharged into the bottom of the tower; the non-condensable gas then enters the alkali spray tower, where the acidic substances in the gas phase react chemically with the alkaline substances in the liquid phase to generate soluble salts, which are discharged into the bottom of the tower; all indicators of the non-condensable gas after double purification treatment by acid and alkali spraying have met the standards, and finally compliant discharge is achieved through the exhaust pipe, and the soluble salts at the bottom of the tower are returned to the submerged combustion evaporation system, and the saturated residual liquid produced in the evaporation process is transported to the salt mud dehydration system through a lifting pump for dehydration treatment. The water content of the salt mud after dehydration is about 40-70%. The final salt mud is packaged and packaged, and regularly processed in a centralized manner; the supernatant continues to flow back to the submerged combustion evaporation system for treatment.

[0078] Application Examples

[0079] The process of the present invention was used to treat fracturing flowback fluid from a well in the Fuling oil and gas field.

[0080] As shown in Data 1 below, this fracturing flowback fluid is highly mineralized, with a TDS of ≥50,000 mg / L; has a high concentration of organic matter and poor biodegradability; contains high concentrations of silica; and has high viscosity. Furthermore, it exhibits high foaming power and strong foam stability, making it challenging to treat using conventional processes.

[0081] Data 1: Fracturing flowback fluid quality

[0082]

[0083]

[0084] The fracturing flowback fluid is directly evaporated to produce condensed water and a small amount of salt mud. The condensed water produced by evaporation is collected and tested. The water quality of the condensed water is shown in Data 2. The data of the condensed water is compared with that of the raw water to calculate the removal rate. The results are as follows: Figure 2 As shown:

[0085] Data 2 Water quality index of evaporation condensate of raw liquid

[0086]

[0087] Depend on Figure 2 It can be seen that when the fracturing flowback fluid is directly subjected to submerged combustion evaporation treatment, COD, ammonia nitrogen, calcium, magnesium, and TDS can meet the first-level emission standards in the "Integrated Wastewater Discharge Standard" (GB8978-1996), but the removal effect of silica and viscosity is poor and does not meet the emission standards.

[0088] Since fracturing flowback fluid foams severely during the evaporation process, it has the characteristics of large foaming volume, large foam volume, strong stability, and not easy to break. These foams will produce mist entrainment, causing pollutants attached to the foam to enter the condensate with the steam. A small amount of mist entrainment is difficult to avoid, but excessive mist entrainment will cause liquid to be carried, resulting in an increase in the concentration of pollutants in the condensate, affecting the water quality. Since guar gum, thickeners, pH regulators, surfactants, clay stabilizers, etc. are usually added to fracturing fluid to increase viscosity and stability, the fracturing flowback fluid contains colloidal silica, resulting in a higher viscosity;

[0089] Inject a certain amount of fracturing flowback fluid into the raw fluid tank. With the concentrate pressure regulating valve fully open, start the inlet pump and slowly adjust the concentrate pressure valve from fully open, while observing the pressure gauge on the ceramic ultrafiltration system's inlet. Set the inlet pressure based on actual conditions, typically no more than 0.3 MPa. By measuring the water production and production time, the ceramic membrane flux can be calculated. Testing the inlet and product water quality of the ceramic ultrafiltration system reveals its pollutant retention rate.

[0090] This patent tests the water produced by ceramic ultrafiltration, and the test results are detailed in Data 3. Figure 3 It can be seen that the ceramic ultrafiltration system has a significant removal effect on COD, silica, and viscosity, and TDS, calcium, and magnesium ions have basically no change before and after entering the membrane.

[0091] Data 3 Ceramic ultrafiltration water quality indicators

[0092]

[0093] The present invention was used to conduct an evaporation experiment on the water produced by ceramic ultrafiltration. Compared with direct evaporation, there was basically no mist entrainment phenomenon. The condensed water produced by evaporation was tested. The removal effect of various pollutants is detailed in Data 4. Figure 5 and Figure 6 After the fracturing flowback fluid is pre-treated by ceramic ultrafiltration and then evaporated, its viscosity is significantly reduced; Data 4 "ceramic ultrafiltration + submerged combustion evaporation" condensate water quality indicators

[0094]

[0095]

[0096] The present invention selects an operating pressure of 0.3 MPa, a pH of 6 to 8, controls the temperature of the membrane-fracturing flowback fluid to 15 to 40°C by a circulating cooling pump, and treats it for 60 minutes. The retention rate of silica in the fracturing flowback fluid by the ceramic membrane is investigated under different temperature conditions. Figure 5 As shown in the figure, as the temperature of the fracturing flowback fluid entering the membrane increases from 15℃ to 40℃, the flux of the ceramic membrane increases from 23.57L / m 2 ·h increased to 98.74L / m 2 h, the retention rate of silica decreased from 94.61% to 61.78%. Therefore, considering the actual application of the project, the inlet liquid temperature can be controlled at 25-30℃.

[0097] Operating pressure is also a key factor affecting the operation of ceramic ultrafiltration systems. It is the driving force behind the ceramic membrane filtration process and has a crucial impact on ceramic membrane flux. Excessively low operating pressure is detrimental to achieving high water flux, while excessively high operating pressure not only increases energy consumption and operating costs but also accelerates ceramic membrane fouling, shortening the operating cycle of the ceramic ultrafiltration system. Therefore, it is necessary to find the optimal operating pressure.

[0098] This patent uses a ceramic ultrafiltration system to treat fracturing flowback fluid under the conditions of an operating temperature of 25°C, a single operating time of 60 minutes, and a pH of 6 to 8. The operating pressure is adjusted by a valve. The relationship between pressure, membrane flux, and viscosity removal rate is shown in Figure 7 and Figure 8 .

[0099] Depend on Figure 7 and Figure 8 As shown in the figure, as the operating pressure increases from 0.1Mpa to 0.4Mpa, the ceramic membrane flux increases from 25.78L / m 2 ·h increased to 50.12 L / m 2The silica retention rate also increases with the increase of the operating pressure. However, when the operating pressure continues to increase to 0.6 MPa, the membrane flux stability is affected by the adsorption of colloidal substances in the fracturing flowback fluid, pore clogging, or gelation, resulting in a decrease in membrane flux and a reduction in the silica retention effect. Therefore, the operating pressure of this patented ceramic ultrafiltration system is 0.2-0.4 MPa.

[0100] like Figure 9 As shown in the figure, the pollutant removal rates of the fracturing flowback fluid after direct "immersion combustion evaporation" and "ceramic ultrafiltration + immersion combustion evaporation" treatment were compared. It was found that the water quality of the effluent after ceramic ultrafiltration pretreatment and then immersion combustion evaporation was better than that of direct immersion combustion evaporation treatment, especially the silica and viscosity indicators.

[0101] The present invention utilizes the "ceramic ultrafiltration + submerged combustion evaporation" process to treat high-mineralization fracturing return fluid. This treatment process can maintain stable treatment efficiency under high-mineralization conditions, and the final water production can meet the emission standards; this process requires a small amount of reagent addition, produces less solid products, and has low solid product disposal costs; this process can operate continuously without the need to frequently start and stop the system; the process has a short process flow, takes up little space, requires fewer operators, and has reduced operating costs, ultimately achieving the goals of high treatment efficiency, short process flow, and low treatment costs for treating high-mineralization fracturing return fluid wastewater.

[0102] In summary, the present invention provides a short-process high-mineralization fracturing return fluid treatment process and system, which treats high-mineralization fracturing return fluid by combining ceramic ultrafiltration and immersion combustion evaporation. First, the high-mineralization fracturing return fluid is pretreated by the interception effect of the ceramic ultrafiltration system, mainly removing silica, viscosity and suspended matter in the water body, and then the immersion combustion evaporation system is used to evaporate and crystallize the fracturing return fluid containing high concentrations of TDS, COD, ammonia nitrogen, calcium, magnesium ions and other pollutants, and finally produces condensed water, non-condensable gas and salt mud. Since more than 90% of the salt is discharged in the form of crystalline salt, its condensed water can meet the first-level standard in the "Integrated Sewage Discharge Standard" (GB8978-1996), and after the non-condensable gas is deeply treated by acid and alkali spraying, all indicators also meet the standards.

[0103] The present invention uses a ceramic ultrafiltration system to pretreat highly mineralized fracturing flowback fluid to remove silica, viscosity and suspended matter, thereby improving the treatment efficiency of the subsequent submerged combustion evaporation system. The system only requires a small amount of membrane cleaning agent and does not generate additional sludge.

[0104] The present invention utilizes a submerged combustion evaporation system to utilize gas fuel for pressurized submerged combustion on the subsurface of the liquid, and forms ultrafine bubbles through a special structure. The ultrafine bubbles are in direct contact with the high-mineralization fracturing return fluid for heat exchange, and the mass transfer and heat transfer efficiency is high. In addition, because there is no partition for heat exchange, scaling and coking will not occur inside the evaporation system. While maintaining efficient processing capacity, the evaporation system can operate continuously and stably without the need for frequent shutdowns to clean equipment for coke scale.

[0105] The present invention combines ceramic ultrafiltration and submerged combustion evaporation systems to treat high-mineralization fracturing flowback fluid, shortening the process flow, reducing costs and energy consumption, reducing floor space, simplifying operation and maintenance, and enhancing adaptability and flexibility to meet the needs of land resource constraints, cost sensitivity, and high environmental requirements.

[0106] Those skilled in the art will appreciate that various combinations and / or combinations of features described in the various embodiments and / or claims of the present invention may be made, even if such combinations and / or combinations are not explicitly described in the present invention. In particular, various combinations and / or combinations of features described in the various embodiments and / or claims of the present invention may be made, without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

Claims

1. A short-process high-mineralization fracturing flowback fluid treatment process, characterized in that: The following steps are involved: S1. High-mineralization fracturing flowback fluid is transported from the raw liquid tank to the ceramic ultrafiltration system through the water inlet pump. Before entering the ceramic membrane, it is filtered through a self-cleaning filter to remove large suspended particles; S2. The pre-treated return liquid enters the ceramic ultrafiltration system. Under the interception effect of the ceramic membrane, the produced water is discharged into the produced water tank through the water outlet, and the concentrated water returns to the raw liquid tank for cyclic treatment; S3, backwashing and chemical cleaning, using the produced water in the produced water tank to backwash the ceramic membrane; S4. The water produced by the ceramic ultrafiltration system is transported to the submerged combustion evaporation system through an evaporation feed pump. Landfill gas, anaerobic biogas or natural gas is used as energy to heat, evaporate, concentrate and crystallize the produced water. The steam and non-condensable gas generated by evaporation are removed from the mist droplets through a separation tower. The steam enters the condensation system for condensation and discharge after meeting the standards. The non-condensable gas enters the non-condensable gas treatment system. S5. The non-condensable gas passes through the acid spray tower and the alkali spray tower in sequence. The alkaline substances in the gas phase react with the acidic substances in the liquid phase to form soluble salts. The acidic substances in the gas phase react with the alkaline substances in the liquid phase to form soluble salts. The treated non-condensable gas is discharged through the exhaust pipe in accordance with regulations. The soluble salts at the bottom of the tower are returned to the submerged combustion evaporation system. S6. The saturated residual liquid produced by evaporation is transported to the salt mud dehydration system through a lifting pump. The dehydrated salt mud is packaged and centrally processed, and the supernatant is returned to the submerged combustion evaporation system.

2. A short-flow high-mineralization fracturing flowback fluid treatment process according to claim 1, characterized in that: In S1, the filtration accuracy is 50 to 500 μm.

3. The short-flow high-mineralization fracturing flowback fluid treatment process according to claim 1, characterized in that: In S2, the ceramic ultrafiltration system comprises a ceramic membrane; The single membrane area of ​​the ceramic membrane is 10 to 25 m 2 , the operating flux is 20~150LMH, the operating pH range is 1~13.5, the operating temperature range is 15~40℃, and the operating pressure range is 0.1~0.6MPa.

4. The short-flow high-mineralization fracturing flowback fluid treatment process according to claim 1, characterized in that: In S3, the ceramic ultrafiltration system is backwashed once every 30 to 60 minutes using produced water, with a backwash time of 30 to 120 seconds, a backwash flux of 40 to 240 LMH, a backwash pH range of 1 to 13.5, and the backwash water enters the raw water tank.

5. A short-flow high-mineralization fracturing flowback fluid treatment process according to claim 4, characterized in that: The ceramic ultrafiltration system is run for 3 to 4 months and then chemically cleaned using sodium hydroxide, citric acid and hydrochloric acid to remove residual organic matter, colloids and microorganisms; The sodium hydroxide concentration is 0.1-1.0%, the citric acid concentration is 5-20%, and the hydrochloric acid concentration is 0.1-0.4%. The cleaning agent enters the ceramic ultrafiltration system through the chemical cleaning system, and the cleaned sewage flows back to the chemical cleaning system.

6. The short-flow high-mineralization fracturing flowback fluid treatment process according to claim 1, characterized in that: In S6, the moisture content of the dehydrated salt mud is 40-70%.

7. A short-flow system for treating high-mineralization fracturing flowback fluid according to any one of claims 1 to 6, characterized in that: Including raw liquid water tank, ceramic ultrafiltration system, produced water tank, backwash system, chemical cleaning system, submerged combustion evaporation system, steam condensation system, non-condensable gas system, salt mud dehydration system, condensate water tank and dosing system; The raw liquid water tank is used to temporarily store the high-mineralization fracturing flowback fluid to be processed; The ceramic ultrafiltration system is used to pre-treat fracturing flowback fluid, remove silica, suspended matter and organic matter in the water, and reduce the viscosity and turbidity of the water; The produced water tank is used to store the produced water treated by the ceramic ultrafiltration system, providing a stable water source for the subsequent submerged combustion evaporation system; The backwash system is used to regularly backwash the ceramic membrane using produced water to prevent clogging of the membrane surface; The chemical cleaning system is used to regularly perform chemical cleaning on the ceramic membrane; The submerged combustion evaporation system is used to deeply treat the water produced by the ceramic ultrafiltration system, removing TDS, COD, ammonia nitrogen, calcium, magnesium ions and salt ions in the water through heating, evaporation, concentration and crystallization; The steam condensation system is used to condense the steam generated by evaporation into liquid water; The non-condensable gas system is used to purify the non-condensable gas generated during the evaporation process; The salt mud dehydration system is used to dehydrate the saturated evaporation residue produced by evaporation to reduce the volume of waste residue; The condensed water tank is used to store the condensed water generated by the steam condensation system as a treated clean water resource; The dosing system is used to add reagents to the submerged combustion evaporation system.

8. A short-flow high-mineralization fracturing flowback fluid treatment system according to claim 7, characterized in that: The water outlet of the raw liquid water tank is connected to the water inlet of the ceramic ultrafiltration system, the water outlet of the ceramic ultrafiltration system is connected to the water inlet of the water production tank, the water inlet of the ceramic ultrafiltration system is connected to the outlet of the backwash system, the water inlet of the ceramic ultrafiltration system is connected to the water outlet of the chemical cleaning system, the water outlet of the water production tank is connected to the water inlet of the submerged combustion evaporation system, the dosing system is connected to the inlet pipe of the submerged combustion evaporation system, the steam and non-condensable gas outlet of the submerged combustion evaporation system is connected to the inlet of the steam condensation system, the steam condensation system outlet is connected to the inlet of the condensation water tank, the non-condensable gas outlet of the steam condensation system is connected to the inlet of the non-condensable gas system, and the residual liquid outlet of the submerged combustion evaporation system is connected to the inlet of the salt mud dehydration system.

Images