A filling-self-dissolving microsphere for reinforcing the formation and its preparation method

Abstract

The present invention belongs to the technical field of hydrate mining, and specifically relates to a filling-self-dissolving microsphere for intra-stratum reinforcement and a preparation method thereof. The filling-self-dissolving microsphere is composed of 10.0 parts of porous hollow microspheres and 1.0-1.5 parts of alkali-soluble materials. During preparation, the molten alkali-soluble materials are absorbed into the hollow of the porous hollow microspheres by a vacuum suction method, and the molten alkali-soluble materials are obtained after cooling and hardening. When used, the filling-self-dissolving microspheres are added to the solidifying liquid as a proppant. The high-strength shell of the filling-self-dissolving microspheres can improve the early strength of the solidifying liquid and prevent the solidifying liquid from being squeezed out before solidification. The holes on the shell wall can form a "sand bridge" and play a certain role in sand prevention. The solidified solid body plays the role of intra-stratum reinforcement in hydrate mining, and realizes long-term mining. After 7 days of solidification and curing, the alkali-soluble material inside the microspheres can be dissolved by cement hydration products, providing new pore space for the microspheres to improve the permeability of the solidified body.

Description

Technical Field

[0001] The invention belongs to the technical field of natural gas hydrate exploitation, and in particular relates to a filling-self-dissolving microsphere for intra-stratum reinforcement and a preparation method thereof. Background Art

[0002] Natural gas hydrate is one of the unconventional natural gas resources with the greatest potential that has not yet been developed. However, most of my country's natural gas hydrate reservoirs are muddy siltstone with weak cementation between rock particles. With the exploitation of hydrates, rock particles are easily transformed into loose sand, resulting in a large amount of sand production in the wellbore until production stops. To address this sand production problem, the inventor proposed to squeeze low-temperature, early-strength, high-permeability solidification liquid into the hydrate layer to form a fracture network for intra-layer reinforcement. While using the low-temperature, early-strength characteristics to reinforce the loose formation, the high-permeability consolidation body can improve the efficiency of hydrate exploitation.

[0003] Since the hydrate reservoir is subject to high closure stress, the crack network opened by pressure is easy to close. In order to reduce the pressure holding construction time and reduce the cost of offshore operations, a proppant is needed to support the cracks during the mining process to provide sufficient space and time for the solidifying liquid to solidify the hydrate layer, and prevent the unsolidified solidifying liquid from being squeezed back after the pressure is removed.

[0004] In order to improve the mining efficiency, the proppants currently used in the market mainly include natural quartz sand, ceramsite proppants and film-coated proppants. Among the three types of fracturing proppants used in oil and natural gas mining, quartz sand has low cost and is easy to pump, but has low strength and is easy to break; film-coated proppants have a short service life and are too expensive, so they are not suitable for use; ceramsite proppants have the advantages of corrosion resistance and high pressure resistance, and the cost is not too high. However, most of the existing proppants are solid spherical materials. Although they have strong supporting capacity, they are also prone to blocking the pore channels inside the consolidation body, which leads to a decrease in the permeability of the consolidation body and a loss of the original high permeability.

[0005] Since the greater the permeability of the solid body during natural gas hydrate exploitation, the higher the natural gas exploitation efficiency, it is necessary to study a high-strength and high-permeability proppant that can not only support the formation but also have no effect on the permeability of the solid body, and can also reduce the blockage of the seepage channel of the solidified liquid in the drilling. Summary of the invention

[0006] In view of the above problems, the purpose of the present invention is to provide a filling-self-dissolving microsphere for intra-stratum reinforcement and a preparation method thereof. The filling-self-dissolving microsphere can be used as a proppant to fill the formation cracks. It can not only support the formation cracks by relying on the high-strength outer shell of the microspheres, but also effectively reduce the blockage of cement seepage channels in drilling, improve the permeability of the consolidated body, and finally rely on the holes on the surface of the outer shell to form a "sand bridge" to play a certain sand prevention role. The solidified consolidated body plays the role of reinforcing the hydrate formation in the layer, and can achieve long-term mining.

[0007] In order to achieve the above-mentioned purpose, the present invention also provides a method for preparing the filling-self-dissolving microspheres, which uses high-strength porous hollow microspheres as carriers, heats the alkali-soluble material in a muffle furnace to convert it into a molten state, and absorbs the molten alkali-soluble material into the hollow of the carrier microspheres by vacuum suction. After cooling and hardening, the filling-self-dissolving microspheres can be obtained.

[0008] The technical solutions adopted are:

[0009] A filling-self-dissolving microsphere for in-layer reinforcement, used as a proppant for natural gas hydrate mining, is prepared from the following components by weight: 10.0 parts of porous hollow microspheres and 1.0-1.5 parts of alkali-soluble materials, wherein the alkali-soluble materials are filled inside the porous hollow microspheres; when used, the filling-self-dissolving microspheres are added to the solidifying liquid as a proppant to fill the formation cracks for hydrate mining, and after solidification, the alkali-soluble materials inside can be dissolved by cement hydration products to improve the permeability of the solidified body. .

[0010] Preferably, the porous hollow microspheres have a diameter of 0.18 to 0.30 mm, and an internal cavity diameter of 0.10 to 0.15 mm.

[0011] Preferably, the mass ratio of the filling-self-dissolving microspheres to the cement in the solidifying liquid is 0.1 to 0.15:1.

[0012] The solidifying liquid is a low-temperature early-strength solidifying liquid, which mainly includes a hardenable material, namely cement. The cement used in this application is any one of G-grade cement and ultra-fine oil well cement.

[0013] Preferably, the alkali-soluble material is one or a mixture of two of polylactic acid powder, polyester powder and polyvinyl chloride powder.

[0014] Preferably, the particle size of the alkali-soluble material is 300-500 mesh.

[0015] A method for preparing filling-self-dissolving microspheres for intra-stratum reinforcement, the method comprising the following steps:

[0016] (1) Preparation and screening of porous hollow microspheres:

[0017] The prepared porous hollow microspheres are screened with a sieve, and porous hollow microspheres with a mesh size of 50 to 80 (i.e., a diameter of 0.18 to 0.30 mm) are screened out for use as carriers;

[0018] (2) Preparation of filling-self-dissolving microspheres by vacuum suction method:

[0019] The porous hollow microspheres and the alkali-soluble material are mixed according to weight, and then placed in a muffle furnace and heated to the melting point of the alkali-soluble material, so that the alkali-soluble material is in a molten state;

[0020] The mixture is then transferred to a vacuum box, heated under a certain pressure to keep the alkali-soluble material in a liquid state, and vacuumed to absorb the alkali-soluble material into the cavity of the porous hollow microsphere carrier. After a certain period of time, the heating is turned off and the mixture is cooled to room temperature.

[0021] After the alkali-soluble material inside the microspheres changes from liquid back to solid, the microspheres bonded together by the alkali-soluble material are taken out, the alkali-soluble material cement on the surface of the microspheres is ground off using a ball mill, and the microspheres are redispersed to obtain the filled-self-dissolving microspheres.

[0022] Preferably, in the step (1), when screening the porous hollow microspheres, the sieve has a mesh size of 50 to 80.

[0023] Preferably, in step (2), the heating temperature in the muffle furnace and the vacuum box is 160° C. to 220° C., and the temperature is adjusted to the melting point of different alkali-soluble materials during preparation.

[0024] Preferably, in step (2), the pressure during heating in the vacuum box is -0.1 MPa.

[0025] Preferably, in step (2), the suction time is 30 to 50 minutes.

[0026] Compared with the prior art, the present invention is beneficial in that:

[0027] The present invention provides a filling-self-dissolving microsphere for intra-stratum reinforcement, which is suitable for intra-stratum reinforcement of oil wells during natural gas hydrate exploitation. The porous hollow microspheres used as carriers are high-strength porous hollow microspheres, which function to support stratum cracks with a high-strength shell to prevent the solidifying liquid from being squeezed out before solidification. The holes on the shell wall can form a "sand bridge" to play a certain role in sand prevention. The internal cavity of the filling-self-dissolving microsphere provides a new pore space to improve the porosity of the consolidated body; the alkali-soluble material is used to fill the microsphere cavity to prevent the solidifying liquid from invading the microsphere before solidification, causing the hollow microsphere to become a solid microsphere; at the same time, along with the progress of cement hydration reaction (the solidifying liquid includes cement), the alkali-soluble material will react and dissolve with calcium hydroxide, one of the cement hydration products, so that the inside of the microsphere becomes a cavity again, reducing the blockage of the oil well cement seepage channel and improving the permeability of the cement stone;

[0028] The self-dissolving microspheres for filling and reinforcing the strata provided by the present invention have the advantage of being easy to use. The porous hollow microspheres and the alkali-soluble material powder are both solid, and have the advantage of being easy to transport. The use thereof does not increase the operation time, and is efficient and convenient.

[0029] The filling-self-dissolving microspheres for intra-stratum reinforcement provided by the present invention have the advantages of long-term effectiveness and no pollution. After curing for 7 days, the filling material in the filling-self-dissolving microspheres dissolves by itself, and the hollow microspheres can improve the permeability of cement stone. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the working principle of the filling-self-dissolving microspheres prepared by the present invention (taking Example 1 as an example).

[0031] Figure 2 This is a micrograph of a small amount of cement invading the inner cavity of porous hollow microspheres that are not filled with alkali-soluble materials.

[0032] Figure 3 This is a micrograph of a cross section of filled-self-dissolving microspheres cured in a curing solution for 1 day.

[0033] Figure 4 This is a micrograph of a cross section of filled-self-dissolving microspheres cured in a curing solution for 7 days.

[0034] Figure 1 In the figure, Figure a shows the filled-self-dissolving microspheres prepared in Example 1, Figure b shows the microspheres in Figure a after curing in cement for 1 day, and Figure c shows the microspheres in Figure a after curing in cement for 7 days; 1-microsphere shell, 2-polylactic acid, 3-self-dissolving process: reaction of polylactic acid with calcium hydroxide, 4-microsphere cavity, 5-cement slurry. DETAILED DESCRIPTION

[0035] The accompanying drawings are only for illustrative purposes; it should be understood that the cases mentioned below are only used to explain the present invention, in order to facilitate the description of the present invention and simplify the description, and therefore, should not be understood as limiting the present invention.

[0036] In order to clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Example 1

[0038] A filling-self-dissolving microsphere for reinforcing a stratum, the preparation method of which comprises the following steps:

[0039] (1) Preparation and screening of porous hollow microspheres:

[0040] 1 g of sodium hydroxide, 5 g of sodium silicate and 5 g of sodium chloride were dissolved in 10 g of saturated salt water to form solution A, and 10 g of metakaolin was added to solution A and stirred for 5 minutes to form slurry B;

[0041] Add slurry B into 200 mL corn oil and stir until slurry B is dispersed into balls. The stirring speed is 550 r / min and the stirring time is 4 h. The temperature of corn oil is maintained at 80 °C.

[0042] The obtained polymer microspheres were filtered and washed with hot water to dissolve the inner core, and then calcined at 880°C for 10 hours to obtain high-strength porous hollow microspheres.

[0043] After screening, the obtained high-strength porous hollow microspheres have a particle size between 0.18 and 0.30 mm (ie, the sieve used for filtering is 50 ≤ mesh ≤ 80, i.e., 50 to 80 mesh), and an internal cavity diameter between 0.10 and 0.15 mm.

[0044] (2) Preparation of filling-self-dissolving microspheres by vacuum suction method:

[0045] Using the porous hollow microspheres prepared in step (1) as a carrier, the porous hollow microspheres are first mixed with polylactic acid, and then placed in a muffle furnace and heated to the melting point of the polylactic acid, so that the polylactic acid material is in a molten state;

[0046] The mixture was then transferred to a vacuum box, heated to about 200°C at a pressure of -0.1 MPa to keep the polylactic acid material in a liquid state, and vacuumed to absorb the polylactic acid material into the cavity of the carrier. After 50 minutes of vacuuming, the heating was turned off and the mixture was cooled to room temperature.

[0047] After the polylactic acid material inside the microspheres changes from liquid back to solid, the microspheres bonded together by the polylactic acid material are taken out, and a small amount of polylactic acid binder on the surface of the microspheres is ground off using a ball mill, and the microspheres are redispersed to obtain multifunctional, highly permeable filling-self-dissolving microspheres.

[0048] The working principle of the present invention is as follows Figure 1 As shown in FIG. a, the filled-self-dissolving microspheres prepared in Example 1 are filled with polylactic acid 2 in the microsphere shell 1. The microspheres filled with polylactic acid 2 are placed in cement slurry 5 for curing for 1 day, as shown in FIG. b. With the progress of cement hydration reaction, polylactic acid 2 undergoes a self-dissolving process 3, that is, it reacts and dissolves with calcium hydroxide, one of the cement hydration products. After curing in cement slurry 5 for 7 days, the filled-self-dissolving microspheres become the microsphere cavities 4 in the microsphere shell 1 as shown in FIG. c.

[0049] Example 2

[0050] A filling-self-dissolving microsphere for reinforcing a stratum, the preparation method of which comprises the following steps:

[0051] (1) preparing and screening porous hollow microspheres, wherein the filtration screen is less than 14 mesh, and the porous hollow microspheres are used as carriers;

[0052] (2) Filling-self-dissolving microspheres were prepared by vacuum suction method.

[0053] Other unmentioned places are the same as those in Example 1.

[0054] Example 3

[0055] A filling-self-dissolving microsphere for reinforcing a stratum, the preparation method of which comprises the following steps:

[0056] (1) preparing and screening porous hollow microspheres, wherein the sieve used for filtering is 14 ≤ mesh number < 30, and the porous hollow microspheres are used as carriers;

[0057] (2) Filling-self-dissolving microspheres were prepared by vacuum suction method.

[0058] Other unmentioned places are the same as those in Example 1.

[0059] Example 4

[0060] A filling-self-dissolving microsphere for reinforcing a stratum, the preparation method of which comprises the following steps:

[0061] (1) preparing and screening porous hollow microspheres, wherein the sieve used for filtering is 30 ≤ mesh number < 50, and the porous hollow microspheres are used as carriers;

[0062] (2) Filling-self-dissolving microspheres were prepared by vacuum suction method.

[0063] Other unmentioned places are the same as those in Example 1.

[0064] Example 5

[0065] A filling-self-dissolving microsphere for reinforcing a stratum, the preparation method of which comprises the following steps:

[0066] (1) preparing and screening porous hollow microspheres, wherein the filtration screen is >80 mesh, and the porous hollow microspheres are used as carriers;

[0067] (2) Filling-self-dissolving microspheres were prepared by vacuum suction method.

[0068] Other unmentioned places are the same as those in Example 1.

[0069] The following is a test and comparison of the beneficial effects and performance of the filled-self-dissolving microspheres prepared in the embodiments of the present invention:

[0070] (1) Performance testing and optimization

[0071] The porous hollow microspheres prepared in step (1) of Examples 1-5 were weighed at 0.1 times the mass of cement, and sorted from small to large according to the screened mesh size (i.e., <14 mesh, 14≤mesh<30, 30≤mesh<50, 50≤mesh≤80 and >80 mesh) to obtain microsphere proppants WQ-1, WQ-2, WQ-3, WQ-4 and WQ-5.

[0072] The effects of WQ-1, WQ-2, WQ-3, WQ-4, and WQ-5 on the compressive strength and permeability of cement paste were tested according to the following steps: WQ-1 to WQ-4 were added to four identical portions of pure cement paste, and cement paste was prepared according to GB / T 19139-2003 with a water-cement ratio of 0.5.

[0073] The 1-day compressive strength and 7-day permeability of the consolidated body at a curing temperature of 15°C were measured. The results are shown in Table 1:

[0074] Table 1. Effect of particle size (mesh size) of unfilled hollow microspheres on compressive strength and permeability of the consolidated body

[0075]

[0076] After testing, it was found that the unfilled porous hollow microspheres WQ-4 with a size of 50 to 80 mesh had a high effect on improving the permeability of cement paste, and the early strength performance of cement paste was also within the design index. The 1d compressive strength of cement paste was 4.84MPa, and the 7d permeability was 7.01×10 -3 μm 2 The permeability enhancement effect is better than that of the same amount of quartz sand. However, the permeability of the cement stone at this time did not reach the expected effect. After cutting it open and observing it under a microscope, it was found that a small amount of cement had penetrated into the microspheres. Figure 2 As shown in the figure, the circles in the figure indicate that the pores of the microspheres are filled with cement. This is because the cement particles are small and enter the microspheres through the pores on the surface of the microspheres, resulting in the microsphere cavities being blocked, affecting the permeability of the microspheres, and thus causing the permeability of the cement paste to fail to achieve the expected effect.

[0077] In order to evaluate the permeability and permeability recovery effect of the prepared filled-self-dissolving microspheres, the microspheres filled with polylactic acid prepared in Example 1 were added to a curing liquid (cement slurry prepared according to GB / T 19139-2003 standard, with a water-cement ratio of 0.5) and cured for 1 day and 7 days, and then cut open and observed under a microscope. The results are as follows: Figure 3 and Figure 4 shown. Figure 3 The area marked in the circle shows that the internal space of the consolidated microspheres after 1 day of curing is still filled with polylactic acid. After 7 days of curing, Figure 4The part of the middle circle that was originally filled with polylactic acid has been dissolved. The hollow space has been opened and no cement intrusion is seen. Figure 1 The schematic diagram of the working principle is the same and the preparation is successful.

[0078] (2) Comparison of the product prepared by the present invention with other proppants

[0079] The effects of unfilled porous hollow microspheres and solid quartz sand on the permeability of cement paste were compared, and then the performance of porous permeable microspheres with different mesh sizes was compared. Then, different amounts of alkali-soluble materials were added for filling, and their effects on the consolidated body were tested. The dosage range of alkali-soluble materials was obtained, and finally, an optimization experiment was conducted on the dosage of high-permeability filling-self-dissolving microspheres.

[0080] Test Example 1

[0081] The natural quartz sand was ground with a ball mill, and then fine-grained quartz sand with a particle size of 50-80 mesh was screened out with a sieve. Quartz sand with a mass of 0.1, 0.2, 0.3, and 0.4 times the mass of cement was weighed respectively (the mass of cement depends on the actual amount of cement used in the formulation of each solidifying liquid. If the mass of cement is 400 g, 40 g, 80 g, 120 g, and 160 g of quartz sand were weighed respectively) to obtain proppants SY-1, SY-2, ST-3, and ST-4.

[0082] The effects of quartz sand proppants SY-1, SY-2, SY-3 and SY-4 on the compressive strength and permeability of low-temperature early-strength and high-permeability consolidation bodies were tested in the following steps: quartz sand proppants SY were added to the low-temperature early-strength solidifying liquid, and cement slurry was prepared according to GB / T19139-2003 standard with a water-cement ratio of 0.5.

[0083] The 1-day compressive strength and 7-day permeability of the consolidated body at a curing temperature of 15°C were measured. The amount of quartz sand proppant added and the evaluation results are shown in Table 2:

[0084] Table 2. Effect of different quartz sand additions on the compressive strength and permeability of high permeability consolidation bodies

[0085]

[0086]

[0087] From the results in Table 2, it can be seen that conventional solid sphere proppants have a certain negative impact on the early strength and permeability of the consolidated body. When the amount added is small, the long-term permeability of the consolidated body decreases. The reason is that the solid quartz sand will occupy part of the pore space, isolate the originally connected pore space, block part of the seepage channel, and cause the permeability of the consolidated body to decrease; when the amount of quartz sand added increases, the quartz sand forms new pore space between each other by stacking, thereby increasing the permeability. However, at this time, the sedimentation stability of the solidifying liquid also becomes very poor, and the increase in the amount of quartz sand added is also accompanied by a decrease in the proportion of cement, which leads to the 1d compressive strength of the consolidated body being too low and failing to meet the early strength index of the consolidated body.

[0088] Test Example 2

[0089] The influence of the mass percentage of filling-self-dissolving microspheres as proppant on the compressive strength and permeability of the consolidated body was tested. The main component of the low-temperature early strength curing liquid is cement, which can be quantified. Filling-self-dissolving microspheres with cement addition of 5%, 10%, 15%, and 20% were selected respectively, and the following steps were followed: the above-added filling-self-dissolving microspheres were added as proppant to the low-temperature early strength curing liquid, and cement slurry was prepared according to GB / T 19139-2003 standard, with a water-cement ratio of 0.5.

[0090] The 1d compressive strength, 1d permeability, 7d permeability and 14d permeability of the consolidated body at a curing temperature of 15°C were measured. The results are shown in Table 3:

[0091] Table 3. Effect of different amounts of filling-self-dissolving microspheres on the compressive strength and permeability of the consolidated body

[0092]

[0093] From the experimental results in Table 3, it can be seen that after adding the filling-self-dissolving microsphere proppant, when curing for 1 day, the inside of the microsphere is still in a filling state, temporarily blocking the seepage channel, resulting in a decrease in the permeability of the consolidated body for 1 day. As the curing time increases, the alkali-soluble material inside the microsphere begins to dissolve, and the filling microspheres are transformed into hollow microspheres and begin to play a certain role in increasing permeability. At this time, the microspheres have almost no effect on the permeability of the consolidated body. However, as the amount of microspheres added is too much, the total amount of alkaline soluble materials carried in the microspheres is also too much, the hydroxide ions in the consolidated body are quickly consumed, the alkalinity is reduced, and it is not enough to dissolve the remaining alkaline soluble materials, resulting in the failure of some microspheres to self-dissolve, continuing to block the seepage channel, and weakening the permeability of the consolidated body.

[0094] From the results, it can be seen that the effect is better when the mass of self-dissolving microspheres added is 10% to 15% of the cement mass, of which 10% is the optimal filling amount. At this time, the 1d compressive strength of the consolidated body is 4.12MPa, and the 14d permeability is 15.13×10 -3 μm2 , meeting the requirements of design indicators.

[0095] From the comparison of Table 2 and Table 3, it can be seen that after adding different amounts of quartz sand to the low-temperature early strength curing liquid, the 1d compressive strength and 7d permeability are lower than those of the curing liquid without adding quartz sand, and after adding filling-self-dissolving microspheres to the low-temperature early strength curing liquid, the 1d compressive strength and 7d permeability are significantly improved, thereby achieving the purpose of the present invention.

[0096] The low-temperature early strength curing liquid used in this application adopts the conventional use standards in the technical field of the prior art. The curing liquid includes a hardenable material (i.e. cement, which is the main component), water, emulsion, permeability enhancer and rheology regulator, and is suitable for low-temperature, high-pressure deep-water shallow environments, has good fluidity and certain permeability, and has a certain strength after consolidation; other materials used, if not otherwise specified, are all in accordance with the standards of conventional use in the prior art. Other places not mentioned are the same as the prior art.

[0097] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A self-dissolving microsphere for filling in strata for reinforcement, characterized in that: The invention is prepared from the following components in parts by weight: 10.0 parts of porous hollow microspheres and 1.0 to 1.5 parts of alkali-soluble materials, wherein the alkali-soluble materials are filled inside the porous hollow microspheres; when used, the filling-self-dissolving microspheres are added to the solidifying liquid as proppants to fill the formation cracks for hydrate mining, and after solidification, the alkali-soluble materials inside the microspheres can be dissolved by cement hydration products to improve the permeability of the solidified body; The method for preparing the porous hollow microspheres comprises: 1 g of sodium hydroxide, 5 g of sodium silicate and 5 g of sodium chloride were dissolved in 10 g of saturated salt water to form solution A, and 10 g of metakaolin was added to solution A and stirred for 5 minutes to form slurry B; Add slurry B into 200 mL corn oil and stir until slurry B is dispersed into balls. The stirring speed is 550 r / min and the stirring time is 4 h. The temperature of corn oil is maintained at 80 °C. After filtering, the obtained polymer microspheres were washed with hot water, the inner core was dissolved, and then calcined at 880°C for 10 h to obtain high-strength porous hollow microspheres; The porous hollow microspheres have a diameter of 0.18 to 0.30 mm, and an internal cavity diameter of 0.10 to 0.15 mm; Filling-The mass ratio of self-dissolving microspheres to cement in the curing liquid is 0.1-0.15:1; The alkali-soluble material is one of polylactic acid powder, polyester powder and polyvinyl chloride powder or a mixture of two of them.

2. The self-dissolving microspheres for filling and reinforcing the formation according to claim 1, characterized in that: The particle size of the alkali-soluble material is 300-500 meshes.

3. A method for preparing a filling-self-dissolving microsphere for intra-stratum reinforcement according to any one of claims 1 or 2, characterized in that: The method comprises the following steps: (1) Preparation and screening of porous hollow microspheres, which are used as carriers; (2) Preparation of filling-self-dissolving microspheres by vacuum suction method: The screened porous hollow microspheres are mixed with the alkali-soluble material by weight, and then placed in a muffle furnace and heated to the melting point of the alkali-soluble material, so that the alkali-soluble material is in a molten state; The mixture is then transferred to a vacuum box, heated under a certain pressure to keep the alkali-soluble material in a liquid state, and vacuumed to absorb the alkali-soluble material into the cavity of the porous hollow microsphere carrier. After a certain period of time, the heating is turned off and the mixture is cooled to room temperature. After the alkali-soluble material inside the microspheres changes from liquid back to solid, the microspheres bonded together by the alkali-soluble material are taken out, and a small amount of alkali-soluble material bonding on the surface of the microspheres is ground off using a ball mill, and the microspheres are redispersed to obtain the filled-self-dissolving microspheres.

4. The method for preparing the self-dissolving microspheres for reinforcing the formation according to claim 3, characterized in that: In the step (1), when screening the porous hollow microspheres, the sieve has a mesh size of 50 to 80.

5. The method for preparing the filling-self-dissolving microspheres for in-layer reinforcement of a stratum according to claim 3, characterized in that: In the step (2), the heating temperature in the muffle furnace and the vacuum box is 160° C. to 220° C.; the pressure during heating in the vacuum box is -0.1 MPa.

6. The method for preparing the self-dissolving microspheres for reinforcing the formation according to claim 3, characterized in that: In the step (2), the suction time is 30 to 50 minutes.

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