A biological depolymerase composite system for oilfield polymer plugging and a preparation method and application thereof

Abstract

This invention discloses a bio-depolymerase composite system for polymer deblocking in oilfields, its preparation method, and its application. For the first time, a ternary synergistic combination of bio-depolymerase, a sugar coenzyme, and an organic acid salt synergist is established. The bio-depolymerase specifically cleaves the main chain or side chain amide groups of polyacrylamide causing blockage in the formation; the sugar coenzyme participates in the enzymatic reaction and stabilizes the enzyme's active conformation, preventing enzyme inactivation under high temperature and high salt conditions; the organic acid salt synergist regulates the reaction microenvironment, chelates metal ions, and enhances the enzymatic reaction rate. The synergistic effect of these three components achieves mild, efficient, and low-residue degradation of various polymers during fracturing oil recovery, providing a green, low-damage, and efficient new technological approach for deep deblocking and increased production in polymer-driven oilfields.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical production enhancement and unblocking technology, and more specifically, to a biopolymer depolymerization enzyme composite system for oilfield polymer unblocking, its preparation method and application. Background Technology

[0002] In the tertiary oil recovery stage of oil and gas fields, polymer flooding and alkali-surfactant-polymer (ASP) ternary composite flooding technologies have become one of the main means to improve oil recovery. These technologies effectively improve sweep efficiency and oil displacement efficiency by significantly increasing the viscosity of the displaced phase, improving the mobility ratio, and expanding the swept volume. However, with long-term and large-scale injection of polymers, polyacrylamide (PAM) and its derivatives undergo adsorption, retention, mechanical capture, and structural rearrangement in the formation, and interact with alkaline components, polyvalent metal ions, and fine clay particles in the formation, easily forming flocculent, network, or filter cake-like blockage structures. This blockage phenomenon is particularly severe in the near-wellbore zone and artificial fractures, leading to a significant decrease in effective formation permeability, weakened fracturing and fracture creation capabilities, and a significantly shortened effective cycle of subsequent acidizing, fracturing, and other production enhancement measures, even resulting in the extreme case of "well blockage".

[0003] Existing deblocking technologies for various types of polymer blockage mainly include: Acid deblocking: Utilizing strong acids to dissolve carbonates and some metal precipitates, but its degradation effect on the polymer itself is limited, and it easily causes secondary precipitation and reservoir acid-sensitive damage. Oxidant depolymerization: Strong oxidants such as persulfate and hydrogen peroxide are commonly used to break down polymer molecular chains, but their effective radius is small, their effective period is short, and residual oxidants may cause reservoir oxidation damage and secondary blockage. Chelating agent / surfactant cleaning: This has some effect on metal ion bridging and emulsion blockage, but its ability to degrade the high molecular weight PAM backbone is weak, and the overall deblocking depth is insufficient.

[0004] The aforementioned chemical methods generally suffer from drawbacks such as limited unblocking radius, poor duration of action, easy to cause secondary damage, and complex and costly backflow fluid treatment, making it difficult to meet the needs of deep, mild, and sustainable unblocking in oilfields after polymer flooding.

[0005] In recent years, although some progress has been made in the research on enzymatic degradation of plugging materials in oilfield fracturing systems, existing enzyme technologies are mostly limited to single enzyme species or laboratory aqueous solutions. These technologies suffer from problems such as enzyme activity being easily deactivated by high temperature, high salt, and pH fluctuations, incomplete degradation, poor adaptability to complex plugging materials (polymer + clay + metal ions), and the possibility that degradation products may still form new plugging materials. A mature unblocking system suitable for oilfield field conditions has not yet been formed.

[0006] In summary, existing technologies still suffer from prominent problems such as low deblocking efficiency, poor selectivity, high damage risk, and insufficient overall economic efficiency when dealing with various types of polymer blockages. There is an urgent need to develop a new biological deblocking technology that can achieve efficient, mild, and thorough degradation under in-situ reservoir conditions, and whose degradation products are easy to return and leave low residues. Summary of the Invention

[0007] The purpose of this invention is to overcome the aforementioned deficiencies in existing technologies and provide a bio-depolymerase composite system for polymer unblocking in oilfields, along with its preparation method and application. This composite enzyme system, composed of bio-depolymerase, sugar coenzymes, and organic acid salt synergists, is particularly suitable for the bio-enzymatic and mild degradation of the most common polyacrylamide (PAM) polymers. This addresses the problems of existing unblocking methods, such as small radius of action, short effective period, and susceptibility to secondary precipitation and reservoir damage. It achieves mild, efficient, and thorough degradation of polymers and significantly improves formation permeability and oil displacement after unblocking. Furthermore, based on this composite system, this invention also provides a method for evaluating the unblocking and displacement effects of this system in the near-wellbore zone after polymer flooding under indoor simulation conditions.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A biopolymer depolymerization enzyme complex system for unclogging polymers in oil fields comprises the following components in weight percentages: 0.001-0.01 wt% biopolymer depolymerization enzyme, 0.001-0.01 wt% carbohydrate coenzyme, 0.001-0.01 wt% organic acid salt synergist, and the balance being water; wherein the biopolymer depolymerization enzyme is selected from one or more of amidase, protease, peroxidase, oxidase, and mannanase; the carbohydrate coenzyme is selected from one or more of monosaccharides, disaccharides, and polysaccharides; and the organic acid salt synergist is selected from one or more of lactate, citrate, acetate, and malate.

[0010] The present invention also discloses a method for preparing the above-mentioned biodepolymerase complex system for oilfield polymer unblocking, comprising: adding biodepolymerase, sugar coenzyme and organic acid salt synergist to water, mixing at room temperature to obtain the biodepolymerase complex system.

[0011] The present invention also discloses the application of the above-described biodepolymerase complex system for oilfield polymer unblocking in oilfield polymer unblocking.

[0012] Implementing the embodiments of the present invention will have the following beneficial effects: Experiments show that this invention, for the first time, combines a ternary synergistic system of biopolymerase, carbohydrate coenzyme, and organic acid salt synergist to achieve mild and efficient degradation of polyacrylamide polymers. Indoor experiments demonstrate that this system depolymerizes polyacrylamide-blocking micelles, achieving directional micelle fragmentation within 24 hours. After 6 days, the system becomes clear with no significant solids. The degradation products are mainly oligomers or low-molecular-weight fragments with a molecular weight below 1000, and the residue after degradation is less than 250 mg / L. In sand pipe displacement evaluation, the oil recovery rate is increased by approximately 10% compared to conventional chemical depolymerization systems. It has the following significant advantages: a mild degradation process, avoiding reservoir damage and secondary precipitation caused by strong acids / oxidants; enzyme activity that is temperature and salt resistant, suitable for medium-high temperature and high-salinity reservoir environments; degradation products that are easily refluxing small-molecule oligomers with low residue and high refluxing efficiency; and inexpensive and readily available components with a simple preparation process, providing a green, low-damage, and efficient technical approach for deep unblocking of oilfields after polymer flooding and subsequent field applications. Attached Figure Description

[0013] Figure 1 , Figure 2 Photographs and experimental results of biological depolymerases with different concentrations of unblocking agents in Experiment Example 1 of this invention.

[0014] Figure 3 The results of biopolymerase activity assays at different temperatures are shown in Experimental Example 1 of this invention.

[0015] Figure 4 The results show the activity of the biopolymerase under different pH conditions in Experiment Example 2 of this invention.

[0016] Figure 5 , Figure 6 The results are the Maldi-TOF measurements of molecular weight after unblocking at 45°C in Experimental Example 5 of this invention.

[0017] Figure 7 , Figure 8 The results are the Maldi-TOF measurements of molecular weight after unblocking at 60℃ in Experimental Example 6 of this invention.

[0018] Figure 9 The results of biopolymerase activity assay under different mineralization conditions in Experiment Example 7 of this invention are shown. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0020] This invention discloses a biodepolymerase complex system for unblocking polymers in oil fields, comprising the following components by mass percentage: 0.001~0.01wt% biodepolymerase, 0.001~0.01wt% carbohydrate coenzyme, 0.001~0.01wt% organic acid salt synergist, and the balance being water.

[0021] Specifically, this invention is the first to combine a biopolymerase, a sugar coenzyme, and an organic acid salt synergist into a composite system. The biopolymerase specifically cuts the polyacrylamide backbone or side chain amide groups that cause blockage in the formation; the sugar coenzyme participates in the enzymatic reaction and stabilizes the enzyme's active conformation, preventing enzyme inactivation under high temperature and high salt conditions; the organic acid salt synergist regulates the reaction microenvironment, chelates metal ions, and enhances the rate of enzymatic reaction. The synergistic effect of the three achieves mild, efficient, and low-residue degradation of the polymer, solving the problems of small radius of action, short effective period, easy secondary precipitation, and reservoir damage in existing unblocking methods.

[0022] In one specific embodiment, the biodepolymerase complex system comprises the following components and their mass fractions: 0.001~0.01 wt% biodepolymerase, 0.002 wt% carbohydrate coenzyme, 0.003 wt% organic acid salt synergist, and the balance being water.

[0023] Furthermore, the biodepolymerase is selected from one or more of amidase, protease, peroxidase, oxidase, and mannanase.

[0024] In one specific embodiment, the biodepolymerase is selected from one or more of amidases, proteases, peroxidases, and oxidases.

[0025] In one specific embodiment, the biodepolymerase is selected from a combination of amidase and one of protease, peroxidase and oxidase in a mass ratio of 1:1.

[0026] In one specific embodiment, the biodepolymerase is selected from a combination of amidase and one of trypsin, laccase, lignin peroxidase, alcohol oxidase and glucose oxidase in a mass ratio of 1:1.

[0027] Furthermore, the carbohydrate coenzyme is selected from one or more monosaccharides, disaccharides, and polysaccharides.

[0028] In one specific embodiment, the sugar coenzyme is selected from one or more of glucose, fructose, sucrose, maltose, and soluble starch. Preferably, the sugar coenzyme is selected from fructose and / or sucrose.

[0029] Furthermore, the organic acid salt synergist is selected from one or more of lactate, citrate, acetate and malate.

[0030] In one specific embodiment, the organic acid salt synergist is selected from sodium citrate and / or sodium acetate.

[0031] In one specific embodiment, the biodepolymerase complex system maintains enzyme activity within a temperature range of 30~100℃ (preferably 40~90℃), wherein the maximum activity is maintained at 60℃; and the enzyme activity is retained at 90℃ by ≥10%.

[0032] In one specific embodiment, to further enhance the degradation ability of the composite blockage (polymer + polysaccharide + clay), the biodepolymerase composite system also includes amylase; wherein the mass fraction of amylase in the biodepolymerase composite system is 0.001~0.01wt%, preferably 0.001wt.

[0033] In one specific embodiment, the amylase includes α-amylase and / or β-amylase for synergistic degradation of the polysaccharide component or blockage in the complex blockage.

[0034] The present invention also discloses a method for preparing a biodepolymerase complex system for unblocking polymers in oil fields as described above, comprising the following steps: adding biodepolymerase, sugar coenzyme and organic acid salt synergist to water and mixing at room temperature to obtain the biodepolymerase complex system.

[0035] In one specific embodiment, the preparation method further includes: adding biodepolymerase, sugar coenzyme, organic acid salt synergist and amylase to water, and mixing at room temperature to obtain a biodepolymerase complex system.

[0036] The present invention also discloses the application of the above-described biodepolymerase complex system for oilfield polymer unblocking in oilfield polymer unblocking.

[0037] In one specific embodiment, the polymer is polyacrylamide.

[0038] In one specific embodiment, the application includes: using a biodepolymerase complex system as a working solution, and contacting the working solution with a polymer-containing plugging medium at room temperature to carry out a depolymerization reaction, wherein the pH of the application environment is 4.0~10.0; the reaction temperature is 30~100℃ (preferably 40~90℃); the reaction time is 24 hours~6 days; and the mineralization range is 0~100000 mg / L.

[0039] In one specific embodiment, when the polymer is polyacrylamide, the degradation products are oligomeric or low-molecular-weight fragments with a molecular weight of less than 1000; the amount of residue after degradation is less than 250 mg / L.

[0040] The present invention also discloses the application of the above-described biodepolymerase complex system for oilfield polymer unblocking in the unblocking of oilfield complex blockages.

[0041] This invention also discloses an indoor polymer declogging and displacement evaluation method based on the above-mentioned biopolymer depolymerase complex system, comprising the following steps: (1) Prepare the unblocking working solution by preparing the biodepolymerase complex system.

[0042] (2) In an indoor simulation device, the working fluid is brought into contact with the polymer-containing blockage medium to carry out a depolymerization reaction. The reaction temperature is 40~60℃ and the reaction time is 24 hours to 6 days.

[0043] (3) Monitor the changes in polymer molecular weight, micelle dispersion, and residue during the reaction process; (4) Conduct displacement experiments in sand pipe or cast pipe models to evaluate the permeability recovery rate and the increase in crude oil recovery rate before and after unblocking.

[0044] In one specific embodiment, the clogging medium is selected from micelles, filter cakes, or sand tube models.

[0045] The following are specific embodiments. Example 1 The biodepolymerization enzyme complex system for oilfield polymer unblocking in this embodiment comprises the following components by weight percentage: 0.001~0.01 wt% biodepolymerization enzyme, 0.002 wt% carbohydrate coenzyme, 0.003 wt% organic acid salt synergist, 0.001 wt% amylase, and the balance being water. The biodepolymerization enzyme is selected from amidase (purchased from MCE) and trypsin (purchased from Beyotime) in a 1:1 mass ratio. The carbohydrate coenzyme is selected from fructose and sucrose in a 1:1 mass ratio. The organic acid salt synergist is selected from sodium citrate and sodium acetate in a 1:1 mass ratio. The amylase is α-amylase (purchased from Beyotime).

[0046] The preparation method of the biodepolymerase complex system for oilfield polymer unblocking in this embodiment includes the following steps: adding biodepolymerase, sugar coenzyme, amylase and organic acid salt synergist to water, mixing at room temperature for 30 minutes to achieve uniform dispersion, and obtaining the biodepolymerase complex system.

[0047] Example 2 The only difference between this embodiment and Example 1 is that: no trypsin is added in this embodiment, and the mass percentage of amidase in the complex system is 0.005%.

[0048] Example 3 The only difference between this embodiment and Embodiment 1 is that no amylase is added in this embodiment.

[0049] Comparative Example 1 The only difference between this comparative example and Example 1 is that no fructose or sucrose is added to this comparative example.

[0050] Comparative Example 2 The only difference between this comparative example and Example 1 is that sodium citrate and sodium acetate are not added to this comparative example.

[0051] Experimental Example Experimental Example 1: Effect and Kinetic Analysis of Formation Micelles in an Oilfield Using the biodepolymerase complex system formulation of Example 1, the mass percentage of biodepolymerase in the complex system was sequentially configured into 10 content gradients: 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007wt%, 0.008%, 0.009%, and 0.01%. Working solutions were then used for unblocking experiments. Figure 1 As shown. 10g of formation polymer micelles were added to each experimental group and incubated at 60℃. The dissolution of the micelles was observed and recorded at regular intervals. The dissolution criterion was that all large solid particles were apparently dispersed, with no obvious solids or suspended matter. The final dissolution time of the micelles was recorded. Figure 2 .

[0052] like Figure 2 The results showed that the dissolution time of the micelles was significantly shortened with increasing concentration of the bio-depolymerase. When the mass percentage reached 0.005%, the micelles could be completely dissolved within 24 hours. Even with further increases in the bio-depolymerase concentration up to a maximum of 0.01%, the dissolution time of the micelles remained at 24 hours.

[0053] Therefore, the results of this experiment show that, under the condition that the mass fraction of the depolymerase is 0.005%~0.01%, the dissolution time of the micelles can be shortened to 24h. Under this system, the micelles can be directionally broken and dissolved, indicating that the depolymerization is mild and efficient, and can play a deblocking role at a low concentration, which is beneficial for cost control in practical applications.

[0054] Experimental Example 2: Biodepolymerase Activity at Different Temperatures Based on the experimental results of Example 1, a system with a biodepolymerase mass fraction of 0.005% was selected to test the biodepolymerase activity at different temperatures. Gradual temperature ranges were constructed, starting from 40°C and reaching a maximum of 90°C, with each range being 5°C. Experiments were conducted at the corresponding temperatures according to the formulation in Example 1, and the degree of reaction was measured by the amount of product, with the highest point at 60°C being taken as 100% relative enzyme activity.

[0055] The results are as follows Figure 3As shown, the enzyme activity of the biodepolymerase system exhibits a pattern of initial increase, followed by a slow decrease, and then a rapid decline with temperature, demonstrating a relatively clear optimal reaction temperature range and good mid-temperature stability. Within the low to mid-low temperature range of 40–60 °C, enzyme activity significantly increases with increasing temperature, with the relative enzyme activity rapidly rising from approximately 70% to over 90%. During this stage, the increased temperature promotes intensified substrate molecule motion and improved enzyme-substrate binding efficiency, thereby accelerating the depolymerization reaction rate. When the temperature reaches 60 °C, the biodepolymerase system exhibits the highest relative enzyme activity (approaching or reaching 100%), indicating that this temperature range represents the optimal reaction temperature range for this enzyme system. Under these conditions, the enzyme protein conformation is stable and the active sites are fully exposed, which is conducive to the efficient and directional depolymerization of polyacrylamide polymers. In the range of 60~70℃, although the enzyme activity decreases slightly from the optimum temperature, it still remains at about 90% overall, and no obvious inactivation occurs. This indicates that the biodepolymerization enzyme system has good tolerance to medium and high temperatures and can meet the application requirements of oilfield indoor evaluation and some medium-temperature reservoir conditions. When the temperature is further increased to above 70℃, the enzyme activity begins to decline, but it can still retain about 10%~20% of the activity at 90℃.

[0056] In summary, the system in this embodiment maintains enzyme activity and good stability within a temperature range of 40–90°C, and also retains a certain level of enzyme activity even at extremely high temperatures of 90°C. This characteristic is beneficial for conducting laboratory experiments related to polymer deblocking under different reservoir conditions, and provides clear temperature basis for subsequent process parameter optimization and system adaptation.

[0057] Experimental Example 3: Biodepolymerase Activity under Different pH Conditions Based on the results of Experiments 1-2, a system with a biopolymerase mass fraction of 0.005% was selected and its enzyme activity was tested at different pH values ​​under 60°C. Gradient pH ranges were constructed from pH 4.0 to pH 10.0. Experiments were conducted according to the formulation in Example 1 under the corresponding pH conditions, and the degree of reaction was measured by the amount of product.

[0058] Depend on Figure 4 It can be seen that the biodepolymerase system maintains a high relative enzyme activity over a wide pH range of 4.0 to 10.0.

[0059] Under slightly acidic conditions (pH 4.0–5.0), the enzyme activity remained at approximately 80%–90%, indicating that the biodepolymerase system has a certain tolerance to acidic environments, and the enzyme protein structure did not undergo significant inactivation or irreversible denaturation. When the pH increased to around 6.0, the system exhibited the highest relative enzyme activity (defined as 100%), indicating that this pH condition is the optimal reaction environment for the biodepolymerase, which is conducive to substrate binding and efficient catalytic reactions. In the neutral to slightly alkaline range (pH 7.0–9.0), although the enzyme activity decreased slightly from the optimal pH, it remained stable above 80%, showing good alkaline stability. This characteristic is of great significance for the neutral or slightly alkaline formation water environments commonly found in oilfield systems, as it is beneficial for the biodepolymerase to continuously exert its depolymerization effect under complex salinity and alkaline conditions. When the pH increased to 10.0, the enzyme activity remained at a high level, indicating that the biodepolymerase system still has a certain activity reserve under strongly alkaline conditions and did not undergo significant rapid inactivation.

[0060] In summary, the system in this embodiment has a wide pH adaptability range and exhibits optimal activity characteristics within the pH range of 4.0 to 9.0. This not only meets the common formation environment requirements in the process of unblocking residual polymers of polyacrylamide in oilfields, but also reduces the dependence on precise pH control of the system. This is beneficial to improving experimental repeatability and process adaptability, and provides a good foundation for its application in the laboratory evaluation and process scale-up research of polymer unblocking.

[0061] Experiment Example 4: Residue Determination Experiment Following the experimental results of Examples 1-3, Example 1 used a system with a biopolymerase mass fraction of 0.005%, and, together with Examples 2-3 and Comparative Examples 1-2, under conditions of 60°C and pH 6.0, after the biopolymerase system was deblocked, the content of insoluble residue in the system was quantitatively determined to evaluate whether the depolymerization process would produce solid residues that are difficult to return or may cause secondary blockage. Three parallel samples were used in the experiment to evaluate the residue level in the depolymerized system.

[0062] Based on the threshold determined by reservoir pore-scale flow safety and engineering practice experience, 250 mg / L is defined as a limit reference value. When the content of insoluble residue is below this level, the residual particles are unlikely to form effective bridging or deposition at the pore throat scale, and usually will not have a significant adverse effect on permeability and flowback process; exceeding this limit may increase the risk of secondary blockage, and therefore it is used as a control standard for evaluating the cleanliness and safety of unblocking systems.

[0063] Table 1 Results of Residue Measurement

[0064] Table 2 Results of Residue Measurement

[0065] The test results show that the amount of residue obtained from the three parallel experiments was significantly lower than the evaluation standard limit of 250 mg / L, and the data distribution was concentrated with good repeatability. This indicates that the bio-depolymerase system can effectively degrade polymer blockages into depolymerization products mainly composed of soluble small molecules during the unblocking process, without producing a large amount of insoluble or non-degradable residues.

[0066] Comparing the residue amount results of Example 1 with those of Examples 2-3 and Comparative Examples 1-2, it is demonstrated that each component in the system is a necessary component in order to achieve the optimal result.

[0067] Further analysis suggests that the directional cleavage of polymer backbones or side chains by depolymerases helps avoid cross-linking precipitation or secondary coagulation that easily form in traditional strong oxidizing or strong acid systems, thus significantly reducing the risk of residue formation after deblocking. Lower residue levels not only facilitate subsequent fluid backflow and system circulation but also effectively reduce the possibility of re-clogging in pores and microcracks.

[0068] Therefore, the above experimental results show that the system of this embodiment has the technical advantages of low residue generation, good system cleanliness and low risk of secondary damage while achieving efficient declogging. It is suitable for the mild and controllable degradation treatment of polymer blockages.

[0069] Experimental Example 5: Molecular weight determination after unblocking at 45℃ To accurately characterize the degradation effect of the biopolymer depolymerization enzyme system on the polymer molecular structure, a standardized deblocking treatment of the test sample is required before molecular weight determination. The specific steps are as follows: The test system containing polyacrylamide polymers is placed at a constant temperature of 45℃. Following the experimental results of Example 4, a system with a biopolymer depolymerization enzyme mass fraction of 0.005% from Example 1 is selected and reacted at pH 6.0 for 24 hours to fully complete the enzymatic depolymerization process of the polymer backbone or side chains. After the reaction, the reaction system is placed in a 100℃ water bath for 1 hour to completely terminate the enzymatic reaction. The sample is then subjected to necessary centrifugation or filtration to remove undissolved impurities and particulate matter. The resulting supernatant is used as the depolymerized sample for matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF) analysis to compare and characterize the changes in polymer molecular weight and its distribution before and after depolymerization.

[0070] Figure 5The results of the charge-to-mass ratio determination after deblocking show that, after deblocking treatment, the charge-to-mass ratio of polymer fragments in the sample is mainly distributed in the range of 1000 m / z. The results show that the signal intensity in the high molecular weight range is significantly weaker, and no significant high molecular weight main peak was observed, indicating that the original high molecular weight polymer backbone has undergone significant breakage. The original high molecular weight polymer has been effectively degraded into medium and low molecular weight fragments after treatment, and the overall molecular weight level has been significantly reduced.

[0071] From the molecular weight distribution range, almost no obvious high molecular weight residues of 1000 m / z were detected in the system, indicating that the depolymerization process can achieve relatively sufficient breakage of the polymer backbone and the depolymerization effect is stable. At the same time, the molecular weight distribution range is relatively concentrated, indicating that the depolymerization products are mainly fragments within a certain molecular weight range, without a large number of extremely low molecular weight fragments or abnormally wide distribution, which is conducive to subsequent backflow and migration.

[0072] Figure 6 To Figure 5 Local magnification of the peaks within the 1000 m / z range revealed that the signal peaks in the spectrum were relatively discrete within this range, exhibiting a multi-peak distribution. Several characteristic peaks with high intensity were observed in the spectrum, indicating the formation of relatively stable low-molecular-weight fragments in the system after gel breaking.

[0073] Experimental Example 6: Molecular weight determination after unblocking at 60℃ The experimental conditions, methods, and detection methods in this experiment are the same as in Experiment 5, but the reaction temperature is adjusted from 45℃ to 60℃.

[0074] Figure 7 The results of the charge-to-mass ratio determination after deblocking show that after deblocking, the charge-to-mass ratio of polymer fragments in the sample is mainly distributed in the range of 1000 m / z. The signal intensity in the high molecular weight range is significantly weaker, and no significant high molecular weight main peak was observed.

[0075] Figure 8 To Figure 7 Local magnification of the peaks in the 1000 m / z range revealed that, within this range, the signal peaks in the spectrum exhibited a relatively discrete peak shape and a multi-peak distribution. Several characteristic peaks with high intensity were observed, indicating the formation of relatively stable low-molecular-weight fragments in the system after gel breaking. Specifically, [the following text appears to be incomplete and requires further context: "..."] Figure 8 and Figure 6 The comparison revealed that the characteristic peaks obtained by the bioenzymatic depolymerization at 60℃ were more diverse, indicating that 60℃ was more conducive to activating the enzyme's cleavage efficiency at various sites.

[0076] In summary, the results of Experiments 6 and 7 demonstrate that after treatment with the bio-depolymerization enzyme system, the polymer molecular chains underwent significant breakage, the high molecular weight components in the system were significantly reduced, and the overall molecular weight distribution shifted towards the low molecular weight range. Furthermore, no obvious secondary cross-linking or insoluble residues were observed. This verifies the effectiveness and stability of the depolymerization system at the molecular structure level in the depolymerization and unblocking process, providing direct data support for the viscosity reduction and depolymerization effects of the bio-depolymerization enzyme system in unblocking applications.

[0077] Experimental Example 7: Biodepolymerase Activity at Different Mineralization Degrees To evaluate the adaptability and stability of the biopolymerase system under different salinity conditions, based on the experimental results of Example 4, the biopolymerase system with a mass fraction of 0.005% from Example 1 was selected. The biopolymerase system was placed in simulated formation water environments with different salinities for treatment. After reacting for 24 hours at a constant temperature of 60℃ and pH 6.0, the changes in relative enzyme activity were measured. The enzyme activity of the system without added salt ions under these conditions was taken as 100% relative enzyme activity. The salinity range was set from low to high salinity to simulate the salinity environment commonly found in oilfield reservoirs.

[0078] Experimental results are as follows Figure 9 As shown in the figure. The results indicate that the enzyme activity of the biodepolymerase system initially increases and then gradually decreases with changes in mineralization. Under low to medium mineralization conditions, the enzyme activity of the system is significantly enhanced, reaching approximately 1.0 × 10⁻⁶. 4 The high activity level achieved at around mg / L of mineralization indicates that an appropriate amount of inorganic salt ions helps maintain the conformational stability of the enzyme protein and promotes the effective expression of the enzyme's active site. As the mineralization level further increases, the enzyme activity gradually decreases, but a certain proportion of residual enzyme activity can still be maintained under higher mineralization conditions, and rapid inactivation does not occur.

[0079] Even in high-salinity environments, the bio-depolymerase system still exhibited detectable enzyme activity levels, indicating that the system has good tolerance to salinity changes. This salt tolerance is beneficial for the depolymerase to continue its depolymerization function under high-salinity reservoir conditions, avoiding a significant decrease in unblocking effect due to salinity shocks.

[0080] Comprehensive analysis suggests that the biopolymerase system of this invention has a certain ability to maintain enzyme activity across a wide range of mineralization, especially exhibiting superior activity levels under medium mineralization conditions. It can adapt to the actual mineralization differences in different oilfield reservoirs, providing a reliable stability guarantee for its unblocking application under complex formation conditions.

[0081] Experiment Example 8: Column Displacement Experiment The oil displacement effect was evaluated using a sand pipe model. A conventional chemical breaker system, with ammonium persulfate as the main active ingredient, degrades and breaks down polymer fracturing fluids through free radical oxidation, was compared with the biopolymerase system of this invention. The conventional chemical breaker system consisted of a 0.05% wt potassium persulfate solution. Experimental results showed that the biopolymerase system significantly improved oil displacement efficiency and enhanced formation oil recovery. This demonstrates that this system not only unblocks but also has positive implications for subsequent engineering and recovery processes.

[0082] Table 3 Comparison of results between conventional ternary composite system for oil displacement and biopolymerase system

[0083] The results of the recovery rate change in Example 1 were compared with those in Examples 2-3 and Comparative Examples 1-2, which fully demonstrated the excellent oil displacement effect of the ternary composite system.

[0084] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A biopolymer depolymerization enzyme composite system for unblocking polymers in oil fields, characterized in that, The components include the following components by mass percentage: 0.001~0.01wt% of biodepolymerase, 0.001~0.01wt% of carbohydrate coenzyme, 0.001~0.01wt% of organic acid salt synergist, and the balance being water; The biodepolymerase is selected from one or more of amidase, protease, peroxidase, oxidase and mannanase; The carbohydrate coenzyme is selected from one or more monosaccharides, disaccharides, and polysaccharides; The organic acid salt synergist is selected from one or more of lactate, citrate, acetate and malate.

2. The biopolymerization enzyme composite system for oilfield polymer unblocking according to claim 1, characterized in that, The sugar coenzyme is selected from one or more of glucose, fructose, sucrose, maltose, and soluble starch; The biodepolymerase is selected from one or more of amidase, protease, peroxidase, and oxidase.

3. The biopolymerization enzyme composite system for oilfield polymer unblocking according to claim 1, characterized in that, The biodepolymerase is selected from a combination of amidase and one of protease, peroxidase and oxidase in a mass ratio of 1:

1. The sugar coenzyme is selected from fructose and / or sucrose; The organic acid salt synergist is selected from sodium citrate and / or sodium acetate.

4. The biopolymer depolymerization enzyme composite system for oilfield polymer unblocking according to claim 1, characterized in that, The biodepolymerase is selected from a combination of amidase and one of trypsin, laccase, lignin peroxidase, alcohol oxidase and glucose oxidase in a mass ratio of 1:

1.

5. The biopolymerization enzyme composite system for oilfield polymer unblocking according to claim 1, characterized in that, The biodepolymerase complex system maintains enzyme activity within a temperature range of 30~100℃, with maximum activity maintained at 60℃; and enzyme activity is retained at ≥10% at 90℃.

6. The biopolymerization enzyme composite system for oilfield polymer unblocking according to claim 1, characterized in that, The biodepolymerase complex system further includes amylase; wherein the mass fraction of the amylase in the biodepolymerase complex system is 0.001~0.01wt%; the amylase includes α-amylase and / or β-amylase.

7. A method for preparing a biopolymer depolymerization enzyme complex system for oilfield polymer unblocking as described in any one of claims 1-6, characterized in that, include: Biodepolymerase, sugar coenzyme, and organic acid salt synergist are added to water and mixed at room temperature to obtain the biodepolymerase complex system.

8. The application of a biopolymerase complex system for oilfield polymer unblocking as described in any one of claims 1-6 in oilfield polymer unblocking.

9. The application according to claim 8, characterized in that, The polymer is polyacrylamide; The application includes: using the bio-depolymerization enzyme complex system as a working solution, contacting the working solution with a polymer-containing plugging medium at room temperature to carry out a depolymerization reaction, wherein the pH of the application environment is 4.0~10.0; the reaction temperature is 30~100℃; the reaction time is 24 hours~6 days; and the mineralization range is 0~100000mg / L.

10. The application according to claim 8, characterized in that, When the polymer is polyacrylamide, the degradation products include oligomers or oligomeric fragments with a molecular weight of less than 1000; the amount of residue after degradation is less than 250 mg / L.

Images