A self-degradable particle temporary plugging agent for fracturing, and its preparation method and application

Abstract

The present invention discloses a self-degradable particle temporary plugging agent for fracturing and its preparation method and application, relating to the field of oilfield chemical technology. According to mass percentage, the temporary plugging agent is obtained by melt blending and crushing the materials including the following components: poly (3-hydroxybutyric acid-co-4-hydroxybutyrate), 70%-85%; auxiliary agent for auxiliary degradation, 2%~10%; nano silicon dioxide 10%~15%; sodium starch glycolate, 1%~7%. The temporary plugging agent of the present invention contains disintegrant sodium starch glycolate, which has a strong water absorption capacity and can quickly absorb water and expand its own volume by 250~300 times, so that the temporary plugging agent expands and cracks appear. On the one hand, in the early stage of plugging, the temporary plugging agent can reduce the gap between particles after absorbing water and expanding, thereby increasing the density of the entire plugging layer, thereby improving the plugging ability. On the other hand, cracks are generated on the surface of the temporary plugging agent after expansion, and water can penetrate into the interior of the temporary plugging agent particles from the cracks, which increases the contact area between the temporary plugging agent and water, thereby promoting its degradation and shortening the time of overall degradation.

Description

Technical Field

[0001] The invention belongs to the field of oilfield chemistry and relates to an efficient oilfield exploitation technology, in particular to a self-degradable particle temporary plugging agent for fracturing, a preparation method and an application thereof. Background Art

[0002] Temporary plugging agents are the core materials in diversion fracturing technology. Once introduced into the formation, they temporarily seal existing cracks. During the fracturing process, they force the fracturing fluid to flow in other directions, creating new cracks. After fracturing is complete, the temporary plugging agents are removed to restore formation permeability. Currently, most temporary plugging agents require the addition of specific substances, such as breakers and acids, to remove the blockage. This involves a complex construction process and increases operating costs. Self-degradable temporary plugging agents, on the other hand, can degrade and remove the blockage themselves, leveraging formation conditions. This eliminates the need for manual intervention, simplifying operations and reducing costs.

[0003] Current self-degradable temporary plugging agent is mostly a granular material obtained by melt blending and slicing a variety of degradable materials and inorganic fillers. After it is sent into the stratum, it forms a bridge in the crack to form a blocking layer, and then gradually unblocks as the granular temporary plugging agent dissolves. For example, the Chinese application for invention disclosure of publication number CN105295321A discloses a degradable material for oil and gas field operations, which melt blends polylactic acid, polyhydroxyalkanoate with polycaprolactone, polybutylene succinate, nanosilica, etc. An ideal temporary plugging agent has an early degradation rate that is slower as possible to increase the effective blocking time, and a later degradation rate that is faster as possible to remove the blocking as soon as possible and resume circulation. However, existing self-degradable temporary plugging agents mostly rely on the accumulation of acidic substances in the degradation products to improve degradation rate, and the degradation rate in the later stage increases limitedly, causing the overall degradation cycle to be longer. Summary of the Invention

[0004] In order to solve the above problems, one object of the present invention is to provide a self-degradable granular temporary plugging agent for fracturing, which utilizes the water absorption and swelling effect of the disintegrant sodium starch glycolate to expand the area during degradation, thereby increasing the degradation rate in the later stage. At the same time, the water absorption and swelling of sodium starch glycolate can increase the density of the early plugging layer and enhance the early plugging effect.

[0005] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0006] A self-degradable granular temporary plugging agent for fracturing is obtained by melt-blending and then crushing the following components, calculated by mass percentage:

[0007] Poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 70% to 85%;

[0008] Auxiliary degradation agents, 2%~10%;

[0009] Nano-silicon dioxide, 10%~15%;

[0010] Sodium starch glycolate, 1%~7%.

[0011] As a specific embodiment of the present invention, the auxiliary agent for assisting degradation is one of polyglycolic acid and polybutylene succinate, or a mixture of both.

[0012] As a specific embodiment of the present invention, the molar content of 4-hydroxybutyrate in poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) is 3% to 15%. It should be noted that the higher the 4-hydroxybutyrate content in poly(3-hydroxybutyric acid-co-4-hydroxybutyrate), the lower the melting point. When the molar content of 4-hydroxybutyrate is 20%, the temporary plugging agent formed has poor compressive strength at high temperatures (such as 130°C), making it difficult to form a stable plugging layer. However, after cooling, its deformation resistance improves, and it can form a stable plugging layer at low temperatures (such as 100°C).

[0013] As a specific embodiment of the present invention, the nano-silica is modified nano-silica whose surface is modified by a silane coupling agent.

[0014] Furthermore, when preparing modified nano-silica, the amount of silane coupling agent used is 1% to 3% of the mass of nano-silica. The silane coupling agent can be KH-560 (γ-(2,3-epoxypropoxy)propyltrimethoxysilane), KH-550 (γ-aminopropyltriethoxysilane), etc.

[0015] In the present invention, the sodium starch glycolate content is 1% to 7%. When the sodium starch glycolate content is relatively high, it is easy to form a gel after absorbing water, which in turn reduces the overall degradation rate.

[0016] Another object of the present invention is to provide a method for preparing a self-degradable granular temporary plugging agent for fracturing, which comprises the following steps:

[0017] S1. Dry all raw materials to remove moisture;

[0018] S2. Grind the sodium starch glycolate to facilitate mixing during the subsequent melt blending. The smaller the size after pulverization, the more complete the mixing.

[0019] S3. All raw materials are melt-blended, then cooled and crushed into particles. The mixing degree of the melt blending is lower than 190°C, and the melt blending temperature should be higher than the melting point of poly (3-hydroxybutyric acid-co-4-hydroxybutyrate), preferably 5 to 10°C higher than the melting point. The lower the melt blending temperature, the better, which is conducive to reducing the degradation of the polymer material.

[0020] As a specific embodiment of the present invention, when polyglycolic acid exists in the raw materials, it is crushed and then melt-blended.

[0021] Another object of the present invention is to provide an application of a self-degradable particle temporary plugging agent for fracturing, wherein the self-degradable particle temporary plugging agent for fracturing is used to temporarily plug cracks during fracturing construction.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The temporary plugging agent of the present invention contains a disintegrant, sodium starch glycolate, which has a strong water absorption capacity and can quickly absorb water and expand its own volume by 250 to 300 times, thereby causing cracks to appear in the temporary plugging agent during expansion. On the one hand, in the early stage of plugging, the temporary plugging agent can reduce the gaps between particles after absorbing water and expanding, thereby increasing the density of the entire plugging layer and improving the plugging capacity. On the other hand, cracks are generated on the surface of the temporary plugging agent after expansion, and water can penetrate into the interior of the temporary plugging agent particles through the cracks, thereby increasing the contact area between the temporary plugging agent and water, thereby promoting its degradation and shortening the overall degradation time. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 3 and 4. It is a trend diagram showing the leakage amount of the temporary plugging agents prepared in Examples 1-3 and Comparative Examples 1-2 changing with time. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0026] In the following examples, poly (3-hydroxybutyric acid-co-4-hydroxybutyrate) was obtained from Tianjin Guoyun Biomaterial Co., Ltd.; polyglycolic acid was obtained from Wuhan Haishan Technology Co., Ltd.; and sodium starch glycolate was obtained from Xi'an Lavia Biotechnology Co., Ltd.

[0027] In the following examples, modified nano-silica was prepared by the following method: drying the nano-silica at 80° C. for 12 hours to remove surface adsorbed moisture; dissolving 2.5% by weight of a silane coupling agent (KH560) in an ethanol aqueous solution (ethanol concentration of 50% by weight) to form a silane coupling agent solution; adding the dried nano-silica to the silane coupling agent solution, continuously stirring, and reacting at 60° C. for 4 hours. After the reaction, the solid obtained by centrifugation was washed three times with deionized water and dried to obtain the modified nano-silica.

[0028] Example 1: S1, poly (3-hydroxybutyric acid-co-4-hydroxybutyrate) (4-hydroxybutyrate content: 5 mol%), polyglycolic acid, modified nano-silica, and sodium starch glycolate were dried at 60° C. for 12 h to remove moisture;

[0029] S2, placing sodium starch glycolate and polyglycolic acid into a ball mill and grinding them for 1 hour, until the powder can pass through a 400-mesh sieve;

[0030] S3. Poly(3-hydroxybutyric acid-co-4-hydroxybutyrate), polyglycolic acid, modified nano-silica, and sodium starch glycolate were mixed in a mass ratio of 76:8:12:4 and stirred for 10 minutes. The mixture was then heated to 180°C at a rate of 10°C / min and melt-blended for 10 minutes. The molten mixture was naturally cooled and then crushed to obtain temporary plugging agent particles.

[0031] Example 2: The steps and raw materials are the same as those in Example 1, except that the content of 4-hydroxybutyrate in poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) is 10 mol%.

[0032] Example 3: The steps and raw materials are the same as those in Example 1, except that the content of 4-hydroxybutyrate in poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) is 15 mol%.

[0033] Comparative Example 1

[0034] The steps and raw materials are the same as those in Example 2, except that sodium starch glycolate is not added.

[0035] Comparative Example 2

[0036] The steps and raw materials used are the same as those in Example 1, except that poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) is replaced by poly(3-hydroxybutyric acid).

[0037] Test Case

[0038] The temporary plugging agents prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to plugging experiments, and a high-temperature plugging test was performed on each temporary plugging agent using a crack model with an inlet width of 5 mm and an outlet width of 3 mm.

[0039] The steps of the plugging experiment are as follows: first, prepare 10×104mg / L sodium chloride solution and add it to the plugging instrument; then, crush the temporary plugging agent and take 70g of 14-16 mesh (can pass through the 14 mesh sieve, not through the 16 mesh sieve) temporary plugging agent and 30g of 25-30 mesh (can pass through the 25 mesh sieve, not through the 30 mesh sieve) temporary plugging agent and add them to the plugging instrument, heat it to 130℃ and apply 10MPa pressure, maintain the pressure stable, open the plugging instrument outlet after two hours to measure the leakage rate (leakage per minute), close the plugging instrument outlet after the measurement, and then measure the leakage rate every hour, and close the plugging instrument outlet after each measurement. The specific data are shown in Table 1 and Figure 1 shown.

[0040] Table 1 Leakage of various temporary plugging agents per unit time at 130°C

[0041]

[0042] Note: “-” indicates that the leakage is large (over 50ml / min) and cannot be measured.

[0043] The test results show that the leakage rate increases with time. This is because the temporary plugging agent bridges and stacks in the cracks to form a plugging layer. There are gaps between the particles of the temporary plugging agent, providing a leakage channel. As the temporary plugging agent gradually degrades, the gaps in the plugging layer will continue to increase, causing its leakage rate to continue to increase.

[0044] It can be seen from Comparative Example 1 and Example 2 that after the addition of the disintegrant (sodium starch glycolate), the leakage of the temporary plugging agent decreases in the early stage and increases in the later stage. This is because the expansion of the temporary plugging agent in the early stage enhances the density of the plugging layer and improves the sealing effect. After the plugging layer fails, the temporary plugging agent particles still absorb water and expand, causing cracks to appear in the temporary plugging agent particles. This increases the contact area between the temporary plugging agent particles and water and promotes the degradation of the particles.

[0045] The temporary plugging agents of Examples 1 to 3 have lower early leakage than those of Comparative Examples 1 and 2, and higher late leakage than those of Comparative Examples 1 and 2, indicating that the addition of disintegrants is beneficial to improving the early plugging ability and increasing the degradation rate in the late stage.

[0046] It can be seen from Comparative Examples 1 and 2 that the temporary plugging agent of Comparative Example 1 has less leakage in the early stage and more leakage in the later stage. This is because the monomer of Comparative Example 1 contains 4-hydroxybutyric acid, which has more carbon atoms on its main chain than 3-hydroxybutyric acid, and the molecule is softer and has stronger deformation ability. Therefore, it has stronger adaptability to cracks, and can seal gaps through deformation, making the sealing layer more compact.

[0047] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A self-degradable granular temporary plugging agent for fracturing, which is obtained by melt-blending and then crushing the following components, calculated by mass percentage: Poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 70% to 85%; Auxiliary degradation agents, 2%~10%; Nano-silicon dioxide, 10%~15%; Sodium starch glycolate, 1% to 7%; The auxiliary degradation agent is one of polyglycolic acid and polybutylene succinate or a mixture of the two; the molar content of 4-hydroxybutyrate in poly (3-hydroxybutyric acid-co-4-hydroxybutyrate) is 3% to 20%.

2. The self-degradable granular temporary plugging agent for fracturing according to claim 1, characterized in that: The molar content of 4-hydroxybutyrate in poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) is 3%~15%.

3. The self-degradable granular temporary plugging agent for fracturing according to claim 1, characterized in that: The nano-silica is modified nano-silica whose surface is modified by using a silane coupling agent.

4. The self-degradable granular temporary plugging agent for fracturing according to claim 3, characterized in that: When preparing the modified nano-silica, the amount of the silane coupling agent used is 1%-3% of the mass of the nano-silica.

5. A method for preparing a self-degradable particle temporary plugging agent for fracturing, for preparing the self-degradable particle temporary plugging agent for fracturing according to any one of claims 1 to 4, characterized in that: The steps include: S1. Dry all raw materials; S2, crushing the sodium starch glycolate to facilitate uniform mixing during subsequent melt blending; S3. All raw materials are melt-blended at a temperature below 190° C. and above the melting point of poly(3-hydroxybutyric acid-co-4-hydroxybutyrate), and then cooled and crushed into particles.

6. The method for preparing the self-degradable granular temporary plugging agent for fracturing according to claim 5, characterized in that: When polyglycolic acid exists in the raw materials, the polyglycolic acid is crushed and then melt-blended.

7. An application of a self-degradable particle temporary plugging agent for fracturing, characterized in that: The self-degradable particle temporary plugging agent for fracturing according to any one of claims 1 to 4 is used to temporarily plug cracks during fracturing construction.

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