Method for inhibiting viscosity loss of polymer solution prepared from oilfield purified water

Abstract

The invention relates to the technical field of oil field polymer flooding, in particular to a method for inhibiting viscosity loss by preparing a polymer solution from oilfield purified water, which comprises the following steps of: 1, cleaning a polymer preparation container and equipment by using a compound degradation inhibitor, and keeping the cleaned polymer preparation container and equipment for later use; 2, purifying the oilfield produced water to obtain oilfield purified water; step 3, adding a required amount of compound degradation inhibitor into the cleaned polymer container and the oilfield purified water in the equipment, and stirring to obtain a polymer solution for polymer injection; and fourthly, after the polymer solution for polymer injection is injected into a reinjection wellhead, oil displacement is carried out. By adding the compound degradation inhibitor into the oilfield purified water, on one hand, the decomposition effect of bacterium breeding on polymers is inhibited, and various pollutants such as oil sludge prone to bacterium breeding in storage tanks and pipelines can be removed; on the other hand, the influence of system pollution on the viscosity of the polymer is eliminated, and the purpose of low viscosity loss in the polymer flooding process is achieved.

Description

Technical Field

[0001] This invention relates to the field of polymer flooding technology in oilfields, and is a method for preparing polymer solutions from purified water in oilfields to suppress viscosity loss. Background Technology

[0002] After secondary oil recovery is completed, polymer flooding, binary composite flooding, and ternary composite flooding are usually carried out to further improve reservoir recovery. By increasing the viscosity of the displacing fluid, reducing the oil-water interfacial tension, reducing the water mobility, decreasing the water-oil mobility ratio, inhibiting water fingering, and increasing the sweep efficiency, the reservoir recovery rate is improved.

[0003] Generally, polymers are formulated using clean water, which results in polymers with high viscosity and good viscosity stability. However, oilfield development produces a large amount of produced water daily, which needs to be purified and reinjected. The reinjection pressure of purified water is relatively high. To solve the problem of utilizing purified water, it is necessary to use purified water for polymer formulation.

[0004] Currently, high-mineralized purified water is affected by various ions, dissolved oxygen, bacteria and other factors, resulting in low viscosity and extremely poor viscosity stability. This makes it difficult to meet the viscosity stability requirements of polymer flooding and binary composite flooding. During implementation, the 30-day viscosity retention rate is only 38.34%, and the wellhead viscosity compliance rate is only 66%.

[0005] Therefore, a new method needs to be developed to reduce the impact of system contamination in oilfield purification water on polymer viscosity. Summary of the Invention

[0006] This invention provides a method for suppressing viscosity loss when preparing polymer solutions with oilfield purified water, overcoming the shortcomings of the prior art. It can effectively solve the problems of secondary pollution and sludge adhesion to pipelines and tanks when preparing polymer solutions with oilfield purified water, resulting in large viscosity losses.

[0007] The technical solution of this invention is achieved through the following measures: a method for preparing polymer solutions from oilfield purified water to suppress viscosity loss, which is carried out according to the following method: The first step is to prepare a compound degradation inhibitor; The second step is to clean the polymerization container and equipment using a compound degradation inhibitor. After cleaning, the polymerization container and equipment are ready for use. The third step is to purify the produced water from the oilfield to obtain purified oilfield water. The fourth step is to add the required amount of compound degradation inhibitor to the oilfield purified water in the cleaned polymer container and equipment, and after stirring, obtain pretreated purified water. The fifth step involves adding the polymer to the pretreated purified water, stirring to dissolve it, and obtaining a polymer solution for injection. The sixth step involves injecting the polymer solution for injection into the reinjection wellhead to drive out oil.

[0008] The following are further optimizations and / or improvements to the above-mentioned technical solution: In the first step above, the compound degradation inhibitor includes an oxygen scavenger, a mixed bactericide, and a flocculant. The required amounts of oxygen scavenger, mixed bactericide, and flocculant are mixed and stirred evenly to obtain the compound degradation inhibitor. The oxygen scavenger is 10 to 15 parts by mass, the mixed bactericide is 10 to 25 parts, and the flocculant is 1 to 2 parts.

[0009] The oxygen scavenger mentioned above is one or more of anhydrous sodium sulfite, zinc sulfate, hydrazine, and acetone oxime.

[0010] The above-mentioned mixed bactericide is a mixed solution composed of polyaldehyde and quaternary ammonium salt. In the mixed solution, the polyaldehyde content is 5% to 95% and the quaternary ammonium salt content is 5% to 95% by mass percentage.

[0011] The aforementioned polyaldehydes are one or more of glutaraldehyde, formaldehyde, and paraformaldehyde, and the quaternary ammonium salt is one or more of dodecyl dimethyl benzyl ammonium chloride and tetradecyl dimethyl benzyl ammonium chloride.

[0012] The aforementioned polyaldehyde is glutaraldehyde, and the quaternary ammonium salt is dodecyl dimethyl benzyl ammonium chloride.

[0013] The above-mentioned antibacterial agent is a small cationic polymer, which is polydimethyldiallylammonium chloride.

[0014] In the second step above, when cleaning the polymerization container and equipment, the amount of compound degradation inhibitor added is 900 mg / L to 1000 mg / L, depending on the volume of the polymerization container and equipment.

[0015] In the fourth step above, the amount of compound degradation inhibitor added per liter of oilfield purified water is 50mg to 100mg.

[0016] In the fifth step above, the mass concentration of the polymer solution used for injection is 1000 mg / L to 3000 mg / L.

[0017] This invention adds a compound degradation inhibitor to the purified water of the oilfield. On the one hand, it inhibits the decomposition of polymers by bacterial growth and removes various pollutants such as oil sludge that are prone to bacterial growth in storage tanks and pipelines. On the other hand, it eliminates the impact of system pollution on polymer viscosity and achieves the goal of low viscosity loss during polymer flooding. Detailed Implementation

[0018] This invention is not limited to the following embodiments; specific implementation methods can be determined based on the technical solution of this invention and actual circumstances. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art.

[0019] The present invention will be further described below with reference to embodiments: Example 1: A method for preparing a polymer solution from purified water in this oilfield to suppress viscosity loss is carried out according to the following method: The first step is to prepare a compound degradation inhibitor; The second step is to clean the polymerization container and equipment using a compound degradation inhibitor. After cleaning, the polymerization container and equipment are ready for use. The third step is to purify the produced water from the oilfield to obtain purified oilfield water. The fourth step is to add the required amount of compound degradation inhibitor to the oilfield purified water in the cleaned polymer container and equipment, and after stirring, obtain pretreated purified water. The fifth step involves adding a polymer (cationic polyacrylamide or anionic polyacrylamide) to the pretreated purified water, stirring to dissolve it, and obtaining a polymer solution for injection. The sixth step involves injecting the polymer solution for injection into the reinjection wellhead to drive out oil.

[0020] In oilfield development, the method of using purified oilfield water to prepare polymer solutions and suppress viscosity loss overcomes the problems of secondary pollution and sludge buildup on pipelines and tanks that cause significant viscosity loss when using purified oilfield produced fluid to prepare polymer solutions for injection. By adding a compound degradation inhibitor that integrates degradation and sludge removal functions, the method achieves low viscosity loss (<11%) in the polymer solution for injection and stable polymer viscosity after addition (100% viscosity retention rate after 30 days). It effectively solves the problem of polymer biochemical degradation caused by bacteria and contaminants, and achieves the goal of low viscosity loss during polymer flooding using purified oilfield produced fluid to prepare polymer solutions.

[0021] Example 2: As an optimization of the above example, in the first step, the compound degradation inhibitor includes an oxygen scavenger, a mixed bactericide, and a flocculant. The required amounts of oxygen scavenger, mixed bactericide, and flocculant are mixed and stirred evenly to obtain the compound degradation inhibitor. The oxygen scavenger is 10 to 15 parts by mass, the mixed bactericide is 10 to 25 parts, and the flocculant is 1 to 2 parts.

[0022] Example 3: As an optimization of the above examples, the oxygen scavenger is one or more of anhydrous sodium sulfite, zinc sulfate, hydrazine, and acetone oxime.

[0023] Example 4: As an optimization of the above examples, the mixed bactericide is a mixed solution composed of polyaldehyde and quaternary ammonium salt. In the mixed solution, the polyaldehyde content is 5% to 95% and the quaternary ammonium salt content is 5% to 95% by mass percentage.

[0024] Example 5: The optimized polyaldehyde in the above examples is one or more of glutaraldehyde, formaldehyde and paraformaldehyde, and the quaternary ammonium salt is one or more of dodecyl dimethyl benzyl ammonium chloride and tetradecyl dimethyl benzyl ammonium chloride.

[0025] Example 6: As an optimization of the above examples, the polyaldehyde is glutaraldehyde and the quaternary ammonium salt is dodecyl dimethyl benzyl ammonium chloride.

[0026] Example 7: As an optimization of the above example, the antibacterial agent is a small cationic polymer, which is polydimethyldiallylammonium chloride.

[0027] Example 8: As an optimization of the above example, in the second step, when cleaning the polymerization container and equipment, the amount of compound degradation inhibitor added is 900 mg / L to 1000 mg / L according to the volume of the polymerization container and equipment.

[0028] Example 9: As an optimization of the above example, in the fourth step, the amount of compound degradation inhibitor added per liter of oilfield purified water is 50mg to 100mg.

[0029] Example 10: As an optimization of the above example, in the fifth step, the mass concentration of the polymer solution used for injection is 1000 mg / L to 3000 mg / L.

[0030] Example 11: In August 2023, the binary composite flooding project of the J1b4+5 reservoir in the Badaowan Formation of a certain oilfield was implemented.

[0031] A mixed bactericide consisting of 10 parts zinc sulfate, 1 part polydimethyl diallyl ammonium chloride, 25 parts glutaraldehyde and dodecyl dimethyl benzyl ammonium chloride (1227) was prepared and stirred evenly to obtain a compound degradation inhibitor. Based on the volume of the polymerization container and equipment, the polymerization container and equipment were cleaned with a compound degradation inhibitor at a dosage of 1000 mg / L. Then, the oilfield produced fluid was treated to obtain purified oilfield water. In the cleaned polymer container and the oilfield purified water inside the equipment, according to the requirement of adding 80mg of compound degradation inhibitor per liter of oilfield purified water, add compound degradation inhibitor, stir evenly, and obtain pretreated purified water; Cationic polyacrylamide was added to the pretreated purified water and stirred to dissolve, resulting in a polymer solution for injection with a mass concentration of 2000 mg / L. After the polymer solution for injection is injected into the wellhead, oil displacement is carried out.

[0032] The oilfield purified water (before the addition of the compound degradation inhibitor) and pretreated purified water (after the addition of the compound degradation inhibitor) were tested, and the results are shown in Table 1.

[0033] After applying the polymer solution for polymer injection, the polymer at the wellhead was tested and compared with the polymer at the wellhead before the application of the polymer solution. The results are shown in Table 1.

[0034] As shown in Table 1, in the purified water from the oilfield, the number of sulfate-reducing bacteria (SRB) decreased from 110,000 CFU / mL to 2.5 CFU / mL, the number of iron bacteria (FB) decreased from 2,500 CFU / mL to 0, the number of saprophytic bacteria (TGB) decreased from 250 CFU / mL to 0, and the dissolved oxygen decreased from 1 mg / L to 5 mg / L to 0.3 mg / L.

[0035] In the wellhead polymer, the concentration of divalent sulfur decreased from 0.4 mg / L to 2.6 mg / L to 0 to 0.1 mg / L, the concentration of sulfate-reducing bacteria decreased from 110,000 CFU / mL to 2.5 CFU / mL, the viscosity compliance rate increased from 66% to 100%, and the viscosity index remained stable.

[0036] Compared to the substandard stage, the viscosity of the same concentration of polymer (cationic polyacrylamide or anionic polyacrylamide) increased by 51%, reducing the annual polymer usage by 711 tons, equivalent to a cost of 12.15 million yuan.

[0037] Therefore, the use of polymer solution for polymer injection inhibits the decomposition of polymer by bacterial growth. At the same time, the agent system has a strong stripping effect. The bactericidal stripping components can remove various pollutants such as sludge that are prone to bacterial growth in storage tanks and pipelines, eliminate the impact of system contamination on polymer viscosity, and effectively improve the performance of the polymer flooding system.

[0038] In summary, by adding a compound degradation inhibitor to the purified water of the oilfield, this invention, on the one hand, inhibits the decomposition of polymers by bacterial growth and removes various pollutants such as oil sludge that are prone to bacterial growth from storage tanks and pipelines; on the other hand, it eliminates the impact of system contamination on polymer viscosity and achieves the goal of low viscosity loss during polymer flooding.

[0039] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for preparing polymer solutions from oilfield purified water to suppress viscosity loss, characterized in that... Perform the following steps: The first step is to prepare a compound degradation inhibitor; The second step is to clean the polymerization container and equipment using a compound degradation inhibitor. After cleaning, the polymerization container and equipment are ready for use. The third step is to purify the produced water from the oilfield to obtain purified oilfield water. The fourth step is to add the required amount of compound degradation inhibitor to the oilfield purified water in the cleaned polymer container and equipment, and after stirring, obtain pretreated purified water. The fifth step involves adding the polymer to the pretreated purified water, stirring to dissolve it, and obtaining a polymer solution for injection. The sixth step involves injecting the polymer solution for injection into the reinjection wellhead to drive out oil.

2. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 1, characterized in that... In the first step, the compound degradation inhibitor includes an oxygen scavenger, a mixed bactericide, and a bacteriostatic agent. The required amounts of oxygen scavenger, mixed bactericide, and bacteriostatic agent are mixed and stirred evenly to obtain the compound degradation inhibitor. The oxygen scavenger is 10 to 15 parts by mass, the mixed bactericide is 10 to 25 parts, and the bacteriostatic agent is 1 to 2 parts.

3. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 2, characterized in that... The oxygen scavenger is one or more of anhydrous sodium sulfite, zinc sulfate, hydrazine, and acetone oxime.

4. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 2 or 3, characterized in that... The mixed bactericide is a mixed solution composed of polyaldehydes and quaternary ammonium salts. In the mixed solution, the polyaldehyde content is 5% to 95% and the quaternary ammonium salt content is 5% to 95% by mass percentage.

5. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 4, characterized in that... The polyaldehyde is one or more of glutaraldehyde, formaldehyde, and paraformaldehyde, and the quaternary ammonium salt is one or more of dodecyl dimethyl benzyl ammonium chloride and tetradecyl dimethyl benzyl ammonium chloride.

6. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 5, characterized in that... The polyaldehyde is glutaraldehyde, and the quaternary ammonium salt is dodecyl dimethyl benzyl ammonium chloride.

7. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 5 or 6, characterized in that... The antibacterial agent is a small cationic polymer, which is polydimethyldiallylammonium chloride.

8. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 2, 3, 5, or 6, characterized in that... In the second step, when cleaning the polymerization container and equipment, the amount of compound degradation inhibitor added is 900 mg / L to 1000 mg / L, depending on the volume of the polymerization container and equipment.

9. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 8, characterized in that... In the fourth step, the amount of compound degradation inhibitor added per liter of oilfield purified water is 50mg to 100mg.

10. The method for preparing polymer solutions from oilfield purified water to suppress viscosity loss according to claim 2, 3, 5, 6, or 9, characterized in that... In the fifth step, the mass concentration of the polymer solution used for injection is 1000 mg / L to 3000 mg / L.

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