A functional fracturing fluid with direct distribution function for complex water quality flowback fluid

Abstract

The present invention discloses a functional fracturing fluid directly prepared from complex water-quality flowback fluid. This fracturing fluid is prepared by directly adding a salt-tolerant polymer and an ion-trapping agent to the flowback fluid. The dosage of the salt-tolerant polymer accounts for 0.15 - 0.3% of the total mass of the fracturing fluid, and the dosage of the ion-trapping agent is 100 - 500 ppm. The salt-tolerant polymer is copolymerized from acrylamide, a salt-tolerant monomer, and an allylquinoline monomer, and the molecular weight of the polymer is 4 - 15 million. The salt-tolerant monomer is sodium acrylamidopolyoxyethylene benzenesulfonate or sodium acrylamidosulfonate. The ion-trapping agent is composed of aminotrimethylenephosphonic acid, diethylenetriamine pentamethylenephosphonic acid, ethylene glycol bis(2-aminoethyl ether) tetraacetic acid, p-tolyldiethanolamine, 2,3-epoxypropyltrimethylammonium chloride, fatty alcohol polyoxyethylene ether, citric acid, and tetrahydrofurfuryl acrylate. The fracturing fluid of the present invention can be directly prepared from the flowback fluid without the need for pretreatment of the flowback fluid, realizing the reuse of the fracturing flowback fluid.

Description

Technical Field

[0001] The present invention relates to the technical field of shale oil and gas fracturing, and in particular to a functional fracturing fluid directly prepared from complex water-quality flowback fluid. Background Art

[0002] During the shale oil and gas fracturing process, a large amount of highly saline flowback fluid is generated, which poses great pressure on environmental protection and cost. Reusing the flowback fluid is an effective measure to reduce environmental protection pressure and cost and increase efficiency. At present, the total salinity of the flowback fluid is as high as (2 - 30)×10 4 mg / L, and the calcium and magnesium ions are as high as (0.5 - 5)×10 4 mg / L. If the flowback fluid is reused for preparing fracturing fluid, it is required that the fracturing fluid directly prepared from the flowback fluid must have extremely high salt tolerance. However, for the current fracturing fluid represented by high molecular weight polyacrylamide, the high-valent metal ions will cause the molecular chain to curl, the viscosity of the polymer to decrease by more than 70%, the sand-carrying performance to decrease by more than 80%, and the drag reduction rate cannot be effectively maintained. At the same time, some flowback fluid contains high iron ions (≥100 mg / L), and the iron ions form metal cross-linked flocculent substances with the acrylate units in the polyacrylamide, blocking the reservoir and the wellbore. At the same time, the injected fracturing fluid is incompatible with the formation fluid / rock, and the high content of Ca 2+ and Mg 2+ in the flowback fluid under high temperature and high pressure conditions scale during the flow in the reservoir and pipeline, resulting in deterioration of the formation physical properties and reduction of the reservoir permeability. Therefore, it is urgent to improve the salt tolerance of the fracturing fluid product, reduce the influence of the flowback fluid on liquid drag reduction, gel breaking and sand carrying, and at the same time prevent scaling to overall increase the production.

[0003] Regarding the utilization of the flowback fluid, developing salt-tolerant polyacrylamide is the current mainstream research direction. Through domestic and foreign literature research and analysis, salt-tolerant polyacrylamide is mainly modified by introducing hydrophobic monomers, sulfonic acid group salt-tolerant monomers, cyclic rigid and other functional monomers into the molecular structure of polyacrylamide. Through hydrophobic association, the insensitivity of the salt-tolerant monomer to divalent ions and the molecular chain rigidity to improve the salt tolerance and temperature resistance. Although these functional groups can increase the viscosity value of the polymer under the water quality conditions of the flowback fluid to a certain extent, there are still problems such as limited increase in viscosity and more than 50% decrease in the sand-carrying performance of the fracturing fluid with the same viscosity of the flowback fluid water quality, and the problem of low drag reduction rate under the water quality conditions of the flowback fluid cannot be effectively solved. Regarding the complex ions such as Fe 2+ ( 3+ )、Al 3+ 、Cu 2+ in the complex water quality conditions of the flowback fluid, research reports that adding external chelating agents to inhibit the influence of these ions on the liquid preparation performance, but due to the high calcium and magnesium ions in the flowback fluid, it is impossible to accurately capture them, and it is even more impossible to directly prepare fracturing fluid from the flowback fluid. Summary of the Invention

[0004] In view of the technical defect in the prior art that the flowback fluid cannot be directly used to prepare fracturing fluid, the present invention provides a functional fracturing fluid directly prepared from complex water-quality flowback fluid.

[0005] The functional fracturing fluid directly prepared from complex water-quality flowback fluid provided by the present invention is prepared by directly adding a salt-tolerant polymer and a high-efficiency ion-trapping agent to the flowback fluid. Among them, the addition amount of the salt-tolerant polymer accounts for 0.15-0.3% of the total mass of the fracturing fluid, and the addition amount of the high-efficiency ion-trapping agent is 100-500 ppm.

[0006] The molecular structure of the salt-tolerant polymer is as follows:

[0007]

[0008] In the formula, R1 is one of the following two structural formulas:

[0009]

[0010] The structural formula of R3 is as follows:

[0011] n is 3-10;

[0012] The structural formula of R2 is as follows:

[0013]

[0014] In the molecular structure of the salt-tolerant polymer, the molar ratio of a:b:c is 1:(0.001-0.2):(0.001-0.05). Preferably, the molar ratio of a:b:c is 1:(0.05-0.1):(0.01-0.03).

[0015] The salt-tolerant polymer is copolymerized from acrylamide, a salt-tolerant monomer, and an allyl quinoline monomer. The salt-tolerant monomer is sodium acrylamidopolyoxyethylene benzenesulfonate or sodium acrylamidosulfonate. The preparation method is as follows:

[0016] Dissolve acrylamide, a salt-tolerant monomer, and an allyl quinoline monomer in water to form an aqueous solution; adjust the pH of the aqueous solution to 8, purge with nitrogen to remove oxygen, add a three-stage composite initiator, and initiate a polymerization reaction at a temperature of -10-30°C to obtain the salt-tolerant polymer. The three-stage composite initiator includes an oxidation-reduction initiator system in the first stage, where the oxidant is ammonium persulfate and the reductant is composed of a composite of ferrous sulfate and sodium bisulfite; an azobispropaneamine initiator in the second stage, and an azodiisobutyramidine dihydrochloride initiator in the third stage. When the temperature of the polymerization reaction system does not rise by more than 1°C within 30 minutes, the polymerization reaction is considered complete. The molecular weight of the salt-tolerant polymer is 400-15 million.

[0017] Preferably, the total mass of the three monomers accounts for 15-35% of the mass of the aqueous solution, and optimally 25-30%.

[0018] Preferably, in the initiator of the first stage, the addition amount of ammonium persulfate accounts for 100-400 ppm of the total mass of the three monomers, ferrous sulfate accounts for 20-100 ppm of the total mass of the three monomers, and sodium bisulfite accounts for 100-400 ppm of the total mass of the three monomers.

[0019] The addition amount of the initiator azobispropaneamine in the second stage is 5-50 ppm of the total mass of the three monomers.

[0020] The initiator azodiisobutyramidine dihydrochloride in the third stage accounts for 5-50 ppm of the total mass of the three monomers.

[0021] Preferably, the polymerization reaction is initiated at a temperature of 0-5 °C.

[0022] In the process of directly preparing fracturing fluid with the flowback fluid, the flowback fluid will be fully mixed with additives such as drag reducers and gel breakers. There are Fe 2+ , Fe 3+ , Al 3+ , Cu 2+ and other ions in the flowback fluid, and these ions have strong electrostatic interactions with polyacrylamide molecules. On the one hand, it causes the polyacrylamide molecules to curl, resulting in a reduction in the viscosity-increasing effect of the drag reducer. At the same time, Fe 2+ will be oxidized to Fe 3+ , and Fe 3+ and Al 3+ act with polyacrylamide molecules to produce flocculants, and these flocculants will precipitate, causing pollution to the formation and seriously blocking the formation pores. There are high concentrations of Ca 2+ , Mg 2+ , SO4 2- , HCO3 - and other ions in the flowback fluid. During the preparation process, HCO3 - decomposes into CO3 2- , and CO3 2- combines with Ca 2+ , Mg 2+ to form CaCO3 and MgCO3 scales. These scales will attach to the pipe wall on the one hand, resulting in a narrowing of the pipe diameter, and at the same time, they will also pollute the formation and even block the formation pores. Therefore, an ion capture agent needs to be added during the preparation of the fracturing fluid to achieve the functions of scale inhibition, iron resistance, and complex ion capture in the system.

[0023] The ion capturer added to the fracturing fluid of the present invention is composed of components in the following parts by weight: 10-15 parts of aminotrimethylenephosphonic acid, 20-25 parts of diethylenetriamine pentamethylenephosphonic acid, 20-25 parts of ethylene glycol bis(2-aminoethyl ether) tetraacetic acid, 10-15 parts of p-tolyldiethanolamine, 5-10 parts of 2,3-epoxypropyltrimethylammonium chloride, 2 parts of fatty alcohol polyoxyethylene ether, 2 parts of anhydrous citric acid, and 2 parts of tetrahydrofurfuryl acrylate.

[0024] Among them, aminotrimethylenephosphonic acid and diethylenetriamine pentamethylenephosphonic acid can effectively chelate Ca 2+ 、Mg 2+ , and play the performance of corrosion and scale inhibition.

[0025] Ethylene glycol bis(2-aminoethyl ether) tetraacetic acid and p-tolyldiethanolamine can efficiently capture Fe 3+ 、Al 3+ 、Cu 2+ , inhibit the interaction of these ions with polyacrylamide, and maintain the stability of the fracturing fluid.

[0026] 2,3-Epoxypropyltrimethylammonium chloride can combine with anions such as CO3 2- 、HCO3 - and SO4 2- in the liquid phase to reduce the concentration of these anions in water, thereby reducing the precipitation of calcium and magnesium ions.

[0027] As a surfactant, fatty alcohol polyoxyethylene ether can improve the wettability of the liquid on the solid surface, promote the contact and penetration of the fracturing acidizing fluid with the formation rock surface, and improve the fracturing effect.

[0028] As an antioxidant, anhydrous citric acid can delay or prevent the oxidation reaction in the liquid through mechanisms such as capturing free radicals, can effectively inhibit the progress of the oxidation reaction, and protect the liquid from oxidation.

[0029] As a synergist, tetrahydrofurfuryl acrylate mainly ensures the formation of a stable dispersion system in water, helps to disperse other components evenly in the solution, and improves the effect of other components. By adding various additives, multi-faceted effect improvement can be achieved, construction efficiency can be improved, and costs can be reduced.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] (1) The salt-tolerant polymer of the present invention introduces a relatively high content of acrylamide polyoxyethylene benzene sulfonate or acrylamide sulfonate as a salt-tolerant monomer on the basis of conventional polyacrylamide monomers. While improving the temperature and salt tolerance of the polymer, it also takes into account the hydrophilicity of the polymer. The sulfonic acid group is beneficial to improving the polymer's resistance to complex ions, and the strong hydrophilicity of the anion increases the dissolution rate of the polymer in brine. At the same time, an allyl quinoline hydrophobic rigid functional monomer is introduced to further improve the rigidity of the polymer main chain. The polymer maintains a high drag reduction performance and a high drag reduction retention rate under saline conditions, and this monomer enables the polymer to have a strong hydrophobic association effect. Under saline conditions, the intermolecular interaction is increased through the association effect, enhancing the viscosity-increasing and sand-carrying performance under complex water quality conditions. In the molecular structure design of the prepared salt-tolerant polymer, no carboxyl group is contained, reducing the possibility of the polymer forming flocs under conditions of high calcium and magnesium ions, iron ions, and aluminum ions, and improving the polymer's resistance to complex ions.

[0032] (2) The present invention synthesizes the salt-tolerant polymer by aqueous solution polymerization. By adding a three-stage composite initiator system, free radicals are gradually and slowly released, and a low free radical concentration is always maintained in the polymerization system, which is beneficial to chain growth, so as to achieve the improvement of the polymer molecular weight, the increase of monomer conversion rate, and further the increase of the viscosity of the product.

[0033] (3) The present invention can be applicable to complex flowback fluid water quality with a total salinity of (10 - 30)×10 4 mg / L, in which the calcium and magnesium ions are as high as (0.5 - 5)×10 4 mg / L, the total iron content is 50 - 400mg / L, the aluminum ion content is 10 - 50mg / L, and the copper ion content is 10 - 50mg / L. The flowback fluid does not require pretreatment and can be directly formulated into a fracturing fluid.

[0034] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0035] Figure 1 It is the infrared spectrum diagram of the polymer in Example 3.

[0036] Figure 2 It is the comparison result of the drag reduction rate of the polymer in Example 3 and the polymer in Comparative Example 1 in 300,000 ppm brine.

[0037] Figure 3 It is the gel-breaking liquid state of the fracturing fluid obtained by adding 0.15% of the polymer in Comparative Example 1 to the simulated brine.

[0038] Figure 4 It is the gel-breaking liquid state of the fracturing fluid obtained by adding 0.15% of the polymer in Example 3 to the simulated brine.

[0039] Figure 5 To simulate the gel-breaking liquid state of the fracturing fluid obtained by adding 0.15% of the polymer of Example 3 and 100 ppm of the ion-trapping agent of Example 19 to the simulated brine. Specific embodiments

[0040] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0041] Examples 1-18 are examples of the preparation method of salt-tolerant polymers. Among them, the molecular structural formulas of sodium acrylamidosulfonate and sodium acrylamidopolyoxyethylene benzenesulfonate are as follows:

[0042] Where R3 is n is 3-10.

[0043] The molecular structure of the allylquinoline monomer is as follows:

[0044]

[0045] Example 1

[0046] Acrylamide, sodium acrylamidopolyoxyethylene benzenesulfonate (n = 5), and allylquinoline monomer were fed in a molar ratio of 1:0.08:0.01, added to a 5000 mL beaker, and made into a mixed solution with a total monomer mass concentration of 28% with deionized water. Stir until dissolved, adjust the pH value of the system to 8 with sodium hydroxide solution, stir the system evenly, place it in a constant temperature water bath, and introduce nitrogen for 30 min. When the temperature is 5 °C, add a three-stage composite initiator to initiate the polymerization reaction. Among them, the concentration of ammonium persulfate is 200 ppm, the concentration of ferrous sulfate is 50 ppm, the concentration of sodium bisulfite is 200 ppm, the concentration of azobispropaneamine is 15 ppm, and the concentration of 2,2'-azobis(2-methylpropionamidine) dihydrochloride is 25 ppm (the addition amount of the initiator is the proportion of the total mass of the three monomers, and the same applies to the subsequent examples). When the temperature rise in the reaction system does not exceed 1 °C within 30 minutes, the polymerization reaction is considered basically complete. One hour after the completion of the polymerization reaction, the colloid was taken out, cut into particles with a size of 3-5 mm, spread out and flattened on a 500-mesh sieve, placed in an oven at a constant temperature of 95 °C and dried for 1-3 h, and then taken out and ground through a grinder and sieved to obtain a salt-tolerant polymer powder with a mesh number ≥ 120.

[0047] The viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 1 was measured and calculated to be 8.25 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0048] Example 2

[0049] According to the same method as in Example 1, only change the molar ratio of acrylamide, polyoxyethylene sodium benzenesulfonate acrylamide (n = 5), and allyl quinoline monomer to 1:0.001:0.01. Use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 2 is 14.95 million.

[0050] Example 3

[0051] According to the same method as in Example 1, only change the molar ratio of acrylamide, polyoxyethylene sodium benzenesulfonate acrylamide (n = 5), and allyl quinoline monomer to 1:0.1:0.01. Use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 3 is 7.12 million.

[0052] The infrared spectrum of the salt-tolerant polymer synthesized in Example 3 is shown in Figure 1 . In the figure, the wave numbers at 3308 cm -1 are attributed to the antisymmetric stretching vibration and symmetric stretching vibration peaks of the N-H bond; the wave numbers at 2930 cm -1 and 1451 cm -1 are respectively attributed to the stretching vibration peak and bending vibration peak of C-H; the wave number at 1663 cm -1 is attributed to the stretching vibration of C=O in the amide I band; the wave number at 1545 cm -1 is the vibration absorption peak of the benzene ring skeleton, and the wave number at 1304 cm -1 is the C-N stretching vibration peak; the wave numbers at 1188 cm -1 , 1041 cm -1 , 627 cm -1 are the stretching vibration peaks of SO3 - ; the wave number at 1120 cm -1 is the stretching vibration peak of the C-O bond; through the above data, it can be proved that the synthesized polymer is a terpolymer.

[0053] Example 4

[0054] According to the same method as in Example 1, only change the molar ratio of acrylamide, polyoxyethylene sodium benzenesulfonate acrylamide (n = 5), and allyl quinoline monomer to 1:0.2:0.01; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 4 is 3.8 million.

[0055] Example 5

[0056] According to the same method as in Example 1, only change the molar ratio of acrylamide, sodium polyoxyethylene benzenesulfonate acrylamide (n = 5), and allyl quinoline monomer to 1:0.08:0.001; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 5 according to GB / T 12005.10-92, which is 11.56 million.

[0057] Example 6

[0058] According to the same method as in Example 1, only change the molar ratio of acrylamide, sodium polyoxyethylene benzenesulfonate acrylamide (n = 5), and allyl quinoline monomer to 1:0.08:0.03; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 6 according to GB / T 12005.10-92, which is 6.89 million.

[0059] Example 7

[0060] According to the same method as in Example 1, only change the molar ratio of acrylamide, sodium polyoxyethylene benzenesulfonate acrylamide (n = 5), and allyl quinoline monomer to 1:0.08:0.05; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 7 according to GB / T 12005.10-92, which is 4.16 million.

[0061] Example 8

[0062] According to the same method as in Example 1, only change the sodium polyoxyethylene benzenesulfonate acrylamide (n = 5) monomer to sodium polyoxyethylene benzenesulfonate acrylamide (n = 3); use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 8 according to GB / T 12005.10-92, which is 8.92 million.

[0063] Example 9

[0064] According to the same method as in Example 1, only change the sodium polyoxyethylene benzenesulfonate acrylamide (n = 5) monomer to sodium polyoxyethylene benzenesulfonate acrylamide (n = 10); use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 9 according to GB / T 12005.10-92, which is 8.53 million.

[0065] Example 10

[0066] According to the same method as in Example 1, only change the acrylamide polyoxyethylene benzene sulfonate (n = 5) monomer to sodium 2-acrylamido-2-methylsulfonate; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 10 is 12.15 million.

[0067] Example 11

[0068] According to the same method as in Example 1, only change the initiation temperature to -10 °C; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 11 is 13.42 million.

[0069] Example 12

[0070] According to the same method as in Example 1, only change the initiation temperature to 15 °C; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 12 is 7.09 million.

[0071] Example 13

[0072] According to the same method as in Example 1, only change the initiation temperature to 30 °C; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 13 is 4.02 million.

[0073] Example 14

[0074] According to the same method as in Example 1, only change the concentration of ammonium persulfate in the composite initiator system to 100 ppm and the concentration of sodium bisulfite to 100 ppm; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 14 is 12.89 million.

[0075] Example 15

[0076] According to the same method as in Example 1, only change the concentration of ammonium persulfate in the composite initiator system to 400 ppm and the concentration of sodium bisulfite to 400 ppm; use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92, and the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 15 is 6.82 million.

[0077] Example 16

[0078] According to the same method as in Example 1, only changing the concentration of ferrous sulfate in the composite initiator system to 20 ppm; using an Ubbelohde viscometer (0.55 mm tube diameter), testing and calculating according to GB / T 12005.10-92, the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 16 is 11.22 million.

[0079] Example 17

[0080] According to the same method as in Example 1, only changing the concentration of V44 azobispropaneamine in the composite initiator system to 50 ppm and the concentration of azodiisobutyramidine dihydrochloride to 50 ppm; using an Ubbelohde viscometer (0.55 mm tube diameter), testing and calculating according to GB / T12005.10-92, the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 17 is 9.53 million.

[0081] Example 18

[0082] According to the same method as in Example 1, only changing the concentration of V44 azobispropaneamine in the composite initiator system to 5 ppm and the concentration of azodiisobutyramidine dihydrochloride to 5 ppm; using an Ubbelohde viscometer (0.55 mm tube diameter), testing and calculating according to GB / T12005.10-92, the viscosity-average molecular weight of the salt-tolerant polymer obtained in Example 18 is 7.38 million.

[0083] Comparative Example 1

[0084] According to the same synthesis method as in Example 1, using acrylamide and sodium acrylate as raw material monomers, with a molar ratio of 1:0.15, using an Ubbelohde viscometer (0.55 mm tube diameter), testing and calculating according to GB / T 12005.10-92, the viscosity-average molecular weight of the ultra-high molecular weight polyacrylamide obtained in Comparative Example 1 is 25 million.

[0085] Comparative Example 2

[0086] According to the same synthesis method as in Example 1, changing the synthesis monomers to acrylamide and acrylamidopolyoxyethylene benzene sulfonate (n = 5), with a molar ratio of 1:0.08, using an Ubbelohde viscometer (0.55 mm tube diameter), testing and calculating according to GB / T 12005.10-92, the viscosity-average molecular weight of the ultra-high molecular weight polyacrylamide obtained in Comparative Example 2 is 9.35 million

[0087] Comparative Example 3

[0088] According to the same synthesis method as in Example 1, changing the synthesis monomers to acrylamide and allyl quinoline monomers, with a molar ratio of 1:0.01, using an Ubbelohde viscometer (0.55 mm tube diameter), testing and calculating according to GB / T 12005.10-92, the viscosity-average molecular weight of the ultra-high molecular weight polyacrylamide obtained in Comparative Example 2 is 13.52 million

[0089] The performance evaluation methods for the salt-tolerant polymers prepared in Examples 1-18 and the polymer powders in Comparative Examples 1-3 are as follows:

[0090] (1) Sticking start time

[0091] Add 200 mL of 20000 ppm simulated water (5000 ppm divalent calcium and magnesium ions) into a 500 mL beaker respectively. Add 0.1 g of polymer powder sample under the condition of 600 r / min rotation speed, and record the sticking start time after adding the powder (when stirring, the sticking phenomenon can be clearly felt and the glass rod can draw filaments). The test results are shown in Table 1.

[0092] (2) Viscosity

[0093] Stir at 600 r / min under different water quality conditions, add a certain amount of polymer powder sample respectively, and test the viscosity when stirring for 3 min after adding the powder. When the powder content is 0.05% (the percentage of powder mass to water mass), use a capillary viscometer to test the kinematic viscosity (mm 2 / s) of the product. When the powder content is 0.15% - 0.3%, use a six-speed viscometer to measure the viscosity value (mPa·s) at 170 s -1 . The test results are shown in Table 1.

[0094] (3) Drag reduction rate

[0095] Test the drag reduction rate of each polymer powder sample in different water qualities. Execute according to the regulations for measuring the drag reduction rate in Chapter 7.13.1.1 of SY / T 6376-2008. Take the 5-min drag reduction rate data as the drag reduction rate value. The test results are shown in Table 2. The comparison of the drag reduction rates of the polymers in Example 3 and Comparative Example 1 in 300,000 ppm brine is shown in Figure 2 .

[0096] The experimental evaluation results of different examples are as follows:

[0097] In 20000 ppm simulated water, the divalent ion content is 5000 ppm;

[0098] In 100000 ppm simulated water, the divalent ion content is 30000 ppm;

[0099] In 300000 ppm simulated water, the divalent ion is 50000 ppm;

[0100] Table 1. Comparison of viscosity values of each polymer powder in different water quality base liquids

[0101]

[0102] Table 2. Comparison of drag reduction rates (5 min) of each polymer powder in different water qualities

[0103]

[0104] Examples 19 - 25 are examples of ion capture agents, where the parts of each component are all parts by weight.

[0105] Example 19

[0106] Mix 10 parts of aminotrimethylenephosphonic acid, 20 parts of diethylenetriamine pentamethylenephosphonic acid, 20 parts of ethylene glycol bis(2 - aminoethyl ether) tetraacetic acid, 10 parts of p - tolyldiethanolamine, 5 parts of 2,3 - epoxypropyltrimethylammonium chloride, 2 parts of surfactant, 2 parts of antioxidant, 2 parts of synergist, and 29 parts of water, and stir well for 0.5 h to obtain an ion capture agent.

[0107] Example 20

[0108] Mix 15 parts of aminotrimethylenephosphonic acid, 25 parts of diethylenetriamine pentamethylenephosphonic acid, 25 parts of ethylene glycol bis(2 - aminoethyl ether) tetraacetic acid, 15 parts of p - tolyldiethanolamine, 10 parts of 2,3 - epoxypropyltrimethylammonium chloride, 2 parts of surfactant, 2 parts of antioxidant, 2 parts of synergist, and 4 parts of water, and stir well for 0.5 h to obtain an ion capture agent.

[0109] Example 21

[0110] Mix 12 parts of aminotrimethylenephosphonic acid, 23 parts of diethylenetriamine pentamethylenephosphonic acid, 23 parts of ethylene glycol bis(2 - aminoethyl ether) tetraacetic acid, 12 parts of p - tolyldiethanolamine, 8 parts of 2,3 - epoxypropyltrimethylammonium chloride, 2 parts of surfactant, 2 parts of antioxidant, 2 parts of synergist, and 16 parts of water, and stir well for 0.5 h to obtain an ion capture agent.

[0111] Example 22

[0112] Mix 15 parts of aminotrimethylenephosphonic acid, 25 parts of ethylene glycol bis(2 - aminoethyl ether) tetraacetic acid, 15 parts of p - tolyldiethanolamine, 10 parts of 2,3 - epoxypropyltrimethylammonium chloride, 2 parts of surfactant, 2 parts of antioxidant, 2 parts of synergist, and 39 parts of water, and stir well for 0.5 h to obtain an ion capture agent.

[0113] Example 23

[0114] Mix 10 parts of aminotrimethylenephosphonic acid, 20 parts of ethylene glycol bis(2 - aminoethyl ether) tetraacetic acid, 10 parts of p - tolyldiethanolamine, 5 parts of 2,3 - epoxypropyltrimethylammonium chloride, 2 parts of surfactant, 2 parts of antioxidant, 2 parts of synergist, and 49 parts of water, and stir well for 0.5 h to obtain an ion capture agent.

[0115] Example 24

[0116] Mix 15 parts of aminotrimethylenephosphonic acid, 25 parts of diethylenetriamine pentamethylenephosphonic acid, 15 parts of p-tolyldiethanolamine, 10 parts of 2,3-epoxypropyltrimethylammonium chloride, 2 parts of surfactant, 2 parts of antioxidant, 2 parts of synergist, and 29 parts of water, and stir well for 0.5 h to obtain an ion capture agent.

[0117] Example 25

[0118] Mix 15 parts of aminotrimethylenephosphonic acid, 15 parts of p-tolyldiethanolamine, 10 parts of 2,3-epoxypropyltrimethylammonium chloride, 2 parts of surfactant, 2 parts of antioxidant, 2 parts of synergist, and 54 parts of water, and stir well for 0.5 h to obtain an ion capture agent.

[0119] Evaluation of the scale inhibition performance of the ion capture agent:

[0120] Test the scale inhibition performance of the ion capture agent in the above examples. The evaluation method refers to the general technical conditions for scale inhibitors for oilfields "SY / T5673-2020". The test results are shown in Table 3.

[0121] Table 3. Test results of the scale inhibition performance of the ion capture agents in Examples 19-25

[0122] Ion Trapping Agent Type Calcium Carbonate Scale Inhibition Rate (%) Calcium Sulfate Scale Inhibition Rate (%) Example 19 90 95 Example 20 89 93 Example 21 89 93 Example 22 84 88 Example 23 75 81 Example 24 85 87 Example 25 56 78

[0123] Evaluation of the performance of the fracturing fluid system against complex ions:

[0124] Prepare simulated brine with a total salinity of 300000 ppm, including 40000 ppm of calcium ions, 10000 ppm of magnesium ions, 200 ppm of Fe 3+ concentration, 20 ppm of Al 3+ concentration, 20 ppm of Cu 2+ concentration, and 400 ppm of HCO3 - concentration.

[0125] Drag reduction rate test: Add the polymer powder of Example 3 to the simulated brine, with the polymer mass accounting for 0.05% of the brine mass, to obtain a fracturing fluid of a single polymer, and test the drag reduction rate for 10 min. Take another portion of simulated brine, add 0.05% of the polymer powder of Example 3 and 100 ppm of one of the ion capture agents in Examples 19-25 to it to obtain a fracturing fluid, and test the drag reduction rate for 5 min. The test results are shown in Table 4.

[0126] Table 4. Test results of the drag reduction rate of different fracturing fluid systems in complex water quality

[0127] Ion Trapping Agent Type Drag Reduction Rate / (%) None 62.0 Example 19 75.8 Example 20 76.2 Example 21 73.5 Example 22 72.4 Example 23 73.1 Example 24 68.5 Example 25 65.2

[0128] Measure and compare the thickening time and mixing viscosity of the single polymer system of 0.15% salt-tolerant polymer powder of Example 3 and different formulated functional fracturing fluid systems of 0.15% salt-tolerant polymer powder of Example 3 plus 100 ppm of complex ion trappers of Examples 19-25. The results are shown in Table 5;

[0129] Thickening time test: Add 200 mL of 300,000 ppm simulated brine into a 500 mL beaker respectively. Add 0.15% salt-tolerant polymer powder of Example 3 under the condition of 600 r / min rotation speed, or add 0.15% salt-tolerant polymer powder of Example 3 and 100 ppm of complex ion trappers of Examples 19-25 simultaneously. Record the thickening time of the solution (it can be obviously felt that the solution thickens during stirring and the glass rod can draw filaments). The test results are shown in Table 5.

[0130] Viscosity test: Under the stirring condition of 600 r / min rotation speed, add 0.15% salt-tolerant polymer powder of Example 3 into 300,000 ppm simulated brine, or add 0.15% salt-tolerant polymer powder of Example 3 and 100 ppm of complex ion trappers of Examples 19-25 simultaneously. Measure the viscosity of the solution system at 3 min of stirring, and measure the viscosity value at 170 s with a six-speed viscometer. The test results are shown in Table 5. -1 The viscosity value is shown in Table 5.

[0131] Table 5. Viscosity test results of different fracturing fluid systems in complex water quality

[0132]

[0133]

[0134] Gel breaking performance test: Under the stirring condition of 600 r / min rotation speed, add 0.15% salt-tolerant polymer powder of Example 3 into 300,000 ppm simulated brine, or add 0.15% salt-tolerant polymer powder of Example 3 and 100 ppm of complex ion trappers of Examples 19-25 simultaneously to form a fracturing fluid system; the quantitative analysis results of complex ion flocs after gel breaking of the fracturing fluid system are shown in Table 6. The test method refers to the test method for residue content in SYT 7627-2021 "Technical Requirements for Water-Based Fracturing Fluids" for detection.

[0135] Table 6. Quantitative analysis test results of flocs after gel breaking of different fracturing fluid systems in complex water quality

[0136] Ion Trapping Agent Type Content of Flocculent Residue in Gel-Breaking Fluid (ppm) None 2200 Example 19 10 Example 20 15 Example 21 25 Example 22 58 Example 23 154 Example 24 65 Example 25 458

[0137] Add 0.15% polymer of Comparative Example 1 into the above simulated brine, and the gel-breaking liquid state of the obtained fracturing fluid is shown in Figure 3 . Add 0.15% polymer of Example 3 into the above simulated brine, and the gel-breaking liquid state of the obtained fracturing fluid is shown inFigure 4 0.15% of the polymer of Example 3 and 100 ppm of the ion scavenger of Example 19 were added to the above-mentioned simulated brine, and the state of the gel-breaking fluid of the obtained fracturing fluid is shown in Figure 5 .

[0138] Scale inhibition test method: Prepare simulated brine with a total salinity of 300,000 ppm, including 40,000 ppm of calcium ions, 10,000 ppm of magnesium ions, 3+ a concentration of 200 ppm of Fe, 3+ a concentration of 20 ppm of Al, 2+ a concentration of 20 ppm of Cu, - a concentration of 400 ppm of HCO3. Add 0.15% of the salt-tolerant polymer powder of Example 3, a gel breaker, and 100 ppm of an ion scavenger to the simulated brine at a rotation speed of 600 r / min to prepare a fracturing fluid. After the fracturing fluid is completely gel broken, take 200 ml of the gel-breaking fluid and put it into a pressure-resistant bottle. Place the pressure-resistant bottle in a constant temperature oven at 70 °C for 16 h, and measure the changes in the concentrations of 2+ Ca and 2+ Mg before and after aging. Refer to the general technical conditions for scale inhibitors for oilfields "SY / T5673-2020" to calculate the scale inhibition rate. The results of the calcium carbonate scale inhibition rate are shown in Table 7.

[0139] Table 7. Analysis and test results of calcium carbonate scale inhibition for different fracturing fluid systems in complex water quality

[0140] Ion Trapping Agent Type Calcium Carbonate Scale Inhibition Rate of Gel-Breaking Fluid with Added Ion Trapping Agent (%) Example 19 80 Example 20 65 Example 21 62 Example 22 70 Example 23 61 Example 24 75 Example 25 35

[0141] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A functional fracturing fluid with direct distribution function for complex water quality flowback fluid, characterized in that, It is prepared by directly adding a salt-tolerant polymer and a high-efficiency ion capturer to the flowback fluid; wherein, the addition amount of the salt-tolerant polymer accounts for 0.15-0.3% of the total mass of the fracturing fluid, and the addition amount of the ion capturer is 100-500 ppm; the molecular structure of the salt-tolerant polymer is as follows: In the formula, R1 is any one of the following two structural formulas: The structural formula of R3 is as follows: n is from 3 to 10; The structural formula of R2 is as follows: In the molecular structure of the salt-tolerant polymer, the molar ratio of a:b:c is 1:(0.001-0.2):(0.001-0.05).

2. The functional fracturing fluid directly prepared from the complex water-quality flowback fluid according to claim 1, wherein the molar ratio of a:b:c is 1:(0.05-0.1):(0.01-0.03).

3. The functional fracturing fluid with direct distribution function for complex water quality flowback fluid as claimed in claim 1, wherein The salt-tolerant polymer is copolymerized from acrylamide, a salt-tolerant monomer, and an allyl quinoline monomer, and the salt-tolerant monomer is sodium acrylamidopolyoxyethylene benzenesulfonate or sodium acrylamidosulfonate.

4. The functional fracturing fluid with direct distribution function for complex water quality flowback fluid according to claim 3, wherein The preparation method of the salt-tolerant polymer is as follows: Dissolve acrylamide, the salt-tolerant monomer, and the allyl quinoline monomer in water, adjust the pH to 8, purge with nitrogen to remove oxygen, add a three-stage composite initiator, and initiate a polymerization reaction at a temperature of -10 to 30 °C to obtain the salt-tolerant polymer; the three-stage composite initiator includes an oxidation-reduction initiator system in the first stage, wherein the oxidant is ammonium persulfate, and the reductant is composed of a composite of ferrous sulfate and sodium bisulfite; an azobispropaneamine initiator in the second stage, and an azodiisobutyramidine dihydrochloride initiator in the third stage.

5. The functional fracturing fluid with the direct distribution function for complex water quality flowback fluid as claimed in claim 4, wherein When the temperature rise in the polymerization reaction system does not exceed 6. The functional fracturing fluid with direct distribution function for complex water quality flowback fluid as claimed in claim 4, wherein, ​ 7. The functional fracturing fluid with direct distribution function for complex water quality flowback fluid according to claim 1, wherein ​ 8. The functional fracturing fluid with direct distribution function for complex water quality flowback fluid according to claim 7, characterized in that, ​ ​

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