Anti-scale alkali for oil displacement, injection liquid and preparation method thereof

Abstract

The invention discloses anti-scale alkali for oil displacement, injection liquid and a preparation method of the injection liquid. The anti-scale alkali comprises an anti-scale component, an alkali component and water, and the anti-scale component is selected from one or more of organic phosphonic acid or salt thereof, polycarboxylic acid or salt thereof and amino carboxylic acid or salt thereof; the mass concentration of the anti-scaling component is 150 to 3000mg / L, and the mass fraction of the alkali component is 8 to 24 percent; the oil displacement injection liquid comprises the anti-scale alkali; the anti-scale alkali can effectively inhibit deposition and scale formation of alkaline earth metal cation compounds in an alkali flooding or synergistic alkali flooding injection system, and solves the problems of serious scaling and frequent acid pickling of an injection allocation system.

Description

Technical Field

[0001] This disclosure relates to the technical field of alkaline flooding and enhanced alkaline flooding (including alkaline-surfactant flooding, alkaline-polymer flooding, alkaline-surfactant-polymer flooding, etc.) in tertiary oil recovery, specifically to an anti-scaling alkali for oil displacement and its preparation method. The purpose is to use the anti-scaling alkali to inhibit scaling of the injection fluid in alkaline flooding and enhanced alkaline flooding, and to ensure the stable operation of the injection system. Background Art

[0002] The statements in this section provide only background information in connection with this disclosure and do not constitute prior art.

[0003] Alkali flooding and enhanced alkali flooding are important technologies for improving oil recovery in oilfields, and their supporting role in the sustainable development of oilfields is constantly increasing. In the industrial-scale promotion and application of alkali flooding and enhanced alkali flooding, sodium carbonate or sodium hydroxide are often used as the alkali for oil displacement. These alkalis have poor compatibility with the prepared water, especially forming large amounts of inorganic scale such as calcium carbonate, magnesium carbonate, or magnesium hydroxide with divalent metal cations like calcium and magnesium. This leads to severe scaling at the injection end, resulting in high failure rates of static mixers, injection pumps, pipelines, and valve assemblies. On average, production needs to be shut down every 1-2 months for acid washing and descaling, seriously affecting the injection efficiency of the preparation and injection system. Therefore, to promote the effective implementation of combined flooding technology for improving oil recovery, the scaling problem in the preparation and injection system needs to be solved.

[0004] Currently, conventional solutions for scaling in alkaline flooding and enhanced alkaline flooding dispensing systems mainly include acid washing and chemical scale prevention. Acid washing involves dissolving scale on equipment and pipe walls with acid after it has formed in the dispensing system. This process requires shutdown and significant manual labor, severely impacting injection efficiency. Furthermore, acid washing wastewater poses serious environmental hazards, and further harmless treatment is costly and carries significant environmental risks. Chemical scale prevention uses scale inhibitors to suppress scaling in the dispensing system. It generally requires separate dosing facilities. Insufficient procurement, management, and maintenance of the agents can affect the efficiency of chemical scale prevention. Moreover, some scale inhibitors are acidic, which can corrode pipes and equipment, especially near the weld joints at the dosing points, leading to a risk of system leakage. Therefore, its practical application is somewhat limited.

[0005] In commonly used alkaline flooding and enhanced alkaline flooding processes in oilfields, the alkaline agent is typically dispersed from solid dry alkaline powder into a liquid alkaline solution with a mass fraction of 8%–24%. Using clean water or shallow surface water consumes a large amount of water resources, resulting in waste. Using wastewater requires pretreatment processes such as activated carbon degreasing and filtration, making the process complex. Furthermore, the water used for alkaline solution preparation needs softening; otherwise, poor compatibility between the alkali and the injection water can cause varying degrees of scaling and blockage in the injection system and reservoir, severely impacting injection efficiency. This has become a major challenge hindering the effective implementation of enhanced oil recovery technologies using combined flooding.

[0006] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art. Summary of the Invention

[0007] In view of this, the present disclosure provides an anti-scaling alkali for oil displacement, which can effectively inhibit the deposition of alkaline earth metal cation compounds into scale in alkaline flooding or enhanced alkaline flooding injection systems, and solve the problems of severe scaling and frequent acid washing in the injection system.

[0008] In addition, this disclosure also provides a method for preparing the anti-scaling alkali, and provides an injection solution using the anti-scaling alkali and a method for preparing the same.

[0009] In a first aspect, the oil displacement scale inhibitor alkali includes a scale inhibitor component, an alkali component, and water, wherein the scale inhibitor component is selected from one or more of organophosphonic acids or their salts, polycarboxylic acids or their salts, and aminocarboxylic acids or their salts.

[0010] The scale inhibitor has a mass concentration of 150–3000 mg / L, and the alkaline component has a mass fraction of 8%–24%.

[0011] In this disclosure and possible embodiments, the organophosphonic acid or its salt comprises:

[0012] Diethylenetriaminepentamylidene phosphate or its salt, ethylenediaminetetramylidene phosphonic acid or its salt, aminotrimylidene phosphonic acid or its salt, polyaminopolyethermylidene phosphate or its salt, 2-phosphonobutane-1,2,4-tricarboxylic acid or its salt, and hydroxyethylidene diphosphonic acid or its salt.

[0013] In this disclosure and possible embodiments, the polycarboxylic acid or its salt comprises:

[0014] Polyphosphonic carboxylic acid or its salt, phosphonocarboxylic acid copolymer or its salt, sodium polyacrylate and 2-acrylamide-2-methylpropanesulfonic acid-hydroxypropyl acrylate terpolymer or its salt.

[0015] In this disclosure and possible embodiments, the aminocarboxylic acid or its salt comprises:

[0016] Ethylenediaminetetraacetic acid or its salts and aminotriacetic acid.

[0017] Secondly, the method for preparing the scale-inhibiting alkali for oil displacement described in the first aspect includes:

[0018] The scale-inhibiting component is dissolved in the water, and then the alkaline component is added. The total hardness of the water is ≤0.03 mmol / L. The scale-inhibiting alkali is obtained after the alkaline component dissolves.

[0019] In this disclosure and possible embodiments, during the dissolution of the alkaline component, the solution temperature difference is controlled to be less than 10°C.

[0020] Thirdly, the oil displacement injection fluid comprises:

[0021] The scale-inhibiting alkali described in the first aspect.

[0022] In this disclosure and possible embodiments, the composition may further include surfactants and / or polymers;

[0023] The surfactant is a petroleum sulfonate or alkylbenzene sulfonate; the polymer is a partially hydrolyzed polyacrylamide with a molecular weight of 12 million to 25 million.

[0024] In this disclosure and possible embodiments, the anti-scaling alkali has a mass fraction of 3% to 20%.

[0025] This disclosure has the following beneficial effects:

[0026] The scale-inhibiting alkali and the alkali-surfactant-polymer flooding injection fluid prepared using the scale-inhibiting alkali disclosed herein are a phase-stable oil displacement system. It can inhibit the formation and deposition of alkaline earth metal carbonates, alkaline earth metal sulfates, or alkaline earth metal hydroxides in alkaline flooding or enhanced alkaline flooding injection fluids, thereby achieving the purpose of inhibiting scaling in the injection system from the source. This effectively ensures the stability of the composite flooding injection fluid in the injection system and reservoir, greatly reducing the loss of manpower and material resources and the impact on the environment caused by subsequent descaling measures such as acid washing. It not only ensures the smooth movement of the injection fluid in the injection system and reservoir, but also ensures the good oil displacement effect of the injection fluid, and improves the injection efficiency of alkaline flooding or enhanced alkaline flooding injection systems. Detailed Implementation

[0027] The present disclosure is described below based on embodiments; however, it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, certain specific details are described in detail. However, those skilled in the art will fully understand the present disclosure for the parts not described in detail.

[0029] Furthermore, unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to."

[0030] In the following embodiments of this disclosure, the antiscaling component is selected from one or more of the following: (1) organophosphonic acids, such as diethylenetriaminepentamylidene phosphate or its salt (DTPMP), ethylenediaminetetramylidene phosphonic acid or its salt (EDTMP), aminotrimylidene phosphonic acid or its salt (ATMP), polyaminopolyethermylidene phosphate or its salt (PAPEMP), 2-phosphonobutane-1,2,4-tricarboxylic acid or its salt (PBTCA), hydroxyethylidene diphosphonic acid or its salt (HEDP); (2) polycarboxylic acids, such as polyphosphonic acid or its salt (PCA), phosphonoacylcarboxylic acid copolymer or its salt (POCA), sodium polyacrylate (PAAS), acrylate-2-acrylamide-2-methylpropanesulfonic acid-hydroxypropyl acrylate terpolymer or its salt (AA / AMPS); (3) aminocarboxylic acids, such as ethylenediaminetetraacetic acid or its salt (EDTA), aminotriacetic acid (ATA). The alkali component is selected from solid sodium carbonate or solid sodium hydroxide.

[0031] In the following embodiments and comparative examples of this disclosure, the simulated injection solution was dispensed into clean colorimetric tubes, sealed, and stored in a 45°C constant temperature drying oven for evaluation of the scale-inhibiting performance of the anti-scaling alkali. The scale-inhibiting performance of the anti-scaling alkali was determined based on the amount of calcium carbonate precipitation. The evaluation method for the scale-inhibiting performance of the anti-scaling alkali is as follows:

[0032] The initial calcium ion concentration C0 value of the prepared water and the calcium ion concentration C value of the simulated injection solution after standing for 90 days were detected. The amount of calcium carbonate precipitation was calculated, and the scale prevention performance of the scale-inhibiting alkali was investigated.

[0033] The formula for calculating the amount of calcium carbonate precipitated is: Q = (C0 - C) × 2.5;

[0034] In the formula, Q is the amount of calcium carbonate precipitated, in mg / L; CO is the mass concentration of calcium ions in the preparation water, in mg / L; and C is the mass concentration of calcium ions in the simulated injection solution after 90 days, in mg / L.

[0035] The following embodiments of this disclosure are carried out according to the following procedure:

[0036] First, prepare the anti-scaling alkali by weighing a predetermined amount of softened water and placing it on a temperature-controlled stirring device. Turn on the heating and stirring function, setting the initial temperature to 30–40°C and the rotation speed to 300–500 r / min. Add the predetermined amount of anti-scaling component and stir until homogeneous. Then, slowly disperse the predetermined amount of alkali component over 5–15 minutes, controlling the temperature difference of the solution to be less than 10°C. Stir until fully dissolved to prepare the anti-scaling alkali. In this anti-scaling alkali, the mass concentration of the anti-scaling component is in the range of 150–3000 mg / L, and the mass fraction of the alkali component is in the range of 8%–24%. Next, use this anti-scaling alkali to prepare a simulated injection solution, in which the mass fraction of the anti-scaling alkali is in the range of 3%–20%. Finally, dispense the simulated injection solution into clean colorimetric tubes, seal them, and place them in a 45°C constant temperature drying oven for static storage. The anti-scaling performance of the anti-scaling alkali will be evaluated periodically.

[0037] Example 1:

[0038] A weakly basic anti-scaling alkali was prepared, and its anti-scaling performance in a simulated injection solution of anti-scaling alkali-surfactant-polymer was evaluated.

[0039] (1) Preparation of scale inhibitor alkali: Weigh 184g of softened water, add 66.7mg of scale inhibitor hydroxyethylidene diphosphonic acid and 66.7mg of sodium polyacrylate, stir to dissolve, then add 16g of sodium carbonate and stir to dissolve thoroughly to prepare scale inhibitor alkali. The mass concentration of scale inhibitor in the scale inhibitor alkali is 667mg / L and the mass fraction of alkali component is 8%.

[0040] (2) Preparation of water for preparation: Take the deep-processed water from Daqing Oilfield and filter it once with double-layer medium-speed qualitative filter paper as the water for preparation.

[0041] (3) Preparation of anti-scaling alkali-surfactant-polymer simulated injection solution: Take 835g of preparation water, add 150g of anti-scaling alkali, add 15g of petroleum sulfonate with a mass fraction of 20% to obtain anti-scaling alkali-surfactant solution; Take 500g of anti-scaling alkali-surfactant solution, add 3.2g of partially hydrolyzed polyacrylamide, stir and mature according to the conventional techniques in this field, the maturation time is usually 2-4h to obtain anti-scaling alkali-surfactant-polymer mother liquor; Take 500g of anti-scaling alkali-surfactant solution and 500g of anti-scaling alkali-surfactant-polymer mother liquor and mix evenly to obtain anti-scaling alkali-surfactant-polymer simulated injection solution.

[0042] The simulated injection solution was dispensed into clean 25mL colorimetric tubes that had undergone high-temperature sterilization. The tubes were filled, capped, sealed with 3M sealing film, and placed in a 45℃ constant temperature drying oven for storage.

[0043] (4) Evaluation of scale prevention performance of simulated injection solution of scale inhibitor-surfactant-polymer: The initial calcium ion mass concentration C0 of the water used for preparation and the calcium ion mass concentration C in the simulated injection solution after standing for 90 days were detected, the amount of calcium carbonate precipitation was calculated, and the scale prevention performance of scale inhibitor was investigated.

[0044] Table 1. Scale prevention performance of simulated injection solutions containing anti-scaling alkali, surfactant, and polymer.

[0045]

[0046] The test results show that, under the condition of an initial calcium ion mass concentration of 39.04 mg / L, the amount of calcium carbonate precipitated is 5.43 mg / L. The scale prevention effect of the scale prevention alkali-surfactant-polymer simulated injection solution prepared by the weakly alkaline scale prevention alkali is significant.

[0047] Example 2:

[0048] A weakly alkaline anti-scaling alkali was prepared, and its anti-scaling performance in the simulated injection solution was evaluated.

[0049] (1) Preparation of scale inhibitor alkali: Weigh 168g of softened water, add 400mg of scale inhibitor disodium ethylenediaminetetraacetate, 66.7mg of sodium polyphosphonate and 66.7mg of sodium aminotrimethylphosphonate, stir to dissolve, add 32g of sodium carbonate, stir to dissolve, and prepare scale inhibitor alkali. The mass concentration of scale inhibitor in the scale inhibitor alkali is 2667mg / L, and the mass fraction of alkali component is 16%.

[0050] (2) Preparation of water for preparation: Take the deep-processed water from Daqing Oilfield and filter it once with double-layer medium-speed qualitative filter paper as the water for preparation.

[0051] (3) Preparation of anti-scaling alkali simulated injection solution: Take 910g of water for preparation and add 90g of anti-scaling alkali to obtain anti-scaling alkali simulated injection solution. Dispense the above simulated injection solution into clean 25mL colorimetric tubes that have been sterilized at high temperature, fill them, cap the tubes, seal them with 3M sealing film, and place them in a 45℃ constant temperature drying oven for static storage.

[0052] (4) Evaluation of the scale prevention performance of the simulated injection solution of the scale prevention alkali: The initial calcium ion mass concentration C0 of the water used for preparation and the calcium ion mass concentration C in the simulated injection solution after standing for 90 days were measured, the amount of calcium carbonate precipitation was calculated, and the scale prevention performance of the scale prevention alkali was examined.

[0053] Table 2. Scale prevention performance of simulated alkaline flooding injection solution

[0054]

[0055] The test results show that, under the condition of an initial calcium ion mass concentration of 46.24 mg / L, the amount of calcium carbonate precipitated is 5.93 mg / L, indicating that the simulated injection solution prepared with a weak alkaline anti-scaling alkali has a significant anti-scaling effect.

[0056] Example 3:

[0057] A weakly basic anti-scaling alkali was prepared, and the anti-scaling performance of the anti-scaling alkali in a simulated injection solution with a surfactant was evaluated.

[0058] (1) Preparation of scale inhibitor alkali: Weigh 160g of softened water, add 166.7mg of scale inhibitor components phosphonocarboxylic acid copolymer, 166.7mg of sodium diethylenetriamine pentamethylidene phosphate and 166.7mg of sodium 2-phosphonobutane-1,2,4-tricarboxylate, stir to dissolve, add 40g of sodium carbonate, stir to dissolve thoroughly to prepare scale inhibitor alkali. The mass concentration of scale inhibitor components in the scale inhibitor alkali is 2500mg / L and the mass fraction of alkali components is 20%.

[0059] (2) Preparation of water for preparation: Take the deep-processed water from Daqing Oilfield and filter it once with double-layer medium-speed qualitative filter paper as the water for preparation.

[0060] (3) Preparation of anti-scaling alkali-surfactant simulated injection solution: Take 935g of water for preparation, add 50g of anti-scaling alkali, and add 15g of petroleum sulfonate with a mass fraction of 20% to obtain the anti-scaling alkali-surfactant simulated injection solution. Dispense the above simulated injection solution into clean 25mL colorimetric tubes that have undergone high-temperature sterilization, fill the tubes, cap them, seal them with 3M sealing film, and place them in a 45℃ constant temperature drying oven for static storage.

[0061] (4) Evaluation of the scale prevention performance of the simulated injection solution of scale inhibitor alkali-surfactant: The initial calcium ion mass concentration C0 of the water used for preparation and the calcium ion mass concentration C in the simulated injection solution after standing for 90 days were measured, the amount of calcium carbonate precipitation was calculated, and the scale prevention performance of the scale inhibitor alkali was examined.

[0062] Table 3. Scale prevention performance of simulated injection solutions with alkali-surfactant mixtures.

[0063]

[0064] The test results show that, under the condition of an initial calcium ion mass concentration of 42.96 mg / L, the amount of calcium carbonate precipitated is 5.98 mg / L, indicating that the scale-inhibiting alkali-surfactant simulated injection solution prepared by the weakly alkaline scale inhibitor has a significant scale-inhibiting effect.

[0065] Example 4:

[0066] A weakly alkaline anti-scaling alkali was prepared, and its anti-scaling performance in a polymer-based simulated injection solution was evaluated.

[0067] (1) Preparation of scale inhibitor alkali: Weigh 176g of softened water, add 133.4mg of scale inhibitor polyamino polyether methylene phosphoric acid and 133.4mg of acrylic acid-2-acrylamide-2-methylpropanesulfonic acid-hydroxypropyl acrylate terpolymer, stir to dissolve, add 24g of sodium carbonate, stir to dissolve thoroughly, and prepare scale inhibitor alkali. The mass concentration of scale inhibitor in the scale inhibitor alkali is 1334mg / L, and the mass fraction of alkali component is 12%.

[0068] (2) Preparation of water for preparation: Take the deep-processed water from Daqing Oilfield and filter it once with double-layer medium-speed qualitative filter paper as the water for preparation.

[0069] (3) Preparation of anti-scaling alkali-polymer simulated injection solution: Take 930g of water for preparation, add 70g of anti-scaling alkali, add 3.2g of partially hydrolyzed polyacrylamide, stir and mature to obtain anti-scaling alkali-polymer simulated injection solution. Dispense the above simulated injection solution into clean 25mL colorimetric tubes that have undergone high-temperature sterilization, fill the tubes, cap them, seal them with 3M sealing film, and place them in a 45℃ constant temperature drying oven for static storage.

[0070] (4) Evaluation of the scale prevention performance of the anti-scale alkali-polymer simulated injection solution: The initial calcium ion mass concentration C0 in the prepared water and the calcium ion mass concentration C in the simulated injection solution after standing for 90 days were detected, the amount of calcium carbonate precipitation was calculated, and the scale prevention performance of the anti-scale alkali was investigated.

[0071] Table 4. Scale prevention performance of the alkali-polymer simulated injection solution.

[0072]

[0073] The test results show that, under the condition of an initial calcium ion mass concentration of 52.64 mg / L, the amount of calcium carbonate precipitated is 7.15 mg / L. The scale-inhibiting alkali-polymer simulated injection solution prepared by using a weakly alkaline scale-inhibiting alkali has a significant scale-inhibiting effect.

[0074] Example 5:

[0075] A strong-base anti-scaling alkali was prepared, and the anti-scaling performance of the anti-scaling alkali in a simulated injection solution of anti-scaling alkali-surfactant-polymer was evaluated.

[0076] (1) Preparation of scale inhibitor alkali: Weigh 168g of softened water, add 166.7mg of scale inhibitor disodium ethylenediaminetetraacetate and 166.7mg of phosphonocarboxylic acid copolymer, stir to dissolve, add 32g of sodium hydroxide, stir to dissolve thoroughly, and prepare scale inhibitor alkali. The mass concentration of scale inhibitor in the scale inhibitor alkali is 1667mg / L, and the mass fraction of alkali component is 16%.

[0077] (2) Preparation of water for preparation: Take the deep-processed water from Daqing Oilfield and filter it once with double-layer medium-speed qualitative filter paper as the water for preparation.

[0078] (3) Preparation of anti-scaling alkali-surfactant-polymer simulated injection solution: Take 805g of water for preparation, add 180g of anti-scaling alkali, and add 15g of alkylbenzene sulfonate with a mass fraction of 20% to obtain an anti-scaling alkali-surfactant solution; take 985g of water for preparation, add 15g of alkylbenzene sulfonate with a mass fraction of 20%, and add 3.2g of partially hydrolyzed polyacrylamide, and stir and mature according to conventional techniques in the art to obtain a surfactant-polymer mother liquor. Take 500g of anti-scaling alkali-surfactant solution and 500g of surfactant-polymer mother liquor and mix them evenly to obtain an anti-scaling alkali-surfactant-polymer simulated injection solution. Dispense the above simulated injection solution into clean 25mL colorimetric tubes that have undergone high-temperature sterilization, fill them completely, cap the tubes, seal them with 3M sealing film, and store them in a 45℃ constant temperature drying oven.

[0079] (4) Evaluation of scale prevention performance of simulated injection solution of scale inhibitor-surfactant-polymer: The initial calcium ion mass concentration C0 of the water used for preparation and the calcium ion mass concentration C in the simulated injection solution after standing for 90 days were detected, the amount of calcium carbonate precipitation was calculated, and the scale prevention performance of scale inhibitor was investigated.

[0080] Table 5. Scale prevention performance of simulated injection solutions containing scale inhibitory alkalis, surfactants, and polymers.

[0081]

[0082] The test results show that, under the condition of an initial calcium ion mass concentration of 34.52 mg / L, the amount of calcium carbonate precipitated is 4.03 mg / L. The scale inhibitor-surfactant-polymer simulated injection solution prepared using a strong alkaline scale inhibitor also achieves the expected scale inhibitor effect.

[0083] Comparative Example:

[0084] Evaluation of scaling degree in conventional weak alkali-surfactant-polymer simulated injection solution.

[0085] (1) Preparation of conventional weak alkali: Weigh 184g of softened water, add 16g of sodium carbonate, stir thoroughly to dissolve, and prepare a conventional alkali solution with a mass fraction of 8%.

[0086] (2) Preparation of water for preparation: Take the deep-processed water from Daqing Oilfield and filter it once with double-layer medium-speed qualitative filter paper as the water for preparation.

[0087] (3) Preparation of conventional weak alkali-surfactant-polymer simulated injection solution: Take 835g of water for preparation, add 150g of the above-mentioned 8% conventional alkali solution, and add 15g of petroleum sulfonate with a mass fraction of 20% to obtain a weak alkali-surfactant solution; take 500g of the weak alkali-surfactant solution, add 3.2g of partially hydrolyzed polyacrylamide, stir and mature to obtain a weak alkali-surfactant-polymer mother liquor; take 500g of the weak alkali-surfactant solution and 500g of the weak alkali-surfactant-polymer mother liquor and mix them evenly to obtain a conventional weak alkali-surfactant-polymer simulated injection solution. Dispense the above simulated injection solution into clean 25mL colorimetric tubes that have undergone high-temperature sterilization, fill them completely, cap the tubes, seal them with 3M sealing film, and store them in a 45℃ constant temperature drying oven.

[0088] (4) Evaluation of the scale prevention performance of the weak base-surfactant-polymer simulated injection solution: The initial calcium ion mass concentration C0 of the prepared water and the calcium ion mass concentration C in the simulated injection solution after standing for 90 days were detected, the amount of calcium carbonate precipitation was calculated, and the degree of scaling of the simulated injection solution was examined.

[0089] Table 6. Scaling Degree of Weak Alkali-Surfactant-Polymer Simulated Injection Solution

[0090]

[0091] The test results show that, under the condition of an initial calcium ion mass concentration of 44.29 mg / L, the amount of calcium carbonate precipitated is as high as 69.03 mg / L, indicating that the scaling degree of the conventional weak alkali-surfactant-polymer simulated injection solution is very serious.

[0092] In practical applications, the scale-inhibiting alkali of this invention can be directly diluted with conventionally treated oilfield water and then introduced into the injection system. The injection system does not require separate chemical dosing facilities, simplifying the process and saving investment. This scale-inhibiting alkali has good compatibility with the injection water, inhibiting scaling in the injection system at its source, while not affecting the stability and oil displacement effect of synergistic alkaline flooding injection solutions such as alkali-surfactant-polymer flooding.

[0093] As can be seen from the above five examples and comparative examples, the conventional alkaline flooding or enhanced alkaline flooding simulated injection solutions in the comparative examples exhibited very severe scaling, while the alkaline flooding or enhanced alkaline flooding simulated injection solutions prepared with anti-scaling alkali in Examples 1-5 all achieved the expected anti-scaling effect.

[0094] In addition, in order to overcome the problems of insufficient complexation and dispersion ability of single-type scale inhibitors in alkaline flooding or enhanced alkaline flooding simulated injection solutions for various alkaline earth metal ions, excessive concentration, and high cost, the scale inhibitor of the present invention can be used in combination with two or more different types of scale inhibitors. The scale inhibitors listed in the present invention can be combined in any proportion, and they all contribute equally to the present invention.

[0095] The embodiments described above are merely illustrative of implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications, equivalent substitutions, and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent disclosure should be determined by the appended claims.

Claims

1. An anti-scaling alkali for oil displacement, comprising an anti-scaling component, an alkali component and water, characterized in that: The anti-scaling component is selected from one or more of organic phosphonic acid or its salt, polycarboxylic acid or its salt, aminocarboxylic acid or its salt; The mass concentration of the anti-scaling component is 150-3000 mg / L, and the mass fraction of the alkali component is 8%-24%.

2. The anti-scaling alkali for oil displacement according to claim 1, characterized in that The organic phosphonic acid or its salt comprises: Diethylenetriamine penta methylenephosphonic acid or its salt, ethylenediaminetetra methylenephosphonic acid or its salt, aminotri methylenephosphonic acid or its salt, polyaminopolyether methylenephosphonic acid or its salt, 2-phosphonobutane-1,2,4-tricarboxylic acid or its salt, and hydroxyethylidene diphosphonic acid or its salt.

3. The anti-scaling alkali for oil displacement according to claim 1, characterized in that The polycarboxylic acid or its salt comprises: Polyphosphinocarboxylic acid or its salt, phosphonocarboxylic acid copolymer or its salt, sodium polyacrylate and acrylic acid-2-acrylamide-2-methylpropanesulfonic acid-hydroxypropyl acrylate terpolymer or its salt.

4. The anti-scaling alkali for oil displacement according to claim 1, characterized in that The aminocarboxylic acid or its salt comprises: Ethylenediaminetetraacetic acid or its salts and aminotriacetic acid.

5. The method for preparing the anti-scaling alkali for oil displacement according to any one of claims 1 to 4, comprising: The anti-scaling component is dissolved in the water and then the alkali component is added, the total hardness of the water is ≤0.03 mmol / L, and the anti-scaling alkali is obtained after the alkali component is dissolved.

6. The method for preparing the anti-scaling alkali for oil displacement according to claim 5, characterized in that: During the dissolution of the alkali component, the temperature difference of the solution is controlled to be less than 10°C.

7. An oil displacement injection fluid, characterized in that: Its composition includes: The anti-scaling alkali according to any one of claims 1 to 4.

8. The injection liquid according to claim 7, characterized in that: The composition may also include surfactants and / or polymers; The surfactant is petroleum sulfonate or alkylbenzene sulfonate; the polymer is partially hydrolyzed polyacrylamide with a molecular weight of 12 to 25 million.

9. The injection liquid according to claim 8 is characterized in that: The mass fraction of the anti-scaling alkali is 3% to 20%.

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