Polyglycolic acid temporary plugging agent with controllable degradation rate as well as preparation method and application of polyglycolic acid temporary plugging agent

Abstract

The invention belongs to the technical field of temporary plugging agents, and relates to a degradation-rate-controllable polyglycolic acid temporary plugging agent as well as a preparation method and application thereof. The temporary plugging agent comprises polyglycolic acid and a degradation regulating agent, the degradation regulating agent is of a core-shell structure, a shell is polylactic acid, and an inner core is a degradation promoting agent. The polyglycolic acid temporary plugging agent is adjustable in degradation performance, can meet the steering temporary plugging fracturing strength requirement of an underground environment at the temperature of 30-100 DEG C, has the fracturing bearing strength larger than 20 MPa, particularly has obvious degradation advantages in a medium and low temperature environment at the temperature of 30-70 DEG C, can be rapidly degraded within 24-72 h after fracturing operation, does not need acidification plugging removal and flowback, and has the advantages of being simple in preparation process, low in cost and the like. The operation efficiency is improved; and the construction cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of temporary plugging agent technology, specifically, it relates to a polyglycolic acid temporary plugging agent with controllable degradation rate, its preparation method and application. Background Technology

[0002] With the continuous increase in water cut in high-permeability, easily exploitable oilfields, attention has been drawn to low-permeability oil and gas reservoirs, which are widely distributed but difficult to develop. my country has proven geological reserves of 5.21 × 10⁻⁶ low-permeability oil reservoirs. 9 The annual proven reserves of low-permeability oil reservoirs account for an increasingly higher proportion of the total proven reserves of oil reservoirs that year, but the recovery rate is only 21.4%. This is because low-permeability formations are characterized by low porosity, low abundance, and low production capacity.

[0003] Diverting fracturing technology is a common method to improve oil and gas recovery in low-permeability oilfields and has been widely used in oilfield development. Traditional non-degradable temporary plugging agents such as quartz sand and walnut shells can cause serious damage to the formation, which is detrimental to the sustainable development of oil and gas resources. In recent years, degradable materials have been widely used in diverting temporary plugging fracturing. These temporary plugging agents can degrade rapidly under high-temperature conditions, eliminating the need for unplugging and backflow, thus improving the efficiency of oilfield operations. CN 109762544 A discloses a high-temperature resistant temporary plugging agent, its preparation method, and its application. The high-temperature resistant temporary plugging agent includes a semi-aromatic polyamide polymer and additives, and has good tensile strength, temperature resistance, and pressure resistance. It can be used at temperatures above 200°C, and after a period of use at this temperature, it can hydrolyze and be discharged with the fluid. CN 112745819 A discloses a biodegradable temporary plugging agent and its preparation method. Polyester materials such as polylactic acid ester, polyglycolic acid, and polybutylene succinate, along with inorganic nanoparticles, are melt-blended, blended, and molded to obtain temporary plugging agent particles with a particle size of 286.3-525.7 μm. The prepared temporary plugging agent has an expansion ratio of up to 38 times, a temporary plugging strength of up to 33 MPa, and a degradation rate of up to 99.3% at 100℃. It exhibits strong plugging ability and rapid unblocking. CN 115141615 A ​​discloses an oil well fracturing temporary plugging agent, its preparation method, and its application. The raw materials of the composition include polyglycolic acid, a nucleating agent, a functional thickener, and a degradation regulator. This temporary plugging agent has a degradation rate of less than 20% in water at 100℃ within 2 hours, and a degradation rate of more than 95% in water at 150℃ after 10 days. US20160298017A1 discloses a temporary plugging agent for drilling, which contains a synthetic resin that has a temporary plugging function for no more than 40 days in a temperature range of 93°C (200°F) to 204°C (400°F); and further discloses that the temporary plugging agent has a temporary plugging function for no less than 2 days and no more than 40 days, wherein the synthetic resin contains a polyglycolic acid resin.

[0004] In summary, biodegradable temporary plugging agents are mainly composed of polyester resin, starch, and bio-adhesives, and are primarily used in high-temperature oil well environments where rapid degradation is possible. However, due to the use of large-volume temporary plugging fluids in hydraulic fracturing during diversion fracturing, the near-wellbore temperature drops sharply, making it difficult to raise the ambient temperature of the temporary plugging agent in the short term, severely impacting its degradation performance. Therefore, developing low-temperature controllable biodegradable temporary plugging agent products while meeting the requirements of diversion fracturing strength is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a polyglycolic acid temporary plugging agent with controllable degradation rate, its preparation method, and its application. The temporary plugging agent includes polyglycolic acid, polylactic acid, and a degradation promoter. Polylactic acid is coated on the surface of the degradation promoter to prepare a core-shell structured degradation regulator. Polyglycolic acid and the degradation regulator are mixed to prepare a polyglycolic acid temporary plugging agent with controllable degradation rate. The polylactic acid shell layer of different thicknesses and the amount of degradation regulator added can affect the degradation rate of the temporary plugging agent, thereby achieving degradation regulation.

[0006] A first aspect of the present invention provides a polyglycolic acid temporary plugging agent with controllable degradation rate, the temporary plugging agent comprising polyglycolic acid and a degradation regulator, wherein the degradation regulator has a core-shell structure, the outer shell being polylactic acid and the core being a degradation promoter.

[0007] Polyglycolic acid is prone to hydrothermal degradation in humid heat or aqueous solutions, producing glycolic acid and its oligomers. This creates an acidic environment that promotes the degradation and rupture of the polylactic acid (especially amorphous racemic polylactic acid) shell from the outside in, thereby releasing the degradation promoters it encapsulates.

[0008] Regarding degradation acceleration, the property that polyglycolic acid (PEG) is more easily degraded than polylactic acid (PLA) under hydrothermal conditions is utilized. The initial degradation products of PEG are used as a "trigger" to induce the release of degradation accelerators from the core-shell structure. The alkaline environment created by the degradation accelerators intensifies the breaking of PEG ester bonds, thereby accelerating the degradation rate of the temporary plugging agent. In terms of degradation rate control, the design of the PLA shell is key. By changing the thickness of the PLA shell, the ease of release of degradation accelerators can be controlled, and / or by changing the addition of degradation regulators, the degradation rate of the temporary plugging agent can be controlled.

[0009] A second aspect of the present invention provides a method for preparing the above-mentioned polyglycolic acid temporary plugging agent, comprising the following steps:

[0010] (1) Mix polylactic acid solution with degradation promoter, stir and disperse evenly, and then spray dry to coat polylactic acid on the surface of degradation promoter to form a degradation regulator with core-shell structure;

[0011] (2) The degradation regulator is blended with polyglycolic acid to obtain the polyglycolic acid temporary plugging agent.

[0012] The third aspect of the present invention provides the application of the above-mentioned polyglycolic acid temporary plugging agent with controllable degradation rate as a temporary plugging agent for oil and gas extraction, preferably applied to well conditions of 30 to 100°C, and more preferably applied to medium and low temperature well conditions of 30 to 70°C.

[0013] A fourth aspect of the present invention provides a method of using the above-mentioned polyglycolic acid temporary plugging agent, comprising the following steps:

[0014] (1) Based on the application environment and / or action time requirements of the temporary plugging agent in oil and gas extraction, set the expected degradation rate of the polyglycolic acid temporary plugging agent;

[0015] (2) Based on the expected degradation rate, determine the ratio of polylactic acid to degradation promoter in the degradation regulator, and the content of degradation regulator in polyglycolic acid temporary plugging agent;

[0016] (3) Based on the parameters determined in step (2), the polyglycolic acid temporary plugging agent is prepared using the above method;

[0017] (4) Apply the polyglycolic acid temporary plugging agent obtained in step (3) to the environment.

[0018] The temporary plugging agent described in this invention has the characteristics of low degradation rate in the early stage and continuously accelerating degradation rate in the later stage. This is because the degradation of the temporary plugging agent in the early stage is mainly the natural degradation of polyglycolic acid. With the release of acidic degradation products, it will promote the degradation of low molecular weight polylactic acid in the shell, especially the preferred amorphous racemic polylactic acid. The shell degradation and rupture will release the degradation promoter to create an alkaline environment, neutralize the degradation products of polyglycolic acid, and promote the accelerated breaking of polyglycolic acid ester bonds, thereby accelerating the degradation rate in the later stage.

[0019] This invention enables the regulation of the degradation rate of poly(ethylene glycol) temporary plugging agents by altering the thickness of the polylactic acid (PLA) shell and / or the content of degradation promoters in the temporary plugging agent. Specifically, it includes: a) controlling the shell thickness of the degradation regulator by changing the ratio of PLA to degradation promoters; that is, increasing the mass ratio of PLA in the degradation regulator increases the thickness of the PLA shell, which slows down the degradation rate of the temporary plugging agent, while decreasing the mass ratio of PLA in the degradation regulator accelerates the degradation rate of the temporary plugging agent; and / or b) changing the amount of degradation regulator added to the temporary plugging agent product; that is, increasing the amount of degradation regulator added accelerates the degradation rate of the temporary plugging agent, while decreasing the amount of degradation regulator added slows down the degradation rate of the temporary plugging agent.

[0020] This invention regulates the degradation performance of polyglycolic acid (PGA) temporary plugging agents, ensuring rapid and effective degradation after fracturing operations. This solves the problem of slow degradation rates in existing biodegradable temporary plugging agents in low- and medium-temperature environments. In particular, the core-shell structure design of the degradation regulator achieves an excellent balance between processability, plugging properties, and degradation performance. The PGA temporary plugging agent of this invention meets the fracturing strength requirements for diversion and temporary plugging in downhole environments of 30-100℃, with a fracturing pressure resistance greater than 20 MPa. It exhibits significant degradation advantages, especially in low- and medium-temperature environments of 30-70℃, rapidly degrading within 24-72 hours after fracturing operations. This eliminates the need for acidizing and backflow, improving operational efficiency and reducing construction costs.

[0021] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0022] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0023] This invention provides a polyglycolic acid temporary plugging agent with controllable degradation rate. The temporary plugging agent includes polyglycolic acid and a degradation regulator. The degradation regulator has a core-shell structure, with the outer shell being polylactic acid and the core being a degradation promoter.

[0024] Degradation accelerators in this field are typically slightly soluble or soluble acids and bases. If directly physically mixed with polyglycolic acid, they are easily dissolved and lost in the temporary plugging solution during actual construction, thus failing to exert their degradation-accelerating effect. Therefore, coating low molecular weight polylactic acid (especially racemic polylactic acid) onto the degradation accelerator surface to form a core-shell structure degradation regulator can avoid premature dissolution and loss of the degradation accelerator.

[0025] According to a preferred embodiment of the present invention, the degradation regulator is a core-shell structured particle with a particle size of 1-500 μm, preferably 50-300 μm, and more preferably 100-200 μm.

[0026] For ease of use, the polyglycolic acid temporary plugging agent is also in granular form, with a particle size of 10-500 mesh, preferably 20-200 mesh.

[0027] The polyglycolic acid temporary plugging agent of the present invention achieves controllable degradation rate by: changing the ratio of polylactic acid and degradation promoter, controlling the core-shell thickness of degradation regulator, and / or changing the amount of degradation regulator added to the temporary plugging agent product.

[0028] According to a preferred embodiment of the present invention, the mass ratio of polyglycolic acid to degradation regulator is 0.5:0.5 to 0.99:0.01, preferably 0.6:0.4 to 0.9:0.1.

[0029] According to a preferred embodiment of the present invention, the mass ratio of polylactic acid to degradation promoter is 0.1:0.9 to 0.99:0.01, preferably 0.2:0.8 to 0.6:0.4.

[0030] The mass ratio of polyglycolic acid to degradation regulator and the mass ratio of polylactic acid to degradation promoter can be adjusted within the above range to obtain a polyglycolic acid temporary plugging agent with the desired degradation rate.

[0031] According to a preferred embodiment of the present invention, the polyglycolic acid has a number-average molecular weight of 50,000-100,000 as determined by gel chromatography, and a melt index of 5-50 g / 10 min under conditions of 230°C and 2.16 kg load.

[0032] According to a preferred embodiment of the present invention, the polylactic acid is L-polylactic acid (PLLA) and / or racemic polylactic acid (PDLLA), preferably racemic polylactic acid, and the number-average molecular weight of the polylactic acid determined by gel chromatography is 20,000-150,000, preferably 20,000-50,000.

[0033] Various conventional degradation promoters can be used in this invention, including but not limited to one or more of organic amine compounds, imidazole compounds, piperazine compounds, triazine compounds, inorganic carbonate compounds, and metal hydroxide compounds.

[0034] According to a preferred embodiment of the present invention, the degradation promoter is a substance that is alkaline when exposed to water. After being released, it can further accelerate the degradation and rupture of the polylactic acid shell from the inside out. The released degradation promoter creates an alkaline environment and also promotes the degradation of polyglycolic acid, the main component of the temporary plugging agent. Therefore, preferably, the degradation promoter is selected from one or more of imidazole compounds, piperazine compounds, triazine compounds, and metal hydroxide compounds.

[0035] The organic amine compounds include, but are not limited to, one or more of ethylenediamine, polyethyleneimine, triethylenetetramine, triisopropanolamine, and trihydroxyethylamine, preferably polyethyleneimine.

[0036] The imidazole compounds include, but are not limited to, one or more of imidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-ethyl-4-methylimidazolium, 2-propylimidazolium, 2-aminoimidazolium, 2-tert-butylimidazolium, and 2-(2-imidazolyl)ethanol, preferably one or more of imidazole, 2-methylimidazolium, 2-ethylimidazolium, and 2-ethyl-4-methylimidazolium.

[0037] The piperazine compounds include, but are not limited to, one or more of piperazine, N-methylpiperazine, 2-methylpiperazine, 1-butylpiperazine, 1-ethylperpiperazine, and 1-phenylpiperazine, preferably one or more of piperazine and 2-methylpiperazine.

[0038] The triazine compounds include, but are not limited to, one or more of 1,3,5-triazine, 2,4-diamino-6-methyl-1,3,5-triazine (methyl melamine / methylguanidine), 2,4,6-trihydroxy-1,3,5-triazine (cyanuric acid), 2,4-diamino-6-phenyl-1,3,5-triazine (phenyl melamine), and 2,4,6-triamino-1,3,5-triazine (melamine).

[0039] The inorganic carbonate compounds include, but are not limited to, one or more of potassium carbonate, sodium carbonate, sodium bicarbonate, calcium carbonate, calcium bicarbonate, barium carbonate, zinc carbonate, magnesium carbonate, and ferrous carbonate, preferably one or more of barium carbonate, calcium carbonate, and zinc carbonate.

[0040] The metal hydroxide compounds include, but are not limited to, one or more of calcium hydroxide, magnesium hydroxide, aluminum hydroxide, zinc hydroxide, iron hydroxide, lead hydroxide, tin hydroxide, and cobalt hydroxide, preferably one or more of calcium hydroxide, magnesium hydroxide, aluminum hydroxide, and zinc hydroxide.

[0041] This invention provides a method for preparing the above-mentioned polyglycolic acid temporary plugging agent, comprising the following steps:

[0042] (1) Mix polylactic acid solution with degradation promoter, stir and disperse evenly, and then spray dry to coat polylactic acid on the surface of degradation promoter to form degradation regulator with core-shell structure; by controlling the ratio of polylactic acid and degradation promoter, degradation regulator with different particle size and shell thickness can be obtained.

[0043] (2) The degradation regulator is blended with polyglycolic acid to obtain the polyglycolic acid temporary plugging agent.

[0044] According to a preferred embodiment of the present invention, the polylactic acid solution is a mixture of polylactic acid and an organic solvent; the organic solvent is preferably at least one selected from dichloromethane, chloroform, acetone, ethyl acetate and tetrahydrofuran, and more preferably chloroform.

[0045] According to a preferred embodiment of the present invention, the volume of the organic solvent used is 2 to 6 mL, based on a total mass of 1 g of polylactic acid and degradation promoter.

[0046] According to the present invention, the degradation regulator and polyglycolic acid can be physically blended or melt blended, preferably physically blended.

[0047] According to a physical blending method of the present invention, the method of blending the degradation regulator with polyglycolic acid includes: pre-crushing the polyglycolic acid, and then mixing it with the degradation regulator in a high-speed stirring device according to the mass ratio to obtain a polyglycolic acid temporary blockage agent.

[0048] According to a melt blending method of the present invention, the method for blending the degradation regulator with polyglycolic acid includes: melt blending polyglycolic acid, degradation regulator and antioxidant through a twin-screw extruder, forming, granulating and drying to obtain modified polyglycolic acid, and then pulverizing the modified polyglycolic acid to obtain a polyglycolic acid temporary plugging agent.

[0049] According to a preferred embodiment of the present invention, the processing temperature of the twin-screw extruder is 180-240°C and the rotation speed is 150-300 r / min.

[0050] The antioxidant can be of various conventional types, including but not limited to one or more of antioxidant 168, antioxidant 1010, antioxidant 626 and antioxidant 618, preferably one or more of antioxidant 168 and antioxidant 1010; the amount of antioxidant added can be 0.1 to 2 parts by weight, based on 100 parts by weight of total polyvinyl alcohol temporary plugging agent.

[0051] In this invention, the pulverization method can be at least one of high-speed mechanical impact pulverization, disc airflow pulverization, ultrafine pulverization and liquid nitrogen cryogenic vibration pulverization, preferably high-speed mechanical impact pulverization.

[0052] Compared to similar products, the polyglycolic acid temporary plugging agent of this invention, with its controllable degradation rate, has significant degradation advantages as a temporary plugging agent for oil and gas extraction, and can meet the operational needs of oilfields for temporary plugging, diversion fracturing, and temporary plugging acidizing. The polyglycolic acid temporary plugging agent is suitable for well conditions ranging from 30 to 100°C, and particularly suitable for medium- and low-temperature well conditions ranging from 30 to 70°C.

[0053] This invention also provides a method for using polyglycolic acid temporary plugging agent, comprising the following steps:

[0054] (1) Based on the application environment and / or action time requirements of the temporary plugging agent in oil and gas extraction, set the expected degradation rate of the polyglycolic acid temporary plugging agent;

[0055] (2) Based on the expected degradation rate, determine the ratio of polylactic acid to degradation promoter in the degradation regulator, and the content of degradation regulator in polyglycolic acid temporary plugging agent;

[0056] (3) Based on the parameters determined in step (2), the polyglycolic acid temporary plugging agent is prepared using the above method;

[0057] (4) Apply the polyglycolic acid temporary plugging agent obtained in step (3) to the environment. The specific application method can be the conventional method of using temporary plugging agents, and the present invention does not particularly limit it.

[0058] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0059] 1. Raw material equipment

[0060] Polyglycolic acid, extrusion grade, Inner Mongolia Pujing Chemical Co., Ltd., has a number-average molecular weight of 55,000 g / mol as determined by gel permeation chromatography. Its melt index at 230℃ and 2.16 kg load is 23.5 g / 10 min, and its density is 1.584 g / cm³. 3 .

[0061] Polylactic acid (PLLA), FY201, Anhui Fengyuan Futailai Polylactic Acid Co., Ltd., has a number-average molecular weight of 23,000 g / mol as determined by gel chromatography.

[0062] Racemic polylactic acid (PDLLA), Hubei Supu Chemical Co., Ltd., had a number-average molecular weight of 22,000 g / mol as determined by gel permeation chromatography.

[0063] Melamine, 2-methylimidazole, AR, Aladdin (Shanghai) Co., Ltd.

[0064] Piperazine, AR, McLean Reagents Ltd.

[0065] Laser particle size analyzer, Mastersizer 3000, Malvern Instruments Ltd., UK.

[0066] Impact mill pulverizer, FD-75, Shandong Fengli Heavy Industry Co., Ltd.

[0067] Spray drying equipment, LPG-100, Changzhou Tailong Drying Technology Co., Ltd.

[0068] Core displacement instrument, HB-2, Haian County Petroleum Scientific Research Instrument Co., Ltd.

[0069] Melt flow rate tester: Tinius Olsen MP600 melt flow rate meter.

[0070] 2. Testing Methods

[0071] Water solubility stability: The water solubility of the temporary plugging agent was evaluated according to standard Q / SH CG0152—2021. The temperature of the constant temperature drying oven was set to 105℃. The experimental filter paper was dried to constant weight and recorded as m1. A certain amount of temporary plugging agent was weighed using an electronic balance and recorded as m2. It was added to a wide-mouth bottle containing 200mL of distilled water and stirred evenly. The wide-mouth bottle was placed in a water bath at a constant temperature of 30℃. After 30 minutes, the sample was removed and filtered through filter paper. Then, the filter paper and sample were placed in an oven at 105℃ and dried to constant weight and recorded as m3. The weight loss before and after washing was calculated using the following formula:

[0072] W(%)=(m1+m2-m3) / m2×100%

[0073] W represents the water-soluble weight loss rate. The lower the W value, the higher the water-soluble stability of the temporary plugging agent.

[0074] Degradation performance evaluation: The degradation performance of the temporary plugging agent was evaluated according to standard Q / SH CG0152—2021. All test samples underwent a wash stability test first: The temperature of the constant temperature drying oven was set to 105℃, and the experimental filter paper was dried to constant weight, recorded as m0. A certain amount of the temporary plugging agent was weighed using an electronic balance, recorded as m1, and added to a wide-mouth bottle containing 200mL of distilled water. After stirring evenly, the bottle was placed in an oven at 70℃ for 48 hours, after which heating was stopped. Within half an hour, the wide-mouth bottle was cooled to approximately 30℃, all samples were poured out, and the samples were dried in an oven at 105℃ to constant weight, recorded as m2. The degradation rate of the temporary plugging agent at 70℃ for 48 hours was calculated using the following formula:

[0075] D(%) = (m2 - m0) / m1 × 100%

[0076] Where m1 is the initial mass of the sample, (m2-m0) is the remaining mass of the sample after 48 hours, and D is the degradation rate.

[0077] Temporary plugging strength test: The temporary plugging pressure bearing capacity of the PGA temporary plugging agent before and after modification was evaluated according to standard Q / SH CG0152—2021. The specific operation is as follows: 1000mL of guar gum base solution was prepared and placed in a beaker, according to 200kg / m 3 Add the temporary plugging agent to the guar gum base solution, mix thoroughly, and then add 0.2%–0.5% crosslinking agent to form a gel containing the temporary plugging agent for later use. Set the outlet width of the wedge-shaped steel core fracture plate to 1 mm, insert it into the core holder, connect the holder to the intermediate container, and heat the core holder to 90°C. Open the connection valve of the intermediate container, start the horizontal flow pump, and conduct a displacement experiment with a flow rate of 40–100 mL / min. Within the rated maximum pressure range of the horizontal flow pump, observe and record the increase in displacement pressure after temporary plugging. When the pressure rises to a certain value and then rapidly decreases, the maximum pressure at this point is the pressure-bearing capacity of the temporary plugging agent.

[0078] The present invention will be described in detail below through embodiments:

[0079] Example 1

[0080] 50g of PDLLA was dissolved in 250mL of dichloromethane and stirred at 60rpm to dissolve. Then, 50g of melamine was added and stirred to disperse evenly. The PDLLA-coated melamine degradation regulator A1 was obtained by spray drying and dried in an oven at 90℃ for 8 hours for later use. Its particle size was 160μm.

[0081] PGA was pulverized into 20-200 mesh powder using an impact mill. 80 parts by weight of the pulverized PGA and 20 parts by weight of the degradation regulator A1 were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product S1.

[0082] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product S1 were tested, and the results are shown in Table 1.

[0083] Comparative Example 1

[0084] 50g of PDLLA was dissolved in 250mL of dichloromethane and stirred at 60rpm. The uncoated PDLLA was obtained by spray drying and used as B1. It was then dried in an oven at 90℃ for 8 hours and the particle size was 115μm.

[0085] PGA was pulverized into 20-200 mesh powder using an impact mill. 80 parts by weight of pulverized PGA, 10 parts by weight of B1 and 10 parts by weight of melamine were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product D1.

[0086] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product D1 were tested, and the results are shown in Table 1.

[0087] Comparative Example 2

[0088] PGA was pulverized into 20-200 mesh powder using an impact mill. 90 parts by weight of pulverized PGA and 10 parts by weight of melamine were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product D2.

[0089] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product D2 were tested, and the results are shown in Table 1.

[0090] Example 2

[0091] 50g of PDLLA was dissolved in 250mL of dichloromethane and stirred at 60rpm to dissolve. Then, 50g of melamine was added and stirred to disperse evenly. The PDLLA-coated melamine degradation regulator A2 was obtained by spray drying and dried in an oven at 90℃ for 8 hours for later use. Its particle size was 160μm.

[0092] PGA was pulverized into 20-200 mesh powder using an impact mill. 70 parts by weight of pulverized PGA and 30 parts by weight of degradation regulator A2 were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product S2.

[0093] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product S2 were tested, and the results are shown in Table 1.

[0094] Example 3

[0095] 30g of PDLLA was dissolved in 250mL of dichloromethane and stirred at 60rpm to dissolve. Then, 70g of melamine was added and stirred to disperse evenly. The PDLLA-coated melamine degradation regulator A3 was obtained by spray drying and dried in an oven at 90℃ for 8 hours for later use. Its particle size was 145μm.

[0096] PGA was pulverized into 20-200 mesh powder using an impact mill. 80 parts by weight of pulverized PGA and 20 parts by weight of degradation regulator A3 were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product S3.

[0097] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product S3 were tested, and the results are shown in Table 1.

[0098] Example 4

[0099] 30g of PDLLA was dissolved in 250mL of dichloromethane and stirred at 60rpm. Then, 70g of piperazine was added and stirred to disperse evenly. The degradation regulator A4, which is PDLLA-coated piperazine, was obtained by spray drying and dried in an oven at 90℃ for 8 hours. Its particle size was 125μm.

[0100] PGA was pulverized into 20-200 mesh powder using an impact mill. 80 parts by weight of pulverized PGA and 20 parts by weight of degradation regulator A4 were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product S4.

[0101] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product S4 were tested, and the results are shown in Table 1.

[0102] Example 5

[0103] 30g of PDLLA was dissolved in 250mL of dichloromethane and stirred at 60rpm. Then, 70g of magnesium hydroxide was added and stirred to disperse evenly. The degradation regulator A5, which is PDLLA coated with magnesium hydroxide, was obtained by spray drying and dried in an oven at 90℃ for 8 hours. Its particle size was 140μm.

[0104] PGA was pulverized into 20-200 mesh powder using an impact mill. 80 parts by weight of pulverized PGA and 20 parts by weight of degradation regulator A5 were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product S5.

[0105] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product S5 were tested, and the results are shown in Table 1.

[0106] Example 6

[0107] 30g of PDLLA was dissolved in 250mL of dichloromethane and stirred at 60rpm. Then, 70g of 2-methylimidazole was added and stirred to disperse evenly. The degradation regulator A6, which is PDLLA-coated with 2-methylimidazole, was obtained by spray drying and dried in an oven at 90℃ for 8 hours. Its particle size was 130μm.

[0108] PGA was pulverized into 20-200 mesh powder using an impact mill. 80 parts by weight of pulverized PGA and 20 parts by weight of degradation regulator A6 were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product S6.

[0109] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product S6 were tested, and the results are shown in Table 1.

[0110] Example 7

[0111] Dissolve 30g PLLA in 250mL dichloromethane and stir at 60rpm. Then add 70g 2-methylimidazole and stir to disperse evenly. Obtain PLLA-coated 2-methylimidazole degradation regulator A7 by spray drying. Dry in an oven at 90℃ for 8h for later use. Its particle size is 135μm.

[0112] PGA was pulverized into 20-200 mesh powder using an impact mill. 80 parts by weight of pulverized PGA and 20 parts by weight of degradation regulator A7 were mixed in a high-speed mixer for 10 minutes to obtain PGA temporary plugging agent product S7.

[0113] The water solubility stability, degradation performance (12h and 72h) and temporary plugging performance of PGA temporary plugging agent product S7 were tested, and the results are shown in Table 1.

[0114] Table 1 Performance test results of the samples

[0115]

[0116]

[0117] Analysis of Example 1 and Comparative Example 1 shows that the water-soluble weight loss rate of Example 1 is only 0.1%, and the degradation rate after 72 hours is 72.5%, while the water-soluble weight loss rate of Comparative Example 1 reaches 8.3%, and the degradation rate after 72 hours is 30.2%. This indicates that preparing a core-shell structured degradation regulator by coating melamine with PDLLA can significantly improve the water-soluble stability of the temporary plugging agent. In actual oilfield construction, the degradation promoter will not be dissolved prematurely by the temporary plugging fluid, allowing it to play a role in promoting degradation in the later stages.

[0118] The analysis of Example 1 and Comparative Example 2 also illustrates the above situation, and the addition of PDLLA helps to improve the temporary plugging strength of the temporary plugging agent. This is because PDLLA softens easily when heated, which can fill the pores between rigid PGA particles and achieve a better sealing effect.

[0119] Analysis of Examples 1, 2 and 3 shows that the degradation regulators formed by coating all have good water solubility stability. By changing the ratio of the degradation promoter in the degradation regulator and the ratio of the degradation regulator in the temporary plugging agent, the degradation rate of the temporary plugging agent can be controlled. The degradation rate at 70℃ and 72h is 58.5-80.6%.

[0120] Examples 3, 4, 5, and 6 illustrate the addition of different types of degradation promoters. Melamine, piperazine, magnesium hydroxide, and 2-methylimidazole all have the effect of promoting PGA degradation. In the presence of the PDLLA coating layer, the water-soluble weight loss rate is low, and the temporary blocking strength is similar. At the same mass ratio, piperazine and 2-methylimidazole are more effective because they have better water solubility and can quickly create a strong alkaline environment to promote PGA degradation after the PDLLA coating layer is broken.

[0121] Analysis of Examples 6 and 7 shows that using PDLLA as a degradation-promoting coating layer has a better degradation effect than PLLA. This is because PDLLA has an amorphous structure, its degradation rate is better than PLLA, and it is easier to degrade and break down in an acidic environment.

[0122] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0123] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A polyglycolic acid temporary plugging agent with controllable degradation rate, characterized in that, The temporary plugging agent includes polyglycolic acid and a degradation regulator, wherein the degradation regulator has a core-shell structure, with the outer shell being polylactic acid and the core being a degradation promoter.

2. The polyglycolic acid temporary plugging agent according to claim 1, wherein, The particle size of the degradation regulator is 1–500 μm, preferably 50–300 μm, and more preferably 100–200 μm.

3. The polyglycolic acid temporary plugging agent according to claim 1, wherein, The particle size of the polyglycolic acid temporary plugging agent is 10-500 mesh, preferably 20-200 mesh.

4. The polyglycolic acid temporary plugging agent according to claim 1, wherein, The mass ratio of polyglycolic acid to degradation regulator is 0.5:0.5 to 0.99:0.01, preferably 0.6:0.4 to 0.9:0.1; the mass ratio of polylactic acid to degradation promoter is 0.1:0.9 to 0.99:0.01, preferably 0.2:0.8 to 0.6:0.

4.

5. The polyglycolic acid temporary plugging agent according to claim 1, wherein, The polyglycolic acid, as determined by gel permeation chromatography, has a number-average molecular weight of 50,000-100,000 g / mol and a melt index of 5-50 g / 10 min under conditions of 230℃ and 2.16 kg load.

6. The polyglycolic acid temporary plugging agent according to claim 1, wherein, The polylactic acid is L-polylactic acid and / or racemic polylactic acid, preferably racemic polylactic acid, and the number-average molecular weight of the polylactic acid, as determined by gel chromatography, is 20,000-150,000 g / mol, preferably 20,000-50,000 g / mol.

7. The polyglycolic acid temporary plugging agent according to claim 1, wherein, The degradation promoter is selected from one or more of organic amine compounds, imidazole compounds, piperazine compounds, triazine compounds, inorganic carbonate compounds, and metal hydroxide compounds; preferably, the degradation promoter is selected from one or more of imidazole compounds, piperazine compounds, triazine compounds, and metal hydroxide compounds.

8. The polyglycolic acid temporary plugging agent according to claim 7, wherein, The organic amine compound is one or more of ethylenediamine, polyethyleneimine, triethylenetetramine, triisopropanolamine, and trihydroxyethylamine, preferably polyethyleneimine; The imidazole compound is one or more selected from imidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-ethyl-4-methylimidazolium, 2-propylimidazolium, 2-aminoimidazolium, 2-tert-butylimidazolium, and 2-(2-imidazolyl)ethanol, preferably one or more selected from imidazole, 2-methylimidazolium, 2-ethylimidazolium, and 2-ethyl-4-methylimidazolium; The piperazine compound is one or more selected from piperazine, N-methylpiperazine, 2-methylpiperazine, 1-butylpiperazine, 1-ethylperpiperazine, and 1-phenylpiperazine, preferably one or more selected from piperazine and 2-methylpiperazine; The triazine compounds are one or more selected from 1,3,5-triazine, 2,4-diamino-6-methyl-1,3,5-triazine, 2,4,6-trihydroxy-1,3,5-triazine, 2,4-diamino-6-phenyl-1,3,5-triazine and 2,4,6-triamino-1,3,5-triazine; The inorganic carbonate compound is one or more of potassium carbonate, sodium carbonate, sodium bicarbonate, calcium carbonate, calcium bicarbonate, barium carbonate, zinc carbonate, magnesium carbonate, and ferrous carbonate, preferably one or more of barium carbonate, calcium carbonate, and zinc carbonate. The metal hydroxide compound is one or more of calcium hydroxide, magnesium hydroxide, aluminum hydroxide, zinc hydroxide, iron hydroxide, lead hydroxide, tin hydroxide, and cobalt hydroxide, preferably one or more of calcium hydroxide, magnesium hydroxide, aluminum hydroxide, and zinc hydroxide.

9. A method for preparing the polyglycolic acid temporary plugging agent according to any one of claims 1-8, comprising the following steps: (1) Mix polylactic acid solution with degradation promoter, stir and disperse evenly, and then spray dry to coat polylactic acid on the surface of degradation promoter to form a degradation regulator with core-shell structure; (2) The degradation regulator is blended with polyglycolic acid to obtain the polyglycolic acid temporary plugging agent.

10. The preparation method according to claim 9, wherein, The polylactic acid solution is a mixture of polylactic acid and an organic solvent; the organic solvent is preferably at least one of dichloromethane, chloroform, acetone, ethyl acetate and tetrahydrofuran, and more preferably chloroform.

11. The preparation method according to claim 10, wherein, Based on a total mass of 1g for polylactic acid and degradation promoter, the volume of the organic solvent used is 2-6mL.

12. The preparation method according to claim 9, wherein, The method of blending the degradation regulator with polyglycolic acid includes: pre-crushing the polyglycolic acid, and then mixing it with the degradation regulator in a high-speed stirring device to obtain a polyglycolic acid temporary plugging agent.

13. The preparation method according to claim 9, wherein, The method of blending the degradation regulator with polyglycolic acid includes: melting and blending polyglycolic acid, degradation regulator and antioxidant through a twin-screw extruder, drawing, granulating and drying to obtain modified polyglycolic acid, and then pulverizing the modified polyglycolic acid to obtain polyglycolic acid temporary plugging agent.

14. The application of the polyglycolic acid temporary plugging agent with controllable degradation rate as described in any one of claims 1-8 as a temporary plugging agent for oil and gas extraction is preferably applied to well conditions of 30-100°C, and more preferably to medium and low temperature well conditions of 30-70°C.

15. A method of using the polyglycolic acid temporary plugging agent according to any one of claims 1-8, comprising the following steps: (1) Based on the application environment and / or action time requirements of the temporary plugging agent in oil and gas extraction, set the expected degradation rate of the polyglycolic acid temporary plugging agent; (2) Based on the expected degradation rate, determine the ratio of polylactic acid to degradation promoter in the degradation regulator, and the content of degradation regulator in polyglycolic acid temporary plugging agent; (3) Prepare the polyglycolic acid temporary plugging agent according to the parameters determined in step (2) using the method described in any one of claims 9-14; (4) Apply the polyglycolic acid temporary plugging agent obtained in step (3) to the environment.

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