Modified rhamnolipid water lock agent for offshore oilfield workover operation and preparation method thereof

Abstract

This invention discloses a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields and its preparation method. The method involves a one-step process where a 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is added dropwise to a rhamnolipin solution, attaching a quaternary ammonium cation to the hydroxyl group of the rhamnolipin. After the reaction is complete and the solution is purified, the modified rhamnolipin waterproofing agent is obtained. The raw materials used in this invention are readily available, the preparation method is simple, and it is conducive to industrial production. The raw materials and products used have low biotoxicity and good environmental friendliness, which is beneficial for application in offshore oilfields. The solution prepared with the modified rhamnolipin waterproofing agent exhibits low surface tension, good temperature and salt resistance, and wetting improvement ability. It can significantly improve the reservoir water-locking permeability recovery rate, demonstrating not only a good waterproofing effect but also alleviating reservoir contamination problems caused by long-term production to a certain extent.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development technology, specifically relating to a modified rhamnolipin waterproofing agent for offshore oilfield well workover operations and its preparation method. Background Technology

[0002] Well workover operations are a crucial part of oilfield development. During the workover process, the entry of foreign fluids into the reservoir alters the water saturation, wettability, and oil-water flow channels in the near-wellbore zone, resulting in increased water cut and decreased production in some wells after workover. Taking the Bohai Oilfield as an example, in 2022, there were 298 well workover operations in the Bohai Oilfield, of which 151 wells experienced increased water cut after workover, accounting for 50.67% of the total operations; in 2023, there were 529 well workover operations in the Bohai Oilfield, with 335 wells experiencing increased water cut after workover, accounting for 63.33% of the total operations, an increase of 19.06% compared to 2022; in the first half of 2024, 59 wells in the Bohai Oilfield experienced increased water cut after conventional tubing string operations, resulting in an overall oil production loss of 495 mg / m³. 3 / d. Analysis of the production characteristics and causes of increased water cut in low-permeability oil wells in the Bohai Oilfield after well workover operations reveals that the main reason for the significant decrease in oil production and the substantial increase in water cut after the workover operations is water-locking damage to the Shahejie reservoir.

[0003] Due to the unique characteristics of offshore oilfield reservoirs, the introduction of foreign fluids during well workover can easily cause severe water-locking damage. This manifests as a significant increase in reservoir water saturation and a marked decrease in reservoir permeability, severely impacting subsequent well production. The continuous intrusion of workover fluid into the formation alters the oil saturation and surface wettability of the rocks, sometimes even reversing these effects, thus reducing the relative permeability of the oil phase and causing water-locking blockage. Studies show that water-locking often reduces the effective permeability of the reservoir to about 10% of its original level, and this damage is difficult to remove, significantly impacting well productivity. Therefore, effective prevention of water-locking damage during offshore oilfield well workover is crucial to improving workover efficiency.

[0004] Adding water-locking agents or using relative permeability improvers to the workover fluid is one of the most common measures to control the rise in water cut in oil wells after workover operations. High-performance water-locking agents and relative permeability improvers can prevent water-locking damage by reducing the surface / interfacial tension of reservoir fluids and changing the wettability of rock surfaces, thereby increasing the drainage rate of reservoir fluids, allowing the water phase retained in the reservoir to be discharged quickly, and reducing the water saturation of the reservoir, so as to achieve the purpose of preventing and eliminating water-locking damage. Based on the analysis of the current research status at home and abroad, high-efficiency water-locking agents should have the following properties: (1) can significantly reduce the interfacial tension of liquid phases; (2) can weaken the water wettability of rock surfaces and increase the contact angle of liquid phases; (3) can significantly restore the formation permeability; (4) has good temperature and salt resistance and good compatibility with other treatment agents; (5) can evaporate quickly at the bottom hole temperature, and can carry away the water retained in the formation during evaporation; (6) the raw materials are cheap and readily available. Currently, biosurfactants are mainly used in oil and gas development to improve crude oil recovery, with limited research on their application in well workover fluids, and even less research on their use in waterproofing and locking agents.

[0005] In summary, it is necessary to tackle the key technologies for biological waterproofing agents and their preparation in low-permeability oil wells in offshore oil fields, and solve the problem of increased water cut in oil wells after well workover. Summary of the Invention

[0006] This invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a modified rhamnolipin waterproofing agent for offshore oilfield well workover operations and its preparation method.

[0007] This invention is achieved through the following technical solution: A method for preparing a modified rhamnolipin waterproofing agent for offshore oilfield well workover operations includes the following steps: S1. Prepare a rhamnolipin solution and adjust the pH value of the rhamnolipin solution; S2. Prepare an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC); S3. The 3-chloro-2-hydroxypropyltrimethylammonium chloride ice-water solution obtained in step S2 is added dropwise to the rhamnolipid solution obtained in step S1. After stirring thoroughly, the temperature is raised to the reaction temperature to carry out the reaction. After the reaction is completed, the temperature is cooled to room temperature and the pH of the reaction solution is adjusted to neutral. S4. The synthesized product was purified to obtain a modified rhamnolipin waterproofing agent.

[0008] In the above technical solution, the mass fraction of rhamnolipid solution in step S1 is 10wt%~15wt%.

[0009] In the above technical solution, the solvent of the rhamnolipid solution is a mixed solution of isopropanol and water, and the mass fraction of isopropanol in the solvent is 30wt%~50wt%.

[0010] In the above technical solution, the pH value of the rhamnolipid solution is 9-11.

[0011] In the above technical solution, the pH value of the rhamnolipid solution is adjusted by using a sodium carbonate solution with a mass fraction of 30wt%~40wt% or a sodium hydroxide solution with a mass fraction of 30wt%~40wt%.

[0012] In the above technical solution, the mass concentration of the 3-chloro-2-hydroxypropyltrimethylammonium chloride ice-water solution in step S2 is 50wt%~75wt%.

[0013] In the above technical solution, the molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to rhamnolipid hydroxyl group in step S3 is 1.5~2:1.

[0014] In the above technical solution, the reaction temperature in step S3 is 40℃~60℃, and the reaction time is 4h~7h.

[0015] In the above technical solution, the pH of the reaction solution in step S3 is adjusted using an acetic acid solution with a mass concentration of 5%.

[0016] In the above technical solution, the method for purifying the synthesized product is as follows: the reaction solution obtained in step S3 is added to an acetone-ethanol mixed solution to precipitate the precipitate, the precipitate is separated, and the precipitate is washed and dried to obtain a white to light yellow solid, which is the modified rhamnolipid waterproofing agent.

[0017] In the above technical solution, the volume ratio of acetone to ethanol in the acetone-ethanol mixed solution is 1:1.

[0018] In the above technical solution, the precipitate is washed three times with an ethanol-water solution at a mass ratio of 1:1.

[0019] In the above technical solution, the drying conditions are vacuum drying at 40°C for 48 hours.

[0020] A modified rhamnolipin waterproofing agent for offshore oilfield well workover operations prepared by the aforementioned method has the following structural formula (Ⅰ): ......(I) In formula (Ⅰ): R1 is selected from L-α-pyranorhamnetosyl or H; R2 is selected from β-hydroxydecanoic acid or H.

[0021] The reaction molecular equation of this invention is: In the above formula: R1 is selected from L-α-pyranorhamnetosyl or H; R2 is selected from β-hydroxydecanoic acid or H.

[0022] The beneficial effects of this invention are: This invention provides a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields and its preparation method. The method employs a one-step process to synthesize the waterproofing agent by attaching quaternary ammonium cations to the hydroxyl groups of rhamnolipin. The raw materials are readily available, the preparation method is simple, and it is conducive to industrial production. The raw materials and products used in this invention have low biotoxicity and good environmental friendliness, which is beneficial for application in offshore oilfields. The solution prepared with the modified rhamnolipin waterproofing agent of this invention exhibits low surface tension; when the mass fraction of the modified rhamnolipin waterproofing agent is 1.0%, the surface tension remains at 25.8 mN / m. The modified rhamnolipin waterproofing agent prepared in this invention also exhibits good temperature resistance, salt resistance, and wetting properties. The modified rhamnolipin waterproofing agent prepared in this invention can significantly improve the water-locking permeability recovery rate of reservoirs under reservoir conditions (temperature 130℃, salinity 35000mg / L), adjusting the contact angle of the reservoir core surface to 70°~110° (neutral wetting). In laboratory evaluation, the water-locking permeability recovery rate of cores injected with the modified rhamnolipin waterproofing agent can reach over 90%. In a pilot test of three wells in a certain block of an offshore oilfield, the average production recovery rate after well repair was 107.37%, and the average oil production recovery rate was 105.45%, demonstrating not only a good waterproofing effect but also alleviating the reservoir pollution problem caused by long-term production to a certain extent. Attached Figure Description

[0023] Figure 1 The infrared spectrum of the synthesized product in Example 1 of this invention; Figure 2 The image shows the 1H-NMR spectrum of the synthesized product in Example 1 of this invention. Figure 3 The image shows the 13C-NMR spectrum of the synthesized product in Example 1 of this invention. Figure 4 The following are contact angle test diagrams for different mass fractions in Embodiment 2 of the present invention (a is a mass fraction of 0%; b is a mass fraction of 0.3%; c is a mass fraction of 0.5%; d is a mass fraction of 0.8%; e is a mass fraction of 1.0%). Figure 5 This is an evaluation of the indoor permeability recovery rate in Example 3 of the present invention; Figure 6 The following are core displacement CT scan test images of the waterproofing and locking performance of the present invention in Example 3: (a) Three-dimensional pore structure of dry core; b) Initial oil-bearing state under bound water saturation; c) Fluid distribution of core before waterproofing and locking agent treatment; d) Fluid distribution of core after aging and positive oil displacement; e) Three-dimensional pore structure of dry core; f) Initial oil-bearing state under bound water saturation; g) Fluid distribution of core after waterproofing and locking agent treatment; h) Fluid distribution of core after aging and positive oil displacement. Figure 7 The images show SEM images of the microstructure of the core surface before and after treatment in Example 4 of this invention (a is before the waterproofing agent treatment; b is after the waterproofing agent treatment). Figure 8 This is a production curve diagram after the application of Embodiment 5 of the present invention in the field at Well A29.

[0024] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Example 1

[0026] A method for preparing a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields, specifically comprising: S1. Dissolve 5g of rhamnolipin in 45g of 30% isopropanol aqueous solution, stir thoroughly to dissolve, and then transfer to a three-necked flask; add 30% sodium carbonate solution to the three-necked flask to adjust the pH of the rhamnolipin solution to 10. S2. Dissolve 8.76 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in 8 mL of ice water to obtain an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC); S3. Add an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) dropwise into a three-necked flask containing a rhamnolipin solution. After stirring thoroughly, heat to 40°C and react for 6.5 hours. Cool to room temperature and neutralize the reaction solution with 5% (w / w) dilute acetic acid to pH 7.0. S4. Add the neutralized reaction solution to a mixture of acetone and ethanol (volume ratio 1:1) to precipitate the precipitate. After centrifugation and filtration, wash the precipitate three times with an ethanol-water solution (mass ratio 1:1) and dry it under vacuum at 40°C for 48 hours to obtain the modified rhamnolipid waterproofing agent.

[0027] Figure 1 This is the infrared spectrum of the modified rhamnolipid waterproofing agent obtained in Example 1. From... Figure 1 As can be seen, the expansion / contraction zone is 3423.53cm. -1 A broad, strong band appears at 2929.98 and 2852.41 cm⁻¹, attributed to the stretching vibration peaks of the glycosyl polyhydroxyl group (-OH). -1 The peaks are for the stretching vibrations of long alkyl chains (-CH3 / -CH2-); for carbonyl groups and quaternary ammonium salts, the peaks are 1718.20 / 1645.31 cm⁻¹. -1Strong absorption peaks for straight-chain esters (C=O); 1473.44 / 1407.89 cm⁻¹ -1 The peak represents the deformation of -CH3 / -CH2- and the bending vibration of quaternary ammonium (N-CH3), with a peak at 1473.44 cm⁻¹. -1 It is most sensitive to quaternary ammonium salts, providing direct evidence of the introduction of quaternary ammonium groups into rhamnolipid molecules; 1046.10 cm -1 The (CO) stretching vibration peaks, which are characteristic absorption peaks of the sugar ring, are for ether / alcohol mixtures; 969.19 and 914.36 cm⁻¹. -1 The characteristic peaks are usually anodic carbons or ring vibration peaks of the sugar ring, which are characteristic fingerprint regions of hexacarbon sugars such as rhamnose; this suggests that the synthesis of rhamnose ester with 3-chloro-2-hydroxypropyltrimethylammonium chloride was successful.

[0028] Figure 2 The modified rhamnolipid waterproofing agent obtained in Example 1 of this invention... 1 H-NMR spectrum, from Figure 2 As can be seen, the triplet at 0.8–1.2 ppm belongs to the -CH3 group in the alkyl chain; the multiplet at 1.3–1.6 ppm comes from the -CH2- group in the alkyl chain, showing a series of complex couplings; the singlet at 2.1 ppm comes from the -CH2 group attached to the electronegative oxygen atom; the signal at 3.3–4.0 ppm comes from -CH2-, where these carbons are attached to oxygen atoms or hydroxyl groups, showing a single signal; the doublet or triplet at 4.5–5.0 ppm usually corresponds to hydrogen atoms attached to oxygen atoms in the molecule, indicating the presence of ether bonds; in the proton NMR spectrum, carbon atoms attached to ether bonds (such as carbons attached to oxygen in sugar rings) usually do not directly show hydrogen signals unless there are hydrogen atoms nearby.

[0029] Figure 3 The modified rhamnolipid waterproofing agent obtained in Example 1 of this invention... 13 C-NMR spectrum, from Figure 3 As can be seen from the data, the signal at 166–167 ppm is the carbonyl carbon (C=O) signal, corresponding to the ester functional group; the signal at 67–68 ppm comes from the carbon atom (-OC-) bonded to oxygen in the sugar ring, indicating the presence of the sugar moiety; the region at 30–40 ppm contains the -CH2- carbon signal in the alkyl chain, which is consistent with the characteristics of the alkyl chain; the signal at 52–55 ppm corresponds to the carbon bonded to oxygen (-OCH2-), which is a typical ether bond signal; the carbon spectroscopy data show that the compound generated after the reaction contains cyclic sugar molecules and alkyl chains connected by ether bonds, and the position of the ether bonds is consistent with expectations. Example 2

[0030] A method for preparing a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields, specifically comprising: S1. Dissolve 2.5g of rhamnolipin in 17.5g of 40% isopropanol aqueous solution, stir thoroughly to dissolve, and then transfer to a three-necked flask; add 30% sodium hydroxide solution dropwise to the three-necked flask to adjust the pH of the rhamnolipin solution to 11. S2. Dissolve 2.84 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in 1 mL of ice water to obtain an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC); S3. Add an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) dropwise into a three-necked flask containing a rhamnolipin solution. After stirring thoroughly, heat to 50°C and react for 5 hours. Cool to room temperature and neutralize the reaction solution with 5% (w / w) dilute acetic acid to pH 7.0. S4. Add the neutralized reaction solution to a mixture of acetone and ethanol (volume ratio 1:1) to precipitate the precipitate. After centrifugation and filtration, wash the precipitate three times with an ethanol-water solution (mass ratio 1:1) and dry it under vacuum at 40°C for 48 hours to obtain the modified rhamnolipid waterproofing agent.

[0031] The modified rhamnolipin waterproofing sealant obtained in Example 2 was subjected to a wetting improvement test. Natural core slices were selected, and the core slices were polished with sandpaper and placed in aqueous solutions of modified rhamnolipin waterproofing sealant with different mass fractions (0.3%, 0.5%, 0.8%, and 1.0%). The slices were soaked for 12 hours at a reservoir temperature of 90°C, removed, and dried. Then, the contact angle of the water phase on the core surface was tested using simulated formation water. The ionic composition, ion concentration, and salinity of the simulated formation water were determined based on the formation water quality analysis report of the target reservoir. The test results are shown in Table 2 and... Figure 4 .

[0032] The simulated formation water ionic composition in this embodiment is shown in Table 1.

[0033] Table 1. Ionic composition of simulated formation water Table 2. Test results of aqueous phase contact angle of core thin sections after treatment with different concentrations of waterproofing sealant. Based on the test results ( Figure 4 It can be seen that the core surface that was not treated with modified rhamnose lipolipid waterproofing agent ( Figure 4 a) Water droplets can spread completely, indicating hydrophilicity; after treatment with the waterproofing agent, the contact angle of the water phase on the core surface increases with the increase of the concentration of the waterproofing agent, reaching a certain value when the concentration is 1.0% ( Figure 4(e) The contact angle is 106.3°, and the wettability of the core surface changes to neutral wettability. This is because the positively charged head groups of the cationic rhamnolipid are firmly adsorbed onto the reservoir core surface through electrostatic attraction. After adsorption, the hydrophobic tail chains (fatty acid chains) of the entire molecule are forced to face outwards, away from the rock surface, thus forming a hydrophobic layer. When a large number of cationic rhamnolipid molecules are adsorbed on the rock surface, a dense "monomodulation" composed of outward-facing hydrocarbon chains is formed. This outward-facing hydrophobic tail chain greatly reduces the free energy of the rock surface, transforming it from a high-energy surface (hydrophilic) to a low-energy surface (oleophilic). At this point, the rock surface is no longer affinity for water, but rather for hydrocarbons such as crude oil, and the contact angle changes from less than 90° (hydrophilic) to greater than 90° (oleophilic). Therefore, modified rhamnolipids can effectively regulate the surface wettability of rocks, reduce capillary forces in the reservoir, and prevent water-locking damage. Example 3

[0034] A method for preparing a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields, specifically comprising: S1. Dissolve 2.5g of rhamnolipin in 14.2g of 35% isopropanol aqueous solution, stir thoroughly to dissolve, and then transfer to a three-necked flask; add 35% sodium carbonate solution to the three-necked flask to adjust the pH of the rhamnolipin solution to 9. S2. Dissolve 4.25g of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in 4mL of ice water to obtain an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC); S3. Add an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) dropwise into a three-necked flask containing a rhamnolipin solution. After stirring thoroughly, heat to 45°C and react for 7 hours. Cool to room temperature and neutralize the reaction solution with 5% (w / w) dilute acetic acid to pH 7.0. S4. Add the neutralized reaction solution to a mixture of acetone and ethanol (volume ratio 1:1) to precipitate the precipitate. After centrifugation and filtration, wash the precipitate three times with an ethanol-water solution (mass ratio 1:1) and dry it under vacuum at 40°C for 48 hours to obtain the modified rhamnolipid waterproofing agent.

[0035] The modified rhamnolipin waterproofing agent obtained in Example 3 was tested for core permeability recovery rate. Natural cores with a gas permeability of 68 mD were used. After vacuuming, the cores were saturated with simulated formation water. Simulated oil was injected forward into the core at a flow rate of 1 mL / min to test the original oil phase permeability. A 0.8% (2 PV) biological waterproofing agent solution was injected backward into the core at a flow rate of 1 mL / min. The cores were then aged in simulated formation water at 90°C for 12 hours. Simulated oil was injected forward into the core at a flow rate of 1 mL / min to test the oil phase permeability after treatment, and the permeability recovery rate was calculated. The test results are shown in Table 3 and [Table data missing]. Figure 5 .

[0036] Table 3 Permeability Recovery Rate Record Table The test results show that the permeability recovery rate of the core without modified rhamnolipin waterproofing agent was 56.7%. After adding the waterproofing agent, the permeability recovery rate gradually increased with the increase of the agent's mass fraction, reaching 100.70% when the agent's mass fraction was 0.8%. This is because, on the one hand, the biological waterproofing agent has good wetting improvement properties, reversing the hydrophilic rock surface to an oleophilic surface. This transformation makes water droplets blocking the throat unstable and easily driven, broken, and discharged by subsequent oil flow, thus releasing the water lock. On the other hand, since clay particles are usually negatively charged, they swell and disperse upon contact with water. The positively charged head groups of cationic rhamnolipin strongly adsorb onto the clay surface, neutralizing its negative charge. The electrostatic repulsion between clay layers weakens, effectively inhibiting the water absorption, swelling, dispersion, and migration of clay, thus maintaining the pore patency. In summary, the addition of modified biological waterproofing agent improves the reservoir's permeability recovery value.

[0037] Figure 6 This is a core displacement CT scan test image of the water-locking performance according to an embodiment of the present invention. The change in water-locking effect in the core pore throat before and after injection of bio-based workover fluid was tested using core CT scans. The same core was used to perform CT visualization experiments on cores before and after treatment with the bio-water-locking agent to eliminate the interference of core heterogeneity on the results and improve the reliability of the comparative conclusions. First, the core was dried to constant weight before scanning. Figure 6 a; Saturate the dry core with formation water, and forward displace kerosene containing 15% iodobutane until no water is produced at the outlet, establishing the oil-bearing state under bound water saturation. Scanning yields... Figure 6 b; Scanning was performed after water was injected in the reverse direction into the core. Figure 6 c; The core was aged at 90℃ for 12 hours. After aging, kerosene containing the same iodinated n-butane was injected forward until no obvious water was observed at the outlet. After the oil injection was completed, the core was scanned to obtain... Figure 6 d.

[0038] To ensure consistency in pore structure and initial oil-bearing state between the two processes, the core samples were washed with oil, then dried again for 24 hours to constant weight, and scanned to obtain... Figure 6 e; Saturate the dried core with formation water, and positively displace the kerosene containing 15% iodobutane until no water is produced at the outlet. Scanning yields... Figure 6 f; A 0.8% biological waterproofing agent solution was injected into the core in the reverse direction and scanned to obtain... Figure 6 g; After aging the core for 12 hours, kerosene containing iodinated n-butane was injected forward until no significant bio-based workover fluid was produced at the outlet. After the injection was completed, a CT scan was performed to obtain... Figure 6 h. A comparison reveals... Figure 6 a represents the initial three-dimensional pore and fracture state of the dried core. Figure 6 e represents the three-dimensional pore structure of the core after initial drying following oil washing and drying. Both three-dimensional pore scan images show a uniform and dense distribution of dark blue dot clouds, indicating that oil washing and repeated drying did not damage the core's pore skeleton structure. Figure 6 b and Figure 6 f represents the state of dry cores first saturated with water and then saturated with kerosene containing 15% iodobutane. Both show that the oil and water phases coexist in the pore space, with the oil phase dominating and some pores being bound by the water phase, thus successfully constructing the initial conditions for water locking. Figure 6 c shows that after water injection, residual oil in the core is present in irregular channels, with a large amount of pore space occupied by the water phase, indicating a severe water-locking effect. This suggests that simply injecting water cannot completely displace the oil phase in the pore throat. In contrast, Figure 6 After injection of the bio-waterproofing agent, g exhibited more thorough and uniform scavenging characteristics. The residual oil phase changed from large-scale, interconnected retention to a finer, more dispersed morphology, indicating that the injection of the bio-waterproofing agent effectively weakened the binding of the oil phase by bound water and displaced the oil from the pores. After aging and subsequent forward oil flooding, g was obtained... Figure 6 d and Figure 6 h, Figure 6 d shows that the residual oil is retained in the form of broad continuous strips and clusters, which reflects the insufficient recovery of the oil phase pore throat connectivity. The bound water continuously hinders the oil phase reflux, and the water lock is strong. Figure 6 The h-axis showed that the flow channels were re-established, the oil phase almost completely refilled the pore space and exhibited a highly uniform dark blue distribution, the pore throat connectivity was significantly restored, and the water-locking effect was significantly reduced. Under the conditions of strictly maintaining core consistency, the same initial oil content and bound water background, and the same aging temperature, this series of dynamic CT visualization results clearly demonstrated the superior performance of the biological waterproofing sealant. Example 4

[0039] A method for preparing a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields, specifically comprising: S1. Dissolve 3g of rhamnolipin in 17g of 45% isopropanol aqueous solution, stir thoroughly to dissolve, and then transfer to a three-necked flask; add 40% sodium carbonate solution to the three-necked flask to adjust the pH of the rhamnolipin solution to 11. S2. Dissolve 6.8 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in 4.53 mL of ice water to obtain an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC); S3. Add an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) dropwise into a three-necked flask containing a rhamnolipin solution. After stirring thoroughly, heat to 50°C and react for 5.5 hours. Cool to room temperature and neutralize the reaction solution with 5% (w / w) dilute acetic acid to pH 7.0. S4. Add the neutralized reaction solution to a mixture of acetone and ethanol (volume ratio 1:1) to precipitate the precipitate. After centrifugation and filtration, wash the precipitate three times with an ethanol-water solution (mass ratio 1:1) and dry it under vacuum at 40°C for 48 hours to obtain the modified rhamnolipid waterproofing agent.

[0040] The surface tension of the modified rhamnolipin waterproofing agent obtained in this embodiment was tested. Solutions of the modified rhamnolipin waterproofing agent with mass fractions of 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, and 1.4% were prepared and their surface tensions were tested. The experimental results are shown in Table 4. Table 4 shows that the surface tension initially decreases with increasing mass fraction of the biological waterproofing agent. When the mass fraction of the biological waterproofing agent exceeds 1.0%, the decrease in surface tension becomes smaller, eventually remaining at 24.6 mN / m. This is because the modified rhamnolipin possesses a structure consisting of a hydrophilic head group (cationic moiety, such as a quaternary ammonium salt) and a hydrophobic tail chain (the inherent fatty acid chain of rhamnolipin). First, the cationic head groups attract and adsorb onto the core surface more quickly and firmly via electrostatic attraction. Second, the electrostatic repulsion between the cationic head groups prevents excessive aggregation or precipitation of molecules at the interface, maintaining appropriate spacing and forming a denser, more ordered monolayer. Finally, the orderly outward-facing hydrophobic chains in this dense layer disrupt the hydrogen bond network of water molecules at the interface, replacing the strong water-water interactions with weak hydrocarbon-hydrogen interactions, thus significantly reducing surface tension. Therefore, cationic rhamnolipids can achieve the basic functions of surfactants through their amphiphilic structure, while their cationic head groups, through electrostatic anchoring and regulation of intermolecular forces, make them more efficient and stable in reducing surface tension, especially showing significant advantages in complex, negatively charged real-world environments.

[0041] Table 4. Surface tension test results of waterproofing sealant at different concentrations Figure 7 SEM images show the surface microstructure of the core sample before and after treatment with the modified rhamnolipin waterproofing agent prepared in Example 4 of this invention. To better analyze the mechanism by which the biological waterproofing agent improves the wetting of the core surface, the microstructure of the core thin sections before and after immersion in a 0.8% (w / w) modified rhamnolipin waterproofing agent solution was observed using scanning electron microscopy. It can be seen that in the SEM images at different magnifications, the untreated original core sample (… Figure 7 a) The surface mineral particles have clear edges and corners, and the cleavage surfaces are flat, resulting in a relatively smooth overall surface; while the core surface treated with waterproofing agent ( Figure 7 (b) Significant changes occurred; all mineral particles were completely covered by a film, exhibiting a typical wrinkled structure. Micro-fractures between particles were also bridged and filled by flocculent material, representing the multi-molecular-layer physicochemical adsorption products of the bio-waterproofing agent and its synergistic polymers on the rock surface. These microscopic morphological changes directly confirm that the bio-waterproofing agent formed a stable and uniform adsorption film on the reservoir core surface, transforming the surface from smooth to a high-roughness, wrinkled state, providing solid microscopic evidence for the adsorption effect of the workover fluid. Example 5

[0042] A method for preparing a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields, specifically comprising: S1. Dissolve 3g of rhamnolipin in 22g of 50% isopropanol aqueous solution, stir thoroughly to dissolve, and then transfer to a three-necked flask; add 32.5% sodium hydroxide solution dropwise to the three-necked flask to adjust the pH of the rhamnolipin solution to 10.5. S2. Dissolve 3.4 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in 3 mL of ice water to obtain an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC); S3. Add an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) dropwise into a three-necked flask containing a rhamnolipin solution. After stirring thoroughly, heat to 60°C and react for 5 hours. Cool to room temperature and neutralize the reaction solution with 5% (w / w) dilute acetic acid to pH 7.0. S4. Add the neutralized reaction solution to a mixture of acetone and ethanol (volume ratio 1:1) to precipitate the precipitate. After centrifugation and filtration, wash the precipitate three times with an ethanol-water solution (mass ratio 1:1) and dry it under vacuum at 40°C for 48 hours to obtain the modified rhamnolipid waterproofing agent.

[0043] The modified rhamnolipin bio-waterproofing interlocking agent obtained in Implementation 5 was pilot-tested in three wells in this oilfield this year. The average production recovery rate after well workover was 107.37%, and the average oil recovery rate was 105.45%, demonstrating not only good waterproofing and interlocking effects but also mitigating reservoir contamination caused by long-term production to some extent. Taking well A29 as an example, a major workover and pump replacement operation was carried out in July due to an electric pump failure. The workover fluid was designed as a modified rhamnolipin bio-type workover fluid of different concentrations. A 0.8% concentration of the bio-waterproofing interlocking agent was used as the working fluid to pre-treat the reservoir before tubing string insertion, thereby altering the reservoir wettability. During the operation, the 0.8% concentration of the bio-waterproofing interlocking agent was used as the well-washing and kill fluid to achieve both waterproofing and kill effects. The operation cycle for this well was 6 days, and the circulating leakage was measured at 6 m³ during the operation. 3 / h, static leakage 2m 3 / h, total leakage 309m 3 Before the operation, the daily fluid production was 82 cubic meters / day, the daily oil production was 23.78 cubic meters / day, and the water cut was 71%. After the operation, the daily fluid production stabilized at 117 cubic meters / day, the daily oil production was 25.92 cubic meters / day, and the water cut was 78%. The calculated fluid production recovery rate was 143.66%, and the production capacity recovery rate was 109%, indicating that the water-lock prevention / dissolving working fluid, with modified rhamnolipid biological water-locking agent as the main agent, played a role in changing the reservoir wettability, enabling the rapid return of lost workover fluid, and to a certain extent restoring the reservoir fluid flow channels. Figure 8 This is a production curve diagram after the application of Embodiment 5 of the present invention in the field of this well.

[0044] Rhamnollipids, as biosurfactants, are non-toxic and environmentally friendly. The modification process of this invention introduces cationic groups, improving the formation adsorption performance of the waterproofing agent; the interfacial tension can reach 10. -2 It has a water-locking agent with mN / m and good temperature and salt resistance. Therefore, the water-locking agent of the present invention modifies rhamnolipid to give it good wettability, and inhibits or eliminates water-locking damage of the workover fluid by adjusting the formation wettability, thus solving the problems of long water cut recovery period and large production loss after well workover in low-permeability offshore oilfields. This provides a new workover fluid technology for reservoir protection in well workover operations in low-permeability offshore oilfields.

[0045] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a modified rhamnolipin waterproofing agent for well workover operations in offshore oilfields, characterized in that: Includes the following steps: S1. Prepare a rhamnolipin solution and adjust the pH value of the rhamnolipin solution; S2. Prepare an ice-water solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride; S3. Add the 3-chloro-2-hydroxypropyltrimethylammonium chloride ice-water solution obtained in step S2 to the rhamnolipid solution obtained in step S1, heat to the reaction temperature, cool to room temperature after the reaction is complete, and adjust the pH of the reaction solution to neutral. S4. The synthesized product was purified to obtain a modified rhamnolipin waterproofing agent.

2. The preparation method of the modified rhamnolipin waterproofing agent for offshore oilfield well workover operations according to claim 1, characterized in that: In step S1, the rhamnolipid solution has a mass fraction of 10wt%~15wt%; the solvent for the rhamnolipid solution is a mixed solution of isopropanol and water, and the mass fraction of isopropanol in the solvent is 30wt%~50wt%; the pH value of the rhamnolipid solution is 9~11; the pH value of the rhamnolipid solution is adjusted by using a sodium carbonate solution with a mass fraction of 30wt%~40wt% or a sodium hydroxide solution with a mass fraction of 30wt%~40wt%.

3. The preparation method of the modified rhamnolipid waterproofing agent for offshore oilfield well workover operations according to claim 1, characterized in that: The mass concentration of the 3-chloro-2-hydroxypropyltrimethylammonium chloride ice-water solution in step S2 is 50wt%~75wt%.

4. The preparation method of the modified rhamnolipid waterproofing agent for offshore oilfield well workover operations according to claim 1, characterized in that: In step S3, the molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to the hydroxyl group of rhamnolipid is 1.5~2:

1.

5. The preparation method of the modified rhamnolipin waterproofing agent for offshore oilfield well workover operations according to claim 1, characterized in that: In step S3, the reaction temperature is 40℃~60℃ and the reaction time is 4h~7h.

6. The preparation method of the modified rhamnolipid waterproofing agent for offshore oilfield well workover operations according to claim 1, characterized in that: In step S3, the pH of the reaction solution is adjusted using a 5% acetic acid solution.

7. The preparation method of the modified rhamnolipin waterproofing agent for offshore oilfield well workover operations according to claim 1, characterized in that: The method for purifying the synthesized product is as follows: the reaction solution obtained in step S3 is added to an acetone-ethanol mixture to precipitate the precipitate, the precipitate is separated, and the precipitate is washed and dried to obtain the modified rhamnolipid waterproofing agent.

8. The preparation method of the modified rhamnolipid waterproofing agent for offshore oilfield well workover operations according to claim 7, characterized in that: The volume ratio of acetone to ethanol in the acetone-ethanol mixed solution is 1:1; the precipitate is washed with an ethanol-water solution with a mass ratio of 1:1; the drying conditions are vacuum drying at 40°C for 48 hours.

9. A modified rhamnolipin waterproofing agent for offshore oilfield well workover operations prepared by the method described in any one of claims 1 to 8, characterized in that: The modified rhamnolipin waterproofing agent has the following structural formula (Ⅰ): ......（Ⅰ） In formula (Ⅰ): R1 is selected from L-α-pyranorhamnetosyl or H; R2 is selected from β-hydroxydecanoic acid or H.

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