Quickly degradable temporary plugging agent suitable for medium and low temperature reservoirs and preparation method thereof

Abstract

The invention belongs to the technical field of temporary plugging agents, and relates to a rapidly degradable temporary plugging agent suitable for medium and low temperature reservoirs and a preparation method thereof, the temporary plugging agent comprises 100 parts of degradable resin, 5-30 parts of a hydrolysis catalyst, 5-40 parts of a hydrolysis accelerator, and 10-40 parts of a filler; the degradable resin comprises degradable polyester and water-soluble resin, the degradable polyester is selected from polyglycolide and / or polylactic acid-glycolic acid copolymer, and the water-soluble resin is polyvinyl alcohol. Compared with the prior art, the temporary plugging agent provided by the invention takes the polylactic acid-glycolic acid copolymer and / or the polyglycolide as a main body material, the polyvinyl alcohol is introduced to promote degradation by utilizing the water swelling characteristic of the polyvinyl alcohol, and meanwhile, the hydrolysis catalyst, the hydrolysis accelerant and the filler are supplemented, so that the temporary plugging agent has the advantages of excellent plugging performance, better degradation performance in a hot water environment and the like; the method has good application potential in oil and gas exploitation of medium and low temperature reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of temporary plugging agents and relates to a rapidly degradable temporary plugging agent suitable for medium and low temperature reservoirs and a preparation method thereof. Background Art

[0002] Temporary plugging agents are substances that can temporarily reduce formation permeability or temporarily seal highly permeable reservoirs. In fields like oil and gas extraction, these agents are often required to provide high mechanical strength in the short term to effectively seal pores and cracks in the rock formation, while also being able to rapidly degrade thereafter. Common degradable materials such as polylactic acid (PLA) and polyglycolic acid (PGA) can generally meet the sealing and degradation requirements of temporary plugging agents at temperatures above 100°C. However, in low- to medium-temperature reservoirs, such as those between 60 and 90°C, PLA or PGA degrade very slowly, failing to meet the requirement for basic degradation within 48 to 72 hours. Summary of the Invention

[0003] The purpose of the present invention is to provide a rapidly degradable temporary plugging agent suitable for medium and low temperature reservoirs and a preparation method thereof, which has the advantages of excellent plugging performance and good degradation performance in hot water environment, and has good application potential in oil and gas exploitation in medium and low temperature reservoirs.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] The first aspect of the present invention provides a temporary plugging agent, comprising the following components and contents in parts by weight: 100 parts of a degradable resin, 5-30 parts of a hydrolysis catalyst, 5-40 parts of a hydrolysis accelerator, and 10-40 parts of a filler;

[0006] The degradable resin includes a degradable polyester and a water-soluble resin, wherein the degradable polyester is selected from one or a combination of polyglycolide (PGA) and polylactic acid-glycolic acid copolymer (PLGA), and the water-soluble resin is polyvinyl alcohol (PVA).

[0007] In some specific embodiments, the temporary plugging agent includes the following components and contents in parts by weight: 100 parts of a degradable resin, 10-20 parts of a hydrolysis catalyst, 10-30 parts of a hydrolysis accelerator, and 20-30 parts of a filler.

[0008] In some specific embodiments, the mass ratio of the degradable polyester to the water-soluble resin is 70:30 to 90:10.

[0009] In some preferred embodiments, the molecular weight of the polyglycolide is 50,000 to 200,000, and the molecular weight of the polylactic acid-co-glycolic acid is 50,000 to 200,000. Unless otherwise specified, the molecular weights in the present invention are weight average molecular weights.

[0010] In some preferred embodiments, the polyvinyl alcohol has a degree of alcoholysis of 85 to 99 mol% and a degree of polymerization of 400 to 1000. Although polyvinyl alcohol can dissolve in water at 60°C, its pressure-bearing performance is poor when used alone. When mixed with polyglycolide and / or polylactic-co-glycolic acid as a dispersed phase, the polyvinyl alcohol swells in water, destroying the skeleton structure of the temporary plugging agent and promoting its degradation.

[0011] In some specific embodiments, the hydrolysis catalyst is an alkaline compound that is slightly soluble in water or insoluble in water; wherein, a slightly soluble substance generally refers to a substance with a solubility of 0.01g to 1g / 100g water at room temperature of 20°C, and a insoluble substance generally refers to a substance with a solubility of less than 0.01g / 100g water at room temperature of 20°C.

[0012] In some preferred embodiments, the hydrolysis catalyst is selected from one or a combination of magnesium oxide, magnesium hydroxide, and calcium hydroxide, which has weak alkalinity. The appropriate addition amount will not cause the decomposition of the degradable resin during processing, and can also promote the degradation rate of the degradable resin during the fracturing process.

[0013] In some specific embodiments, the hydrolysis promoter is an inorganic salt that is readily soluble in water. A readily soluble substance generally refers to a substance with a solubility greater than 10 g / 100 g water at room temperature of 20°C.

[0014] In some preferred embodiments, the hydrolysis promoter is selected from at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate. It is easily soluble in water, has a small particle size, low hygroscopicity in the air, and is easy to be made into powder. Other water-soluble inorganic salts are easy to deliquesce or agglomerate, and are difficult to be evenly dispersed in the temporary plugging agent during processing; after the hydrolysis promoter is dissolved, the specific surface area of ​​the remaining temporary plugging agent in contact with water is greatly increased, thereby accelerating the hydrolysis reaction.

[0015] In some specific embodiments, the filler is an inorganic reinforcing agent, selected from at least one of calcium carbonate, aluminum oxide, aluminum hydroxide, zinc oxide, and zinc hydroxide. While reducing the cost of the temporary plugging agent, it can increase the strength of the temporary plugging agent, does not affect the degradation rate, and can be dissolved by the acid generated by resin hydrolysis without residue.

[0016] In some specific embodiments, the hydrolysis catalyst, hydrolysis accelerator, and filler are all powders, and the average particle size is preferably less than 100 μm.

[0017] A second aspect of the present invention provides a method for preparing a temporary plugging agent, comprising:

[0018] Mixing the degradable polyester and the water-soluble resin in proportion to form a resin material;

[0019] Mixing the hydrolysis catalyst, the hydrolysis accelerator, and the filler in proportion to form a powder material;

[0020] The resin material and the powder material are heated and mixed uniformly, and then extruded into particles or blocks through an extruder. The particles or blocks are crushed to obtain the temporary plugging agent.

[0021] In some specific embodiments, during the heating and mixing, the mixing temperature is 190-240°C.

[0022] In some preferred embodiments, the heating and mixing is performed in an internal mixer. More preferably, because the particle size of the biodegradable resin (e.g., 2-5 mm) is significantly different from the particle size of the powder material (e.g., <100 μm), and the large amount of powder material added makes uniform mixing difficult, the resin material is fed through the main feed port and the powder material is fed through the side feed port. This feeding method allows the powder additive to be evenly dispersed in the biodegradable resin.

[0023] In some specific embodiments, the particle size of the granules obtained by extrusion granulation is 5 to 6 mm.

[0024] In some specific embodiments, the crushed material obtained by crushing the particles or blocks is classified by a vibrating screen to obtain temporary plugging agents of different particle sizes.

[0025] In some specific embodiments, the particle size distribution range of the temporary plugging agent is 75 μm to 6 mm.

[0026] In some preferred embodiments, temporary plugging agents of different particle sizes are mixed together in a proportion and used, and the temporary plugging agent is a mixture of granular materials and powder; more preferably, it is a mixture of granular materials with a particle size range of 5 to 6 mm and powder materials with a size of 100-200 mesh; further preferably, the granular materials and powder materials are mixed in a mass ratio of 1:(0.5 to 1.5).

[0027] The present invention uses polylactic acid-glycolic acid copolymer and / or polyglycolide as the main material, introduces polyvinyl alcohol to utilize its water-swelling property to promote degradation, and is supplemented with a hydrolysis catalyst, a hydrolysis accelerator and a filler to produce a high-efficiency temporary plugging agent with the advantages of excellent plugging performance and good degradation performance in hot water environments. It has great application potential in oil and gas production in medium and low-temperature reservoirs.

[0028] Compared with the prior art, the present invention has the following characteristics:

[0029] 1) The present invention uses degradable polyester polylactic acid-co-glycolic acid (PLGA) and / or polyglycolide (PGA) as the main component of the temporary plugging agent. They have high mechanical strength and can block oil reservoirs. At the same time, they can be hydrolyzed in water into water-soluble small molecules to play a role in unblocking. This meets the requirements of high strength when used as a temporary plugging agent and degradable when unblocking.

[0030] 2) The present invention uses polyvinyl alcohol (PVA) resin as an auxiliary component of the temporary plugging agent. After being blended with PGA and / or PLGA, it exists in the temporary plugging agent as a dispersed phase. During the degradation process of the temporary plugging agent, the PVA swells, accelerating the disintegration of the skeleton structure of the degradable resin, further promoting the degradation process;

[0031] 3) The present invention accelerates the hydrolysis reaction of PGA and / or PLGA by introducing a hydrolysis catalyst, thereby accelerating the dissolution rate of the temporary plugging agent;

[0032] 4) The present invention introduces a hydrolysis promoter to achieve rapid dissolution, thereby increasing the contact area between PGA and / or PLGA and water and accelerating the dissolution rate of the temporary plugging agent;

[0033] 5) The present invention introduces a filler to increase the strength of the temporary plugging agent, and the filler can be dissolved by the acid generated by the hydrolysis of the resin without any residue. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0035] The following are more detailed implementation cases, which further illustrate the technical solutions of the present invention and the technical effects that can be obtained.

[0036] In the following examples, unless otherwise specified, raw materials, reagents or processing techniques are all conventional commercially available products or conventional processing techniques in the art.

[0037] In the following examples, the weight-average molecular weight of poly(lactic acid-co-glycolic acid) (PLGA, GA / LA is 70 / 30) is 170,000, the weight-average molecular weight of poly(glycolide) (PGA) is 180,000, and polyvinyl alcohol (PVA) is purchased from Kuraray, with a degree of alcoholysis of 97% to 99% and a degree of polymerization of 400.

[0038] Example:

[0039] A rapidly degradable temporary plugging agent suitable for medium and low temperature reservoirs, the preparation method of which comprises the following steps:

[0040] S1: The biodegradable resins in Table 1 are mixed uniformly in proportion to obtain a resin material; the hydrolysis catalyst, hydrolysis accelerator, and filler in Table 1 are mixed uniformly in proportion using a mixer to obtain a powder material;

[0041] Table 1 Formulation of temporary plugging agent

[0042]

[0043]

[0044] S2: Set the temperature of the internal mixer to 220°C, feed the resin material through the main feed port, and add the powder material into the feed bin of the side feed port in small amounts and multiple times (3 to 5 times) during the internal mixer process to ensure that it is fully mixed in the internal mixer;

[0045] S3: Transfer the mixed material in the internal mixer to a single screw extruder. Set the extrusion temperature at 238°C, extrude, strand and pelletize, and control the particle size to 5-6mm; or extrude into blocks;

[0046] S4: The cut particles or blocks are crushed, and the obtained crushed materials are then classified by a vibrating screen to obtain temporary plugging agents of different particle sizes.

[0047] Application Example: Plugging Performance Test

[0048] This example is used to test the plugging performance of the temporary plugging agents prepared in the examples and comparative examples. The rock mass crack model used for the test adopts a wedge-shaped crack steel rock (crack width is 1 mm). The specific test method is as follows:

[0049] Step 1: Prepare a guar gum base solution (0.4% guar gum + 0.15% to 0.3% sodium carbonate): Measure 1000 mL of distilled water, 4.0 g of hydroxypropyl guar gum, and 1.5 g to 3.0 g of sodium carbonate, mix well, pour the solution into a wide-mouth bottle, cover, and place in a 30°C water bath for 4 hours;

[0050] Step 2: Measure 1000mL of guar gum base liquid and place it in a beaker. 3 The temporary plugging agent (3-5mm particles and 100-200 mesh powder in a mass ratio of 1:1) is added to the guar gum base liquid and the mixture is stirred evenly to form a temporary plugging agent-containing gel;

[0051] Step 3: Place the wedge-shaped fracture steel rock into the core holder and heat the core holder to 70°C;

[0052] Step 4: Place the gel containing the temporary plugging agent into the intermediate container and connect the intermediate container to the inlet pipeline of the core holder;

[0053] Step 5: Open the connecting valve on the inlet pipeline, start the horizontal flow pump, set the horizontal flow pump displacement to 40mL / min, and the pressure limit to 5MPa, conduct a displacement experiment, observe and record the pressure rise after temporary plugging, and when the pressure rises to 10MPa after temporary plugging, record the time from being able to stabilize at 10MPa (pressure fluctuation value ≤0.2MPa) to being unable to stabilize at 10MPa (pressure fluctuation value ≥0.5MPa), which is the effective plugging time;

[0054] Step 6: Based on step 5, continue to increase the displacement of the horizontal flow pump and conduct displacement experiments at a displacement of 40mL / min to 100mL / 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, the pressure drops rapidly. The maximum pressure at this time is the plugging strength of the temporary plugging agent.

[0055] The plugging performance test results show that, by using polylactic acid-glycolic acid copolymer and / or polyglycolide as the main material, the temporary plugging agents 1-9 prepared in the examples and the temporary plugging agents prepared in comparative examples 1, 2, 4, and 6 can all achieve a plugging strength of more than 20 MPa and an effective plugging time of more than 1 hour, which can effectively block the pores and cracks in the rock formation and meet the plugging requirements of oil and gas production scenarios. However, the plugging performance of comparative examples 3 and 5 does not meet the standards, which may be due to excessive addition of a hydrolysis catalyst or a hydrolysis promoter, resulting in too fast an initial hydrolysis rate of the temporary plugging agent and / or poor formability of the temporary plugging agent.

[0056] Application Example: Degradation Performance Test

[0057] This example is used to test the degradation performance of the temporary plugging agents prepared in the examples and comparative examples. The specific test method is as follows: particles with a particle size distribution of 3-5 mm and powders with a size distribution of 100-200 mesh are placed in 70°C distilled water, and a degradation rate (i.e., the mass change rate of the degradation agent) ≥ 90% is defined as complete degradation. The degradation performance of the temporary plugging agent is evaluated based on the time taken for complete degradation.

[0058] The degradation performance test results are shown in Table 2.

[0059] Table 2

[0060]

[0061]

[0062] Degradation performance test results show that, compared with temporary plugging agent 9, Comparative Example 1 does not contain a hydrolysis catalyst or a hydrolysis promoter. The complete dissolution time of the temporary plugging agents of both particle sizes in Comparative Example 1 is over 280 hours. Comparative Examples 2 and 3 do not contain a hydrolysis promoter, and the amount of hydrolysis catalyst contained in Comparative Example 3 is the sum of the weight of the hydrolysis catalyst and hydrolysis promoter contained in temporary plugging agent 9. The test results show that the introduction of a hydrolysis catalyst can significantly reduce the complete dissolution time of the temporary plugging agent. Increasing the amount of hydrolysis catalyst added can further promote the hydrolytic degradation of the temporary plugging agent. However, excessive addition has a negative impact on its plugging performance, resulting in the plugging performance of Comparative Example 3 not meeting the standard.

[0063] Compared with temporary plugging agent 9, comparative examples 4 and 5 do not contain a hydrolysis catalyst, wherein the amount of hydrolysis promoter contained in comparative example 5 is the sum of the weight parts of the hydrolysis catalyst and the hydrolysis promoter contained in temporary plugging agent 9. The test results show that the introduction of the hydrolysis promoter can also reduce the complete dissolution time of the temporary plugging agent, but its hydrolysis-promoting effect is weaker than that of the hydrolysis catalyst. Similarly, the more the amount of hydrolysis promoter added, the more it can promote the hydrolysis and degradation of the temporary plugging agent, and excessive addition has a negative impact on its plugging performance.

[0064] Compared with temporary plugging agent 9, comparative example 6 does not contain polyvinyl alcohol. The temporary plugging agent with a powder particle size of 100-200 mesh in comparative example 6 can be completely dissolved within 72 hours, and the temporary plugging agent with a powder particle size of 3-5 mm can be completely dissolved in more than 84 hours.

[0065] The temporary plugging agents 1-9 prepared in the examples of the present invention can be completely degraded in a hot water environment within 48 hours at the earliest and 72 hours at the latest, meeting the degradation requirements of the temporary plugging agent. Polyvinyl alcohol is introduced into the main resin material, and the swelling property of polyvinyl alcohol in contact with water is utilized to destroy the skeleton structure of the temporary plugging agent from the inside, thereby promoting its degradation. In addition, with the use of hydrolysis catalysts such as magnesium oxide, hydrolysis promoters such as sodium chloride, and fillers such as calcium carbonate, the temporary plugging agent can be rapidly degraded while ensuring an effective plugging time. The synergistic use of the hydrolysis catalyst and the hydrolysis promoter exhibits excellent degradation-promoting properties.

[0066] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A temporary plugging agent, characterized in that: The invention comprises the following components and their contents by weight: 100 parts of degradable resin, 5-30 parts of hydrolysis catalyst, 5-40 parts of hydrolysis accelerator, and 10-40 parts of filler; The degradable resin includes a degradable polyester and a water-soluble resin, wherein the degradable polyester is selected from one or a combination of polyglycolide and polylactic acid-glycolic acid copolymer, and the water-soluble resin is polyvinyl alcohol.

2. The temporary plugging agent according to claim 1, characterized in that The invention comprises the following components and their contents in parts by weight: 100 parts of degradable resin, 10-20 parts of hydrolysis catalyst, 10-30 parts of hydrolysis accelerator and 20-30 parts of filler.

3. The temporary plugging agent according to claim 1 or 2, characterized in that: The mass ratio of the degradable polyester to the water-soluble resin is 70:30 to 90:

10.

4. The temporary plugging agent according to claim 3, characterized in that: The molecular weight of the polyglycolide is 50,000 to 200,000; the molecular weight of the polylactic acid-glycolic acid copolymer is 50,000 to 200,000; The polyvinyl alcohol has an alcoholysis degree of 85-99 mol% and a polymerization degree of 400-1000.

5. The temporary plugging agent according to claim 1 or 2, characterized in that: The hydrolysis catalyst is an alkaline compound that is slightly soluble or difficult to dissolve in water; Preferably, the hydrolysis catalyst is selected from one or a combination of magnesium oxide, magnesium hydroxide, and calcium hydroxide.

6. The temporary plugging agent according to claim 1 or 2, characterized in that: The hydrolysis accelerator is an inorganic salt that is easily soluble in water; Preferably, the hydrolysis promoter is selected from at least one of sodium chloride, potassium chloride, sodium sulfate and potassium sulfate.

7. The temporary plugging agent according to claim 1 or 2, characterized in that: The filler is selected from at least one of calcium carbonate, aluminum oxide, aluminum hydroxide, zinc oxide, and zinc hydroxide.

8. The temporary plugging agent according to claim 1 or 2, characterized in that: The hydrolysis catalyst, hydrolysis accelerator and filler are all powders; Preferably, the average particle size of the hydrolysis catalyst, hydrolysis accelerator and filler is less than 100 microns.

9. A method for preparing the temporary plugging agent according to any one of claims 1 to 8, characterized in that: include: Mixing the degradable polyester and the water-soluble resin in proportion to form a resin material; Mixing the hydrolysis catalyst, the hydrolysis accelerator, and the filler in proportion to form a powder material; The resin material and the powder material are heated and mixed uniformly, and then extruded into particles or blocks through an extruder, and the particles or blocks are crushed to obtain the temporary plugging agent.

10. The method for preparing a temporary plugging agent according to claim 9, characterized in that: The heating and mixing is carried out in an internal mixer, the resin material is fed through the main feeding port, and the powder material is fed through the side feeding port, and the mixing temperature is 190-240°C; and / or, the crushed material obtained by crushing the particles or blocks is classified to obtain temporary plugging agents of different particle sizes; And / or, the particle size distribution range of the temporary plugging agent is 75 μm to 6 mm.

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