Temporary plugging agent for fracturing acidification and preparation method thereof

Abstract

The application belongs to the technical field of oil exploitation, and particularly relates to a temporary plugging agent for fracturing acidification and a preparation method thereof. The preparation method is as follows: in a reactor, itaconic acid, p-styrene sulfonic acid, 2-allyloxy methyl-2-hydroxymethyl propane-1,3-diol, vinyl pyridine, pentaerythritol diacrylate, buffer salt and deionized water are sequentially added, stirring is conducted, the pH value is adjusted, and all raw materials are completely dissolved; an initiator is added from a high-position dropping tank, the reaction is automatically heated, the reaction is kept, a reducing agent is added, the reaction is terminated, the pH value is adjusted, and a temporary plugging agent solution is obtained; the temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent. The preparation method has the characteristics of simple synthesis process and no by-products; the temporary plugging agent has the advantages of large water absorption, large plugging strength, high breakthrough pressure, self-degradation and designable degradation time.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a temporary plugging agent for fracturing and acidizing and its preparation method. Background Technology

[0002] my country has a wide distribution and large reserves of low-permeability oil and gas reservoirs, with the discovered low-permeability oil and gas resources accounting for more than 50% of the proven reserves. However, due to severe stratigraphic heterogeneity, small reservoir pore throats, and large variation coefficients of interlayer permeability, it is necessary to modify the rock formations.

[0003] Fracturing and acidizing is a crucial measure for large-scale production enhancement in carbonate oil and gas fields. Two main factors control the success of fracturing and acidizing: the effective length of the final acid-fracturing fracture and the conductivity of the acid-etched fracture after fracturing. Acid loss significantly impacts both factors, with a more pronounced effect on the extension of the artificial main fracture. During large-scale acid fracturing production enhancement in fractured carbonate reservoirs, acid loss is severe, primarily through natural fractures. Temporary plugging agents are needed during fracturing to temporarily seal natural fractures and promote the extension of artificial fractures to more distant wellbore areas.

[0004] To address this issue, temporary plugging fracturing acidizing technology has emerged, and the performance of the plugging agent is key to the effective implementation of this technology.

[0005] Temporary plugging agents are chemical agents that temporarily seal fractures, used to protect non-target formations from operational damage during oil and water well operations. The degradation performance of the temporary plugging agent directly affects its effectiveness in sealing fractures and its ability to unblock them. If the temporary plugging agent has poor degradation properties, it will not degrade quickly after fracturing operations, remaining trapped between proppant layers for an extended period, preventing normal oil and gas penetration. While it may achieve the fracturing objective, it will not increase oil and gas field production and may even negatively impact yields.

[0006] CN107090282A discloses a mixed temporary plugging agent, a mixture of temporary plugging agents, a temporary plugging method, and its application. The mixed temporary plugging agent comprises the following components in parts by weight: 1-9 parts water-soluble polymer, 3-29 parts sand, and 0-19 parts soluble or biodegradable fiber. The mixed temporary plugging agent is prepared into a mixture using 10-100 parts by weight of a carrier fluid. This mixture is then used to displace the plugging agent into a predetermined location in the downhole fracture using a displacement fluid, thus forming a temporary plugging wall with a certain viscosity. This invention can be applied to vertical well stratified fracturing, horizontal well staged fracturing, and repeated fracturing of old wells. The plugging location can be controlled by adjusting the adhesion time (based on the temporary plugging agent concentration) and injection rate (based on wellbore volume and displacement fluid volume), achieving 100% plugging success and high plugging strength, which is beneficial for subsequent fracturing to open new fractures (increasing new drainage area) and further improving oil and gas well production. However, after construction, the temporary plugging agent cannot automatically degrade, requiring the addition of ammonium persulfate for depolymerization, increasing the construction difficulty.

[0007] CN106905940A discloses a medium-to-high density elastic liquid plug and a well workover method, relating to the oil and gas chemical industry. The medium-to-high density elastic liquid plug is mainly composed of the following components by weight, prepared through a cross-linking reaction: 3-5 parts polymer, 0.25-1.5 parts first cross-linking agent, 2-4 parts second cross-linking agent, 0.015-0.035 parts stabilizer, 0.2-0.8 parts additive, and 98-102 parts weighting agent solution. The concentration of the weighting agent solution is 40-85 × 10⁻⁶. 4 A potassium formate aqueous solution at a concentration of mg / L. The density can reach 1.2-1.3 g / cm³. 3 A method for preparing the aforementioned medium-to-high density elastic liquid plug is disclosed. This medium-to-high density elastic liquid plug exhibits good fluidity at low temperatures and can rapidly undergo a cross-linking reaction at high downhole temperatures. It possesses advantages such as adjustable density, temperature and pressure resistance, good pumpability, good stability, no need for a rupture process, and efficient backflow. However, after well workover, a certain amount of external force is required to concentrate and break the liquid plug into elastic plug particles for degradation, followed by flushing with brine kill fluid circulation, making the process complex.

[0008] CN113150758A discloses a pH-sensitive temporary plugging agent, its preparation method, and its application in the exploitation of low-permeability oil reservoirs, relating to the field of oilfield exploitation technology. The temporary plugging agent provided by this invention comprises the following raw materials in weight percentages: 3-8% carboxymethyl chitosan, 0.2-0.7% gelatin, 0.1-0.6% initiator, 5-15% toughening agent, and water as the balance. This invention uses carboxymethyl chitosan and gelatin as the main materials. Carboxymethyl chitosan and gelatin can copolymerize. With the addition of toughening agent and initiator, the resulting temporary plugging agent is a pH-sensitive one. When the pH value in the medium changes, the hydrophilicity of the free amino and carboxyl groups on the carboxymethyl chitosan and gelatin molecular chains changes significantly, exhibiting different swelling properties. The pH-sensitive temporary plugging agent provided by this invention not only has good plugging effect but also strong acid resistance, remaining stable under acidic conditions and degradable with alkaline solvents, causing minimal damage to the formation. However, the temporary plugging agent of this invention only has a plugging rate of about 90%, and the plugging effect needs to be further improved. Summary of the Invention

[0009] This invention addresses the shortcomings of existing technologies by providing a temporary plugging agent for fracturing and acidizing, and its preparation method. The preparation method features a simple synthesis process and no byproducts; the temporary plugging agent has advantages such as high water absorption, high plugging strength, high breakthrough pressure, self-degradability, and the ability to design degradation time.

[0010] One objective of this invention is to disclose a temporary plugging agent for fracturing and acidizing, the molecular structure of which is as follows:

[0011]

[0012] in:

[0013] a = 500 - 20000

[0014] b = 20000 - 200000

[0015] c = 4000 - 40000

[0016] d = 8000 - 80000

[0017] e = 4000 - 40000

[0018] f = 500 - 20000

[0019] g = 20000 - 200000

[0020] h = 4000 - 40000

[0021] i = 8000 - 80000

[0022] j = 4000 - 40000.

[0023] Preferably, the viscosity-average molecular weight of the temporary plugging agent is 25,000,000-35,000,000.

[0024] Another objective of this invention is to disclose a method for preparing the aforementioned temporary plugging agent for fracturing and acidizing, the specific steps of which are as follows:

[0025] (1) Add itaconic acid, p-styrene sulfonic acid, 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, vinylpyridine, pentaerythritol diacrylate, buffer salt, and deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 5-10 minutes to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 until all raw materials are completely dissolved.

[0026] (2) Add the initiator dropwise from the high-level drop tank. The reaction will automatically heat up. After the temperature stops rising, continue the reaction for 10-20 minutes. Raise the temperature to 55-60℃ and keep it at that temperature for 30-60 minutes. Add the reducing agent to terminate the reaction. Adjust the pH to 7-7.5 to obtain the temporary plugging agent solution.

[0027] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0028] Preferably, based on 1 mole of itaconic acid, the amounts of p-styrenesulfonic acid, 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, vinylpyridine, and pentaerythritol diacrylate are 0.1-0.2, 0.2-0.4, 0.1-0.2, and 0.01-0.05 moles, respectively.

[0029] Preferably, in step (1), the buffer salt is one of sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, and diammonium hydrogen phosphate, and the weight ratio of the buffer salt to itaconic acid is 0.05-0.1:1.

[0030] More preferably, the buffer salt is one of sodium dihydrogen phosphate, potassium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0031] Preferably, in step (1), the weight ratio of deionized water to itaconic acid is 5-8:1.

[0032] Preferably, in step (2), the initiator is one of potassium persulfate aqueous solution, ammonium persulfate aqueous solution, or sodium persulfate aqueous solution, with a concentration of 8-12 wt% and a weight ratio of itaconic acid of 0.1-0.3:1.

[0033] Preferably, in step (2), the reducing agent is one of sodium sulfite aqueous solution, potassium sulfite aqueous solution, sodium bisulfite aqueous solution, and potassium bisulfite aqueous solution, with a concentration of 8-12 wt% and a weight ratio of itaconic acid of 0.1-0.3:1.

[0034] The reaction equation for the synthesis of the temporary plugging agent for fracturing and acidizing in this invention is as follows:

[0035]

[0036] The temporary plugging agent for fracturing acidification of the present invention is a five-component polymer, wherein the polymer monomers are itaconic acid, p-styrene sulfonic acid, 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, vinylpyridine, and pentaerythritol diacrylate. Itaconic acid, as the polymer matrix, contains two carboxyl groups in its molecule, exhibiting excellent water absorption, which significantly increases the product's volume and the clogging sweep volume. P-Styrenesulfonic acid, a hard surfactant, enhances the product's shear resistance, wettability, and permeability, allowing the molecule to adhere tightly to the rock surface and significantly improve the clogging effect. 2-Allyloxymethyl-2-hydroxymethylpropane-1,3-diol, a polyol, also significantly increases the product's volume and the clogging sweep volume. Vinylpyridine, a rigid monomer, improves the product's clogging strength and shear resistance, while also possessing surface activity, which is beneficial for wetting the hydrophobic profile of the formation and increasing the clogging rate. Pentaerythritol diacrylate, a crosslinking agent, transforms the entire molecule from a one-dimensional structure to a two-dimensional or three-dimensional structure, significantly increasing the molecular weight, sweep volume, clogging capacity, and compressive strength. Furthermore, the acrylate can hydrolyze at high temperatures, allowing for control of the degradation time by adjusting the dosage.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) The raw materials for the temporary plugging agent for fracturing acidizing of the present invention are readily available, the synthesis process is simple, and there are no by-products.

[0039] (2) The temporary plugging agent for fracturing acidizing of the present invention can be automatically degraded by adjusting the formula ratio and the degradation time can be controlled within 12-54 hours, making construction simple;

[0040] (3) The temporary plugging agent for fracturing acidizing of the present invention has a high plugging rate and unplugging rate, both reaching over 98%;

[0041] (4) The temporary plugging agent for fracturing and acidizing of the present invention has high plugging strength, and the breakthrough pressure gradient of low permeability core can reach up to 265 MPa / m, and the breakthrough pressure gradient of high permeability core can reach up to 190 MPa / m. Detailed Implementation

[0042] 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.

[0043] Example 1

[0044] (1) Add 0.5 mol itaconic acid, 0.05 mol p-styrene sulfonic acid, 0.2 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.05 mol vinylpyridine, 0.005 mol pentaerythritol diacrylate, 3.25 g sodium dihydrogen phosphate, and 325 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 5 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0045] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 13.4g of 8wt% potassium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 20 minutes. Heat up to 55℃ and keep the reaction at that temperature for 60 minutes. Add the reducing agent. The reducing agent is 12.8g of 8wt% potassium sulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0046] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0047] Example 2

[0048] (1) Add 0.5 mol itaconic acid, 0.07 mol p-styrene sulfonic acid, 0.16 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.06 mol vinylpyridine, 0.008 mol pentaerythritol diacrylate, 3.83 g sodium dihydrogen phosphate, and 447 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 6 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0049] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 8.98g of 10wt% potassium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 10min. Heat up to 60℃ and keep the reaction at that temperature for 30min. Add the reducing agent. The reducing agent is 10.3g of 12wt% potassium sulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0050] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0051] Example 3

[0052] (1) Add 0.5 mol itaconic acid, 0.06 mol p-styrene sulfonic acid, 0.14 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.07 mol vinylpyridine, 0.01 mol pentaerythritol diacrylate, 5.84 g potassium dihydrogen phosphate, and 500 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 8 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0053] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 6.5g of 12wt% potassium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 15 minutes. Heat up to 60℃ and keep the reaction at that temperature for 30 minutes. Add the reducing agent, which is 6.5g of 12wt% potassium bisulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0054] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0055] Example 4

[0056] (1) Add 0.5 mol itaconic acid, 0.08 mol p-styrene sulfonic acid, 0.12 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.08 mol vinylpyridine, 0.013 mol pentaerythritol diacrylate, 6.5 g dipotassium hydrogen phosphate, and 474 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 10 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0057] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 19.5g of 8wt% ammonium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 15min. Heat up to 55℃ and keep the reaction at that temperature for 60min. Add the reducing agent. The reducing agent is 11.3g of 12wt% sodium sulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0058] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0059] Example 5

[0060] (1) Add 0.5 mol itaconic acid, 0.09 mol p-styrene sulfonic acid, 0.14 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.09 mol vinylpyridine, 0.017 mol pentaerythritol diacrylate, 4.76 g ammonium dihydrogen phosphate, and 520 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 7 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0061] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 12.7g of 10wt% ammonium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 13 minutes. Heat up to 58℃ and keep the reaction at that temperature for 40 minutes. Add the reducing agent. The reducing agent is 12.1g of 10wt% sodium bisulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0062] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0063] Example 6

[0064] (1) Add 0.5 mol itaconic acid, 0.1 mol p-styrene sulfonic acid, 0.1 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.08 mol vinylpyridine, 0.02 mol pentaerythritol diacrylate, 5.22 g disodium hydrogen phosphate, and 383 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 10 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0065] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 19.5g of 8wt% ammonium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 18 minutes. Heat up to 58℃ and keep the reaction at that temperature for 30 minutes. Add the reducing agent, which is 19.5g of 8wt% potassium bisulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0066] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0067] Example 7

[0068] (1) Add 0.5 mol itaconic acid, 0.07 mol p-styrene sulfonic acid, 0.18 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.05 mol vinylpyridine, 0.022 mol pentaerythritol diacrylate, 6.13 g dipotassium hydrogen phosphate, and 417 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 5 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0069] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 16g of 12wt% sodium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 15min. Heat up to 56℃ and keep the reaction at that temperature for 50min. Add the reducing agent. The reducing agent is 15g of 12wt% sodium sulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0070] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0071] Example 8

[0072] (1) Add 0.5 mol itaconic acid, 0.08 mol p-styrene sulfonic acid, 0.16 mol 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, 0.1 mol vinylpyridine, 0.025 mol pentaerythritol diacrylate, 6.11 g diammonium hydrogen phosphate, and 464 g deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 8 min to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 with sodium hydroxide solution until all raw materials are completely dissolved.

[0073] (2) Add the initiator dropwise from the high-level drop tank. The initiator is 18g of 8wt% sodium persulfate solution. The reaction automatically heats up. After the temperature stops rising, continue the reaction for 20min. Heat up to 55℃ and keep the reaction at that temperature for 60min. Add the reducing agent. The reducing agent is 18.8g of 10wt% sodium bisulfite solution. Terminate the reaction. Adjust the pH to 7-7.5 with sodium hydroxide solution to obtain the temporary plugging agent solution.

[0074] (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

[0075] Example 9

[0076] A 50,000 mg / L sodium chloride solution was added to several pressure-resistant wide-mouth bottles. The pH was adjusted to 1-1.5 with hydrochloric acid. The bottles were heated to 90°C in an oil bath. A certain mass of temporary plugging agent was added, and the temperature was maintained at 90°C. After a period of time, the bottles were removed, and the temporary plugging agent was filtered through a standard sieve. The filtered water was returned to the wide-mouth bottles, and the mass of the temporary plugging agent was quickly weighed. The temporary plugging agent was returned to the wide-mouth bottles, and the temperature was maintained at 90°C. The expansion ratio n was calculated. A comparative experiment was conducted using JX temporary plugging agent from Chengdu Jianxiang Shuguan Technology Co., Ltd. The test results are shown in Table 1.

[0077] n = m1 / m0

[0078] in:

[0079] n—expansion factor;

[0080] m1—mass of the temporary plugging agent after expansion, in grams;

[0081] m0 — Mass of temporary plugging agent, in grams.

[0082] As can be seen from Table 1:

[0083] (1) The temporary plugging agent for fracturing and acidizing of the present invention (Examples 1-8) has an expansion ratio of more than 10 after 15 minutes at 90°C, reaching a maximum of 12.6 (Example 6), while the expansion ratio of the temporary plugging agent of Chengdu Jianxiang Shuguan Technology Co., Ltd. is 6, which is significantly lower than that of the present invention;

[0084] (2) The temporary plugging agent for fracturing and acidizing of the present invention (Examples 1-8) has an expansion ratio of more than 17 at 90°C for 60 min, reaching a maximum of 20.7 (Example 6), while the expansion ratio of the temporary plugging agent of Chengdu Jianxiang Shuguan Technology Co., Ltd. is 11, which is significantly lower than that of the present invention;

[0085] (3) The temporary plugging agent for fracturing and acidizing of the present invention (Examples 1-8) has an expansion ratio of more than 21 and a maximum of 25 (Example 6) at 90°C for 150 min, while the expansion ratio of the JX temporary plugging agent of the comparative example Chengdu Jianxiang Shuguan Technology Co., Ltd. is 14, which is significantly lower than that of the present invention.

[0086] The temporary plugging agent for fracturing and acidizing of the present invention has a good water plugging effect.

[0087] Example 10

[0088] In Example 9, after continuous testing for 150 minutes, the temporary plugging agent basically stopped absorbing water. The temporary plugging agent was left in the wide-mouth bottle. After a period of time, it was found that the temporary plugging agent gradually dissolved. The time after complete dissolution is the degradation time of the temporary plugging agent. A comparative experiment was conducted using JX temporary plugging agent from Chengdu Jianxiang Shuguan Technology Co., Ltd. The test results are shown in Table 2.

[0089] As shown in Table 2, the degradation time of the temporary plugging agent for fracturing and acidizing of the present invention (Examples 1-8) is within the range of 12-54 hours. The degradation time can be controlled by adjusting the proportion of monomers in the temporary plugging agent according to the needs of the construction operation. However, adding a de-plugging agent to the proportioned agent increases the difficulty of construction.

[0090] Example 11

[0091] The temporary plugging rate and permeability recovery rate (unblocking rate) were tested according to the method in Q / SH1020 2187—2018 "General Technical Conditions for Water-Soluble Temporary Plugging Agents". A comparative experiment was conducted using JX temporary plugging agent from Chengdu Jianxiang Shuguan Technology Co., Ltd. The test results are shown in Table 2.

[0092] As can be seen from Table 2, the temporary plugging rate and permeability recovery rate (unplugging rate) of the fracturing acidizing temporary plugging agent of the present invention (Examples 1-8) are both greater than 98%, with the highest temporary plugging rate reaching 99.5% (Example 1) and the highest permeability recovery rate (unplugging rate) reaching 99.2% (Example 8). In contrast, the temporary plugging rate and permeability recovery rate of the JX temporary plugging agent of Chengdu Jianxiang Shuguan Technology Co., Ltd., a comparative example, are 94% and 89.6%, respectively, which are significantly lower than those of the present invention.

[0093] Example 12

[0094] At 90℃, artificially sealed rock cores with different permeabilities were used (the permeability of the low-permeability core was 0.0472 μm). 2 The core sample is 6.3 cm long and has a permeability of 0.286 μm. 2 A temporary plugging agent with a concentration of 10 g / L was injected into the sample (6.5 cm in length). The breakthrough pressure and breakthrough pressure gradient of the temporary plugging agent were tested. A comparative experiment was conducted using JX temporary plugging agent from Chengdu Jianxiang Shuguan Technology Co., Ltd. The test results are shown in Table 3.

[0095] Table 1 Test results of different time expansion ratios

[0096]

[0097]

[0098] Table 2. Test results of degradation time, temporary plugging rate, and permeability recovery rate.

[0099] Temporary plugging agent Degradation time, h Congestion rate, % Permeability recovery rate, % Example 1 54 99.5 98.1 Example 2 46 99.2 98.4 Example 3 37 99 98.5 Example 4 28 98.8 98.6 Example 5 22 98.5 98.7 Example 6 17 98.4 99 Example 7 15 99.3 98.4 Example 8 12 98.2 99.2 Comparative Example Non-degradable 94 89.6

[0100] Table 3. Test results of different core breakthrough pressures and breakthrough pressure gradients

[0101]

[0102]

[0103] As can be seen from Table 3, the temporary plugging agent for fracturing and acidizing of the present invention (Examples 1-8) has a high plugging strength. The breakthrough pressure gradient of low-permeability cores reaches more than 195 MPa / m, with a maximum of 265 MPa / m (Example 8), and the breakthrough pressure gradient of high-permeability cores reaches more than 130 MPa / m, with a maximum of 190 MPa / m. The breakthrough pressure gradients of the JX temporary plugging agent of Chengdu Jianxiang Shuguan Technology Co., Ltd. in the comparative example are 87.3 MPa / m and 64.6 MPa / m for low-permeability cores and high-permeability cores, respectively, which are significantly lower than those of the temporary plugging agent of the present invention.

[0104] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a temporary plugging agent for fracturing and acidizing, characterized in that, The specific steps of the preparation method are as follows: (1) Add itaconic acid, p-styrene sulfonic acid, 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, vinylpyridine, pentaerythritol diacrylate, buffer salt, and deionized water to the reactor in sequence. Purge the reactor and pipelines with nitrogen for 5-10 minutes to ensure a slight positive pressure of nitrogen. Turn on the stirring and adjust the pH to 7-7.5 until all raw materials are completely dissolved. Based on 1 mole of itaconic acid, the amounts of p-styrene sulfonic acid, 2-allyloxymethyl-2-hydroxymethylpropane-1,3-diol, vinylpyridine, and pentaerythritol diacrylate are 0.1-0.2, 0.2-0.4, 0.1-0.2, and 0.01-0.05 moles, respectively. (2) Add the initiator dropwise from the high-level drop tank. The reaction will automatically heat up. After the temperature stops rising, continue the reaction for 10-20 minutes. Heat up to 55-60℃ and keep the reaction at that temperature for 30-60 minutes. Add the reducing agent to terminate the reaction. Adjust the pH to 7-7.5 to obtain the temporary blocking agent solution. (3) The above temporary plugging agent solution is dried and granulated to obtain the product temporary plugging agent with a particle size of 0.4-2 mm.

2. The preparation method of the temporary plugging agent for fracturing and acidizing as described in claim 1, characterized in that, In step (1), the buffer salt is one of sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, and diammonium hydrogen phosphate, and the weight ratio of the buffer salt to itaconic acid is 0.05-0.1:

1.

3. The method for preparing a temporary plugging agent for fracturing and acidizing as described in claim 2, characterized in that, The buffer salt is one of sodium dihydrogen phosphate, potassium dihydrogen phosphate, and ammonium dihydrogen phosphate.

4. The method for preparing a temporary plugging agent for fracturing and acidizing as described in claim 1, characterized in that, In step (1), the weight ratio of deionized water to itaconic acid is 5-8:

1.

5. The method for preparing a temporary plugging agent for fracturing and acidizing as described in claim 1, characterized in that, In step (2), the initiator is one of potassium persulfate aqueous solution, ammonium persulfate aqueous solution, or sodium persulfate aqueous solution, with a concentration of 8-12 wt% and a weight ratio of itaconic acid of 0.1-0.3:

1.

6. The method for preparing a temporary plugging agent for fracturing and acidizing as described in claim 1, characterized in that, In step (2), the reducing agent is one of sodium sulfite aqueous solution, potassium sulfite aqueous solution, sodium bisulfite aqueous solution, and potassium bisulfite aqueous solution, with a concentration of 8-12 wt% and a weight ratio of itaconic acid of 0.1-0.3:

1.

7. A temporary plugging agent for fracturing and acidizing, characterized in that, The molecular structure of the temporary plugging agent is as follows: in: a = 500-20000 b = 20000-200000 c = 4000-40000 d = 8000-80000 e = 4000-40000 f = 500-20000 g = 20000-200000 h = 4000-40000 i = 8000-80000 j = 4000-40000。 8. The temporary plugging agent for fracturing and acidizing as described in claim 7, characterized in that, The temporary plugging agent has a viscosity-average molecular weight of 25,000,000-35,000,000.

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