Capsule polymer for oil displacement and preparation method and application thereof

Abstract

The application belongs to the technical field of oil and gas field development engineering, and provides a capsule polymer for oil displacement and a preparation method and application thereof.The preparation method comprises the following steps: adding base oil A and emulsifier I into a sodium alginate aqueous solution, stirring and uniformly dispersing to obtain a sodium alginate emulsion; mixing the polymer emulsion and the sodium alginate emulsion, stirring and uniformly dispersing to obtain a mixed emulsion; adding a calcium salt aqueous solution into the mixed emulsion, reacting, forming a calcium alginate coating layer, and obtaining a single-shell capsule polymer for oil displacement; or, then continuously adding the sodium alginate emulsion and the calcium salt aqueous solution, and then repeating the above steps to obtain the capsule polymers for oil displacement with different thicknesses and compactnesses.The capsule polymer has long-term stability, good dispersibility in an aqueous solution, can slowly release the effective components in water, and has temperature response characteristics, which can well meet the actual application requirements of conventional oil reservoir deep targeted viscosity increase.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development engineering technology, specifically relating to an oil displacement capsule polymer and its preparation method and application. Background Technology

[0002] Polymer flooding is an important technology for enhancing oil recovery by increasing the viscosity of the aqueous phase. Polymer-based chemical flooding (multi-component composite flooding and heterogeneous composite flooding) has been widely applied in my country's oilfield sector as a means of improving oil recovery. However, the high solution viscosity leads to problems such as high injection pressure and significant viscosity loss during injection into the formation, placing high demands on pipelines and injection equipment. Furthermore, the polymers exhibit poor stability.

[0003] To address the aforementioned issues, Chinese patent document CN111423543A discloses a nano-microcapsule delayed thickening polymer and its preparation method. The polymer prepared by this invention has a core-shell structure, with the core being acrylamide polymerized via photoinitiation. The polymer is encapsulated within an oily polyurethane shell. After the nanocapsules are injected into the formation, they gradually release their active ingredients with changes in temperature and pH, achieving a delayed thickening effect. However, its preparation method is complex, and the reaction conditions are not mild enough. Furthermore, Chinese patent document CN116003705A discloses a method for preparing and applying a nano-network structure delayed thickening polymer emulsion. This method provides a nano-network structure delayed thickening polymer emulsion where the core is polymerized from nano-silica, double-bonded silane coupling agents, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid monomers, while the protective shell is formed by azobisisobutyronitrile initiating the formation of propylene-1,3-sulfonate lactone. It can be pumped and provides delayed thickening in ultra-low permeability and complex fault-block sandstone reservoirs, but the high cost of the shell material limits its application in actual production.

[0004] Therefore, it is of great significance to develop an environmentally friendly capsule polymer for oil displacement with a simple synthesis process and controllable release of the core polymer. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an encapsulated polymer for oil displacement, its preparation method, and its application. This invention uses calcium alginate as the shell material to microencapsulate a polymer emulsion, which can largely control the release of the core polymer. By encapsulating the polymer in the microcapsule material and controlling the release temperature and rate, the polymer can be more easily injected into the formation and achieve a release and viscosity-enhancing effect in distant well formations.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing an oil displacement capsule polymer includes the following steps:

[0008] (1) Add base oil A and emulsifier I to the sodium alginate aqueous solution, stir and disperse evenly to obtain sodium alginate emulsion;

[0009] (2) Mix the polymer emulsion and the sodium alginate emulsion obtained in step (1), stir and disperse evenly to obtain a mixed emulsion;

[0010] (3) Add an aqueous solution of calcium salt to the mixed emulsion obtained in step (2) to react and form a calcium alginate coating layer, thereby obtaining a single-shell oil displacement capsule polymer; or,

[0011] (4) Add sodium alginate emulsion and calcium salt aqueous solution to the single-shell oil displacement capsule polymer obtained in step (3) and react. Then repeat the above steps to obtain oil displacement capsule polymers with different thicknesses and densities.

[0012] According to a preferred embodiment of the present invention, the mass concentration of the sodium alginate aqueous solution in step (1) is 1 to 6 wt%; the sodium alginate is not particularly limited.

[0013] According to a preferred embodiment of the present invention, the base oil A in step (1) is one of white oil, kerosene, or liquid paraffin; the white oil is not particularly limited, but preferably 3#, 5#, 7#, or 10# white oil; the mass ratio of the base oil A to the sodium alginate aqueous solution is 0.5 to 1.5:1, and more preferably 1 to 1.2:1.

[0014] According to a preferred embodiment of the present invention, the emulsifier I in step (1) is one or more of fatty alcohol polyoxyethylene ether MOA-9, fatty alcohol polyoxyethylene ether MOA-3, Span80, Span85, Tween80, Tween60 and alkylphenol polyoxyethylene ether OP-10; the mass of the emulsifier I is 1 to 15% of the mass of the base oil A.

[0015] According to a preferred embodiment of the present invention, the stirring temperature in step (1) is 20-30°C and the stirring speed is 400-600 r / min.

[0016] According to a preferred embodiment of the present invention, the comonomer of the polymer in step (2) is one or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, styrene sulfonic acid, and N-alkylmaleimide; and the viscosity-average molecular weight of the polymer is 10 million to 22 million.

[0017] According to a preferred embodiment of the present invention, the method for preparing the polymer emulsion in step (2) is prior art; preferably, the polymer emulsion is prepared according to the following method:

[0018] (a) Dissolve the comonomer in deionized water, adjust the pH of the system to 7-7.5 using sodium hydroxide, then add a water-soluble initiator, stir until homogeneous, and obtain an aqueous phase;

[0019] (b) Add emulsifier II to base oil B and stir until homogeneous to obtain the oil phase;

[0020] (c) Under stirring conditions, the aqueous phase is added dropwise to the oil phase, and then the temperature is raised to the reaction temperature to carry out the reaction, thereby obtaining a polymer emulsion.

[0021] Preferably, the mass ratio of the comonomer to deionized water in step (a) is 0.35 to 3:1.

[0022] Preferably, the water-soluble initiator in step (a) is one or more of ammonium persulfate, sodium persulfate, and azobisisobutyramidine hydrochloride; the mass fraction of the water-soluble initiator in the aqueous phase is 0.1-0.5%.

[0023] Preferably, the emulsifier II in step (b) is one or more of Span80, Span60, OP-10, cetyltrimethylammonium bromide, Tween40, Tween60, and Tween80; the mass fraction of emulsifier II in the oil phase is 3-10%.

[0024] Preferably, the base oil B in step (b) is the same as the base oil A.

[0025] Preferably, in step (c), the dropping rate of the aqueous phase is 3-5 mL / min; the mass ratio of the aqueous phase to the oil phase is 0.8-1.3:1.

[0026] Preferably, in step (c), nitrogen gas is passed through during the dropwise addition of the aqueous phase to remove oxygen.

[0027] Preferably, the reaction temperature in step (c) is 45-50°C, the reaction time is 2-3 hours, and the stirring speed during the reaction process is 550-850 r / min.

[0028] Preferably, in step (c), after heating to the reaction temperature, nitrogen gas is continuously purged for 45 to 60 minutes, and the nitrogen purging time is included in the reaction time.

[0029] According to a preferred embodiment of the present invention, the polymer content in the polymer emulsion in step (2) is 14 to 40 wt%.

[0030] According to a preferred embodiment of the present invention, the mass ratio of the polymer emulsion and the sodium alginate emulsion in step (2) is 1:0.5 to 5.

[0031] According to a preferred embodiment of the present invention, the stirring temperature in step (2) is 20-30°C and the stirring speed is 400-600 r / min.

[0032] According to a preferred embodiment of the present invention, the calcium salt in step (3) is one or more of calcium chloride, calcium bicarbonate, and calcium acetate; the mass concentration of the aqueous solution of the calcium salt is 1 to 15 wt%.

[0033] According to a preferred embodiment of the present invention, the mass ratio of the calcium salt aqueous solution to the sodium alginate emulsion in step (3) is 1:5 to 15; the calcium salt aqueous solution is added dropwise to the mixed emulsion at a dropping rate of 1 to 2 drops / s.

[0034] According to a preferred embodiment of the present invention, the reaction time in step (3) is 0.5 to 1 hour.

[0035] According to a preferred embodiment of the present invention, the sodium alginate emulsion in step (4) is the same as that in step (1), and the calcium salt aqueous solution is the same as that in step (3); both the sodium alginate emulsion and the calcium salt aqueous solution are added dropwise to the system at a dropping rate of 1 to 2 drops / s. After the sodium alginate emulsion is added, the system is stirred for 0.5 to 1 hour before adding the calcium salt aqueous solution.

[0036] According to a preferred embodiment of the present invention, in step (4), the mass ratio of sodium alginate emulsion to polymer emulsion added each time is 0.1 to 0.3:1; the mass ratio of calcium salt aqueous solution added each time to sodium alginate solution added each time is 1:5 to 15.

[0037] According to a preferred embodiment of the present invention, the reaction time in step (4) is 0.5 to 1 hour.

[0038] According to a preferred embodiment of the present invention, in step (4), the number of repetitions is 0 to 10 times; the repetition of the above steps refers to the repeated steps of adding sodium alginate emulsion and calcium salt aqueous solution to react.

[0039] The present invention also provides an oil displacement capsule polymer prepared by the above preparation method.

[0040] According to the present invention, the application of the above-mentioned oil displacement capsule polymer in oil displacement is specifically carried out by dispersing and diluting the capsule polymer with water, and then injecting it into the formation; the specific dilution ratio is determined according to the required viscosity of the formation, for example, a dilution of 50 to 500 times is acceptable.

[0041] The technical features and beneficial effects of this invention are as follows:

[0042] 1. The oil displacement capsule polymer of this invention is made by encapsulating an oil displacement polymer with sodium alginate, a natural polymer material, and then rapidly solidifying it with calcium ions under relatively mild conditions to form a calcium alginate film, thereby obtaining the capsule polymer. The sodium alginate used in this invention is non-toxic, has good molding and film-forming properties, is more environmentally friendly, and has a simple preparation process. This invention uses calcium alginate as the shell material to microencapsulate the polymer emulsion. On the one hand, it encapsulates the polymer molecules, preventing their viscosity from being released, making it easier to inject. On the other hand, it can effectively control the release of the core polymer. After injection into the formation, the capsule polymer is affected by the formation temperature, causing the calcium alginate shell to swell and rupture, releasing the core polymer. By controlling the number of times the calcium alginate film is modified, the release and viscosity-enhancing time of the encapsulated polymer can be controlled, making the polymer easier to inject into the formation and achieving the release and viscosity-enhancing effect in the far-well formation.

[0043] 2. The capsule polymer synthesis process of the present invention is simple. Its temperature and salt resistance can be enhanced by adjusting the composition of the polymer comonomer in the core. The release rate of the core polymer can be controlled by adjusting the number of shell modifications.

[0044] 3. The microcapsule emulsion prepared by this invention has high long-term stability, the capsule polymer has good dispersibility in aqueous solution and can slowly release the internal effective components, and its temperature response characteristics have great application potential in targeted thickening of deep conventional oil reservoirs. Attached Figure Description

[0045] Figure 1 The graph shows a comparison of the delayed thickening properties of the oil displacement capsule polymers prepared in Examples 1, 2, and 3.

[0046] Figure 2 A comparative graph showing the effect of different trigger temperatures on the thickening properties of the oil displacement capsule polymer prepared in Example 2.

[0047] Figure 3 Microscopic images showing the particle size swelling of the capsule polymer prepared in Example 2 in aqueous solution, where (a) shows swelling for 0.5 h, (b) shows swelling for 6 h, (c) shows swelling for 11 h, and (d) shows swelling for 16 h. Detailed Implementation

[0048] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, but the content and scope of protection of the present invention are not limited to the following embodiments.

[0050] In this invention, "parts" refers to parts by weight.

[0051] The polymer emulsions used in the examples were prepared according to the following method:

[0052] 50 parts acrylamide and 18 parts acrylic acid were dissolved in 32 parts deionized water at 30°C. The pH of the system was adjusted to 7.5 with sodium hydroxide, and 0.42 parts azobisisobutyramidine hydrochloride were added and stirred until homogeneous to obtain an aqueous phase. 3 parts Span80 and 2 parts Tween80 were added dropwise to 92 parts white oil (5#), and emulsified by stirring at 30°C for 30 min to obtain an oil phase. The resulting aqueous phase was added dropwise to the oil phase at a rate of 5 mL / min, with a stirring speed of 350 r / min. Nitrogen gas was purged during the dropwise addition of the aqueous phase to remove oxygen. The temperature was then raised to 46°C, the stirring speed was 800 r / min, and nitrogen gas was purged for another 50 min. The reaction was carried out at a constant temperature for 2.5 h to obtain a polymer emulsion, denoted as P(AM-AA). The polymer content in the emulsion was 34 wt%, and the viscosity-average molecular weight was 15 million.

[0053] Example 1

[0054] A method for preparing an oil displacement capsule polymer includes the following steps:

[0055] Sodium alginate was dissolved in deionized water to prepare a 3 wt% sodium alginate aqueous solution. 100 parts of white oil (5#) and 10 parts of Span80 were added to 100 parts of the sodium alginate aqueous solution, and the mixture was stirred and dispersed at 30°C and 500 r / min to form a homogeneous and stable sodium alginate emulsion. 100 parts of the above sodium alginate emulsion were added to 100 parts of P(AM-AA) emulsion, and the mixture was stirred at 30°C and 500 r / min for 0.5 h to form a homogeneous and stable mixed emulsion. 10 parts of a 10 wt% CaCl2 solution were added dropwise (2 drops / s) to the above mixed emulsion, and the reaction was allowed to proceed for 0.5 h to obtain the oil displacement capsule polymer, denoted as [Ca-SA]1 / P(AM-AA).

[0056] The delayed viscosity enhancement test was conducted as follows: The viscosity of the polymer emulsion (polyacrylamide-acrylic acid) and the oil displacement capsule polymer [Ca-SA]1 / P (AM-AA) coated with calcium alginate was measured using a digital rotational viscometer (NDJ-9S, rotor No. 1, 60 r / min). 1 mL of the emulsion and the capsule polymer were diluted to 100 mL with water, respectively, and stirred thoroughly in a water bath at 500 r / min. The viscosity of the aqueous solution was measured at regular intervals. The results are shown below. Figure 1 .

[0057] Example 2

[0058] A method for preparing an oil displacement capsule polymer includes the following steps:

[0059] (1) Dissolve sodium alginate in deionized water to prepare a sodium alginate aqueous solution with a mass concentration of 3wt%; add 100 parts of white oil (5#) and 10 parts of Span80 to 100 parts of sodium alginate aqueous solution, and stir and disperse at 30℃ and 500r / min to form a uniform and stable sodium alginate emulsion.

[0060] (2) Add 100 parts of sodium alginate emulsion obtained in step (1) to 100 parts of P(AM-AA) emulsion, stir at 30°C and 500 r / min for 0.5 h to form a homogeneous and stable mixed emulsion; add 10 parts of 10 wt% CaCl2 solution to the above mixed emulsion dropwise (2 drops / s), react for 0.5 h to obtain the capsule polymer, denoted as [Ca-SA]1 / P(AM-AA);

[0061] (3) Continue to add the sodium alginate emulsion (20 parts) obtained in step (1) dropwise (2 drops / s) to the above capsule polymer [Ca-SA]1 / P(AM-AA), stir for 0.5 h, and then add 2 parts of CaCl2 solution with a concentration of 10 wt% dropwise (2 drops / s), react for 0.5 h to obtain the oil displacement capsule polymer, denoted as [Ca-SA]2 / P(AM-AA).

[0062] The obtained sample was tested according to the method described in Example 1, and the test results are shown below. Figure 1 .

[0063] Example 3

[0064] A method for preparing an oil displacement capsule polymer includes the following steps:

[0065] Based on Example 2, sodium alginate emulsion (20 parts) obtained in step (1) was added dropwise (2 drops / s) to the oil displacement capsule polymer [Ca-SA]2 / P(AM-AA). After stirring for 0.5 h, 10 wt% CaCl2 solution (2 parts) was added dropwise (2 drops / s) and reacted for 0.5 h to obtain the oil displacement capsule polymer, denoted as [Ca-SA]3 / P(AM-AA).

[0066] The obtained sample was tested according to the method described in Example 1, and the test results are shown below. Figure 1 .

[0067] Figure 1The figure shows a comparison of the delayed thickening properties of the capsule polymers synthesized according to the synthesis methods of Example 1, Example 2, and Example 3. As can be seen from the figure, the polymer microcapsules coated with calcium alginate exhibit a significantly prolonged thickening time, and the polymer release rate decreases with the increase of the number of calcium alginate modification cycles.

[0068] Figure 2 This is a comparative graph showing the effect of different dissolution temperatures on the thickening properties of the polymer used in the oil displacement capsules of Example 2. As can be seen from the graph, at 25°C, the viscosity of the polymer remained at a low level (below 10 mPa·s) within 2 hours, and the thickening rate increased with increasing temperature.

[0069] Figure 3 The images show microscopic images of the capsule polymer synthesized according to Example 2 in aqueous solution. Figures (a)-(d) show the swelling of the microparticles in water at room temperature for 0.5 h, 6 h, 11 h, and 16 h, respectively. As can be seen from the figures, after the calcium alginate shell swells, the polyacrylamide in the core is gradually released from the pores.

[0070] As can be seen from Examples 1-3, the delayed release effect of polymer viscosity after uncoated, coated once, coated twice, and coated three times reveals that the polymer emulsion rapidly breaks down and releases viscosity. With each modification of the polymer emulsion, the viscosity-increasing time is progressively prolonged, indicating that increasing the number of modifications can delay viscosity increase. However, it is also evident that more modifications are not necessarily better. More modifications result in a higher proportion of calcium alginate in the outer shell, leading to a progressively worse viscosity-increasing effect of the capsule polymer at the same concentration. Therefore, the number of modifications needs to be controlled within the limits of this invention.

Claims

1. A method for preparing an oil displacement capsule polymer, characterized in that, The steps include the following: (1) Add base oil A and emulsifier I to the sodium alginate aqueous solution, stir and disperse evenly to obtain sodium alginate emulsion; (2) Mix the polymer emulsion and the sodium alginate emulsion obtained in step (1), stir and disperse evenly to obtain a mixed emulsion; (3) Add an aqueous solution of calcium salt to the mixed emulsion obtained in step (2) to react and form a calcium alginate coating layer to obtain a single-shell oil displacement capsule polymer; or, (4) Add sodium alginate emulsion and calcium salt aqueous solution to the single-shell oil displacement capsule polymer obtained in step (3) and react. Then repeat the above steps to obtain oil displacement capsule polymers with different thicknesses and densities. The comonomers of the polymer in step (2) are acrylamide and acrylic acid; the polymer emulsion is prepared according to the following method: (a) Dissolve the comonomer in deionized water, adjust the pH of the system to 7-7.5 using sodium hydroxide, then add the water-soluble initiator, stir until homogeneous, and obtain the aqueous phase; (b) Add emulsifier II to base oil B and stir until homogeneous to obtain the oil phase; (c) Under stirring conditions, the aqueous phase is added dropwise to the oil phase, and then the temperature is raised to the reaction temperature to carry out the reaction, thereby obtaining a polymer emulsion.

2. The method for preparing the oil displacement capsule polymer according to claim 1, characterized in that, The mass concentration of the sodium alginate aqueous solution in step (1) is 1~6wt%; the base oil A is one of white oil, kerosene, and liquid paraffin; the mass ratio of the base oil A to the sodium alginate aqueous solution is 0.5~1.5:

1.

3. The method for preparing the oil displacement capsule polymer according to claim 1, characterized in that, In step (1), the emulsifier I is one or more of fatty alcohol polyoxyethylene ether MOA-9, fatty alcohol polyoxyethylene ether MOA-3, Span80, Span85, Tween80, Tween60 and alkylphenol polyoxyethylene ether OP-10; the mass of the emulsifier I is 1 to 15% of the mass of the base oil A; the stirring temperature is 20 to 30°C and the stirring speed is 400 to 600 r / min.

4. The method for preparing the oil displacement capsule polymer according to claim 1, characterized in that, The viscosity-average molecular weight of the polymer in step (2) is 10 million to 22 million; the mass content of the polymer in the polymer emulsion is 14 to 40 wt%.

5. The method for preparing the oil displacement capsule polymer according to claim 1, characterized in that, In the preparation of the polymer emulsion, the mass ratio of the comonomer to deionized water in step (a) is 0.35~3:1; the water-soluble initiator is one or more of ammonium persulfate, sodium persulfate, and azobisisobutyramidine hydrochloride; the mass fraction of the water-soluble initiator in the aqueous phase is 0.1~0.5%; The emulsifier II mentioned in step (b) is one or more of Span80, Span60, OP-10, cetyltrimethylammonium bromide, Tween40, Tween60, and Tween80; the mass fraction of emulsifier II in the oil phase is 3-10%; the base oil B is the same as the base oil A. In step (c), the dropping rate of the aqueous phase is 3~5 mL / min; the mass ratio of the aqueous phase to the oil phase is 0.8~1.3:1; nitrogen gas is purged during the dropping of the aqueous phase to remove oxygen; the reaction temperature is 45~50℃, the reaction time is 2~3 h, and the stirring speed during the reaction process is 550~850 r / min; after the temperature is raised to the reaction temperature, nitrogen gas is purged for another 45~60 min.

6. The method for preparing the oil displacement capsule polymer according to claim 1, characterized in that, In step (2), the mass ratio of the polymer emulsion to the sodium alginate emulsion is 1:0.5~5; the stirring temperature is 20~30℃ and the stirring speed is 400~600r / min.

7. The method for preparing the oil displacement capsule polymer according to claim 1, characterized in that, The calcium salt mentioned in step (3) is one or more of calcium chloride, calcium bicarbonate, and calcium acetate; the mass concentration of the calcium salt aqueous solution is 1~15wt%; The mass ratio of the calcium salt aqueous solution to the sodium alginate emulsion is 1:5~15; the calcium salt aqueous solution is added dropwise to the mixed emulsion at a dropping rate of 1~2 drops / s; the reaction time is 0.5~1h.

8. The method for preparing the oil displacement capsule polymer according to claim 1, characterized in that, The sodium alginate emulsion mentioned in step (4) is the same as that in step (1), and the calcium salt aqueous solution is the same as that in step (3); both the sodium alginate emulsion and the calcium salt aqueous solution are added dropwise to the system at a dropping rate of 1~2 drops / s. After the sodium alginate emulsion is added, the mixture is stirred for 0.5~1h before the calcium salt aqueous solution is added. The mass ratio of sodium alginate emulsion to polymer emulsion added each time is 0.1~0.3:1; the mass ratio of calcium salt aqueous solution added each time to sodium alginate solution added each time is 1:5~15; the reaction time is 0.5~1h; In step (4), the number of repetitions is 0 to 10.

9. A capsule polymer for oil displacement, characterized in that, It was prepared using the preparation method described in claim 1.

10. The application of the oil displacement capsule polymer according to claim 9 in oil displacement, characterized in that, The specific method of use is as follows: disperse and dilute the capsule polymer with water, and then inject it into the formation.

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