High-strength oil-gas well temporary plugging agent and preparation method thereof

Abstract

The invention discloses a high-strength oil-gas well temporary plugging agent and a preparation method thereof.The preparation method of the temporary plugging agent comprises the steps that hydroxypropyl guar gum, chitosan, dibenzoyl peroxide and deionized water are mixed and then put into a reaction kettle, acrylamide and polyvinyl alcohol are added for a mixed reaction, cooling is conducted, and modified hydroxypropyl guar gum is obtained; the preparation method comprises the following steps: mixing kaolin obtained by crushing, calcining and ball-milling kaolinite with ethyl cellulose, 2, 5-furandimethanol and deionized water, adding dimethyl sulfoxide and potassium acetate, carrying out ultrasonic treatment, and drying to obtain modified kaolin; mixing the modified hydroxypropyl guar gum, polylactic acid, sodium carboxymethyl cellulose and deionized water to obtain a colloidal solution; and homogenizing the colloidal solution, the modified kaolin, phytic acid and N-hydroxysuccinimide to obtain the oil and gas well temporary plugging agent. The prepared temporary plugging agent has the advantages of high temporary plugging strength, high temperature resistance, high pressure resistance and long plugging time, and the used raw materials are all environment-friendly raw materials, so that the damage to the stratum and the environment is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of oil production engineering for oil and gas wells, and particularly relates to a high-strength temporary plugging agent for oil and gas wells and a preparation method thereof. Background Art

[0002] During the process of petroleum gas extraction, due to problems such as abnormal formation pressure and loss of drilling fluid, leakage points such as cracks and holes occur in the oil and gas wells, resulting in continuous leakage of the drilling fluid into the cracks or holes, unable to complete the circulation, making the drilling operation unable to continue. At the same time, the appearance of cracks or holes is also likely to cause the loss of substances such as mud in the oil and gas wells, affecting the stability and oil production efficiency of the oil and gas wells.

[0003] An oil and gas well temporary plugging agent is a substance that can temporarily reduce the formation permeability or temporarily plug high-permeability oil layers. The use of the temporary plugging agent can temporarily plug the leakage points in the oil and gas wells, control the flow of the oil layer, prevent the cross-flow of oil and water, thereby protecting the non-target layer from being damaged during the operation of the oil and gas well, preventing problems such as the loss of drilling fluid or mud, thus improving the oil and gas extraction efficiency and ensuring production safety.

[0004] Currently, the temporary plugging agents on the market have problems such as insufficient plugging strength, poor temperature and pressure resistance performance, short plugging time, difficult degradation, and poor plugging effect, and it is difficult to meet the requirements of complex well conditions.

[0005] Therefore, there is an urgent need to provide a high-strength temporary plugging agent for oil and gas wells and a preparation method thereof to improve the plugging strength, temperature and pressure resistance performance, and plugging time of the temporary plugging agent, thereby improving the oil and gas extraction efficiency and ensuring production safety. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-strength temporary plugging agent for oil and gas wells and a preparation method thereof to solve the problems of insufficient plugging strength, poor temperature and pressure resistance performance, short plugging time, difficult degradation, and poor plugging effect of the temporary plugging agent mentioned in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solution: A high-strength temporary plugging agent for oil and gas wells, comprising the following components in parts by weight: 30 - 35 parts of modified hydroxypropyl guar gum, 25 - 28 parts of polylactic acid, 18 - 22 parts of modified kaolin, 10 - 12 parts of phytic acid, 4 - 7 parts of sodium carboxymethylcellulose, 2 - 3 parts of N-hydroxysuccinimide, and 40 - 45 parts of deionized water.

[0008] Further, the modified hydroxypropyl guar gum is prepared by mixing and reacting the following components in parts by weight: 55 - 60 parts of hydroxypropyl guar gum, 15 - 18 parts of chitosan, 6 - 8 parts of benzoyl peroxide, 3 - 5 parts of acrylamide, 1 - 3 parts of polyvinyl alcohol, and 70 - 80 parts of deionized water.

[0009] Further, the modified kaolin is prepared by mixing and modifying the following components in parts by weight: 40-45 parts of kaolin, 20-23 parts of ethyl cellulose, 10-15 parts of dimethyl sulfoxide, 8-10 parts of potassium acetate, 2-5 parts of 2,5-furandimethanol, and 50-55 parts of deionized water.

[0010] Further, the preparation method of the high-strength oil and gas well temporary plugging agent includes the following steps:

[0011] Step 1, preparation of modified hydroxypropyl guar gum: Mix hydroxypropyl guar gum, chitosan, benzoyl peroxide and deionized water, stir, put them into a reaction kettle, add acrylamide and polyvinyl alcohol, react and cool to obtain modified hydroxypropyl guar gum.

[0012] Step 2, preparation of modified kaolin: Put kaolinite into a calcination furnace at 780-820 °C for calcination for 3-3.5 h, and then ball mill to obtain kaolin; Mix kaolin, ethyl cellulose, 2,5-furandimethanol and deionized water in proportion, put them into an ultrasonic device, then add dimethyl sulfoxide and potassium acetate, ultrasonically treat for 110-120 min, and then dry to obtain modified kaolin.

[0013] Step 3, mix and stir the modified hydroxypropyl guar gum, polylactic acid, sodium carboxymethyl cellulose and deionized water in proportion to obtain a uniform colloidal solution.

[0014] Step 4, put the colloidal solution in Step 3 into a homogenizer, add modified kaolin, phytic acid and N-hydroxysuccinimide for homogenization to obtain the oil and gas well temporary plugging agent.

[0015] As a preferred technical solution of the present invention, the temperature of the reaction kettle is 120-125 °C and the reaction time is 35-40 min.

[0016] As a preferred technical solution of the present invention, before calcining the kaolinite, it also includes: crushing the kaolinite, and the particle size of the kaolinite is all greater than or equal to 0.6 mm and less than or equal to 1.0 mm.

[0017] As a preferred technical solution of the present invention, the particle size of the ball-milled kaolin is 600-700 mesh.

[0018] As a preferred technical solution of the present invention, the ultrasonic frequency is 120-150 Hz and the temperature is 55-60 °C.

[0019] As a preferred technical solution of the present invention, the rotation speed of the homogenizer is 80-90 rpm, the temperature is 70-80 °C, and the homogenization time is 35-40 min.

[0020] As a preferred technical solution of the present invention, the viscosity of the temporary plugging agent is 60 to 70 mPa·s.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. In the present invention, hydroxypropyl guar gum, chitosan, and acrylamide are mixed and modified together. The amino groups (-NH2) and hydroxyl groups (-OH) on the chitosan molecular chain can undergo a condensation reaction with the hydroxyl groups in hydroxypropyl guar gum to form ether bonds (-O-) or amide bonds (-CONH-); react with carboxyl groups (-COOH) to form ionic bonds or amide bonds, thereby forming a dense network structure, improving the strength and stability of the temporary plugging agent, increasing the specific surface area and porosity of the temporary plugging agent, thus providing more adsorption sites, enhancing the ability to adsorb impurities and hard particulate matters in oil and gas wells, and improving the plugging efficiency. At the same time, this dense network structure enhances the bonding force between the temporary plugging layer and the rock surface, preventing the temporary plugging layer from falling off or failing due to changes in downhole pressure or fluid erosion in oil and gas wells. The introduction of acrylamide improves the solubility and dispersibility of hydroxypropyl guar gum in water, enhances the intermolecular interaction, improves the film-forming performance and adsorption ability of hydroxypropyl guar gum, and enhances the uniformity, mechanical strength, elasticity, and toughness of the temporary plugging agent, thereby improving the plugging effect of the temporary plugging agent. Adding initiator benzoyl peroxide and surfactant polyvinyl alcohol during the modification process of hydroxypropyl guar gum can promote the progress of the modification reaction, thereby improving the thermal stability, salt resistance, and shear resistance of the temporary plugging agent.

[0023] 2. The present invention calcines kaolinite under high-temperature conditions, which improves the whiteness, specific surface area, thermal stability and activity of kaolinite, thereby enhancing the high-temperature resistance performance and plugging effect of the temporary plugging agent. Ultrasonic waves can promote the diffusion and penetration of dimethyl sulfoxide and potassium acetate intercalating agent molecules between the kaolinite layers. At the same time, the added 2,5-furandimethanol can reduce the interfacial tension between the intercalating agent molecules and the kaolinite surface, which helps the intercalating agent molecules to better wet and adsorb on the kaolinite surface, thus promoting the progress of the intercalation reaction. The S=O functional group in dimethyl sulfoxide can form a bond with the hydroxyl groups on the inner surface of kaolinite, enabling the dimethyl sulfoxide molecules to smoothly insert between the kaolinite layers, increasing the layer spacing of kaolinite, enhancing the specific surface area of kaolinite, improving the dispersibility and stability of kaolinite in the temporary plugging agent, and further being able to more effectively promote the filling and plugging of the pores and fractures in the formation by the temporary plugging agent. The C=O functional group of potassium acetate combines with the hydroxyl groups (-OH) of the aluminum oxide layer or the oxygen (O) of the silicon oxide layer of kaolinite to form hydrogen bonds, enabling the potassium acetate molecules to be embedded between the kaolinite layers, increasing the kaolinite layer spacing, and improving the intercalation efficiency and intercalation rate of kaolinite. The modified kaolinite has a larger specific surface area and layer spacing, can adsorb more plugging substances on its surface, thereby enhancing the plugging effect of the temporary plugging agent; at the same time, the modification of kaolinite can endow it with stronger binding force, making the temporary plugging agent more stable when bearing the formation pressure, helping to prevent the temporary plugging agent from falling off or deforming under the formation pressure, thereby extending the effective plugging time of the temporary plugging agent; furthermore, the modified kaolinite has better fluidity, high-temperature resistance and chemical corrosion resistance, enabling the temporary plugging agent to be more easily injected into the formation, and being able to maintain stable plugging performance and the stability of structure and performance in a high-temperature environment.

[0024] 3. The present invention adds phytic acid during the preparation of the temporary plugging agent. Phytic acid can chelate metal ions such as calcium and magnesium in the formation to form a single-molecule dense protective film, reducing the interference of these ions during the temporary plugging process and preventing the penetration and leakage of fluids, thereby improving the plugging performance of the temporary plugging agent. Phytic acid also has excellent antioxidant and anti-corrosion properties, which can improve the stability of the temporary plugging agent and reduce the failure of the temporary plugging agent caused by improper storage or long-term storage of the temporary plugging agent.

[0025] 4. The raw materials used in the present invention are all environmentally friendly raw materials, which are non-polluting to the formation and easy to degrade. The temporary plugging agent is an environmentally friendly colloidal substance, which can quickly achieve the plugging effect by pumping during use, and is easily dissolved and removed under high-temperature conditions after plugging, without causing damage to the formation and the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the preparation flow chart of the temporary plugging agent for oil and gas wells of the present invention;

[0027] Figure 2 is the viscosity broken line chart of the temporary plugging agent of the present invention;

[0028] Figure 3 This is the broken line graph of the temporary plugging strength of the temporary plugging agent of the present invention. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] A large number of hydrophilic amino groups (-NH2), hydroxyl groups (-OH) and other active groups are contained in the chitosan molecular chain. These active groups can undergo a condensation reaction with the hydroxyl groups (-OH) in hydroxypropyl guar gum to form ether bonds (-O-) or amide bonds (-CONH-); react with carboxyl groups (-COOH) to form ionic bonds or amide bonds; and can interact with the hydroxypropyl groups in hydroxypropyl guar gum to promote the occurrence of cross-linking reactions, thereby forming a dense network structure and improving the strength and stability of the temporary plugging agent.

[0031] Impurities and particulate matters in oil and gas wells are the main reasons for the increase in formation permeability or the formation of high-permeability oil layers. The dense network structure formed by chitosan and hydroxypropyl guar gum can increase the specific surface area and porosity of the temporary plugging agent, thereby providing more adsorption sites and enhancing the ability to adsorb impurities and hard particulate matters in oil and gas wells. At the same time, this dense network structure can increase the binding force between the temporary plugging layer and the rock surface, preventing the temporary plugging layer from falling off or failing due to changes in the downhole pressure of oil and gas wells or the erosion of fluids.

[0032] The introduction of acrylamide increases the amide groups and other hydrophilic groups in the hydroxypropyl guar gum molecule, improves the solubility and dispersibility of hydroxypropyl guar gum in water, improves the film-forming performance and adsorption ability of hydroxypropyl guar gum, and enhances the uniformity and plugging efficiency of the temporary plugging agent. The branched chain structure of acrylamide is introduced into the hydroxypropyl guar gum molecular chain, enhancing the intermolecular interaction and improving the mechanical strength, elasticity and toughness of hydroxypropyl guar gum. Adding initiator benzoyl peroxide and surfactant polyvinyl alcohol during the modification process of hydroxypropyl guar gum can promote the progress of the modification reaction, thereby improving the thermal stability, salt resistance and shear resistance of the temporary plugging agent.

[0033] Kaolinite is an important clay mineral, mainly containing silicon dioxide and aluminum oxide, and also containing a small amount of impurity elements such as calcium, magnesium, potassium, sodium, iron, and titanium. In the present invention, kaolinite is crushed into a suitable particle size and then calcined under high-temperature conditions. High-temperature calcination can remove the hydroxyl groups on the surface of kaolinite, improving the whiteness, specific surface area, thermal stability, and activity of kaolinite, thereby enhancing the high-temperature resistance performance and plugging effect of the temporary plugging agent. The calcined kaolin is placed in an ultrasonic device for modification. Ultrasonic waves can promote the diffusion and penetration of dimethyl sulfoxide and potassium acetate intercalating agent molecules between the kaolinite layers through cavitation effects, microjets, and microstirring. At the same time, the added surfactant 2,5-furandimethanol can reduce the interfacial tension between the intercalating agent molecules and the kaolin surface, helping the intercalating agent molecules to better wet and adsorb on the kaolin surface, thereby promoting the intercalation reaction. The S=O functional group in dimethyl sulfoxide can form a bond with the hydroxyl groups on the inner surface of kaolinite, enabling the dimethyl sulfoxide molecules to smoothly insert between the kaolinite layers, increasing the layer spacing of kaolinite, enhancing the aspect ratio and specific surface area of kaolinite, thereby improving the dispersibility and stability of kaolinite in the temporary plugging agent, and further being able to more effectively promote the filling and plugging of pores and fractures in the formation by the temporary plugging agent. The C=O functional group of potassium acetate combines with the hydroxyl group (-OH) of the kaolinite alumina layer or the oxygen (O) of the silica layer to form a hydrogen bond, enabling the potassium acetate molecules to be embedded between the kaolinite layers, increasing the kaolinite layer spacing, thereby improving its physical and chemical properties. The potassium acetate intercalating agent can also improve the intercalation efficiency and intercalation rate of kaolinite. The modified kaolin has a large specific surface area and layer spacing, can adsorb more plugging substances on its surface, thereby enhancing the plugging effect of the temporary plugging agent; at the same time, the modification of kaolin can endow it with stronger binding force, making the temporary plugging agent more stable when bearing the formation pressure, helping to prevent the temporary plugging agent from falling off or deforming under the formation pressure, thereby extending the effective plugging time of the temporary plugging agent; furthermore, the modified kaolin has better fluidity, high-temperature resistance, and chemical corrosion resistance, enabling the temporary plugging agent to be more easily injected into the formation, and maintaining stable plugging performance and the stability of structure and performance in a high-temperature environment.

[0034] Phytic acid is an organic phosphoric acid compound containing active phosphate groups and has the ability to complex with various metal ions. It can chelate metal ions such as calcium and magnesium in the formation, forming a single-molecule dense protective film, while reducing the interference of these ions during the temporary plugging process and preventing the penetration and leakage of fluids, thereby improving the plugging performance of the temporary plugging agent. Phytic acid also has excellent antioxidant and anti-corrosion properties. Adding phytic acid to the temporary plugging agent can improve the stability of the temporary plugging agent and reduce the failure of the temporary plugging agent caused by improper storage or long-term storage of the temporary plugging agent.

[0035] In this embodiment, kaolinite is crushed so that the particle size of kaolinite is all greater than or equal to 0.6 mm and less than or equal to 1.0 mm.

[0036] When the particle size of kaolinite is too small, the powder particles are prone to agglomeration during high-temperature calcination, resulting in an increase in the contact area between particles, making heat transfer and mass exchange during the calcination process relatively difficult, thus affecting the calcination effect. Moreover, kaolinite with too small a particle size is prone to fly during the calcination process, which will not only increase the difficulty of calcination operation, but also may cause environmental pollution and waste of raw materials. For kaolinite particles with too large a particle size, their specific surface area is relatively small, and the contact area with oxygen is limited, which will lead to uneven heat transfer during the calcination process, and some particles may not be fully calcined. Moreover, when the particle size of kaolinite is too large, the carbonaceous matter inside the particles cannot come into full contact with oxygen, resulting in incomplete oxidative removal, and the product may show a black heart phenomenon. Moreover, kaolinite with too large a particle size requires a longer calcination time and a higher calcination temperature to achieve an ideal calcination effect, which will increase energy consumption and production costs.

[0037] As Figure 1 shown, a preparation method of a high-strength oil and gas well temporary plugging agent provided by an embodiment of the present application includes the following steps: Step 1: Mix hydroxypropyl guar gum, chitosan, benzoyl peroxide, and deionized water and stir, then place them in a reaction kettle, add acrylamide and polyvinyl alcohol for a mixed reaction, and cool to obtain modified hydroxypropyl guar gum. Step 2: Crush kaolinite and place it in a calcination furnace at 780-820 °C for calcination for 3-3.5 h, and then ball mill to obtain kaolin with a particle size of 600-700 mesh; mix kaolin, ethyl cellulose, 2,5-furandimethanol, and deionized water and place them in an ultrasonic device, then add dimethyl sulfoxide and potassium acetate and perform ultrasonic treatment for 110-120 min, and then dry to obtain modified kaolin. Step 3: Mix modified hydroxypropyl guar gum, polylactic acid, sodium carboxymethyl cellulose, and deionized water in proportion and stir to obtain a uniform colloidal solution. Step 4: Place the colloidal solution in Step 3 into a homogenizer, add modified kaolin, phytic acid, and N-hydroxysuccinimide, and homogenize for 35-40 min to obtain an oil and gas well temporary plugging agent.

[0038] The raw materials used in the present invention are all commercially available raw materials.

[0039] Example 1:

[0040] A high-strength oil and gas well temporary plugging agent includes the following components in parts by weight: 30 parts of modified hydroxypropyl guar gum, 25 parts of polylactic acid, 18 parts of modified kaolin, 10 parts of phytic acid, 4 parts of sodium carboxymethyl cellulose, 2 parts of N-hydroxysuccinimide, and 40 parts of deionized water.

[0041] A preparation method of a high-strength oil and gas well temporary plugging agent includes the following steps:

[0042] Step 1. Preparation of modified hydroxypropyl guar gum: Mix 55 parts by weight of hydroxypropyl guar gum, 15 parts by weight of chitosan, 6 parts by weight of benzoyl peroxide, and 70 parts by weight of deionized water, stir, then place them into a reaction kettle at 120 °C, add 3 parts by weight of acrylamide and 1 part by weight of polyvinyl alcohol, mix and react for 40 min, and cool to obtain modified hydroxypropyl guar gum.

[0043] Step 2. Preparation of modified kaolin: Crush kaolinite, screen kaolinite with a particle size greater than or equal to 0.6 mm and less than or equal to 1.0 mm, place it into a calcination furnace at 780 °C for calcination for 3.5 h, and then ball mill to obtain kaolin with a particle size of 600 - 700 mesh; Mix 40 parts by weight of kaolin, 20 parts by weight of ethyl cellulose, 2 parts by weight of 2,5 - furandimethanol, and 50 parts by weight of deionized water, place them into an ultrasonic device, then add 10 parts by weight of dimethyl sulfoxide and 8 parts by weight of potassium acetate, and perform ultrasonic treatment at a frequency of 120 Hz and a temperature of 55 °C for 120 min, and then dry to obtain modified kaolin.

[0044] Step 3. Mix the modified hydroxypropyl guar gum, polylactic acid, sodium carboxymethyl cellulose, and deionized water in proportion and stir to obtain a uniform colloidal solution.

[0045] Step 4. Place the colloidal solution in Step 3 into a homogenizer with a rotation speed of 80 rpm and a temperature of 70 °C, add the modified kaolin, phytic acid, and N - hydroxysuccinimide, and homogenize for 40 min to obtain an oil and gas well temporary plugging agent with a viscosity of 68 mPa·s.

[0046] Example 2:

[0047] A high - strength oil and gas well temporary plugging agent, comprising the following components in parts by weight: 35 parts of modified hydroxypropyl guar gum, 28 parts of polylactic acid, 22 parts of modified kaolin, 12 parts of phytic acid, 7 parts of sodium carboxymethyl cellulose, 3 parts of N - hydroxysuccinimide, and 45 parts of deionized water.

[0048] A preparation method of a high - strength oil and gas well temporary plugging agent, comprising the following steps:

[0049] Step 1. Preparation of modified hydroxypropyl guar gum: Mix 60 parts by weight of hydroxypropyl guar gum, 18 parts by weight of chitosan, 8 parts by weight of benzoyl peroxide, and 80 parts by weight of deionized water, stir, then place them into a reaction kettle at 125 °C, add 5 parts by weight of acrylamide and 3 parts by weight of polyvinyl alcohol, mix and react for 35 min, and cool to obtain modified hydroxypropyl guar gum.

[0050] Step 2. Preparation of modified kaolin: Crush kaolinite, screen kaolinite with a particle size greater than or equal to 0.6 mm and less than or equal to 1.0 mm, place it in a calcination furnace at 820 °C for 3 h, and then ball-mill to obtain kaolin with a particle size of 600 - 700 mesh; Mix 45 parts by weight of kaolin, 23 parts by weight of ethyl cellulose, 5 parts by weight of 2,5-furandimethanol, and 55 parts by weight of deionized water, place it in an ultrasonic device, and then add 15 parts by weight of dimethyl sulfoxide and 10 parts by weight of potassium acetate, and perform ultrasonic treatment at a frequency of 150 Hz and a temperature of 60 °C for 110 min, and then dry to obtain modified kaolin.

[0051] Step 3. Mix and stir the modified hydroxypropyl guar gum, polylactic acid, sodium carboxymethyl cellulose, and deionized water in proportion to obtain a uniform colloidal solution.

[0052] Step 4. Place the colloidal solution in Step 3 into a homogenizer with a rotation speed of 90 rpm and a temperature of 80 °C, add modified kaolin, phytic acid, and N-hydroxysuccinimide, and homogenize for 35 min to obtain an oil and gas well temporary plugging agent with a viscosity of 63 mPa·s.

[0053] Example 3:

[0054] A high-strength oil and gas well temporary plugging agent, comprising the following components in parts by weight: 32 parts of modified hydroxypropyl guar gum, 26 parts of polylactic acid, 20 parts of modified kaolin, 11 parts of phytic acid, 5 parts of sodium carboxymethyl cellulose, 2.5 parts of N-hydroxysuccinimide, and 42 parts of deionized water.

[0055] A preparation method of a high-strength oil and gas well temporary plugging agent, comprising the following steps:

[0056] Step 1. Preparation of modified hydroxypropyl guar gum: Mix 56 parts by weight of hydroxypropyl guar gum, 16 parts by weight of chitosan, 7 parts by weight of benzoyl peroxide, and 75 parts by weight of deionized water, stir and place it in a reaction kettle at 122 °C for 35 min, add 4 parts by weight of acrylamide and 2 parts by weight of polyvinyl alcohol, mix and react, and cool to obtain modified hydroxypropyl guar gum.

[0057] Step 2. Preparation of modified kaolin: Crush kaolinite, screen kaolinite with a particle size greater than or equal to 0.6 mm and less than or equal to 1.0 mm, place it in a calcination furnace at 800 °C for 3.5 h, and then ball-mill to obtain kaolin with a particle size of 600 - 700 mesh; Mix 42 parts by weight of kaolin, 22 parts by weight of ethyl cellulose, 3 parts by weight of 2,5-furandimethanol, and 52 parts by weight of deionized water, place it in an ultrasonic device, and then add 12 parts by weight of dimethyl sulfoxide and 9 parts by weight of potassium acetate, and perform ultrasonic treatment at a frequency of 130 Hz and a temperature of 55 °C for 120 min, and then dry to obtain modified kaolin.

[0058] Step 3: Mix modified hydroxypropyl guar gum, polylactic acid, sodium carboxymethyl cellulose, and deionized water in proportion and stir to obtain a uniform colloidal solution.

[0059] Step 4: Place the colloidal solution from Step 3 into a homogenizer with a rotation speed of 85 rpm and a temperature of 75 °C, add modified kaolin, phytic acid, and N-hydroxysuccinimide, and homogenize for 40 min to obtain an oil and gas well temporary plugging agent with a viscosity of 65 mPa·s.

[0060] Comparative Example 1:

[0061] The difference from Example 1 is that the modified hydroxypropyl guar gum in Example 1 is removed.

[0062] Comparative Example 2:

[0063] The difference from Example 1 is that the hydroxypropyl guar gum in Example 1 is directly added to the raw materials for preparing the temporary plugging agent without modification.

[0064] Comparative Example 3:

[0065] The difference from Example 1 is that the modified kaolin in Example 1 is removed.

[0066] Comparative Example 4:

[0067] The difference from Example 1 is that the phytic acid in Example 1 is removed.

[0068] Perform performance tests on the temporary plugging agents prepared in Example 1, 2, 3 and Comparative Example 1, 2, 3, 4.

[0069] Place the temporary plugging agent on a borehole plugging simulation device to test the temporary plugging strength and temporary plugging time. The diameter of the ball seat hole of the simulation device is 3.0 mm. Place the simulation device in a core holder and fix it. Raise the temperature of the core holder to the experimental temperature, which is set to 140 °C, 160 °C, 180 °C. Inject the temporary plugging agent at a constant rate. After the pressure rises, continue to increase the pressure to the set pressure value and maintain the pressure. The highest bearing pressure value is the temporary plugging strength, and the time for forming an effective plugging state is the temporary plugging time. Record the temporary plugging strength and temporary plugging time. The results are shown in Table 1.

[0070] Table 1: Temporary plugging strength and temporary plugging time of the temporary plugging agent

[0071]

[0072] As shown in Table 1, the temporary plugging strength and temporary plugging time of the temporary plugging agent in the examples are both higher than those in the comparative examples. Moreover, with the increase of the set temperature, the temporary plugging strength and temporary plugging time of the temporary plugging agent in both the examples and the comparative examples decrease. Under the temperature condition of 180 °C, the temporary plugging strengths of Examples 1, 2, and 3 are 74.6 MPa, 72.3 MPa, and 73.4 MPa respectively, and the temporary plugging times are 13.5 h, 14.0 h, and 13.5 h respectively. While the temporary plugging strengths of Comparative Examples 1, 2, 3, and 4 are 48.5 MPa, 66.3 MPa, 47.5 MPa, and 70.2 MPa respectively, and the temporary plugging times are 10.5 h, 12.5 h, 9.5 h, and 12.5 h respectively. This shows that the temporary plugging agent in the examples still has strong temporary plugging strength and temporary plugging time under high-temperature conditions, while the temporary plugging agent in the comparative examples has poor temporary plugging strength and short temporary plugging time under high-temperature conditions. The modified hydroxypropyl guar gum can form a dense network structure, which can improve the film-forming property and adsorption capacity of the temporary plugging agent, thereby enhancing the strength, thermal stability, and plugging effect of the temporary plugging agent. The modified kaolin can make it have stronger binding force, making the temporary plugging agent more stable when bearing the formation pressure, which helps to prevent the temporary plugging agent from falling off or deforming under the formation pressure, thus prolonging the effective plugging time of the temporary plugging agent. The addition of phytic acid can reduce the interference of metal ions during the temporary plugging process, prevent the penetration and leakage of fluids, and thereby improve the plugging performance of the temporary plugging agent.

[0073] The temporary plugging agents prepared in Examples 1, 2, and 3 were respectively mixed with water in a ratio of 1:5 in a beaker and then placed under the condition of 180 °C to test the viscosity of the mixed liquid in the beaker. As Figure 2 shown, the viscosities of the temporary plugging agents of Examples 1, 2, and 3 and water after being mixed evenly in the beaker are 44.3 mPa·s, 44.2 mPa·s, and 43.7 mPa·s respectively. With the increase of time, the viscosity of the mixed liquid in the beaker shows a downward trend. The downward trend is relatively gentle in the first 60 h and becomes obvious after 60 h. The viscosities of Examples 1, 2, and 3 at 90 h are 3.5 mPa·s, 3.2 mPa·s, and 3.4 mPa·s respectively, and the viscosity remains at about 2.5 mPa·s after 90 h. The temporary plugging agent prepared by the present invention is soluble in water and all uses environmentally friendly raw materials. It can be self-degraded and backflowed after construction, and will not cause damage to the formation and the environment.

[0074] After storing the temporary plugging agents prepared in Example 1 and Comparative Example 4 at room temperature for 3 months, 6 months, 9 months, 12 months, 15 months, and 18 months, the temporary plugging strength of the temporary plugging agent was tested under the condition of 160 °C. As Figure 3As shown, with the extension of the storage time, the temporary plugging strength of the temporary plugging agent shows a downward trend. After the temporary plugging agent of Comparative Example 4 is stored for 12 months, its temporary plugging strength decreases significantly. When stored for 18 months, the temporary plugging strengths of the temporary plugging agents of Example 1 and Comparative Example 4 are 68.5 MPa and 33.0 MPa respectively. Phytic acid has excellent antioxidant and anti-corrosion properties, which can improve the stability of the temporary plugging agent, reduce the failure of the temporary plugging agent caused by improper storage or long-term storage, and thus affect its temporary plugging strength.

[0075] In summary, the temporary plugging agent prepared by the present invention has high temporary plugging strength, high temperature and pressure resistance performance, long plugging time, and the raw materials used are all environmentally friendly raw materials. After construction, it can be self-degraded and backflowed, and will not cause damage to the formation and environment.

[0076] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent replacements or modifications made based on the present invention to solve basically the same technical problems and achieve basically the same technical effects are all covered by the protection scope of the present invention.

Claims

1. A high-strength temporary plugging agent for oil and gas wells, characterized in that, It comprises the following components in parts by weight: 30 - 35 parts of modified hydroxypropyl guar gum, 25 - 28 parts of polylactic acid, 18 - 22 parts of modified kaolin, 10 - 12 parts of phytic acid, 4 - 7 parts of sodium carboxymethyl cellulose, 2 - 3 parts of N-hydroxysuccinimide, and 40 - 45 parts of deionized water; The modified hydroxypropyl guar gum is prepared by mixing and reacting the following components in parts by weight: 55 - 60 parts of hydroxypropyl guar gum, 15 - 18 parts of chitosan, 6 - 8 parts of benzoyl peroxide, 3 - 5 parts of acrylamide, 1 - 3 parts of polyvinyl alcohol, and 70 - 80 parts of deionized water; The modified kaolin is prepared by mixing and modifying the following components in parts by weight: 40 - 45 parts of kaolin, 20 - 23 parts of ethyl cellulose, 10 - 15 parts of dimethyl sulfoxide, 8 - 10 parts of potassium acetate, 2 - 5 parts of 2,5-furandimethanol, and 50 - 55 parts of deionized water.

2. The preparation method of a high-strength temporary plugging agent for oil and gas wells according to claim 1, characterized in that, It includes the following steps: Step 1, Preparation of modified hydroxypropyl guar gum: Mix hydroxypropyl guar gum, chitosan, benzoyl peroxide and deionized water, stir, put them into a reaction kettle, add acrylamide and polyvinyl alcohol, mix and react, and cool to obtain modified hydroxypropyl guar gum; Step 2, Preparation of modified kaolin: Put kaolinite into a calcination furnace at 780 - 820 °C for calcination for 3 - 3.5 h, then ball mill to obtain kaolin; Mix kaolin, ethyl cellulose, 2,5-furandimethanol and deionized water in proportion, put them into an ultrasonic device, then add dimethyl sulfoxide and potassium acetate, carry out ultrasonic treatment for 110 - 120 min, and then dry to obtain modified kaolin; Step 3, Mix and stir the modified hydroxypropyl guar gum, polylactic acid, sodium carboxymethyl cellulose and deionized water in proportion to obtain a uniform colloidal solution; Step 4, Put the colloidal solution in Step 3 into a homogenizer, add modified kaolin, phytic acid and N-hydroxysuccinimide for homogenization to obtain an oil and gas well temporary plugging agent.

3. The preparation method of a high-strength temporary plugging agent for oil and gas wells according to claim 2, characterized in that, The temperature of the reaction kettle is 120 - 125 °C, and the reaction time is 35 - 40 min.

4. The preparation method of a high-strength temporary plugging agent for oil and gas wells according to claim 2, characterized in that, Before calcining the kaolinite, it also includes: pulverizing the kaolinite, and the particle size of the kaolinite is all greater than or equal to 0.6 mm and less than or equal to 1.0 mm.

5. The preparation method of a high-strength oil and gas well temporary plugging agent according to claim 2, characterized in that, The particle size of the ball-milled kaolin is 600 - 700 mesh.

6. The preparation method of a high-strength temporary plugging agent for oil and gas wells according to claim 2, characterized in that, The ultrasonic frequency is 120 - 150 Hz, and the temperature is 55 - 60 °C.

7. The preparation method of a high-strength temporary plugging agent for oil and gas wells according to claim 2, characterized in that, The rotation speed of the homogenizer is 80 - 90 rpm, the temperature is 70 - 80 °C, and the homogenization time is 35 - 40 min.

8. The preparation method of a high-strength temporary plugging agent for oil and gas wells according to claim 2, characterized in that, The viscosity of the temporary plugging agent is 60 - 70 mPa·s.

Images