Indoor test-based polymer-surfactant binary combination flooding produced sewage availability evaluation method

Abstract

The invention relates to the technical field of oil and gas field development, in particular to a polymer-surfactant binary combination flooding produced sewage availability evaluation method based on indoor testing. The method comprises five parts of water quality characteristic determination, rock core permeability damage evaluation, reinjection decision chart construction, back flushing and permeability recovery evaluation and oil displacement effect verification. The water quality characteristics of the polymer-surfactant binary combination flooding produced sewage and the damage mechanism of the polymer-surfactant binary combination flooding produced sewage to a rock core are comprehensively evaluated, a method for preparing a backwashing medium from the produced sewage to help permeability recovery is provided, a basis is provided for a plug removal process, meanwhile, a scientific reinjection chart is established, oilfield sewage reinjection practice is guided, environmental protection and economic benefits are achieved, and the method is suitable for popularization and application. And finally, the oil displacement effect of the polymer system prepared from the produced sewage is verified, and technical support is provided for resource reutilization.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a method for evaluating the availability of produced wastewater from polystyrene-based binary composite flooding based on indoor testing. Background Technology

[0002] As oilfield development enters the high water-cut stage, chemical flooding technology has become a key means to improve oil recovery. Among them, ternary composite flooding (i.e., alkali-surfactant-polymer composite flooding) technology is widely used. However, the alkali in this system can react with formation fluids and minerals, leading to a significant tendency for silicate and carbonate scaling in the produced water, an increase in suspended solids concentration, and abnormally stable oil-water emulsions, which greatly increases the difficulty of produced water treatment and the risk of reinjection.

[0003] To avoid the severe scaling and pollution problems caused by alkali agents, the more efficient and environmentally friendly polymer-surfactant composite flooding technology is gradually being promoted and applied. However, the produced wastewater from polymer-surfactant composite flooding still contains a large amount of residual polymers and surfactants. These substances result in high viscosity of the wastewater, small particle size of residual oil droplets, and strong stability, forming unique physicochemical properties. The influence of these substances on the treatment process and reinjection formation is still unclear.

[0004] In summary, the current methods for treating wastewater produced by polymer-table distillation and flooding systems suffer from technical problems such as incomplete testing, unclear feasibility of resource utilization, and reliance on a single indicator for evaluation and utilization. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating the availability of wastewater produced by poly- and surface-based binary composite flooding based on indoor testing, thereby solving the technical problems of incomplete testing, unclear feasibility of resource utilization, and reliance on a single indicator for evaluation and utilization methods for wastewater produced by poly- and surface-based binary composite flooding.

[0006] To achieve the above objectives, the present invention provides a method for evaluating the availability of produced wastewater from polymer-based binary composite flooding based on indoor testing. The method includes the following steps: Water quality characteristics determination: Wastewater samples were collected from the polymer-based binary flooding system, and their suspended solids particle size distribution, suspended solids mass concentration, oil mass concentration, polymer mass concentration, suspended solids chemical composition, and residual polymer micromorphology were determined. Core permeability damage assessment: Cores with different permeabilities were selected, and the initial core permeability K1 was measured after saturation with formation water. Wastewater samples were extracted using collected polystyrene-to-surface composite flooding to displace the cores. The core permeability K2 was then measured again, and the core permeability loss rate D was calculated based on K1 and K2. Constructing a reinjection decision chart: Based on multiple sets of experimental data obtained from step-by-step core permeability damage assessment, correlation analysis was performed on the suspended solids concentration and oil concentration in produced wastewater and the permeability loss rate of the corresponding core. A decision chart was then drawn to determine whether the produced wastewater is suitable for reinjection and the reinjection conditions. Backwashing and permeability recovery evaluation: Select the produced wastewater that meets the standards in the decision chart, prepare the backwashing medium, and backwash the blocked core after the core permeability damage evaluation in the step. Measure the permeability of the core after backwashing, calculate the permeability recovery rate, and evaluate the unblocking effect of the produced wastewater as the flushing medium. Oil displacement effect verification: Selected produced wastewater that meets the standards in the decision chart is used to dilute polymer mother liquor to prepare polymer oil displacement system. Through core oil displacement experiments, the oil displacement efficiency of the polymer system prepared with different wastewater quality is analyzed to determine the optimal wastewater configuration parameters.

[0007] In the step of water quality characteristic determination, the suspended solids particle size distribution is measured using a laser particle size analyzer in accordance with GB / T 19077-2024. The mass concentration of suspended solids was determined using the double-layer filter membrane gravimetric method. The oil content and polymer content were determined by ultraviolet spectrophotometry using a standard curve. The chemical composition of the suspended matter was analyzed by X-ray fluorescence spectroscopy. The microstructure of the residual polymer was observed using a scanning electron microscope.

[0008] In the core permeability damage assessment step, K1 and K2 are calculated using the core permeability calculation formula, which is as follows: ; In the formula, K is the core permeability in mD; μ is the fluid viscosity in mPa∙s; L is the core length in cm; Q is the flow rate in mL / min; A is the effective cross-sectional area of ​​the core in cm2; and Dp is the pressure difference in MPa. In the step-by-step core permeability damage assessment, the specific formula for calculating the core permeability loss rate D is as follows: ; In the formula: D is the core water permeability loss rate, in %; K1 is the water permeability of the prepared formation water, in mD; K2 is the water permeability after wastewater displacement, in mD.

[0009] In the core permeability damage assessment step, when using the collected polydimethylsiloxane binary composite flooding to extract wastewater samples to displace the core, the annular pressure was set to 4-6 MPa, the pump speed was set to 0.2-0.4 mL / min, and the displacement pore volume ratio was 8-12 PV.

[0010] In the step of constructing the reinjection decision chart, the decision chart is a parallel coordinate graph whose dimensions include oil mass concentration, suspended solids mass concentration, and core permeability. It is further divided into corresponding intervals based on the numerical range of the permeability loss rate D. The specific interval division is as follows: D ≤ 30% indicates that direct re-injection is possible; 30% < D ≤ 50% indicates a re-injection after processing; D > 50% indicates no re-injection.

[0011] In the backwashing and permeability recovery evaluation step, the backwashing medium is prepared by adding acid and additives to qualified produced wastewater as a matrix.

[0012] In the step of verifying the oil displacement effect, the polymer oil displacement system is prepared by diluting the polymer mother liquor to the target concentration using qualified produced wastewater, and the polymer is partially hydrolyzed polyacrylamide.

[0013] This invention presents a method for evaluating the availability of produced wastewater from polymer-based binary composite flooding based on indoor testing. The method comprises five parts: water quality characteristic determination, core permeability damage assessment, construction of reinjection decision charts, evaluation of backflushing and permeability recovery, and verification of oil displacement effect. It comprehensively evaluates the water quality characteristics of produced wastewater from polymer-based binary composite flooding and its damage mechanism to the core, proposes a method for preparing backflushing media from produced wastewater to aid permeability recovery, providing a basis for unblocking processes, and establishes a scientific reinjection chart to guide oilfield wastewater reinjection practices, achieving both environmental and economic benefits. Finally, it verifies the oil displacement effect of polymer systems prepared from produced wastewater, providing technical support for resource reuse. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart of the steps in the method for evaluating the availability of wastewater from polystyrene-based binary composite flooding based on indoor testing, provided by the present invention.

[0016] Figure 2This is a flowchart of an indoor flow experiment provided by the present invention.

[0017] Figure 3 This is a graph showing the effect of suspended matter mass concentration on core permeability loss rate in a specific embodiment of the present invention.

[0018] Figure 4 This is a diagram showing the effect of oil mass concentration on core permeability loss rate in a specific embodiment of the present invention.

[0019] Figure 5 This is a graph showing the relationship between polymer mass concentration and permeation loss rate in a specific embodiment of the present invention.

[0020] Figure 6 This is a diagram of wastewater reinjection from a polymer-based binary composite flooding system provided by the present invention.

[0021] Figure 7 This is a permeability recovery rate diagram provided in a specific embodiment of the present invention. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] Please see Figures 1 to 7 This invention provides a method for evaluating the availability of wastewater from polymer-based binary composite flooding based on indoor testing. The method includes the following steps: Water quality characteristics determination: Wastewater samples were collected from the polymer-based binary flooding system, and their suspended solids particle size distribution, suspended solids mass concentration, oil mass concentration, polymer mass concentration, suspended solids chemical composition, and residual polymer micromorphology were determined. Core permeability damage assessment: Cores with different permeabilities were selected, and the initial core permeability K1 was measured after saturation with formation water. Wastewater samples were extracted using collected polystyrene-to-surface composite flooding to displace the cores. The core permeability K2 was then measured again, and the core permeability loss rate D was calculated based on K1 and K2. Constructing a reinjection decision chart: Based on multiple sets of experimental data obtained from step-by-step core permeability damage assessment, correlation analysis was performed on the suspended solids concentration and oil concentration in produced wastewater and the permeability loss rate of the corresponding core. A decision chart was then drawn to determine whether the produced wastewater is suitable for reinjection and the reinjection conditions. Backwashing and permeability recovery evaluation: Select the produced wastewater that meets the standards in the decision chart, prepare the backwashing medium, and backwash the blocked core after the core permeability damage evaluation in the step. Measure the permeability of the core after backwashing, calculate the permeability recovery rate, and evaluate the unblocking effect of the produced wastewater as the flushing medium. Oil displacement effect verification: Selected produced wastewater that meets the standards in the decision chart is used to dilute polymer mother liquor to prepare polymer oil displacement system. Through core oil displacement experiments, the oil displacement efficiency of the polymer system prepared with different wastewater quality is analyzed to determine the optimal wastewater configuration parameters.

[0024] In this embodiment, the method comprises five parts: water quality characteristic determination, core permeability damage assessment, construction of reinjection decision chart, evaluation of backflushing and permeability recovery, and verification of oil displacement effect. It comprehensively evaluates the water quality characteristics of produced wastewater from polymer-flooded binary composite flooding and its damage mechanism to the core, proposes a method for preparing backflushing media from produced wastewater to aid permeability recovery, providing a basis for unblocking processes, establishes a scientific reinjection chart to guide oilfield wastewater reinjection practices, and combines environmental and economic benefits. Finally, it verifies the oil displacement effect of the polymer system prepared from produced wastewater, providing technical support for resource reuse.

[0025] Further, the specific details of the water quality characteristic determination steps are as follows: Wastewater from the polymer-to-surface binary composite flooding project was collected from the oilfield's wastewater treatment plant. Before the experiment, the wastewater underwent preliminary treatment according to its workflow, including filtration of suspended solids, extraction of multiphase oil, and dilution. Referring to the standard GB / T 19077-2024 "Particle Size Analysis - Laser Diffraction Method," a laser particle size analyzer was used to measure the particle size of suspended solids in the wastewater, with three tests performed and the average value taken. The mass concentration of suspended solids in the wastewater from the polymer-to-surface binary composite flooding project was determined. X-ray fluorescence spectrometry was used to detect the elemental composition of the suspended solids. Scanning electron microscopy was used to observe the morphology of residual polymers in the wastewater. Ultraviolet spectrophotometry was used to plot standard curves for polymer mass concentration and oil content mass concentration, respectively, and the polymer mass concentration and oil content mass concentration in the oily wastewater were measured.

[0026] In this embodiment, a laser particle size analyzer is used to measure the particle size of suspended solids in the collected wastewater. First, the circulation pump is turned on and preheated for 30 minutes to allow the laser output power to stabilize. Distilled water is slowly added to the sample cell, followed by the sample solution to be tested. The particle size distribution is tested, with the number of tests set to 3 and the error to be less than 1%. The suspended solids concentration in wastewater collected by a polystyrene-based binary flooding system was determined using a double-layer filter membrane method. The instruments used in this study included an all-glass microporous membrane filter, a mixed cellulose membrane with a pore size of 0.45 μm and a diameter of 47 mm, a suction flask, a vacuum pump, toothless flat-tipped tweezers, beakers, and a separatory funnel. First, the collected wastewater was extracted with petroleum ether, and the lower layer (volume V) was taken as the test sample. Then, the microporous membrane was placed in a weighing bottle using toothless flat-tipped tweezers and dried in an oven at 105℃ for half an hour before being weighed. The weight difference between two weighings was recorded as m1 and m2. The constant-weighted microporous membrane was then placed on the filter membrane filter, the funnel was capped, and secured with clamps. The membrane was moistened with distilled water, and continuous suction filtration was performed. 100 mL of the well-mixed sample was measured and filtered through the filter membrane. All water was allowed to pass through the membrane. Wash the filter membrane three times with 10 mL of distilled water each time, and continue to filter to remove trace amounts of water. Repeat the above drying and weighing steps until the weight difference between two weighings is ≤0.4 mg. Record the filter membrane mass m3 and m4. Calculate the suspended solids concentration using the following formula; ; In the formula: C is the mass concentration of suspended solids, in mg / L; V is the volume of the liquid to be tested, in mL; m3 is the mass of the upper filter membrane after filtration, in g; m1 is the mass of the upper filter membrane before filtration, in g; m4 is the mass of the lower filter membrane after filtration, in g; m2 is the mass of the lower filter membrane before filtration, in g. The oil content concentration was determined according to SY / T 5329-2012 "Recommended Indicators and Analytical Methods for Injection Water Quality in Clastic Rock Oil Reservoirs". First, 0.1 g of crude oil was accurately weighed and dissolved in a 100 mL volumetric flask with petroleum ether, then diluted to the mark. This standard oil solution had an oil content concentration of 1000 mg / L. The 1000 mg / L standard oil solution was then diluted to 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, and 500 mg / L, respectively. A standard curve was plotted using 255 nm as the absorption wavelength, with petroleum ether as the reference solution, oil content concentration (mg / L) as the abscissa and absorbance (A) as the ordinate. Then, using petroleum ether as the reference solution, the absorbance of the produced wastewater was measured and substituted into the standard equation to calculate the oil content concentration in the produced wastewater. The polymer concentration in produced water was determined using a UV-2601 ultraviolet spectrophotometer. First, a polymer concentration standard curve was plotted. A 1000 mg / L polymer stock solution was prepared with water and diluted with produced water to obtain standard solutions with concentrations of 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, and 500 mg / L. 5 mL of sodium acetate solution was added to a 50 mL volumetric flask, followed by 2 mL of the test sample and 20 mL of distilled water. 1 mL of saturated bromine water was then added to the volumetric flask, and after reacting for 10 min, 5 mL of 1% sodium formate solution was added. After reacting for another 5 min, 5 mL of starch-cadmium iodide reagent was added, and the solution was diluted to the mark with distilled water. 2 mL of each standard solution was taken, and the absorbance was measured at 221 nm using distilled water as a reference. A standard curve was plotted with absorbance (A) on the ordinate and polymer concentration (c) on the abscissa. Based on parallel experiments of the extracted fluid samples, the average absorbance A was obtained, and then the concentration of polymer in the sample was determined from the standard curve.

[0027] Further, the specific steps of the core permeability damage assessment are as follows: After drying and vacuuming the core, saturate it with formation water, set the annular pressure and pump speed, and then measure the initial permeability (K1) using formation water. Displace the core with produced wastewater of different parameters for 10 PV, recording the pressure and flow rate. After displacement, test the permeability again with formation water (K2), and calculate the core permeability loss rate D according to the formula. Then, combine the suspended solids concentration, oil concentration, and polymer concentration in the produced wastewater to conduct a core permeability damage assessment.

[0028] In this embodiment, core samples with a gas permeability of 200-1000 mD were first collected and dried in an oven at 80°C for 24 hours. Their dry weight, length, and diameter were measured. After vacuuming the cores for 12 hours, they were saturated with prepared formation water for 12 hours, and their wet weight was measured to calculate the pore volume. Then, the viscosity of wastewater with different water quality parameters was measured at 45°C. An annular pressure of 5 MPa was set to overcome the influence of capillary forces during displacement. The pump speed was set to 0.3 mL / min, and the experiment was conducted in a constant temperature chamber at 45°C. The water permeability K1 of the cores was measured using prepared formation water. In the preliminary experiment, wastewater displacement of the cores showed that the damage to the cores tended to stabilize after 10 PV. Therefore, produced wastewater with different parameters was used to displace each core sample by 10 PV. Once liquid flowed out, the time, pressure, and outflow volume were recorded. The water permeability K2 of the cores was measured again, and the permeability loss rate D was calculated to evaluate the degree of core damage.

[0029] K1 and K2 are calculated using the core permeability calculation formula, which is as follows: ; In the formula, K is the core permeability in mD; μ is the fluid viscosity in mPa∙s; L is the core length in cm; Q is the flow rate in mL / min; A is the effective cross-sectional area of ​​the core in cm2; and Dp is the pressure difference in MPa. The specific formula for calculating the core permeability loss rate D is as follows: ; In the formula: D is the core water permeability loss rate, in %; K1 is the water permeability of the prepared formation water, in mD; K2 is the water permeability after wastewater displacement, in mD.

[0030] Table 1 shows that the larger the core water permeability loss rate (D) value, the higher the degree of core blockage and the more severe the damage caused by the produced wastewater. Based on the oil and gas industry standard SY / T5358—2010 "Evaluation Method for Reservoir Sensitivity Flow Experiments," and after experimental verification, the degree of damage to the oil reservoir by injected water was redefined according to the wastewater properties in this study. A permeability loss rate of ≤30% is defined as low damage to the oil reservoir; a permeability loss rate of ≥30% but ≤50% is defined as moderate damage; and a permeability loss rate of >50% is defined as high damage.

[0031] Table 1 Oil Reservoir Damage Assessment Table

[0032] In this technical solution, the oil concentration is set at 60 mg / L. Under the same permeability conditions, the effect of suspended solids concentration on the core permeability loss rate is analyzed. Figure 3 This is a graph showing the effect of suspended solids concentration on core permeability loss rate.

[0033] In this technical solution, the suspended solids concentration is set at 90 mg / L. Under the same permeability conditions, the effect of oil concentration on the core permeability loss rate is analyzed. Figure 4 This is a graph showing the effect of oil concentration on the core permeability loss rate.

[0034] In this technical solution, the concentrations of suspended solids and oil content are both set at 30 mg / L. Under the same permeability conditions, the effect of polymer concentration on the core permeability loss rate is analyzed. Figure 5 It is a graph showing the relationship between polymer mass concentration and permeation loss rate.

[0035] Furthermore, in the step of constructing the reinjection decision chart, the chart is a parallel coordinate graph with oil content, suspended solids concentration, and permeability as variable dimensions. Different colored curves are used to show the distribution of permeability loss rate under different combinations of variables. Different curves represent different parameter relationships, and the right side is divided into intervals such as "not recommended for use", "usable after treatment", and "available" based on the permeability loss rate. Figure 6 The diagram shows the wastewater reinjection from the polymer-table distillate binary flooding system. Referring to the diagram, reinjection is possible when D < 30%, reinjection is recommended when D is between 30% and 50%, and reinjection is advised when D > 50%.

[0036] Furthermore, the specific content of the backflushing and permeability recovery evaluation steps is as follows: A backflushing experiment will be conducted using produced wastewater that meets the reinjection conditions and is planned to be used as backflushing fluid. [The text then abruptly shifts to a seemingly unrelated topic:] ...the blocked... Core samples The core was placed in a core washing machine for washing. After washing, the core was backwashed to simulate the actual unblocking process. The specific steps and equipment operation of backwashing were similar to those of forward washing, but the flow direction of the washing medium was opposite to that of the fluid entering the core tube in the core permeability damage experiment. After washing, the core permeability was measured and the permeability recovery rate was calculated.

[0037] In this embodiment, firstly, a non-alkali ternary produced wastewater solution with a suspended solids concentration of 90 mg / L and an oil concentration of 60 mg / L is prepared and injected into 10PV core samples of 200 mD, 400 mD, 600 mD, 800 mD, and 1000 mD to cause a certain degree of blockage. The blocked core samples are then placed in a core washing apparatus. An ethanol-benzene solvent is prepared at a 1:3 ratio and injected into the solvent chamber, with the amount added not less than 2 / 3 of the solvent chamber volume. The pressure gauge is set to an upper limit of 0.4 MPa, and the temperature to approximately 105°C. When the pressure inside the apparatus begins to rise, the vent valve is opened to release the air inside the apparatus, and the pressure is controlled by adjusting the cooling water flow rate. When the pressure reaches 0.4 MPa, it is stabilized for approximately 30 hours. During the cycle of heating, distillation, and soaking the core, when the solvent in the solvent chamber becomes colorless and transparent, heating is stopped, and soaking continues for at least 8 hours. Referring to the produced wastewater reinjection chart drawn in the previous steps, produced wastewater with a concentration (D) < 30% was selected for backflushing solution preparation. Using produced wastewater with a D < 30% concentration as the matrix, 6% HCl + 4% organic diacid + 5% organic polymeric carboxylic acid + 4% fluoride + 2% fluoroborate were added to prepare the backflushing solution. After washing the oil, this backflushing solution was used for backflushing into 2PV. Then, the core permeability after backflushing was measured according to the experimental procedures of the core permeability damage experiment. The specific steps and equipment operation of backflushing are similar to those of forward flushing, but the flow direction of the flushing medium is opposite to the direction in which the fluid enters the core tube in the core permeability damage experiment.

[0038] In this technical solution, the permeability was restored to a certain extent after the blocked core was flushed in both forward and reverse directions. Figure 7 This is a permeability recovery rate diagram after forward and reverse flushing of core samples at different permeabilities.

[0039] Further, the specific content of the step-by-step oil displacement effect verification is as follows: Oil displacement experiments are conducted using produced wastewater that meets the reinjection conditions and is planned to be used to configure the polymer system. First, a polymer mother liquor for oil production, such as a partially hydrolyzed polyacrylamide solution with a concentration of 6000 mg / L, is prepared using clean water. Produced wastewater of different qualities is then used to dilute the polymer mother liquor to 1200 mg / L to prepare the polymer system. Core samples closely adhering to the target reservoir are selected, vacuumed, and saturated with water. Oil-water flooding is then performed until no more water is produced. After aging at a constant temperature for 12 hours, a waterflooding experiment is conducted. During the displacement, pressure, oil production, and liquid production are recorded at regular intervals. Waterflooding is performed until the water cut reaches 98%, and the waterflood recovery rate is calculated. Then, polymer displacement experiments are conducted using produced wastewater until the water cut reaches above 98%, and the increase in recovery rate after polymer flooding is calculated. The impact of polymers prepared with different wastewater qualities on oil displacement efficiency is analyzed to determine the optimal wastewater configuration parameters.

[0040] In this embodiment, core samples with a permeability of 400 mD were selected based on the typical permeability of the target reservoir. Polymer mother liquor was diluted to 1200 mg / L using wastewater produced by polymer-surface binary composite flooding with three different water qualities (suspended solids concentration and oil content concentration combinations of 30 mg / L and 20 mg / L, 60 mg / L and 30 mg / L, and 90 mg / L and 60 mg / L). The oil displacement effect of each system was evaluated through oil displacement experiments.

[0041] In this technical solution, the same core experimental apparatus is used. The core is evacuated for 3-5 hours and then saturated with water for 2-4 hours. The viscosity of each polymer system is measured at 45℃. The core is placed in a 45℃ constant temperature chamber, and water is pumped through the oil until no more water is discharged from the outlet. The core is then aged at this constant temperature for 12 hours. A water flooding experiment is conducted at an injection rate of 0.3 mL / min, first pumping until the water cut is above 98%. Pressure, oil production, and fluid production are recorded at regular intervals to calculate the water flooding recovery rate. Then, an alkali-free ternary produced wastewater displacement experiment is conducted, injecting 1 PV of polymer until the water cut is above 98%. Pressure, oil production, and fluid production are recorded at regular intervals to calculate the increase in recovery rate after polymer flooding. A control experiment is also set up, using a water + polymer system to repeat the above experimental steps.

[0042] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for evaluating the availability of wastewater produced by polystyrene-based binary composite flooding based on indoor testing, characterized in that, Includes the following steps: Water quality characteristics determination: Wastewater samples were collected from the polymer-based binary flooding system, and their suspended solids particle size distribution, suspended solids mass concentration, oil mass concentration, polymer mass concentration, suspended solids chemical composition, and residual polymer micromorphology were determined. Core permeability damage assessment: Cores with different permeabilities were selected, and the initial core permeability K1 was measured after saturation with formation water. Wastewater samples were extracted using collected polystyrene-to-surface composite flooding to displace the cores. The core permeability K2 was then measured again, and the core permeability loss rate D was calculated based on K1 and K2. Constructing a reinjection decision chart: Based on multiple sets of experimental data obtained from step-by-step core permeability damage assessment, correlation analysis was performed on the suspended solids concentration and oil concentration in produced wastewater and the permeability loss rate of the corresponding core. A decision chart was then drawn to determine whether the produced wastewater is suitable for reinjection and the reinjection conditions. Backwashing and permeability recovery evaluation: Select the produced wastewater that meets the standards in the decision chart, prepare the backwashing medium, and backwash the blocked core after the core permeability damage evaluation in the step. Measure the permeability of the core after backwashing, calculate the permeability recovery rate, and evaluate the unblocking effect of the produced wastewater as the flushing medium. Oil displacement effect verification: Selected produced wastewater that meets the standards in the decision chart is used to dilute polymer mother liquor to prepare polymer oil displacement system. Through core oil displacement experiments, the oil displacement efficiency of the polymer system prepared with different wastewater quality is analyzed to determine the optimal wastewater configuration parameters.

2. The method for evaluating the availability of wastewater produced by polystyrene-based binary composite flooding based on indoor testing as described in claim 1, characterized in that, In the step of water quality characteristic determination, the suspended solids particle size distribution is measured using a laser particle size analyzer in accordance with GB / T 19077-2024; The mass concentration of suspended solids was determined using the double-layer filter membrane gravimetric method. The oil content and polymer content were determined by ultraviolet spectrophotometry using a standard curve. The chemical composition of the suspended matter was analyzed using X-ray fluorescence spectroscopy. The microstructure of the residual polymer was observed using scanning electron microscopy.

3. The method for evaluating the availability of wastewater produced by polystyrene-based binary composite flooding based on indoor testing as described in claim 2, characterized in that, In the core permeability damage assessment step, K1 and K2 are calculated using the core permeability calculation formula, which is as follows: ； In the formula, K is the core permeability in mD; μ is the fluid viscosity in mPa∙s; L is the core length in cm; Q is the flow rate in mL / min; A is the effective cross-sectional area of ​​the core in cm2; and Dp is the pressure difference in MPa. In the step-by-step core permeability damage assessment, the specific formula for calculating the core permeability loss rate D is as follows: ； In the formula: D is the core water permeability loss rate, in %; K1 is the water permeability of the prepared formation water, in mD; K2 is the water permeability after wastewater displacement, in mD.

4. The method for evaluating the availability of wastewater produced by polymer-based binary composite flooding based on indoor testing as described in claim 3, characterized in that, In the step of core permeability damage assessment, when using the collected polystyrene-polydimethylamine binary composite flooding to extract wastewater samples to displace the core, the annular pressure was set to 4-6 MPa, the pump speed was set to 0.2-0.4 mL / min, and the displacement pore volume ratio was 8-12 PV.

5. The method for evaluating the availability of wastewater produced by polystyrene-based binary composite flooding based on indoor testing as described in claim 4, characterized in that, In the step of constructing the reinjection decision chart, the decision chart is a parallel coordinate graph, whose dimensions include oil mass concentration, suspended solids mass concentration, and core permeability. It is divided into corresponding intervals based on the numerical range of the permeability loss rate D. The specific interval division is as follows: D ≤ 30% indicates that direct re-injection is possible; 30% < D ≤ 50% is considered a post-treatment reinjection; D > 50% indicates no chance of re-betting.

6. The method for evaluating the availability of wastewater produced by polymer-based binary composite flooding based on indoor testing as described in claim 5, characterized in that, In the backwashing and permeability recovery evaluation step, the backwashing medium is prepared by adding acid and additives to qualified produced wastewater as a matrix.

7. The method for evaluating the availability of wastewater produced by polystyrene-based binary composite flooding based on indoor testing as described in claim 6, characterized in that, In the step of verifying the oil displacement effect, the polymer oil displacement system is prepared by diluting the polymer mother liquor to the target concentration using produced wastewater that meets the standards, and the polymer is partially hydrolyzed polyacrylamide.

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