A particle-polymer aggregate composite oil displacement agent and its use

Abstract

This invention relates to a particle-polymer aggregate composite oil displacement agent and its application. The oil displacement agent of this invention comprises: (A) a particle suspension containing particles and water, wherein the mass fraction of the particles is 200-2000 ppm; and (B) a polymer solution containing a polymer and water, wherein the mass fraction of the polymer is 0.01-10 ppm, and the polymer is one of the following: (B1), (B2), or (B3): (B1) an ionic polymer, wherein the ionic polymer is a cationic or anionic polymer, wherein the charge of the ionic groups on the polymer molecular chain is opposite to the charge of the particle surface; (B2) a mixture of cationic and anionic polymers; (B3) a naturally aged nonionic polymer. The oil displacement agent of this invention is low in cost, easy to inject, has a high sealing effect, and good oil displacement effect.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the fields of new energy and energy efficiency, specifically to a particulate-polymer aggregate composite oil displacement agent and its application. Background Technology

[0003] Polymers and particles are two representative additive components. Polymer flooding typically utilizes the thickening properties of polymers to improve the mobility ratio, or uses their viscoelasticity to generate flow field oscillations to mobilize residual oil. It is highly effective in improving oil recovery in high-permeability reservoirs, but suffers from problems such as difficult injection and high long-term injection costs. Particle suspension flooding utilizes the plugging effect of particles to regulate the distribution of flow resistance in heterogeneous reservoirs and suppress dominant flows, but faces challenges such as difficulty in injecting large particles and difficulty in plugging small particles. Existing research on the synergistic effect of these two methods mostly focuses on particles assisting in improving wettability or enhancing thickening effects, without considering the impact of particle-polymer interactions on the plugging effect. Summary of the Invention

[0004] The problem the invention aims to solve

[0005] There is still much room for improvement in the existing oil displacement agents in terms of low cost, easy injection, high sealing effect, and good oil displacement effect.

[0006] The purpose of this invention is to provide an oil displacement agent that is low in cost, easy to inject, has a high sealing effect, and a good oil displacement effect, and its application.

[0007] Solution for solving the problem

[0008] To address the aforementioned problems, the inventors conducted long-term and in-depth research and proposed to enhance particle capture and aggregation through particle-polymer interaction, thereby improving blockage diversion performance and increasing oil displacement efficiency, thus completing this invention.

[0009] Specifically, the present invention solves the problems of the present invention through the following solutions.

[0010] [1] An oil displacement agent comprising the following:

[0011] (A) A particulate suspension comprising particles and water, wherein the mass fraction of the particles is 200-2000 ppm; and

[0012] (B) A polymer solution comprising a polymer and water, wherein the polymer has a mass fraction of 0.01 to 10 ppm, and the polymer is one of the following (B1), (B2), or (B3):

[0013] (B1) Ionic polymer, wherein the ionic polymer is a cationic polymer or anionic polymer, wherein the charge of the ionic groups on the polymer molecular chain is opposite to the charge of the particle surface;

[0014] (B2) A mixture of cationic and anionic polymers;

[0015] (B3) Nonionic polymers that have undergone natural aging.

[0016] [2] According to the oil displacement agent described in [1], the volume ratio of (A) particulate suspension to (B) polymer solution is 1: (1~5).

[0017] [3] According to the oil displacement agent of [1], wherein the particles are selected from one or more of silica particles, polymer microspheres, clay mineral particles, calcium carbonate particles, cellulose nanocrystals, and chitosan-based particles; and the average diameter of the particles is 0.1~10μm.

[0018] [4] According to the oil displacement agent described in [1], wherein the (B1) ionic polymer is one or more selected from cationic polyacrylamide, anionic polyacrylamide, and xanthan gum; the weight-average molecular weight of the (B1) ionic polymer is 2 million to 8 million; and the degree of ionization of the (B1) ionic polymer is 20% to 40%.

[0019] [5] According to the oil displacement agent of [1], wherein the cationic polymer of (B2) is cationic polyacrylamide; the weight-average molecular weight of the cationic polymer of (B2) is 6 million to 10 million; and the degree of ionization of the cationic polymer of (B2) is 20% to 40%.

[0020] The anionic polymer of (B2) is anionic polyacrylamide and / or xanthan gum; the weight-average molecular weight of the anionic polymer of (B2) is 6 million to 10 million; the degree of ionization of the anionic polymer of (B2) is 20% to 40%.

[0021] [6] According to the oil displacement agent described in [1], wherein the nonionic polymer of (B3) is nonionic polyacrylamide, and the weight-average molecular weight of the nonionic polyacrylamide of (B3) is 10 million to 20 million; and the natural aging time is more than 1 month.

[0022] [7] According to the oil displacement agent of [1], wherein the polymer in the polymer solution of (B) has a mass fraction of 0.1 to 8 ppm.

[0023] [8] According to the oil displacement agent of [1], in the case where the polymer is a mixture of (B2) cationic polymer and anionic polymer, the content of polymers whose ionic groups have the opposite charge to the charge of the particle surface is greater than that of polymers whose ionic groups have the same charge as the particle surface. Preferably, the content of polymers whose ionic groups have the opposite charge to the charge of the particle surface is 1.05 to 1.5 times that of polymers whose ionic groups have the same charge as the particle surface.

[0024] [9] An oil displacement method comprising the following steps:

[0025] Inject the polymer solution of (B) in any one of the displacement agents according to [1] to [8] into the reservoir, and then inject the particulate suspension of (A) in any one of the displacement agents according to [1] to [8].

[0026]

[10] An oil displacement method comprising the following steps:

[0027] The (A) particulate suspension and (B) polymer solution in any one of [1] to [8] are mixed, and the resulting mixture is injected into the reservoir; wherein the polymer in the (B) polymer solution is (B2) or (B3).

[0028] The effects of the invention

[0029] The oil displacement agent of this invention is low in cost, easy to inject, highly effective in plugging, and provides excellent oil displacement. In this invention, only a trace amount of polymer aggregates is needed to significantly enhance particle capture and aggregation through particle-polymer interactions, improving plugging and diversion performance and increasing oil displacement efficiency. Due to the extremely low polymer concentration used, it is economical, with costs far lower than conventional polymer flooding, and the cost increase compared to single-particle suspension flooding is almost negligible. Simultaneously, the prepared polymer aggregates can significantly enhance the particle plugging effect through the formation of a special banded aggregation structure, showing great application potential. Attached Figure Description

[0030] Figure 1 (a) is a schematic diagram of the construction of the single cylindrical structure microfluidic chip used in the single cylindrical structure experiment;

[0031] Figure 1 (b) is the image of the final moment recorded in the single cylindrical structure experiment;

[0032] Figure 2 The image shows the final moment recorded in the single cylindrical structure experiment;

[0033] Figure 3 This is an image of the final moment recorded during the array porous media experiment;

[0034] Figure 4 (a) is a schematic diagram of the structure and a two-dimensional pore size distribution of the porous medium model of the reservoir chip used in the oil displacement experiment;

[0035] Figure 4 (b) is an image of the final state recorded in the oil displacement experiment of the porous medium micromodel of the reservoir chip;

[0036] Figure 5 (a) is an image of the banded aggregate structure formed inside the porous medium at the final moment in the oil displacement experiment using a particle-polymer aggregate composite system in the porous medium micromodel of the oil reservoir chip.

[0037] Figure 5 (b) shows the pressure difference evolution curves at the inlet and outlet ends in the oil displacement experiment conducted using a particle-polymer aggregate composite system in the porous medium micromodel of the reservoir chip. Detailed Implementation

[0038] The present invention will now be described in detail. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

[0039] In this specification, unless otherwise expressly stated, the “molecular weight” described for polymers refers to the weight-average molecular weight, which can be determined, for example, by gel permeation chromatography (GPC) based on polystyrene standards.

[0040] In this specification, "room temperature" refers to a temperature in the range of 15~35 ℃, preferably 25 ℃.

[0041] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0042] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0043] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0044] In this specification, the terms "optionally" or "optionally" are used to indicate the use or non-use of certain substances, components, procedures, application conditions, etc.

[0045] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" indicates weight or mass percentage.

[0046] In this specification, references to "preferred embodiments," "implementation methods," etc., mean that a specific element (e.g., feature, structure, property, and / or characteristic) related to that embodiment is included in at least one of the embodiments described herein, and may or may not be present in other embodiments. Furthermore, it should be understood that the elements may be combined in any suitable manner in various embodiments.

[0047] <Oil displacement agent>

[0048] One object of the present invention is to provide an oil displacement agent comprising the following:

[0049] (A) A particulate suspension comprising particles and water, wherein the mass fraction of the particles is 200-2000 ppm; and

[0050] (B) A polymer solution comprising a polymer and water, wherein the polymer has a mass fraction of 0.01 to 10 ppm, and the polymer is one of the following (B1), (B2), or (B3):

[0051] (B1) Ionic polymer, wherein the ionic polymer is a cationic polymer or anionic polymer, wherein the charge of the ionic groups on the polymer molecular chain is opposite to the charge of the particle surface;

[0052] (B2) A mixture of cationic and anionic polymers;

[0053] (B3) Nonionic polymers that have undergone natural aging.

[0054] The oil displacement agent of this invention forms polymer aggregates that interact with particles to create a particle-polymer aggregate composite system, thereby enhancing particle capture and aggregation, improving blockage and diversion performance, and increasing oil displacement efficiency. The polymer aggregates in this invention are fundamentally different from conventional cross-linked polymer microspheres or polymer solutions based on the characteristics described herein (including but not limited to their preparation method and electrical characteristics). They exist between a strongly cross-linked gel state and a dispersed monomolecular state in solution, and are also different from a flocculated sedimentation state, but rather in a very weakly physically cross-linked state, exhibiting a loose network structure and viscoelastic fluidization behavior.

[0055] The oil displacement agent of the present invention is a two-component formulation: (A) a particulate suspension and (B) a polymer solution. These two agents can be mixed before use, or they can be injected into the reservoir separately without pre-mixing. The method of using the oil displacement agent of the present invention can be found in the oil displacement method described below.

[0056] In some embodiments, the volume ratio of (A) particulate suspension to (B) polymer solution is 1:(1~5), preferably 1:(1~4).

[0057] The following describes in detail various aspects of the oil displacement agent of the present invention.

[0058] (A) Particle suspension

[0059] In this invention, various particles commonly used in oil displacement agents can be used as the particles, including, for example, one or more of the following: silica particles, polymer microspheres, clay mineral particles, calcium carbonate particles, cellulose nanocrystals, and chitosan-based particles. The polymer microspheres can be polyacrylamide microspheres, polystyrene microspheres, etc.; the clay mineral particles can be montmorillonite particles, kaolinite particles, etc.

[0060] These particles typically carry a trace amount of charge naturally on their surfaces. The sources of charge on the particle surface include ionization of surface groups and adsorption of salt ions. For example, the aforementioned silica particles and polymer microspheres are usually negatively charged (but can be positively charged through, for example, amino modification), clay mineral particles are usually strongly negatively charged, calcium carbonate particles are pH-sensitive and can be positively or negatively charged, cellulose nanocrystals are negatively charged, and chitosan-based particles are usually positively charged.

[0061] The particle size is suitable for formulation into an aqueous suspension, for example, the average particle size can be 0.1~10 μm, preferably 0.5~8 μm, more preferably 0.8~5 μm.

[0062] Preferably, the mass fraction of particles in the particle suspension is 200~2000 ppm, more preferably 300~1500 ppm, and even more preferably 400~1000 ppm.

[0063] Particle suspensions can be prepared by conventional methods, such as mixing particles with water and stirring thoroughly.

[0064] (B) Polymer solution

[0065] In the polymer solution, the polymer mass fraction is 0.01~10 ppm, preferably 0.1~8 ppm, more preferably 0.5~5 ppm. Preferably, the polymer mass fraction is less than 1% of the mass fraction of particles in the particulate suspension, more preferably less than 0.5%. When the polymer concentration is much lower than the particle concentration, the particle-polymer aggregate composite system can self-grow on the rock surface to form a special banded aggregate structure to enhance the sealing effect. At the same time, the low polymer concentration can also avoid negative effects such as particle flocculation and injection difficulties, and significantly reduce costs. Preferably, the polymer mass fraction is more than 0.001% of the mass fraction of particles in the particulate suspension, more preferably more than 0.01%, more preferably more than 0.05%, and even more preferably more than 0.1%. By making the polymer concentration within the above range, it is beneficial to the formation of the particle-polymer aggregate composite system and improve the sealing effect.

[0066] (B1) Ionic polymers

[0067] In some embodiments, the polymer in the polymer solution (B) is a (B1) ionic polymer, i.e., a cationic or anionic polymer. In a (B1) ionic polymer, the charge of the ionic groups on the molecular chain is opposite to the charge of the particle surface. For example, if the particle surface is negatively charged, the (B1) ionic polymer can be a cationic polymer; if the particle surface is positively charged, the (B1) ionic polymer can be an anionic polymer.

[0068] In these implementations, particle-polymer aggregate composite systems are formed by triggering aggregation through electrostatic interactions between the particles and the ionic polymer by making the particles have opposite electrical properties to the ionic polymer.

[0069] In some embodiments, (B1) the ionic polymer is one or more selected from cationic polyacrylamide, anionic polyacrylamide, and xanthan gum. Examples of cationic polyacrylamide include copolymers of acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DMC). Examples of anionic polyacrylamide include copolymers of acrylamide (AM) and acrylic acid (AA) and hydrolyzed polyacrylamide.

[0070] Preferably, the weight-average molecular weight of (B1) ionic polymer is 2 million to 8 million, more preferably 3 million to 7 million, and even more preferably 4 million to 6 million.

[0071] Preferably, the degree of ionization of (B1) ionic polymer is 20-40%, more preferably 25-30%.

[0072] In this article, the “degree of ionicity” described for various ionic polymers refers to the molar percentage of monomer units (structural units) with ionic groups in the polymer chain to the total number of monomer units (structural units).

[0073] (B2) A mixture of cationic and anionic polymers

[0074] In some embodiments, (B) the polymer solution contains a mixture of (B2) cationic and anionic polymers. In these embodiments, the cationic and anionic polymers pre-form polymer aggregates through electrostatic attraction and form a particle-polymer aggregate composite system upon contact with the particles.

[0075] Preferably, the content of polymers with ionic groups on the molecular chain having opposite charges to those on the particle surface is greater than that of polymers with ionic groups having the same charges as those on the particle surface. For example, if the particle surface is negatively charged, the content of the cationic polymer is greater than that of the anionic polymer in a mixture of (B2) cationic and anionic polymers; if the particle surface is positively charged, the content of the anionic polymer is greater than that of the cationic polymer in a mixture of (B2) cationic and anionic polymers. Thus, in addition to forming aggregates through the mixing of cationic and anionic polymers, the excess polymer molecules with opposite charges can also aggregate through electrostatic interactions between particles and polymers, as described above, to form a particle-polymer aggregate composite system.

[0076] Preferably, the content of polymers whose ionic groups have the opposite charge to that of the particle surface is 1.05 to 1.5 times that of polymers whose ionic groups have the same charge as that of the particle surface, more preferably 1.1 to 1.4 times, and more preferably 1.15 to 1.3 times.

[0077] Preferably, the cationic polymer of (B2) is cationic polyacrylamide; specifically, copolymers of acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DMC) can be listed.

[0078] Preferably, the weight-average molecular weight of the cationic polymer of (B2) is 6 million to 10 million, more preferably 7 million to 9 million.

[0079] Preferably, the degree of ionization of the cationic polymer of (B2) is 20-40%, more preferably 25-35%.

[0080] Preferably, the anionic polymer of (B2) is anionic polyacrylamide and / or xanthan gum. Specific examples of anionic polyacrylamide include copolymers of acrylamide (AM) and (meth)acrylic acid (AA), hydrolyzed polyacrylamide, etc.

[0081] Preferably, the weight-average molecular weight of the anionic polymer of (B2) is 6 million to 10 million, more preferably 7 million to 9 million.

[0082] Preferably, the degree of ionization of the anionic polymer of (B2) is 20-40%, more preferably 25-35%.

[0083] (B3) Naturally aged nonionic polymers

[0084] In some embodiments, the polymer in (B) the polymer solution is (B3) a naturally aged nonionic polymer. In these embodiments, the nonionic polymer forms polymer aggregates during natural aging through the attraction of van der Waals forces and hydrogen bonds, and forms a particle-polymer aggregate composite system upon contact with particles.

[0085] Preferably, (B3) the nonionic polymer is nonionic polyacrylamide.

[0086] Preferably, the molecular weight of the (B3) nonionic polymer is 10 million to 20 million, more preferably 17 million to 19 million.

[0087] Preferably, the nonionic polymer is prepared into an aqueous solution and then subjected to natural aging to obtain polymer solution (B).

[0088] Preferably, the natural aging time is more than one month, more preferably more than 1.5 months. From an efficiency perspective, the natural aging time is preferably less than 5 months, more preferably less than 4 months, for example less than 3 months.

[0089] Preferably, natural aging is carried out at a temperature of 20~40℃, more preferably 25~30℃.

[0090] Preferably, natural aging is carried out under light-protected conditions.

[0091] Preferred implementation scheme

[0092] In some preferred embodiments, the oil displacement agent of the present invention comprises: (A) a particulate suspension and (B) a polymer solution, wherein the polymer in the (B) polymer solution is (B1). In these preferred embodiments, aggregation is triggered by electrostatic interaction between the particles and the ionic polymer to form a particle-polymer aggregate composite system.

[0093] In some preferred embodiments, the oil displacement agent of the present invention comprises: (A) a particulate suspension and (B) a polymer solution, wherein the polymer in the (B) polymer solution is (B2) or (B3). In these preferred embodiments, the polymer in the polymer solution is pre-formed into aggregates and forms a particulate-polymer aggregate composite system upon contact with the particles.

[0094] In some preferred embodiments, the oil displacement agent of the present invention comprises: (A) a particulate suspension and (B) a polymer solution, wherein the surface of the particulates is negatively charged, and the polymer in the (B) polymer solution is a cationic polyacrylamide.

[0095] In some preferred embodiments, the oil displacement agent of the present invention comprises: (A) a particulate suspension and (B) a polymer solution, wherein the polymer in the (B) polymer solution is a mixture of (B2) cationic polyacrylamide and anionic polyacrylamide.

[0096] In some preferred embodiments, the oil displacement agent of the present invention comprises: (A) a particulate suspension and (B) a polymer solution, wherein the polymer in the (B) polymer solution is (B3) naturally aged nonionic polyacrylamide.

[0097] (B) Method for preparing polymer solutions

[0098] The polymer solution (B) in this invention can be prepared by conventional methods, such as by mixing the polymer with water and optionally applying stirring to dissolve the polymer.

[0099] When the polymer in polymer solution (B) is (B2) or (B3), it is preferable to mix the polymer with water, stir thoroughly at 400-1000 rpm for 4-12 hours, let it stand, and then take the supernatant as polymer solution (B). By thoroughly stirring, letting it stand, and taking the supernatant, excessively large aggregates can be removed to avoid adversely affecting the effectiveness of the present invention.

[0100] <Oil removal methods>

[0101] The present invention also provides a method for oil displacement using the oil displacement agent of the present invention, particularly a method for enhancing oil recovery. As described above, the two agents of the oil displacement agent of the present invention can be pre-mixed and injected or injected separately.

[0102] One object of the present invention is to provide an oil displacement method comprising the following steps:

[0103] The polymer solution of (B) in the oil displacement agent of the present invention is injected into the oil reservoir, followed by the injection of the particulate suspension of (A) in the oil displacement agent of the present invention.

[0104] When injecting the (B) polymer solution, it is preferable to maintain a low injection rate (e.g., 10). -8 ~10 -5 (m / s) to promote the adsorption and accumulation of polymers on the rock surface. When injecting the (A) particle suspension, a relatively high injection rate (e.g., 10 m / s) is preferred. -5 ~10 -3(m / s) to promote the formation and extension of particle-polymer ribbon-like aggregate structures.

[0105] Preferably, the oil displacement method of the present invention includes the steps of injecting multiple (e.g., 2 to 20) polymer solutions of the oil displacement agent of the present invention into the reservoir, followed by the injection of a suspension of particles (A) of the oil displacement agent of the present invention. Alternatively, the oil displacement method of the present invention includes the steps of alternately injecting polymer solutions of the oil displacement agent of the present invention and suspensions of particles (A) of the oil displacement agent of the present invention into the reservoir. Each injection of polymer solution (B) followed by injection of particle suspension (A) is referred to as an alternating injection unit, and the oil displacement method of the present invention includes 2 to 20 alternating injection units.

[0106] More preferably, the injection pressure is monitored while injecting the (A) particle suspension. When the injection pressure no longer increases (indicating that the aggregate structure and particle capture amount have basically stabilized), the injection of the (A) particle suspension is stopped, and then the injection of the (B) polymer solution in the next alternating injection unit begins.

[0107] One object of the present invention is to provide an oil displacement method comprising the following steps:

[0108] The (A) particulate suspension and (B) polymer solution in the oil displacement agent according to the present invention are mixed, and the resulting mixture is then injected into the reservoir; wherein the polymer in the (B) polymer solution is (B2) or (B3).

[0109] Since the polymer in the polymer solution is (B1), mixing the particulate suspension with the polymer solution easily forms flocculent dense aggregates, which is not conducive to achieving in-situ banded aggregation of the composite system. Therefore, in the method of pre-mixing and then injecting, the polymer in the (B) polymer solution is (B2) or (B3).

[0110] In this embodiment, since the polymer aggregates have already formed under pre-mixed injection conditions and easily adhere to the rock surface, a slightly higher injection rate (e.g., 10) can be used. -6 ~10 -3 (m / s) to improve harvesting efficiency.

[0111] Example

[0112] The present invention will be further illustrated below with reference to examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention. It should be understood that the present invention is not limited to the specific embodiments described below, and those skilled in the art can make various modifications or variations within the scope of the claims.

[0113] The following describes the two agents included in the preparation of the oil displacement agent.

[0114] (A) Particle suspension

[0115] The particles used were green fluorescent polystyrene microspheres with a diameter of 1 μm. The surface was not modified and was naturally negatively charged. The manufacturer was Tianjin Bestlite Chromatography Technology Development Center (product number 7-3-0100). A suspension with a mass fraction of 500 ppm was prepared using pure water.

[0116] (B) Polymer solution

[0117] (B-1) Prepare an aqueous solution of cationic polyacrylamide with a mass fraction of 1 ppm, wherein the cationic polyacrylamide is a copolymer of acrylamide (AM) with a molecular weight of 5 million and acryloyloxyethyltrimethylammonium chloride (DMC) with an ionicity of 30%;

[0118] (B-2) Prepare a mixed solution of cationic polyacrylamide and anionic polyacrylamide in a mass ratio of 1.2:1, with a total mass fraction of 1 ppm; wherein the cationic polyacrylamide is a copolymer of acrylamide (AM) with a molecular weight of 8 million and acryloyloxyethyltrimethylammonium chloride (DMC) with an ionicity of 30%; and the anionic polyacrylamide is a copolymer of acrylamide (AM) with a molecular weight of 8 million and acrylic acid (AA) with an ionicity of 30%.

[0119] (B-3) Prepare a nonionic polyacrylamide aqueous solution with a mass fraction of 1 ppm. After preparation, place it in a clean wide-mouth bottle, seal it, and store it in the dark for 2 months for natural aging. The nonionic polyacrylamide is an acrylamide (AM) polymer with a molecular weight of 18 million.

[0120] (B-4) Prepare an aqueous solution of cationic polyacrylamide with a mass fraction of 50 ppm, wherein the cationic polyacrylamide is a copolymer of acrylamide (AM) with a molecular weight of 5 million and acryloyloxyethyltrimethylammonium chloride (DMC) with an ionicity of 30%;

[0121] (B-5) Prepare an aqueous solution of cationic polyacrylamide with a mass fraction of 1 ppb, wherein the cationic polyacrylamide is a copolymer of acrylamide (AM) with a molecular weight of 5 million and acryloyloxyethyltrimethylammonium chloride (DMC) with an ionicity of 30%;

[0122] All polymer solutions were stirred thoroughly at 450 rpm for 5 hours during preparation, and the supernatant was taken for use after standing.

[0123] <Performance Evaluation>

[0124] I. Experiment with a single cylindrical structure

[0125] like Figure 1As shown in (a), the single cylindrical microfluidic chip used in this experiment was prepared by photolithography of PDMS material. The microchannel has a length of 3.5 mm, a width of 2 mm, and a depth of 40 μm. There is a cylindrical obstacle in the center of the microchannel with a diameter of 50 μm and a depth the same as the depth of the microchannel.

[0126] In this experiment, an alternating injection method was used, employing a constant flow syringe pump (Harvard Pump 11 Elite) and a microsyringe (Hamilton). First, 2.5 mL of polymer solution was injected, followed by the particle suspension until the retention volume stabilized. The injection flow rate was 50 μL / min. Images were recorded 15 min after injection. The microscope used was a Nikon SMZ18 in fluorescence imaging mode, with a magnification of 13.5x and an image resolution of 0.22 μm / pixel.

[0127] Experiments were conducted using the polymer solutions (B-1) to (B-5) described above, and the results are as follows: Figure 1 (b) and Figure 2 As shown in the figure, the bright spots are the retained particles.

[0128] Typically, because particles cannot directly block the channels, the particle retention in a single cylindrical structure obtained by directly injecting a particle suspension is almost negligible; for example... Figure 1 As shown in (b), the composite system of particle-polymer aggregates can significantly enhance particle retention. Polymer solutions with a polymer concentration of 1 ppm (B-1), (B-2) and (B-3) all resulted in the retention particles forming an ideal banded aggregate structure, but the specific aggregation intensity varied due to the different interaction types.

[0129] The choice of polymer concentration has a crucial impact on the formation of banded aggregate structures; for example... Figure 2 As shown, in the electrostatic interaction between negatively charged polystyrene microspheres and cationic polyacrylamide aqueous solution, when the polymer concentration is too high (50 ppm), the band structure is weakened, and particle flocculation begins to occur in other areas of the channel (the inlet shown in the figure), making it difficult to continue injection. When the polymer concentration is too low (1 ppb), the particles can only form an adhesive layer on the surface, and the retention is relatively limited.

[0130] II. Experiments with Arrayed Porous Media

[0131] The microfluidic chip with an array porous dielectric structure used in this experiment was fabricated using PDMS material by photolithography. Its structure is similar to that of the single-cylinder microfluidic chip used in the single-cylinder structure experiment, except that there are multiple cylindrical obstacles within the microchannels. The microchannels are 3.5 mm long, 2 mm wide, and 40 μm deep. The cylinders have a diameter of 150 μm and a depth matching the microchannel depth, arranged in a uniformly spaced pattern. This experiment used four different array structures (fluid flowing between the cylinders) with spacings of 350 μm, 100 μm, 50 μm, and 20 μm.

[0132] In this experiment, the injection method was pre-mixed injection (the instrument used for injection was the same as that used in the single-cylinder structure experiment). The mixing method involved mixing equal volumes of the particle suspension and the polymer solution, using the aforementioned polymer solution (B-3). The injection flow rate was 10 μL / min. Images were recorded 20 min after injection. The microscope used was a Nikon SMZ18, in fluorescence imaging mode, with a magnification of 5x and an image resolution of 0.59 μm / pixel.

[0133] Experiments were conducted on microfluidic chips with arrayed porous dielectric structures using the four array structures described above, and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that, under the same conditions, as the cylinder spacing decreases (corresponding to the decrease in the pore size of the porous medium), the ribbon-like aggregate structure changes from a suspended mode to a self-stabilizing bridging mode; under the condition of a spacing of 20 μm (still much larger than the particle size), the particle-polymer aggregate composite system can already achieve effective pore sealing, indicating that the sealing ability is far superior to that of a single particle system.

[0134] III. Oil Displacement Experiments Using Porous Media Micromodels on Reservoir Chips

[0135] The structure of the porous media model of the reservoir chip used in this experiment was generated by a four-parameter random algorithm according to the description in literature CN111060428A. The structure porosity is 40%, and the rock matrix is ​​divided into two levels: large rock particles and small rock particles, with a volume ratio of 1:2 and average sizes of 300μm and 60μm, respectively. Figure 4(a) shows the structural schematic and two-dimensional pore size distribution of the obtained reservoir chip porous media model. It can be seen that the structure has a wide pore size distribution and heterogeneous characteristics, which can effectively simulate real reservoir oil displacement conditions. After generating the porous media structure, silicon material was used, and inductively coupled plasma-deep reactive ion etching was employed to obtain the corresponding microfluidic chip. The channel length is 8 mm, the width is 6 mm, and the depth is 40 μm. The rock matrix portion is the solid region, and the other portion is the pore channel region. A pressure sensor (Fluigent, MFCS-8C) was connected at the chip inlet, and the outlet was kept at atmospheric pressure. The pressure sensor output value was the inlet and outlet pressure difference.

[0136] In each experiment, oil (fluorescently stained n-decane, dyed with 100 ppm Nile Red) was continuously injected into the porous medium until all air was expelled. Subsequently, in each experiment, pure water (water-driven), pure particle suspension (particle suspension-driven), and a particle-polymer aggregate composite system (same as in the array porous medium experiment, (A) + (B-3), particle-polymer aggregate composite-driven) were injected, with a constant injection flow rate of 1 μL / min. The instruments used for injecting the fluids were the same as in the single-cylinder structure experiment. Images were taken continuously at 2-second intervals using a Nikon SMZ18 microscope in fluorescence imaging mode, with a magnification of 1.5x and an image resolution of 1.98 μm / pixel.

[0137] During the experiment, it was noted that the fluorescence intensity of the oil phase was much greater than that of the particulate suspension under the same conditions. Therefore, the influence of particulate fluorescence during image processing can be ignored. For the captured images, binarization was performed and subtracted from the image of saturated oil at the initial moment. The non-zero value in the binarized image represents the area occupied by the water phase at that moment. Dividing this area by the total area of ​​the pore space gives the saturation at that moment. When the saturation change after 10 minutes of injection (corresponding to 10 PV) is less than 1%, the final state is considered to have been reached, and the saturation at this point is taken as the recovery rate. The phase distribution obtained from the fluorescence image of the final state after the above image processing is as follows: Figure 4 As shown in (b).

[0138] Depend on Figure 4 As can be seen from (b), since the size of the particles used is much smaller than the average pore size of the porous medium, the recovery rate of the pure particle suspension is only increased by 3%, while the recovery rate of the particle-polymer aggregate composite system is increased by 18%, showing a significant improvement effect.

[0139] Figure 5(a) shows the banded aggregate structure formed inside the porous medium at the final moment in the experiment using a particle-polymer aggregate composite system, captured by bright-field imaging mode (the black stripes are the retained particles; bright-field imaging mode is used here to facilitate direct visualization of the particle morphology in the pore space), indicating that the composite system promotes particle retention during the multiphase displacement process. Figure 5 Figure (b) shows the pressure difference evolution curves at the inlet and outlet ends, which shows that the improved sealing effect of the composite system leads to an increase in pressure and continuous fluctuations.

[0140] Industrial availability

[0141] The oil displacement agent and oil displacement method of the present invention can be widely used to improve oilfield recovery.

Claims

1. An oil displacement agent, characterized in that, Including the following: (A) A particulate suspension comprising particles and water, wherein the mass fraction of the particles is 200-2000 ppm; and (B) A polymer solution comprising a polymer and water, wherein the polymer has a mass fraction of 0.01 to 10 ppm, and the polymer is one of the following (B1), (B2), or (B3): (B1) Ionic polymer, wherein the ionic polymer is a cationic polymer or anionic polymer, wherein the charge of the ionic groups on the polymer molecular chain is opposite to the charge of the particle surface; (B2) A mixture of cationic and anionic polymers; (B3) Nonionic polymers that have undergone natural aging.

2. The oil displacement agent according to claim 1, characterized in that, The volume ratio of (A) particulate suspension to (B) polymer solution is 1:(1~5).

3. The oil displacement agent according to claim 1, characterized in that, The particles are selected from one or more of silica particles, polymer microspheres, clay mineral particles, calcium carbonate particles, cellulose nanocrystals, and chitosan-based particles; the average diameter of the particles is 0.1~10μm.

4. The oil displacement agent according to claim 1, characterized in that, The (B1) ionic polymer is selected from one or more of cationic polyacrylamide, anionic polyacrylamide, and xanthan gum; the weight-average molecular weight of the (B1) ionic polymer is 2 million to 8 million; and the degree of ionization of the (B1) ionic polymer is 20% to 40%.

5. The oil displacement agent according to claim 1, characterized in that, The cationic polymer of (B2) is cationic polyacrylamide; the weight-average molecular weight of the cationic polymer of (B2) is 6 million to 10 million; the degree of ionization of the cationic polymer of (B2) is 20% to 40%. The anionic polymer of (B2) is anionic polyacrylamide and / or xanthan gum; the weight-average molecular weight of the anionic polymer of (B2) is 6 million to 10 million; the degree of ionization of the anionic polymer of (B2) is 20% to 40%.

6. The oil displacement agent according to claim 1, characterized in that, The nonionic polymer of (B3) is nonionic polyacrylamide, and the weight-average molecular weight of the nonionic polyacrylamide of (B3) is 10 million to 20 million; the natural aging time is more than 1 month.

7. The oil displacement agent according to claim 1, characterized in that, The polymer in the (B) polymer solution has a polymer mass fraction of 0.1~8 ppm.

8. The oil displacement agent according to claim 1, characterized in that, In the case where the polymer is a mixture of (B2) cationic and anionic polymers, the content of polymers in which the charge of the ionic groups is opposite to that of the particle surface is greater than that of polymers in which the charge of the ionic groups is the same as that of the particle surface. Preferably, the content of polymers in which the charge of the ionic groups is opposite to that of the particle surface is 1.05 to 1.5 times that of polymers in which the charge of the ionic groups is the same as that of the particle surface.

9. An oil displacement method, characterized in that, Includes the following steps: The polymer solution of (B) in the oil displacement agent according to any one of claims 1 to 8 is injected into the reservoir, followed by the injection of the particulate suspension of (A) in the oil displacement agent according to any one of claims 1 to 8.

10. An oil displacement method, characterized in that, Includes the following steps: The (A) particulate suspension and (B) polymer solution in the oil displacement agent according to any one of claims 1 to 8 are mixed, and the resulting mixture is then injected into the reservoir; wherein the polymer in the (B) polymer solution is (B2) or (B3).

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