Self-degradable particle temporary plugging agent for fracturing as well as preparation method and application of self-degradable particle temporary plugging agent

Abstract

The invention discloses a self-degradable granular temporary plugging agent for fracturing as well as a preparation method and application thereof, and relates to the technical field of oilfield chemistry. The temporary plugging agent is prepared by melting, blending and crushing the following materials in percentage by mass: 70%-85% of poly (3-hydroxybutyrate-co-4-hydroxybutyrate), 10%-20% of poly (3-hydroxybutyrate-co-4-hydroxybutyrate), 10%-20% of poly (3-hydroxybutyrate), 2%-10% of an auxiliary agent for assisting degradation; 10%-15% of nano silicon dioxide; 1%-7% of sodium starch glycolate. The temporary plugging agent disclosed by the invention contains the disintegrant glycolic acid starch sodium which is extremely high in water absorption capacity, and can rapidly absorb water and expand the volume of the temporary plugging agent by 250-300 times, so that the temporary plugging agent expands to generate cracks, on one hand, gaps among particles can be reduced after the temporary plugging agent absorbs water and expands in the early stage of plugging, and the compactness of a whole plugging layer is increased; on the other hand, cracks are generated on the surface of the temporary plugging agent after expansion, and water can permeate into temporary plugging agent particles from the cracks, so that the contact area between the temporary plugging agent and the water is increased, the degradation of the temporary plugging agent is promoted, and the overall degradation time is shortened.

Description

Technical Field

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

[0002] Temporary plugging agents are the core materials in the diversion fracturing technology. After entering the formation, they can temporarily block the original cracks. During the fracturing process, the fracturing fluid is forced to flow in other directions to create new cracks. After the fracturing work is completed, the temporary plugging agent is unblocked to restore the formation permeability. As for the unblocking method of temporary plugging agents, most temporary plugging agents currently require the addition of specific substances to unblock them, such as debonding agents, acids, etc., which involves related construction processes and increases operating costs. Self-degradable temporary plugging agents can degrade and unblock themselves with the help of formation conditions, without the need for subsequent manual operations, which can simplify operations and reduce costs.

[0003] Most of the current self-degradable temporary plugging agents are granular materials obtained by melt blending and slicing of various degradable materials and inorganic fillers. After being sent into the formation, they bridge in the cracks to form a plugging layer, and then gradually unblock as the granular temporary plugging agent dissolves. For example, the Chinese application invention with publication number CN105295321A discloses a degradable material for oil and gas field operations, which melt blends polylactic acid, polyhydroxyalkanoate with polycaprolactone, polybutylene succinate, nano silicon dioxide, etc. An ideal temporary plugging agent has a slower degradation rate in the early stage, so as to increase the effective plugging time, and a faster degradation rate in the later stage, so as to remove the plugging as soon as possible and resume circulation. However, most of the existing self-degradable temporary plugging agents rely on the accumulation of acidic substances in the degradation products to increase the degradation rate, and the degradation rate in the later stage is limited, resulting in a relatively long overall degradation cycle. 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 degradation area, thereby increasing the degradation rate in the later stage. At the same time, the water absorption and swelling of sodium starch glycolate can improve the compactness of the early plugging layer and enhance the early plugging effect.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A self-degradable granular temporary plugging agent for fracturing is obtained by melting, blending and then crushing the following components, calculated by mass percentage: Poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 70% to 85%; Auxiliary agents for auxiliary degradation, 2%~10%; Nano-silicon dioxide, 10%~15%; Sodium starch glycolate, 1%~7%.

[0006] 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.

[0007] 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 content of 4-hydroxybutyrate 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 by it has poor compressive strength under high temperature conditions (such as 130°C) and is difficult to form a stable plugging layer. However, after cooling, its deformation resistance is improved, and a stable plugging layer can be formed under low temperature conditions (such as 100°C).

[0008] As a specific embodiment of the present invention, the nano-silica is modified nano-silica whose surface is modified by a silane coupling agent.

[0009] 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.

[0010] In the present invention, the sodium starch glycolate is 1% to 7%. When the content of sodium starch glycolate is relatively large, it is easy to form a gel after absorbing water, which reduces the overall degradation rate.

[0011] Another object of the present invention is to provide a method for preparing a self-degradable particle temporary plugging agent for fracturing, which is used to prepare the self-degradable particle temporary plugging agent for fracturing, comprising the following steps: S1. Dry all raw materials to remove moisture; S2, crushing the sodium starch glycolate to facilitate mixing during the subsequent melt blending. The smaller the size after crushing, the more complete the mixing; 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 temperature of the melt-blending 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 temperature of the melt-blending, the better, which is beneficial to reducing the degradation of the polymer material.

[0012] As a specific embodiment of the present invention, when polyglycolic acid exists in the raw materials, it is crushed and then melt-blended.

[0013] 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.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The temporary plugging agent of the present invention contains a disintegrant, sodium starch glycolate, which has a very strong water absorption capacity and can quickly absorb water and expand its own volume by 250 to 300 times, so that cracks appear in the expansion of the temporary plugging agent. On the one hand, in the early stage of plugging, the temporary plugging agent can reduce the gap between particles after absorbing water and swelling, increase the density of the entire plugging layer, and thus improve 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 overall degradation time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a trend diagram of the leakage amount of the temporary plugging agents prepared in Examples 1 to 3 and Comparative Examples 1 to 2 changing with time. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0017] In the following examples, poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) was from Tianjin Guoyun Biomaterial Co., Ltd.; polyglycolic acid was from Wuhan Haishan Technology Co., Ltd.; and sodium starch glycolate was from Xi'an Lavia Biotechnology Co., Ltd.

[0018] In the following embodiments, modified nano-silica was prepared by the following method: drying the nano-silica at 80° C. for 12 hours to remove moisture adsorbed on the surface; dissolving 2.5% of the mass of the nano-silica in an ethanol aqueous solution (ethanol mass concentration of 50%) 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, and after the reaction, washing the solid obtained by centrifugation with deionized water three times and drying to obtain modified nano-silica.

[0019] Example 1: S1, poly (3-hydroxybutyric acid-co-4-hydroxybutyrate) (4-hydroxybutyrate content of 5 mol%), polyglycolic acid, modified nano-silica, and sodium starch glycolate were dried at 60° C. for 12 h to remove moisture; S2, putting sodium starch glycolate and polyglycolic acid into a ball mill and grinding them for 1 hour respectively, and the powder after grinding can pass through a 400-mesh sieve; S3. Poly(3-hydroxybutyric acid-co-4-hydroxybutyrate), polyglycolic acid, modified nano-silica, and sodium starch glycolate are mixed in a mass ratio of 76:8:12:4 and stirred for 10 minutes, then heated to 180°C at a rate of 10°C / min for melt blending for 10 minutes, naturally cooled the molten mixture, and then crushed to obtain temporary plugging agent particles.

[0020] Example 2: The steps and raw materials are the same as those of Example 1, except that the content of 4-hydroxybutyrate in poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) is 10 mol%.

[0021] Example 3: The steps and raw materials are the same as those of Example 1, except that the content of 4-hydroxybutyrate in poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) is 15 mol%.

[0022] Comparative Example 1 The steps and raw materials are the same as those in Example 2, except that sodium starch glycolate is not added.

[0023] Comparative Example 2 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).

[0024] Test Case The temporary plugging agents prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were used for 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.

[0025] 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, take 70g of 14-16 mesh (can pass through the 14 mesh sieve, but not through the 16 mesh sieve) temporary plugging agent, and 30g of 25-30 mesh (can pass through the 25 mesh sieve, but 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.

[0026] Table 1 Leakage of each temporary plugging agent per unit time at 130℃

[0027] Note: “-” means the leakage is large (more than 50ml / min) and cannot be measured.

[0028] It can be seen from the test results 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.

[0029] It can be seen from Comparative Example 1 and Example 2 that after the disintegrant (sodium starch glycolate) is added, the leakage of the temporary plugging agent decreases in the early stage and increases in the later stage. This is because the expansion effect of the temporary plugging agent in the early stage enhances the compactness of the plugging layer and improves the sealing effect. After the plugging layer fails, each temporary plugging agent particle still absorbs water and expands, causing cracks in the temporary plugging agent particles, which increases the contact area between the temporary plugging agent particles and water and promotes the degradation of the particles.

[0030] The temporary plugging agents of Examples 1 to 3 have lower leakage in the early stage than those of Comparative Examples 1 and 2, and higher leakage in the later stage than those of Comparative Examples 1 and 2, indicating that the addition of disintegrants is beneficial to improving the plugging ability in the early stage and increasing the degradation rate in the later stage.

[0031] 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 the 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 the gaps through deformation, making the sealing layer more compact.

[0032] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A self-degradable granular temporary plugging agent for fracturing, which is obtained by melting, blending and then crushing the following materials, calculated by mass percentage: Poly(3-hydroxybutyrate-co-4-hydroxybutyrate), 70% to 85%; Auxiliary agents for auxiliary degradation, 2%~10%; Nano-silicon dioxide, 10%~15%; Sodium starch glycolate, 1%~7%.

2. The self-degradable granular temporary plugging agent for fracturing according to claim 1, characterized in that: The auxiliary agent for assisting degradation is one of polyglycolic acid and polybutylene succinate or a mixture of the two.

3. 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%.

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

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

6. A method for preparing a self-degradable particle temporary plugging agent for fracturing, used for preparing the self-degradable particle temporary plugging agent for fracturing according to any one of claims 1 to 5, characterized in that: The steps include: S1, drying 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.

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

8. 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 5 is used for temporarily plugging cracks during fracturing construction.

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