PPG in-situ color development marking method and migration trajectory visual characterization method

Abstract

The invention relates to a PPG in-situ color development marking method and a migration track visual characterization method, specifically, on the basis of a color development mechanism realized by generating a precipitate, color development precipitant ions are pre-loaded in a swollen PPG three-dimensional network, then an in-situ reaction with subsequent color development ions is performed to generate an insoluble characteristic color precipitate, and the color development precipitant ions are pre-loaded in the swollen PPG three-dimensional network. Only stable and high-contrast dyeing is carried out on the PPG, and the background liquid in the pores still keeps the primary color or extremely light color, so that the migration front edge, the retention point and the plugging form of the PPG in the core porous medium are clearly and accurately revealed; the method effectively solves the problems of observation signal distortion and fuzzy background caused by falling of a marking agent in a traditional external dyeing marking method, enables an experimental result to be more persuasive, and provides extremely reliable visual evidence for accurately analyzing a deep profile control and displacement mechanism of PPG and evaluating migration and plugging performance of PPG.

Description

Technical Field

[0001] This disclosure relates to the field of enhanced oil recovery technology in oilfield development, specifically to a PPG in-situ colorimetric labeling method and a method for visualizing migration trajectories. Background Technology

[0002] Pre-crosslinked polymer gel particles (PPG), as key functional materials in deep oilfield regulation and water shut-off operations, play a crucial role in determining the effectiveness of deep fluid flow redirection and the extent of enhanced oil recovery through their dynamic migration path, selective retention location, and final sealing behavior within the complex pore structure of the formation after injection. Accurately elucidating this process is of paramount importance for optimizing PPG particle size design, concentration optimization, and injection process parameters.

[0003] However, the inherent opacity of formation rock media (such as sandstone and carbonate rocks) and the complexity of their occurrence environments (high temperature, high pressure, formation water salinity) make direct, in-situ observation of the actual behavior of PPG underground a long-standing technical challenge. Currently, the mainstream research method in the industry mainly relies on indoor physical simulation experiments, that is, conducting displacement experiments of PPG suspensions in sand-filled pipes or artificial / natural rock cores. By monitoring the changes in pressure difference and flow rate at the inlet and outlet ends during the displacement process, the macroscopic migration and plugging laws of PPG can be indirectly inverted. Although this method can obtain macroscopic parameters such as breakthrough pressure and plugging strength, it cannot intuitively reveal the three-dimensional distribution characteristics of PPG within the pore space, the heterogeneous response mechanism (such as the formation and plugging of dominant channels), and the details of particle-pore interactions.

[0004] To visualize the migration trajectory of PPGs, an external staining labeling method was attempted. The common practice is to stain the PPG suspension with a conventional water-soluble dye (such as methylene blue or Congo red) before displacement, and then trace the stained PPG to infer its path. However, this method has a serious drawback: because conventional dye molecules adhere to the PPG surface only through weak physical adsorption (such as van der Waals forces and electrostatic interactions), the bond between them is very weak. During prolonged displacement and continuous scouring by formation water, dye molecules easily desorb and detach from the PPG surface. These detached dye molecules dissolve in the displacement solution or formation water, staining the entire pore fluid background and creating severe background interference. This makes it difficult to clearly distinguish where the real PPG retention points (stained particle clusters) are and where the areas are merely stained by pore water when the core is cut open for observation. This seriously interferes with visual judgment and image analysis (such as digital image processing and color recognition), ultimately leading to significant deviations in the judgment of PPG migration paths, key retention locations, and effective plugging status, resulting in low reliability of the conclusions.

[0005] Therefore, developing a PPG staining method that can achieve a firm bond between the dye and PPG, effectively resist long-term scouring by formation fluids, and significantly reduce or eliminate background interference from the liquid phase has become an urgent technical requirement for accurately and intuitively characterizing the underground behavior of PPG, deepening the study of its microscopic mechanism of action, and thus scientifically optimizing the design scheme for plugging and regulating. Summary of the Invention

[0006] In view of this, this disclosure provides a PPG in-situ colorimetric labeling method and a method for visualizing the migration trajectory, which solves the problem that existing external staining labeling methods are unreliable due to poor staining, resulting in serious background interference, affecting visual discrimination and image analysis.

[0007] To achieve the aforementioned objectives, in a first aspect, the PPG in-situ colorimetric labeling method disclosed herein includes: PPG is immersed in an aqueous solution containing colorimetric precipitant ions, causing the PPG to swell and form a loose three-dimensional network structure. The colorimetric precipitant ions diffuse into the three-dimensional network structure, and the PPG loaded with colorimetric precipitant ions is obtained by filtration. A colorimetric ion solution is brushed or sprayed onto the surface of PPG loaded with colorimetric precipitant ions. The colorimetric precipitant ions and colorimetric ions react in situ within the three-dimensional network structure of PPG to generate a sparingly soluble precipitate with a characteristic color, thus obtaining PPG with in situ colorimetric labeling.

[0008] Preferably, the combination of the color-developing precipitant ion and the color-developing ion includes, but is not limited to, [Fe(CN)6]. 4− with Fe 3+ [Fe(CN)6] 4− With Cu 2+ CrO4 2− With Pb 2+ CrO4 2− With Ag + Fe(CN)6] 3− with Fe 2+ C4H7N2O 2− with Ni 2+ and MoO4 2− With PO4 3+ .

[0009] Preferably, the combination of the color-developing precipitant ion and the color-developing ion is [Fe(CN)6]. 4− with Fe 3+ [Fe(CN)6] 4− Provided by dissociation of potassium ferrocyanide aqueous solution, the Fe 3+ Provided by a soluble ferric salt solution.

[0010] Preferably, the soluble ferric salt includes, but is not limited to, ferric chloride, ferric nitrate, and ferric sulfate.

[0011] Preferably, the method of immersing PPG in an aqueous solution containing chromogenic precipitant ions, causing the PPG to swell and form a loose three-dimensional network structure, and allowing the chromogenic precipitant ions to diffuse and penetrate into the three-dimensional network structure, and then filtering to obtain PPG loaded with chromogenic precipitant ions, includes: PPG is immersed in a saturated or nearly saturated aqueous solution containing color-developing precipitant ions. After the color-developing precipitant ions diffuse and penetrate to a set degree, the PPG is filtered to separate it. The color-developing precipitant ions attached to the surface of the PPG are removed by washing with water to obtain PPG loaded with color-developing precipitant ions.

[0012] Preferably, the PPG is immersed in an aqueous solution containing colorimetric precipitant ions for 2-5 hours, and is subjected to low-speed stirring at 100-300 r / min to promote the diffusion and penetration of the colorimetric precipitant ions.

[0013] Preferably, the method for separating PPG and washing away the potassium ferrocyanide adhering to its surface includes: PPG is separated by filtration through a filter screen. The surface of PPG is then rinsed with deionized water at a flow rate of 5-10 mL / s for 10-30 seconds. The amount of rinsing water is 1-2 times the volume of PPG to prevent the ion of the color-developing precipitant from desorbing from the three-dimensional network structure of PPG.

[0014] Secondly, the PPG migration trajectory visualization representation method disclosed herein includes: PPG is in-situ coloredly labeled using any of the methods described in the first aspect. Core displacement experiments are conducted based on the in-situ coloredly labeled PPG. After the experiment, the core model is cut along the axial direction or the experimental design profile. The characteristic color on the cut section is used to visualize the migration trajectory of PPG inside the core.

[0015] Preferably, if the characteristic color on the cut section does not exhibit the set contrast, a color-developing ion solution is brushed or sprayed onto the cut section, and the color-developing ions react in situ with the color-developing precipitant ions, so that the characteristic color of PPG meets the set contrast.

[0016] Preferably, the color distribution on the cut section is recorded by visual observation, or by taking pictures with a set resolution optical camera or stereomicroscope / digital microscope system. The area, distribution uniformity, penetration depth and leading edge position along the flow direction of the characteristic color region are quantitatively extracted and analyzed using image analysis software to evaluate the transport performance, blocking effect and regulation mechanism of PPG.

[0017] The beneficial effects of this invention are: This disclosed PPG in-situ chromogenic labeling method utilizes diffusion to allow chromogenic precipitant ions to gradually penetrate into the three-dimensional cross-linked network structure of the swollen polymer gel particles. A chromogenic ion solution is then used to allow the chromogenic precipitant ions to meet and react with the chromogenic ions inside the PPG particles, generating a stable chromogenic precipitate in situ. This effectively constructs an "in-situ encapsulation" structure. On the one hand, the chromogenic precipitate is uniformly distributed inside the PPG, avoiding uneven loading on the PPG surface; on the other hand, due to the physical entanglement and spatial constraint of the polymer chains during the formation process, the chromogenic precipitate is firmly fixed in the PPG matrix, thus ensuring its stability during subsequent injection, migration, and formation scour. During the process, it is not easily detached due to fluid shearing or ion exchange; based on the above two reasons, since the chromogenic precipitate is firmly locked inside the PPG body, the migration trajectory of the chromogenic precipitate is obviously completely synchronized with the PPG particles as the carrier. Therefore, on the core model cutting section after the core displacement experiment, the visualized dyed area can truly and accurately reflect the migration path, retention position, accumulation morphology and blocking range of the PPG particles themselves. Therefore, the method of this invention can fundamentally solve the signal distortion and background blurring problems caused by the detachment of the marker in the traditional external dyeing and labeling method, and provide reliable visual evidence for studying the deep regulation and dispersal mechanism of PPG and evaluating its migration and blocking performance. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the specification, serve to illustrate the technical solutions of this disclosure.

[0019] Figure 1 This is a microscopic three-dimensional network structure diagram of PPG after swelling at the micrometer scale; Figure 2 This is a graph showing experimental data from an embodiment of this disclosure; Figure 3 This is a colorimetric diagram showing the migration pattern of PPG in the core after polymer injection until the pressure stabilizes and subsequent water flooding until the pressure stabilizes, according to an embodiment of this disclosure (a: blocked, b: unblocked, left end is the injection end, right end is the production end). Figure 4 This is a color diagram showing the migration pattern of PPG in the core during the continuous increase of core pressure in the polymer injection process until the critical point is reached by the outer rubber sleeve of the core (a: blocked, b: unblocked, left end is the injection end, right end is the extraction end). Detailed Implementation

[0020] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. Although various aspects of embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise. The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0021] To address the technical problems described in the background, the core technology of the PPG in-situ colorimetric labeling method disclosed in this invention lies in: Depend on Figure 1 As shown, the microscopic three-dimensional network structure of PPG after swelling resembles a dynamic molecular sieve, allowing the passage of small ions and water molecules, but physically blocking the outward migration of large particles. Therefore, based on the mechanism of achieving color development through precipitate formation, the color-developing precipitant ions react in situ with the color-developing ions to generate insoluble characteristic color precipitates, which are then loaded inside the PPG. On the one hand, since the precipitates are solid particles or aggregates, their size is much larger than that of a single ion and often larger than or close to the average grid size of the network. Therefore, they are "wrapped" within the three-dimensional network of PPG after swelling, meaning that the three-dimensional network of PPG after swelling physically blocks the outward migration of large characteristic color precipitate particles. On the other hand, during the formation and growth of the precipitates, they interact with the surrounding crisscrossing... In this process, misaligned polymer chains become entangled and interlocked, enveloping precipitate particles like a spider web. The particles become trapped between the cross-linking points of the network, requiring energy to break the elastic structure of the entire polymer network to release them. Therefore, the characteristic-colored precipitate particles will not detach during subsequent injection, migration, or formation water scouring due to fluid shearing, ion exchange, or competitive adsorption, ensuring the long-term stable binding of the precipitate used for color marking with the PPG particles. Furthermore, the characteristic-colored precipitate particles have extremely low solubility in water, with almost no pathway for them to redissolve into ions and diffuse out again; they can only exist as solid particles. These solid particles are firmly locked in by the network described above, preventing staining of the background fluid within the core pores. Based on these reasons, by generating characteristic-colored precipitates inside or on the surface of PPG, stable and high-contrast staining is achieved only on the PPG itself, while the background fluid within the pores remains its original color or a very light color. This clearly and accurately reveals the migration front, retention points, and blockage morphology of PPG in the porous core medium.

[0022] Based on the above-mentioned core technologies, the PPG in-situ colorimetric labeling method described in this disclosure adopts the following technical solution: PPG is immersed in an aqueous solution containing chromogenic precipitant ions, causing the PPG to swell and form a loose three-dimensional network structure. The chromogenic precipitant ions diffuse and penetrate into the three-dimensional network structure. The PPG loaded with chromogenic precipitant ions is then obtained by filtration. This method does not rely on electrostatic adsorption, so it is suitable for core pore media with different electrical environments, and the loaded ions are not easily lost due to ion exchange during subsequent displacement. The chromogenic ion solution is then brushed or sprayed onto the surface of the PPG loaded with chromogenic precipitant ions. The chromogenic precipitant ions react in situ with the chromogenic ions within the three-dimensional network structure of the PPG to generate a sparingly soluble precipitate with a characteristic color, thus achieving in-situ chromogenic labeling of the PPG.

[0023] In specific embodiments, the combination of the color-developing precipitant ions and the color-developing ions includes, but is not limited to, [Fe(CN)6]. 4− with Fe 3+ [Fe(CN)6] 4− With Cu 2+ CrO4 2− With Pb 2+ CrO4 2− With Ag + Fe(CN)6] 3− with Fe 2+ C4H7N2O 2− with Ni 2+ and MoO4 2− With PO4 3+ If the core displacement experiment uses a wastewater mixture, since the wastewater is pale yellow, to better distinguish this color, the precipitate should preferably be blue or another color clearly different from it. Therefore, the preferred combination of the chromogenic precipitant ions and the chromogenic ions is [Fe(CN)6]. 4− with Fe 3+ [Fe(CN)6] 4− Provided by dissociation of potassium ferrocyanide aqueous solution, the Fe 3+ It is provided by a soluble ferric salt solution; the soluble ferric salt includes, but is not limited to, ferric chloride, ferric nitrate and ferric sulfate; the concentration of the soluble ferric salt solution is 0.05 mol / L.

[0024] In a specific embodiment, the method of immersing PPG in an aqueous solution containing chromogenic precipitant ions, causing the PPG to swell and form a loose three-dimensional network structure, and allowing the chromogenic precipitant ions to diffuse and penetrate into the three-dimensional network structure to obtain PPG loaded with chromogenic precipitant ions, includes: The ion aqueous solution of the colorimetric precipitant is saturated or nearly saturated. PPG is immersed in the ion aqueous solution of the colorimetric precipitant to allow the PPG to swell fully. The colorimetric precipitant ions diffuse into the three-dimensional network structure of the swollen PPG through diffusion. After the colorimetric precipitant ions have fully penetrated, the PPG is filtered out and washed with water to remove the colorimetric precipitant ions attached to the surface, thus obtaining PPG loaded with colorimetric precipitant ions.

[0025] In a specific embodiment, the PPG is immersed in the ion aqueous solution of the colorimetric precipitant for 2-5 hours, and is accompanied by low-speed stirring at 100-300 r / min to promote the diffusion and penetration of the colorimetric precipitant ions.

[0026] In a specific embodiment, the method for separating PPG and washing away the surface-adhered colorimetric precipitant ions includes: PPG is separated by a filter screen. The surface of PPG is rinsed with deionized water at a flow rate of 5-10 mL / s for 10-30 seconds. The amount of rinsing water is 1-2 times the volume of PPG to prevent the ion of the color-developing precipitant from desorbing from the three-dimensional network structure of PPG.

[0027] The PPG migration trajectory visualization representation method provided in this disclosure includes: The PPG in-situ colorimetric labeling method described in this disclosure is used to perform in-situ colorimetric labeling of PPG. Core displacement experiments are conducted based on the in-situ colorimetric labeled PPG. After the experiment, the core model is cut along the axial direction or the experimental design profile. The characteristic color on the cut section is used to visualize the migration trajectory of PPG inside the core.

[0028] In a specific embodiment, if the characteristic color on the cut section does not present the set contrast, the color-developing ion solution is brushed or sprayed onto the cut section, and the color-developing ions and color-developing precipitant ions continue to react in situ until the characteristic color of PPG meets the set contrast.

[0029] In a specific embodiment, the color distribution on the cut section is recorded by visual observation, or by taking pictures with a set resolution optical camera or stereomicroscope / digital microscope system. The area, distribution uniformity, penetration depth and leading edge position along the flow direction of the characteristic color region are quantitatively extracted and analyzed using image analysis software to evaluate the transport performance, blocking effect and regulation mechanism of PPG.

[0030] The following are preferred embodiments of this disclosure. Example

[0031] This embodiment illustrates the process of visualizing and characterizing the migration trajectory of PPG using the method of this invention by performing in-situ colorimetric labeling of PPG and conducting displacement experiments based on the in-situ colorimetric labeled PPG. Specifically, it includes five steps: ion permeation loading of PPG with a colorimetric precipitant, reaction with the colorimetric ions to form internal precipitate, core displacement experiment, core sectioning and colorimetric observation, and PPG migration trajectory analysis and quantitative characterization. S1. PPG colorimetric precipitant ion-permeable loading Electronically neutral pre-crosslinked polymer gel particles (PPG) are immersed in a high-concentration potassium ferrocyanide (PG) aqueous solution. Utilizing the water-induced swelling and network structure expansion properties of PPG particles, driven by a high concentration gradient, ferrocyanide ions in the solution gradually diffuse into the internal voids and hydration layer of the swollen PPG particle network through free diffusion. By systematically controlling the concentration of the immersion solution, the ambient temperature, and the immersion time, a sufficient amount of ferrocyanide ions can be effectively "encapsulated" and "retained" within the three-dimensional network structure of the PPG particles.

[0032] In this embodiment, firstly, the high-concentration potassium ferrocyanide aqueous solution is prepared to be saturated or nearly saturated (approximately 0.05 mol / L) to provide maximum concentration driving force. If conventional short-term immersion or low-concentration solutions are used, the electrically neutral PPG is almost unable to effectively load the colorimetric precipitant ions due to the lack of electrostatic attraction and insufficient diffusion driving force. Then, to ensure sufficient ferrocyanide ions are effectively "encapsulated" and "retained" within the three-dimensional network structure of the PPG particles, the PPG particles are completely immersed in the prepared high-concentration potassium ferrocyanide aqueous solution and stirred for 2 hours. Under these conditions, the PPG particles swell sufficiently, allowing the ferrocyanide ions dissociated from the potassium ferrocyanide sufficient time to diffuse deep into the interior of the PPG particles. After stirring, the PPG particles are separated using a filter screen, and the surface is quickly rinsed with a small amount of deionized water. Prolonged rinsing should be avoided; only the free potassium ferrocyanide ions adhering to the surface are removed, retaining the [Fe(CN)6] loaded inside the PPG particles. 4− The ions were loaded with [Fe(CN)6]. 4− Wet PPG particles with ions.

[0033] S2. Reacts with colorimetric ions to form an internal precipitate. The above was loaded with [Fe(CN)6] 4− Wet PPG particles containing ions are contacted with a colorimetric ion solution. In this embodiment, a ferric chloride solution with a concentration of 0.05 mol / L is selected as the colorimetric ion solution to ensure sufficient colorimetric reaction and minimal background interference. During the contact process, the Fe in the colorimetric ion solution... 3+ The ions rapidly diffused into the interior of the PPG particles, interacting with the already loaded [Fe(CN)6]4− Ions undergo an in-situ chemical reaction, forming a sparingly soluble, brightly colored Prussian blue precipitate within the network structure of the PPG particles. This step completes the colorimetric labeling of PPG, firmly "locking" the label (precipitate) inside the PPG particles.

[0034] S3. Core Displacement Experiment The internal load [Fe(CN)6] prepared in step S1 4− PPG particles were prepared into a suspension of a certain concentration and injected into a square cast core model measuring 4.5 cm × 4.5 cm × 30 cm according to the standard core displacement experiment procedure. Displacement experiments were conducted under set displacement rates (e.g., 0.33 ml / min), temperatures (e.g., 45℃), and corresponding simulated formation brine conditions to realistically simulate the migration, retention, and plugging behavior of PPG particles in porous media. The displacement process could continue until the preset pressure differential and injection volume conditions were exceeded or reached. Specific displacement parameters are shown in Table 1 below. Figure 2 : Table 1: Experimental Data Parameter Table

[0035] S4. Core cutting and colorimetric observation After the displacement experiment, the core model was removed. To observe the distribution of PPG inside, the core was precisely cut along the axial direction or a specific profile to expose the fresh internal section. At this point, because the PPG particles were pre-loaded with Prussian blue precipitate, the deep blue or bluish-black PPG particles could be directly observed after cutting, clearly showing their migration path, retention location, accumulation morphology, and blocking range, with minimal background interference, thus achieving high-contrast differentiation between the PPG-marked area and the background.

[0036] In this embodiment, color development through in-situ precipitation is used to obtain... Figure 3 The diagram shows the migration patterns of PPG in the core after polymer injection until pressure stabilizes, followed by water flooding until pressure stabilizes (a: plugged, b: unplugged); and... Figure 4The diagram shows the migration pattern of PPG in the core as the core pressure continuously increases during polymer injection until it reaches the critical point borne by the outer sheath (a: blocked, b: unblocked). As can be seen from the two diagrams, in high-permeability large pores, the particle size is usually much smaller than the pore throat, so PPG can migrate freely or only experience brief, easily unblocked, weak retention, which is characterized as "unblocked". In medium- and low-permeability small pores, when the particle size matches the throat size, PPG forms a stable "bridging blockage," effectively sealing the dominant water flow channel; if the particles are much larger than the throat, they will be screened out at the inlet, forming an ineffective surface filter cake. More importantly, PPG is elastic and can "deform and pass" under pressure, thus achieving a dynamic migration process of "bridging blockage → pressurization → deformation breakthrough → deep re-blocking".

[0037] S5. PPG transport trajectory analysis and quantitative characterization Color distribution on core sections was recorded by visual observation, high-resolution optical cameras, or stereomicroscopes / digital microscopes. Deep blue / blue-black areas clearly indicate the migration paths, accumulation points, and plugging morphologies of PPG particles within the core. Using specialized image analysis software, the area, uniformity of distribution, depth of penetration, and leading edge position along the flow direction of the blue areas can be quantitatively extracted and analyzed, providing intuitive and reliable experimental data to evaluate PPG migration performance, plugging effectiveness, and modulatory mechanisms.

[0038] In summary, the effectiveness of traditional electrostatic adsorption-based loading methods highly depends on the electrical matching between the particle surface charge and the target ions. However, the chromogenic precipitant ion diffusion-penetration-PPG three-dimensional network encapsulation and retention mechanism employed in this invention fundamentally overcomes this limitation. Regardless of whether the target PPG particles are electrically neutral, positively charged, or negatively charged under specific mineralization conditions, high concentrations of target chromogenic precipitant ions can diffuse freely into the swollen PPG polymer three-dimensional network driven by the concentration gradient. This not only gives the method excellent universality, independent of particle surface electrical properties, applicable to various polymer gel systems, but also means that the chromogenic precipitant ions are loaded inside the three-dimensional network of the PPG particles, rather than merely adhering to the surface. Therefore, this invention effectively overcomes the shortcomings of existing dyeing techniques, such as easy staining agent detachment and significant background interference, forming a PPG particle labeling and color development method based on in-situ chemical reaction to generate insoluble color precipitates.

[0039] This method combines chemical colorimetric reactions with internal loading of PPG particles, greatly expanding the robustness of visual labeling technology in chemical agent research in complex reservoirs. This results in stable and vivid label colors, effectively improving the accuracy and clarity of PPG migration trajectory observation in displacement experiments.

[0040] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A PPG in-situ colorimetric labeling method, characterized in that, include: PPG is immersed in an aqueous solution containing colorimetric precipitant ions, causing the PPG to swell and form a loose three-dimensional network structure. The colorimetric precipitant ions diffuse into the three-dimensional network structure, and the PPG loaded with colorimetric precipitant ions is obtained by filtration. A colorimetric ion solution is brushed or sprayed onto the surface of PPG loaded with colorimetric precipitant ions. The colorimetric precipitant ions and colorimetric ions react in situ within the three-dimensional network structure of PPG to generate a sparingly soluble precipitate with a characteristic color, thus obtaining PPG with in situ colorimetric labeling.

2. The PPG in-situ colorimetric labeling method according to claim 1, characterized in that: The combination of the colorimetric precipitant ions and the colorimetric ions includes, but is not limited to, [Fe(CN)6]. 4− with Fe 3+ [Fe(CN)6] 4− With Cu 2+ CrO4 2− With Pb 2+ CrO4 2− With Ag + Fe(CN)6] 3− with Fe 2+ C4H7N2O 2− with Ni 2+ and MoO4 2− With PO4 3+ .

3. The PPG in-situ colorimetric labeling method according to claim 2, characterized in that: The combination of the colorimetric precipitant ion and the colorimetric ion is [Fe(CN)6]. 4− with Fe 3+ [Fe(CN)6] 4− Provided by dissociation of potassium ferrocyanide aqueous solution, the Fe 3+ Provided by a soluble ferric salt solution.

4. The PPG in-situ colorimetric labeling method according to claim 3, characterized in that: The soluble ferric salts include, but are not limited to, ferric chloride, ferric nitrate, and ferric sulfate.

5. The PPG in-situ colorimetric labeling method according to any one of claims 1-4, characterized in that, The method of immersing PPG in an aqueous solution containing chromogenic precipitant ions, causing the PPG to swell and form a loose three-dimensional network structure, and allowing the chromogenic precipitant ions to diffuse and penetrate into the three-dimensional network structure, and then filtering to obtain PPG loaded with chromogenic precipitant ions, includes: PPG is immersed in a saturated or nearly saturated aqueous solution containing color-developing precipitant ions. After the color-developing precipitant ions diffuse and penetrate to a set degree, the PPG is filtered to separate it. The color-developing precipitant ions attached to the surface of the PPG are removed by washing with water to obtain PPG loaded with color-developing precipitant ions.

6. The PPG in-situ colorimetric labeling method according to claim 5, characterized in that: The PPG is immersed in an aqueous solution containing colorimetric precipitant ions for 2-5 hours, and is stirred at a low speed of 100-300 r / min to promote the diffusion and penetration of the colorimetric precipitant ions.

7. The PPG in-situ colorimetric labeling method according to claim 5, characterized in that, The method for separating PPG and washing away the potassium ferrocyanide adhering to its surface includes: PPG is separated by filtration through a filter screen. The surface of PPG is then rinsed with deionized water at a flow rate of 5-10 mL / s for 10-30 seconds. The amount of rinsing water is 1-2 times the volume of PPG to prevent the ion of the color-developing precipitant from desorbing from the three-dimensional network structure of PPG.

8. A method for visualizing and representing the migration trajectory of PPGs, characterized in that, include: PPG is in-situ coloredly labeled using the method described in any one of claims 1-7. Core displacement experiments are conducted based on the in-situ coloredly labeled PPG. After the experiment, the core model is cut along the axial direction or the experimental design profile. The characteristic color on the cut section is used to visualize the migration trajectory of PPG inside the core.

9. The PPG transport trajectory visualization representation method according to claim 8, characterized in that: If the characteristic color on the cut section does not show the set contrast, the color-developing ion solution is brushed or sprayed onto the cut section, and the color-developing ions and color-developing precipitant ions continue to react in situ until the characteristic color of PPG meets the set contrast.

10. The PPG transport trajectory visualization representation method according to claim 8 or 9, characterized in that: Color distribution on the cut section is recorded by visual observation, or by taking pictures with a set resolution optical camera or stereomicroscope / digital microscope system. Image analysis software is used to quantitatively extract and analyze the area, distribution uniformity, penetration depth and leading edge position along the flow direction of the characteristic color region, so as to evaluate the transport performance, blocking effect and regulation mechanism of PPG.

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