Colored ultralow-density proppant for crack monitoring and preparation method of colored ultralow-density proppant

Abstract

The invention provides a colored ultralow-density proppant for crack monitoring and a preparation method, and belongs to the technical field of proppant preparation. The colored ultralow-density proppant comprises a flexible inner core, a dyed resin layer and an elastic shell layer which are sequentially arranged from inside to outside in a wrapping manner, wherein the flexible inner core is a shell particle and / or a kernel particle, a dyeing component is distributed in a porous structure of the shell particle and / or the kernel particle, and the dyeing component and the dyeing resin layer both comprise resin and oily pigment. According to the invention, agriculture and forestry solid waste fruit shells or kernels form a flexible inner core, and are not easy to break to cause exposure and fading; meanwhile, the dyeing component is adsorbed in the porous structure and on the outer surface of the shell or the kernel by utilizing the porous adsorption characteristic of the shell or the kernel, so that stable coloring is formed, and the fading of the proppant can be effectively prevented; in addition, the elastic shell layer is coated outside the dyeing resin layer, so that the proppant is further prevented from being broken in the pumping process.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of proppant preparation, and particularly relates to a colored ultra-low density proppant for fracture monitoring and a preparation method thereof. Background Art

[0002] With the rapid economic development, the consumption of oil and natural gas in various countries around the world is increasing day by day. However, with long-term exploitation, the reserves of limited mineral resources such as oil and natural gas are decreasing day by day, and the difficulty of oil and natural gas exploitation is also increasing. The resulting energy crisis has become an urgent problem to be solved. In order to extract oil and gas resources with higher yields, hydraulic fracturing technology has become one of the most important extraction technologies.

[0003] Hydraulic fracturing is an important measure for increasing production and injection in oil and gas fields, and has achieved good results in the stimulation and transformation of oil and gas reservoirs. It uses a ground high-pressure pump truck group to inject a high-viscosity liquid into the well, forming high pressure at the bottom of the well. When the bottom-hole pressure is greater than the formation fracture pressure, fractures are generated. Continuing to inject a sand-carrying fluid with proppant, the fractures extend forward and are filled with proppant. After shutting in and flowing back, the fractures close on the proppant, enabling the fractures to be supported, thereby forming a sand-filled fracture with high conductivity in the reservoir, and ultimately achieving the purpose of increasing production and injection. Since the successful experiment of hydraulic fracturing technology in the United States, this technology has become a key technology for increasing the production of oil and gas resources. The support situation of the fractures determines whether the oil and gas wells can produce stably and highly. Therefore, analyzing the fracture support situation has an important guiding role in improving fracturing technology. Currently, it mainly relies on microseismic detection, or electromagnetic, fluorescence, and radioactive tracer proppants. However, microseismic has a high cost and inconvenient operation. The current monitoring distance of tracer proppants is limited, and only the fracture support situation in the near-wellbore area can be monitored.

[0004] Therefore, it is necessary to develop new tracer proppants. In recent years, people have studied dyed proppants, mainly achieved by resin coating. Although it has been applied in the field, this kind of proppant is easy to break, making it difficult to identify during later analysis. In response to this, it is necessary to further develop a tracer proppant system that is not easy to break, fade, or have color layer peeling. Summary of the Invention

[0005] The present disclosure aims to at least solve one of the technical problems existing in the prior art, and provides a colored ultra-low density proppant for fracture monitoring and a preparation method thereof.

[0006] On the one hand, the present disclosure provides a colored ultra-low density proppant for fracture monitoring, including: a flexible inner core, a dyed resin layer, and an elastic outer shell layer, which are sequentially wrapped from the inside to the outside; wherein,

[0007] The flexible core uses shell particles and / or pit particles with a porous structure, and a dyeing component is distributed in the porous structure of the shell particles and / or pit particles;

[0008] Both the dyeing component and the dyeing resin layer include resin and oil-based pigments.

[0009] Optionally, the content of the resin is 40-60 parts by mass;

[0010] The content of the oil-based pigment is 10-30 parts by mass.

[0011] Optionally, the resin is epoxy resin or phenolic resin.

[0012] Optionally, when the resin is epoxy resin, the dyeing component further includes an active diluent.

[0013] Optionally, the shell particles are walnut shell particles or coconut shell particles;

[0014] The pit particles are peach pit particles.

[0015] Optionally, the particle size of the shell particles or pit particles is 0.106-0.85 mm.

[0016] Optionally, the elastic outer shell layer is formed by foaming epoxy resin or polyurethane resin.

[0017] Optionally, the thickness of the elastic outer shell layer is 10-50 μm.

[0018] On the other hand, the present disclosure provides a method for preparing the colored ultra-low density proppant described above, and the method includes:

[0019] Mix resin and oil-based pigment to form a dyeing component;

[0020] Mix shell particles or pit particles with the dyeing component, after aging treatment, mix it with a first curing agent, and after dispersion and heating treatment, obtain a flexible core layer. The dyeing component is distributed in the porous structure inside the flexible core and also on the outer surface of the flexible core to form a dyeing resin layer;

[0021] Mix the flexible core with epoxy resin or polyurethane resin, add a second curing agent, and after foaming and curing treatment, obtain the proppant.

[0022] Optionally, the time of the aging treatment is 20-28 h; and / or,

[0023] The temperature of the heating treatment is 110-130 °C, and the time is 1-3 h.

[0024] Optionally, the temperature of the curing treatment is 150-170 °C and the time is 1-3 h.

[0025] The present disclosure provides a colored ultra-low density proppant for fracture monitoring and a preparation method thereof. The colored ultra-low density proppant includes a flexible inner core, a dyed resin layer, and an elastic outer shell layer, which are sequentially wrapped from the inside to the outside; wherein, the flexible inner core uses fruit shell particles and / or fruit pit particles with a porous structure, and a dyeing component is distributed in the porous structure of the fruit shell particles and / or fruit pit particles; both the dyeing component and the dyed resin layer include resin and oil-based pigments. The present disclosure forms a flexible inner core with a porous structure from agricultural and forestry solid waste fruit shells or fruit pits, uses oil-soluble pigments in combination with flexible liquid resin to impregnate the fruit shells, and the pigments penetrate into the interior of the fruit shell particles or fruit pit particles, so that the flexible inner core is doped with a dyeing component, and it is not easy to break and cause exposed color fading; at the same time, a dyed resin layer and an elastic outer shell layer are further coated on the outer surface of the flexible inner core to further improve the dyeing effect and prevent the proppant from breaking during the pumping process. Description of the Drawings

[0026] Figure 1 is a schematic structural diagram of a colored ultra-low density proppant for fracture monitoring according to a specific embodiment of the present disclosure;

[0027] Figure 2 is a flow chart of a preparation method of a colored ultra-low density proppant for fracture monitoring according to a specific embodiment of the present disclosure. Specific Embodiments

[0028] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure, which are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present disclosure.

[0029] As Figure 1 shown, on the one hand, the present disclosure provides a colored ultra-low density proppant 100 for fracture monitoring, including: a flexible inner core 110, a dyed resin layer 120, and an elastic outer shell layer 130, which are sequentially wrapped from the inside to the outside; wherein, the flexible inner core 110 uses fruit shell particles 111 and / or fruit pit particles 112 with a porous structure, and a dyeing component 113 is distributed in the porous structure of the fruit shell particles 111 and / or fruit pit particles 112. Both the dyeing component and the dyed resin layer include resin and oil-based pigments. That is to say, the dyeing component formed by resin and oil-based pigments is distributed in both the porous structure and the outer surface of the flexible inner core, and the dyeing component on the outer surface forms a dyed resin layer.

[0030] In this embodiment, based on the fact that the shell particles and the pit particles have a pore structure, these pores are interconnected or exist independently, forming a complex pore network structure. Utilizing the porous adsorption characteristics of the shell or pit particles is conducive to adsorbing and loading liquid components such as epoxy resin and oil-based pigments, enabling the pigments to be adsorbed within the voids of the shell. In this way, by mixing the shell particles or pit particles with the dyeing components, the dyeing components can be evenly distributed in these pores, making them better adhere to the porous structure inside the shell or pit. At the same time, the dyeing components can also adhere to the outer surface of the shell or pit, forming a dyed resin layer to achieve stable coloring. Furthermore, when reacting with a curing agent and the like subsequently, a composite proppant structure with better performance is formed. Meanwhile, the pore structure will also have a certain impact on the properties of the proppant such as density and strength, which helps to improve the stability and flow conductivity of the proppant in the fracture to a certain extent. In addition, by wrapping an elastic outer shell layer outside the dyed resin layer, the overall strength and toughness of the proppant are improved, so that when it is subjected to downhole pressure, impact force, etc. during the pumping process, it is not easily broken or deformed, and it can prevent the shell particles or pit particles, dyeing components, etc. in the flexible core from being affected by formation fluids, temperature, etc., prevent the dyeing components from fading or falling off, ensure the tracer effect, facilitate accurate monitoring of the fracture situation, and at the same time can maintain the fracture flow conductivity to ensure the oil and gas production efficiency.

[0031] It should be noted that in this embodiment, the type and content of the resin are not specifically limited. For example, the resin can preferably be epoxy resin, or it can preferably be phenolic resin. Of course, it should be understood that when choosing epoxy resin, an active diluent needs to be further added to adjust the viscosity of the resin. The diluted resin and the pigment can be easily soaked into the voids of the nut shell or pit to achieve stable coloring.

[0032] In some preferred embodiments, the resin is preferably phenolic resin, and the content of this resin is 40 - 60 parts by mass.

[0033] In some other preferred embodiments, the resin is preferably epoxy resin, and its epoxy value can preferably be 0.44 - 0.51. The content of this resin is 40 - 60 parts by mass. Correspondingly, an active diluent (such as butyl glycidyl ether, phenyl glycidyl ether, allyl glycidyl ether, ethylene glycol diglycidyl ether, etc.) should also be added, and its content can be 10 - 30 parts. That is to say, the dyeing components include epoxy resin, active diluent, and oil-based pigment.

[0034] Further, the content of the oil-based pigment in this embodiment is 10 - 30 parts by mass. The oil-based pigment can preferably be an azo pigment. This type of pigment has high coloring power and bright colors, can provide obvious color markings for the proppant, and has good light fastness and chemical resistance, and can maintain color stability in different environments, which is beneficial for tracking and identifying the proppant during oil extraction and other processes. Of course, phthalocyanine pigments can also be preferably used. This type of pigment has excellent light fastness, weather resistance, acid and alkali resistance, and chemical stability, with bright colors and strong coloring power. Adding a small amount in the proppant can achieve a good dyeing effect, and can adapt to complex downhole chemical environments and is not easy to fade or change color. Of course, other oil-based pigments can also be selected, and no specific limitations are made here.

[0035] Furthermore, this embodiment does not make specific limitations on the type and particle size of the fruit shell particles or fruit pit particles. For example, the fruit shell particles can be walnut shell particles, coconut shell particles, and other nut shell particles, and the fruit pit particles can be peach pit particles, etc. The particle size of the fruit shell particles or fruit pit particles is 0.106 - 0.85 mm. The fruit shell particles or fruit pit particles within this particle size range have appropriate size and shape, enabling them to have a certain strength and wear resistance. At the same time, when stacked, they can form a relatively uniform structure and have a relatively stable bulk density.

[0036] It should be understood that in this embodiment, each nut shell or each fruit pit can be crushed to form particles with a particle size of 0.106 - 0.85 mm as the matrix of the flexible inner core for adsorbing the oil-based pigment, effectively reducing costs and improving waste utilization. Note that in this embodiment, fruit shell particles can be used, fruit pit particles can also be used, and multiple fruit shell particles and multiple fruit pit particles can also be used simultaneously, etc., and no specific limitations are made on this.

[0037] Furthermore, the elastic outer shell layer in this embodiment is formed by foaming epoxy resin or polyurethane resin. That is to say, epoxy resin and polyurethane resin are foamed to form the elastic outer shell layer for wrapping the flexible inner core, which can provide additional compressive strength for the proppant, prevent breakage and deformation, ensure that the proppant maintains a good supporting effect in the fracture, maintain the opening state of the fracture, and ensure the smooth extraction of oil and gas.

[0038] In some preferred embodiments, the thickness of the elastic outer shell layer is 10 - 50 μm. The elastic outer shell layer within this thickness range can provide just the right buffering effect. During the process of the proppant being lowered into the formation, etc., it can effectively absorb and disperse the external impact force, prevent the proppant from breaking due to collisions, etc., and at the same time, it will not be too soft as a whole due to being too thick, affecting the supporting effect, and can better maintain the integrity and stability of the proppant, ensuring that it plays a good supporting role and color maintenance in the fracture.

[0039] Such as Figure 2As shown, on the other hand of the present disclosure, a method S200 for preparing the color ultra-low density proppant described above is proposed, which specifically includes the following steps S210 to S230:

[0040] S210. Mix the resin and the oil-based pigment to form a dyed component.

[0041] Specifically, 40-60 parts by mass of epoxy resin and 10-30 parts by mass of active diluent are uniformly mixed, and then 10-30 parts by mass of oil-based pigment are added and stirred evenly to form a dyed component. Alternatively, 40-60 parts by mass of phenolic resin are mixed with 10-30 parts by mass of oil-based pigment to form a dyed component.

[0042] S220. Mix the fruit shell particles and / or fruit core particles with the dyed component. After aging treatment, mix it with the first curing agent, and after dispersion and heat treatment, a flexible inner core is obtained. The dyed component is distributed in the porous structure inside the flexible inner core and also on the outer surface of the flexible inner core to form a dyed resin layer.

[0043] Specifically, 400-600 parts by mass of fruit shell particles and / or fruit core particles are mixed with the dyed component, sealed and aged for 20-28 h, and then 20-40 parts of the first curing agent are added. After mixing and dispersion, heat treatment is carried out in an oven at 110-130 °C for 1-3 h. That is to say, the fruit shell particles or fruit core particles are impregnated with the dyed component, and it penetrates into the porous structure inside the particles. At the same time, the dyed component also adheres to the outer surface of the particles to form a dyed resin layer. In this way, the dyed component adheres to both the inside and outside of the particles, and the color can be maintained even if the particles are broken.

[0044] It should be understood that in step S220, when the resins in the dyed component are different, the corresponding curing agents are also different. For example, when using epoxy resin, amine curing agents or anhydride curing agents can be used. For example, diaminodiphenylmethane curing agent. When using phenolic resin, thermoplastic phenolic resin curing agents or thermosetting phenolic resin curing agents can be used. For example, hexamethylenetetramine, organic hydrazides, etc.

[0045] S230. Mix the flexible inner core with the dyed resin layer on the outside and the dyed component distributed inside with epoxy resin or polyurethane resin, and add the second curing agent. After foaming and curing treatment, a proppant is obtained.

[0046] Specifically, the flexible core formed in step S220 is added to a sand mixer, and 40 - 60 parts of epoxy resin, 5 - 15 parts of reactive diluent, and 1 - 3 parts of acetone are added and stirred evenly. Then, 20 - 40 parts of a second curing agent are added, and it is cured at 150 - 170 °C for 1 - 3 h. Of course, 40 - 60 parts of polyurethane resin and 1 - 3 parts of acetone can also be added to the sand mixer, stirred evenly, and then 20 - 40 parts of the second curing agent are added, and it is also cured at 150 - 170 °C for 1 - 3 h.

[0047] It should be noted that the curing agent in step S230 also needs to be selected according to the type of resin. For example, when using epoxy resin, curing agents such as dicyandiamide powder can be selected; when using polyurethane resin, isocyanate curing agents or amine curing agents can be used, such as ethylenediamine, dicyandiamide, diphenylmethane diisocyanate, etc.

[0048] It should also be noted that since acetone has the effects of diluting, heating and volatilizing to foam epoxy resin, it can reduce the viscosity of epoxy resin or polyurethane resin, enabling it to better mix with other components fully. Also, it is convenient to evenly coat the surface of the two kinds of particles after being added to the sand mixer, ensuring the uniformity of the subsequent curing reaction. At the same time, acetone can also dissolve part of the curing agent, making the curing agent more evenly dispersed in the resin system. The evenly dispersed curing agent can come into full contact with the resin, which is beneficial to the smooth progress of the curing reaction during the subsequent heating and curing process, improving the degree and efficiency of the curing reaction, and making the performance of the cured product more stable and uniform. In addition, during the heating process, acetone will gradually volatilize. Since acetone is evenly distributed in the resin system, tiny bubble nuclei will be formed in the system during its volatilization. These bubble nuclei provide starting points for the subsequent foaming of epoxy resin, helping to form a uniform cell structure. The volatilization rate and amount of acetone can control the growth and size of the cells to a certain extent during the resin foaming process. By adjusting the dosage of acetone and the heating conditions, the size and distribution of the cells can be adjusted, thereby obtaining resin foam materials with different foaming effects and properties to form an elastic outer shell layer.

[0049] The preparation method of the colored ultra - low - density proppant will be further described below with specific examples:

[0050] Example 1

[0051] This example gives the preparation method of the colored ultra - low - density proppant, including the following steps:

[0052] 1), 50 g of epoxy resin (epoxy value 0.51) is mixed evenly with 20 g of reactive diluent (butyl glycidyl ether), then 20 g of oil - based pigment is added, and after stirring evenly, it is reserved for use to obtain a dyed component;

[0053] 2), Weigh 500 g of walnut shell particles (particle size 0.106 - 0.425 mm), mix them with the dyeing component in step 1), seal and age for 24 hours, then mix with 30 g of diaminodiphenylmethane powder to obtain flexible core particles. The dyeing component is distributed in the porous structure inside the flexible core and also synchronously distributed on the outer surface of the flexible core to form a dyeing resin layer;

[0054] 3), Add the flexible core particles into a sand mixer, add a mixture of 50 g of epoxy resin (epoxy value 0.51), 10 g of active diluent and 2 g of acetone, stir well, add 30 g of dicyandiamide powder, cure at 160 °C for 2 h, and obtain colored proppants after screening.

[0055] Furthermore, the particle size of the colored proppants obtained in this example is 0.106 - 0.425 mm.

[0056] Even further, the proppants obtained in this example were subjected to impact resistance evaluation and temperature and salt resistance evaluation tests. Among them, the impact resistance evaluation process is as follows: Add the proppants and water into a beaker according to a volume ratio of 1:5, use a screw pump to pump the mixture to impact an iron plate, observe and dry after two rounds, measure the change in the average particle diameter, and the particle color fading situation. As shown in Table 1, the particles did not show color fading, and the particle size basically did not change. This shows that the proppants obtained in this example have impact resistance. Secondly, the temperature and salt resistance evaluation test process is as follows: Add 30 g of proppants into 100 g of 10% sodium chloride solution, seal and heat in a water bath at 90 °C for 15 days, and compare with the original proppants to observe the color change. As shown in Table 1, compared with the proppants before treatment, there was no color change. This shows that the proppants obtained in this example have high temperature and salt resistance.

[0057] Example 2

[0058] This example gives a preparation method of colored ultra-low density proppants, including the following steps:

[0059] 1), Add 20 g of oil-based pigment into 50 g of phenolic resin, stir well and set aside to obtain a dyeing component;

[0060] 2), Weigh 500 g of coconut shell particles (particle size 0.425 - 0.212 mm), mix them with the dyeing component in step 1), seal and age for 24 hours, then mix with 10 g of hexamethylenetetramine to obtain flexible core particles. The dyeing component is distributed in the porous structure inside the flexible core and also synchronously distributed on the outer surface of the flexible core to form a dyeing resin layer;

[0061] 3), Add the flexible core particles into a sand mixer, add a mixture of 50 g of epoxy resin (epoxy value 0.51), 10 g of active diluent and 2 g of acetone, stir well, add 30 g of dicyandiamide powder, cure at 160 °C for 2 h, and obtain colored proppants after screening.

[0062] Further, the particle size of the colored proppants obtained in this example is 0.212 - 0.425 mm.

[0063] Furthermore, the obtained proppants in this example were evaluated for impact resistance and temperature and salt resistance. Among them, the impact resistance evaluation process is as follows: Add proppants and water into a beaker according to a volume ratio of 1:5, use a screw pump to pump the mixture to impact an iron plate, observe and dry after two rounds, measure the change in the average particle diameter and the color fading of the particles. As shown in Table 1, the particles did not show color fading and the particle size basically did not change, which indicates that the proppants obtained in this example have impact resistance. Secondly, the temperature and salt resistance evaluation test process is as follows: Add 30 g of proppants into 100 g of 10% sodium chloride solution, seal and heat in a water bath at 90 °C for 15 days, and compare with the original proppants to observe the color change. As shown in Table 1, compared with the untreated proppants, there is no color change, which indicates that the proppants obtained in this example have high temperature and salt resistance.

[0064] Example 3

[0065] This example presents a preparation method of colored ultra-low density proppants, including the following steps:

[0066] 1), Mix 50 g of epoxy resin (epoxy value 0.44) with 20 g of active diluent (butyl glycidyl ether) evenly, then add 20 g of oil-based pigment, stir well and set aside to obtain a dyeing component;

[0067] 2), Weigh 500 g of coconut shell particles (particle size 0.425 - 0.85 mm), mix them with the dyeing component in step 1), seal and age for 24 hours, then mix with 30 g of diaminodiphenylmethane powder to obtain flexible core particles. The dyeing component is distributed in the porous structure inside the flexible core and also synchronously distributed on the outer surface of the flexible core to form a dyeing resin layer;

[0068] 3), Add the flexible core particles into a sand mixer, add a mixture of 50 g of polyurethane resin and 2 g of acetone, stir well, add 2.5 g of dicyandiamide, cure at 160 °C for 2 h, and obtain colored proppants after screening.

[0069] Further, the particle size of the colored proppants obtained in this example is 0.425 - 0.85 mm.

[0070] Furthermore, in this embodiment, impact resistance evaluation and temperature and salt tolerance evaluation tests were carried out on the obtained proppant. Among them, the impact resistance evaluation process is as follows: The proppant and water were added to a beaker at a volume ratio of 1:5, and the mixture was pumped by a screw pump to impact an iron plate. After two rounds, the mixture was observed after drying, and the change in the average particle diameter and the discoloration of the particles were measured. As shown in Table 1, the particles did not show discoloration, and the particle size basically did not change. This shows that the proppant obtained in this embodiment has impact resistance. Secondly, the temperature and salt tolerance evaluation test process is as follows: 30 grams of proppant was added to 100 grams of 10% sodium chloride solution, and after sealing and heating in a water bath at 90 °C for 15 days, it was observed in comparison with the original proppant, and the color change was observed. As shown in Table 1, compared with the proppant before treatment, there was no color change. This shows that the proppant obtained in this embodiment has high temperature and salt tolerance.

[0071] Table 1 Impact resistance evaluation and temperature and salt tolerance evaluation results of the proppants in Examples 1-3

[0072] Example 1 Example 2 Example 3 Anti-impact color fading result No color fading No color fading No color fading Anti-impact particle size range 0.106 - 0.212mm 0.212 - 0.425mm 0.425 - 0.85mm Temperature and salt tolerance evaluation result No color change No color change No color change

[0073] The present disclosure provides a colored ultra-low density proppant for fracture monitoring and a preparation method thereof, which has the following beneficial effects compared with the prior art:

[0074] First, in the present disclosure, the agricultural and forestry solid waste fruit shells form a flexible inner core, which is not easily broken and causes bare discoloration; at the same time, a dyeing component is doped in the flexible inner core, and an oil-soluble pigment is combined with a flexible liquid resin to impregnate the fruit shells, and the pigment penetrates into the interior of the fruit shell particles or fruit core particles, which can effectively prevent the proppant from discoloring;

[0075] Second, in the present disclosure, an elastic outer shell layer is coated on the flexible inner core to further prevent the proppant from breaking during the pumping process.

[0076] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present disclosure, and the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also regarded as the protection scope of the present disclosure.

Claims

1. A colored ultra-low density proppant for fracture monitoring, characterized in that, Comprising: A flexible core, a dyed resin layer, and an elastic outer shell layer are sequentially wrapped from the inside to the outside; wherein, The flexible core adopts husk particles and / or pit particles with a porous structure, and a dyeing component is distributed in the porous structure of the husk particles and / or pit particles; Both the dyeing component and the dyed resin layer include resin and an oil-based pigment.

2. The colored ultra-low density proppant for fracture monitoring according to claim 1, wherein The content of the resin is 40-60 parts by mass; The content of the oil-based pigment is 10-30 parts by mass.

3. The colored ultra-low density proppant for fracture monitoring according to claim 1, wherein The resin is epoxy resin or phenolic resin.

4. The colored ultra-low density proppant for fracture monitoring according to claim 1, wherein When the resin is epoxy resin, the dyeing component further includes an active diluent.

5. The colored ultra-low density proppant for fracture monitoring according to claim 1, wherein The husk particles are walnut shell particles, coconut shell particles; The pit particles are peach pit particles.

6. The colored ultra-low density proppant for fracture monitoring according to claim 1, characterized in that, The particle size of the husk particles or pit particles is 0.106-0.85 mm.

7. The colored ultra-low density proppant for fracture monitoring according to claim 1, characterized in that, The elastic outer shell layer is formed by foaming epoxy resin or polyurethane resin.

8. The colored ultra-low density proppant for fracture monitoring according to claim 1, wherein The thickness of the elastic outer shell layer is 10-50 μm.

9. A method for preparing a colored ultra-low density proppant as described in any one of claims 1 to 8, characterized in that, The method includes: Mixing the resin and the oil-based pigment to form a dyeing component; Mixing the husk particles and / or pit particles with the dyeing component, after aging treatment, mixing it with a first curing agent, and through dispersion and heating treatment, obtaining a flexible core, the dyeing component is distributed in the porous structure inside the flexible core, and at the same time is also distributed on the outer surface of the flexible core, forming a dyed resin layer; Mixing the flexible core with a dyed resin layer on the outside and a dyeing component distributed inside with epoxy resin or polyurethane resin, adding a second curing agent, and through foaming and curing treatment, obtaining a proppant.

10. The method according to claim 9, wherein The time of the aging treatment is 20-28 h; and / or, The temperature of the heating treatment is 110-130 °C, and the time is 1-3 h; and / or, the temperature of the curing treatment is 150-170 °C, and the time is 1-3 h.

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