Modified calcium carbonate particles and fracturing fluids containing the same

Abstract

The present application relates to a modified calcium carbonate particle and a fracturing fluid containing the same. The modified calcium carbonate particle is an oleic acid modified calcium carbonate particle. The fracturing fluid comprises a thickening agent, a viscosity stabilizing and cleanup agent, a crosslinking agent, water and the modified calcium carbonate particle, and the pH value of the fracturing fluid is 6 to 7.

Description

Technical Field

[0001] This invention relates to the field of fracturing fluids, and particularly to a fracturing fluid containing modified calcium carbonate particles. Background Technology

[0002] Tight shale gas reservoirs typically exhibit low porosity and low permeability, resulting in naturally low production capacity. Therefore, volumetric fracturing is necessary to achieve optimal production. Polymer fracturing fluids are generally used in fracturing operations. Polymer fracturing fluids are mainly composed of thickeners, clay stabilizers, drainage aids, and crosslinking agents. To improve the complexity of fractures during shale gas reservoir fracturing and enhance the overall oil and gas release rate, temporary plugging fracturing techniques are commonly used both domestically and internationally. Traditional oil-soluble, rigid plugging agents suffer from poor plugging effectiveness and incomplete dissolution. While fully soluble polymer plugging agents and plugging balls can temporarily plug fracture openings and some fractures to a certain extent, they cannot effectively plug micro-fractures, the matrix, and pore throats in the reservoir. Consequently, they cannot effectively reduce the damage caused by large amounts of fracturing fluid entering the core matrix under high-pressure displacement, thus affecting the natural gas production release of the shale gas reservoir.

[0003] Therefore, there is an urgent need to develop a multi-scale temporary plugging fracturing fluid for shale gas that can meet the requirements of bridging and temporary plugging while effectively reducing the large amount of fluid loss, thereby reducing the damage of the fluid to the reservoir matrix and adapting to the fracturing and stimulation technology needs of more low-permeability gas reservoirs. Summary of the Invention

[0004] One aspect of the present invention provides a modified calcium carbonate particle, wherein the modified calcium carbonate particle is an oleic acid modified calcium carbonate particle.

[0005] In one specific embodiment, the oleic acid content is 1% to 4% and the calcium carbonate content is 96% to 99%, based on the total mass of the modified calcium carbonate particles as 100%.

[0006] In one specific embodiment, the calcium carbonate particles (i.e., the unmodified calcium carbonate particles) have a particle size of 100 nm to 1000 nm. The modified calcium carbonate particles have a similar particle size to the unmodified particles, also ranging from 100 nm to 1000 nm.

[0007] The second aspect of the present invention provides a method for preparing the modified calcium carbonate particles described in any one of the first aspects of the present invention, comprising the following steps:

[0008] 1) Mix calcium carbonate particles with ethanol and disperse to obtain a calcium carbonate dispersion;

[0009] 2) The calcium carbonate dispersion is mixed with oleic acid and dispersed to obtain a modified calcium carbonate dispersion;

[0010] 3) Separate the modified calcium carbonate particles from the modified calcium carbonate dispersion.

[0011] In one specific embodiment, in steps 1) and 2), stirring and dispersion are carried out independently at 40 to 60°C.

[0012] In one specific implementation, in steps 1) and 2), the mixture is stirred and dispersed independently for 50 minutes to 2 hours.

[0013] In one specific embodiment, in step 3), the modified calcium carbonate dispersion is filtered, and the filtered product is dried to obtain the modified calcium carbonate particles.

[0014] The third invention provides a fracturing fluid comprising a thickener, a viscosity stabilizer and flow aid, a crosslinking agent, water, and modified calcium carbonate particles as described in any one of the inventions, wherein the fracturing fluid has a pH value of 6 to 7.

[0015] In one specific embodiment, the modified calcium carbonate particles include modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 100nm to 200nm, modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 300nm to 500nm, and modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 800nm ​​to 1000nm.

[0016] In one specific embodiment, the mass ratio of modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 100nm to 200nm, modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 300nm to 500nm, and modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 800nm ​​to 1000nm is (1-5):(1-3):(1-2).

[0017] In one specific embodiment, the thickener is polyacrylamide with a number average molecular weight of 10 million and / or acrylamide-acrylic acid copolymer with a number average molecular weight of 15 million.

[0018] In one specific embodiment, the viscosity stabilizer and drainage aid is a fluorocarbon surfactant and an inorganic salt.

[0019] In one specific embodiment, the crosslinking agent is an organozirconium crosslinking agent.

[0020] In one specific embodiment, the fluorocarbon surfactant is ammonium perfluorooctyl sulfonate and / or sodium perfluorononenoxybenzenesulfonate.

[0021] In one specific embodiment, the inorganic salt is potassium chloride and / or ammonium chloride.

[0022] In one specific embodiment, the mass ratio of the fluorocarbon surfactant to the inorganic salt is (5 to 10): (50 to 60).

[0023] In one specific embodiment, based on the mass of water (100%), the amount of the thickener is 0.1% to 1.2%, the amount of the viscosity stabilizer and drainage aid is 0.1% to 0.2%, the amount of the crosslinking agent is 0.2% to 0.5%, and the amount of the modified calcium carbonate particles is 0.3% to 1.0%.

[0024] The fourth invention provides the application of fracturing fluid according to any one of the third invention in shale gas reservoirs.

[0025] The beneficial effects of this invention are:

[0026] The modified calcium carbonate particles of the present invention can significantly improve the dispersibility and affinity in high-viscosity polymers, and can generate interfacial interactions with high-viscosity polymers, thereby improving their plugging performance when added to fracturing fluids.

[0027] The fracturing fluid of this invention contains multi-scale modified calcium carbonate particles, which can prevent large amounts of fluid from entering the reservoir matrix during construction, thereby reducing damage.

[0028] Compared with Comparative Example 2, the fracturing fluid containing multi-scale modified calcium carbonate particles increased the displacement pressure by ≥0.4 MPa, significantly reduced the matrix damage to tight reservoirs, with a damage rate of less than 20% and a damage reduction rate of over 40%. Attached Figure Description

[0029] Figure 1 The results of infrared spectroscopy measurements of the modified calcium carbonate particles prepared in Example 1 and the calcium carbonate particles of Comparative Example 1 are shown. Detailed Implementation

[0030] The present invention will be further described in detail below through preferred embodiments, but these embodiments do not constitute a limitation thereof.

[0031] Unless otherwise specified, all reagents used in the embodiments of this invention are commercially available.

[0032] Preparation of modified calcium carbonate

[0033] Example 1

[0034] Step 1. Add 200 mL of anhydrous ethanol to an enamel bucket, then add 96 g of unmodified calcium carbonate with a particle size of 100 nm to 200 nm. When the temperature is raised to 40 °C, start the stirrer and stir at a constant temperature of 400 rpm for 1 hour to obtain a calcium carbonate dispersion.

[0035] Step 2. Add 4g of oleic acid to the calcium carbonate dispersion and continue stirring at 400 rpm for 1 hour at 40°C to obtain the modified calcium carbonate dispersion.

[0036] Step 3. Filter the modified calcium carbonate dispersion, dry it at 105℃, and weigh it to 100g, indicating that the modified calcium carbonate particles contain 96g of calcium carbonate and 4g of oleic acid.

[0037] Example 2

[0038] Step 1. Add 200mL of anhydrous ethanol to an enamel bucket, then add 97g of unmodified calcium carbonate with a particle size of 100nm to 200nm. When the temperature is raised to 45℃, start the stirrer and stir at a constant temperature of 400 rpm for 1 hour to obtain a calcium carbonate dispersion.

[0039] Step 2. Add 3g of oleic acid to the calcium carbonate dispersion and continue stirring at 400 rpm for 1 hour at 45°C to obtain the modified calcium carbonate dispersion.

[0040] Step 3. Filter the above mixture, dry it at 105℃, and weigh it to 100g, indicating that the modified calcium carbonate granules contain 97g of calcium carbonate and 3g of oleic acid.

[0041] Example 3

[0042] Step 1. Add 200 mL of anhydrous ethanol to an enamel bucket, then add 97 g of unmodified calcium carbonate with a particle size of 300 nm to 500 nm. When the temperature is raised to 50 °C, start the stirrer and stir at a constant temperature of 400 rpm for 1 hour to obtain a calcium carbonate dispersion.

[0043] Step 2. Add 3g of oleic acid to the calcium carbonate dispersion and continue stirring at 400 rpm for 1 hour at 50°C to obtain the modified calcium carbonate dispersion.

[0044] Step 3. Filter the modified calcium carbonate dispersion, dry it at 105℃, and weigh it to 100g, indicating that the modified calcium carbonate particles contain 97g of calcium carbonate and 3g of oleic acid.

[0045] Example 4

[0046] Step 1. Add 200 mL of anhydrous ethanol to an enamel bucket, then add 98 g of unmodified calcium carbonate with a particle size of 300 nm to 500 nm. When the temperature is raised to 55 °C, start the stirrer and stir at a constant temperature of 400 rpm for 1 hour to obtain a calcium carbonate dispersion.

[0047] Step 2. Add 2g of oleic acid to the calcium carbonate dispersion and continue stirring at 400 rpm for 1 hour at 55℃ to obtain the modified calcium carbonate dispersion.

[0048] Step 3. Filter the modified calcium carbonate dispersion, dry it at 105℃, and weigh it to 100g, indicating that the modified calcium carbonate particles contain 98g of calcium carbonate and 2g of oleic acid.

[0049] Example 5

[0050] Step 1. Add 200 mL of anhydrous ethanol to an enamel bucket, then add 99 g of unmodified calcium carbonate with a particle size of 800 nm to 1000 nm. When the temperature is raised to 60 °C, start the stirrer and stir at a constant temperature of 400 rpm for 1 hour to obtain a calcium carbonate dispersion.

[0051] Step 2. Add 1g of oleic acid to the calcium carbonate dispersion and continue stirring at 400 rpm for 1 hour at 60℃ to obtain the modified calcium carbonate dispersion.

[0052] Step 3. Filter the modified calcium carbonate dispersion, dry it at 105℃, and weigh it to 100g, indicating that the modified calcium carbonate particles contain 99g of calcium carbonate and 1g of oleic acid.

[0053] Comparative Example 1

[0054] Step 1. Add 200mL of anhydrous ethanol to an enamel bucket, then add 90g of unmodified calcium carbonate with a particle size of 100nm to 200nm. When the temperature is raised to 40℃, turn on the stirrer and stir at a constant temperature of 400 rpm for 1 hour to obtain a calcium carbonate dispersion.

[0055] Step 2. Add 10g of oleic acid to the calcium carbonate dispersion and continue stirring at 400 rpm for 1 hour at 40℃ to obtain the modified calcium carbonate dispersion.

[0056] Step 3. Filter the modified calcium carbonate dispersion, dry it at 105℃, and weigh it to 100g, indicating that the modified calcium carbonate particles contain 90g of calcium carbonate and 10g of oleic acid.

[0057] Comparative Example 2

[0058] Step 1. Add 200 mL of anhydrous ethanol to an enamel bucket, then add 99.5 g of unmodified calcium carbonate with a particle size of 100 nm to 200 nm. When the temperature is raised to 40 °C, start the stirrer and stir at a constant temperature of 400 rpm for 1 hour to obtain a calcium carbonate dispersion.

[0059] Step 2. Add 0.5g of oleic acid to the calcium carbonate dispersion and continue stirring at 400 rpm for 1 hour at 40°C to obtain the modified calcium carbonate dispersion.

[0060] Step 3. Filter the modified calcium carbonate dispersion, dry it at 105℃, and weigh it to 100g, indicating that the modified calcium carbonate particles contain 99.5g of calcium carbonate and 0.5g of oleic acid.

[0061] Comparative Example 3

[0062] Unmodified calcium carbonate with a particle size of 100nm to 200nm.

[0063] Infrared spectroscopy was performed on the modified calcium carbonate particles prepared in Example 1 and the calcium carbonate particles of Comparative Example 1. The results are shown in the figure. Figure 1 .from Figure 1 It can be seen that the absorption peaks of unmodified calcium carbonate mainly appear at 732, 923, 1783, 2318, and 2651 cm⁻¹. -1 Location. 1783cm -1 The peak at 923 cm⁻¹ represents the C=O vibration of calcite-type carbonate. -1 and 732cm -1 The absorption peaks at these locations are the υ2 and υ4 absorption peaks in calcite crystals, respectively. The absorption peaks of oleic acid-modified calcium carbonate mainly appear at 615, 723, 941, 1783, 2399, 2659, and 3027 cm⁻¹. -1 Location. 3027cm -1 and 2659cm -1 The presence of both asymmetric and symmetric vibrational peaks of the methylene (H—C—H) group at the surface indicates the presence of Ca on the surface of the calcium carbonate powder. 2+ It reacted with organic matter, and the product contained organic matter.

[0064] The activation degree of the products of each example and comparative example was measured according to GB / T 19281—2003 "Analytical Methods for Calcium Carbonate", and the results are shown in Table 1.

[0065] Table 1

[0066] Example 1 88.87 Example 2 89.32 Example 3 89.95 Example 4 90.89 Example 5 87.43 Comparative Example 1 55.74 Comparative Example 2 50.31 Comparative Example 3 40.16

[0067] Preparation of fracturing fluid

[0068] Example 6

[0069] Step 1. Accurately weigh 100g of clean water, 0.1g of polyacrylamide with a number average molecular weight of 10 million, 0.3g of modified calcium carbonate granules, 0.1g of viscosity stabilizer and drainage aid (ammonium perfluorooctyl sulfonate: potassium chloride = 5:50), and 0.2g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.1g of the modified calcium carbonate granules obtained in Example 1, Example 3, and Example 5 are included.

[0070] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0071] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0072] Step 4. Add modified calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0073] The viscosity of the fracturing fluid in this embodiment was measured to be 1.5 mPa·s, and the pH value was 6.

[0074] Example 7

[0075] Step 1. Accurately weigh 100g of water, 0.2g of acrylamide-acrylic acid copolymer with a number average molecular weight of 15 million, 0.3g of modified calcium carbonate granules, 0.1g of viscosity stabilizer and drainage aid (ammonium perfluorooctyl sulfonate: ammonium chloride = 10:50), and 0.3g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.15g of the modified calcium carbonate granules obtained in Example 1, 0.1g of the modified calcium carbonate granules obtained in Example 3, and 0.05g of the modified calcium carbonate granules obtained in Example 5.

[0076] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0077] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0078] Step 4. Add modified calcium carbonate and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0079] The viscosity of the fracturing fluid in this embodiment was measured to be 3 mPa·s, and the pH value was 6.

[0080] Example 8

[0081] Step 1. Accurately weigh 100g of clean water, 0.4g of polyacrylamide with a number average molecular weight of 10 million, 0.4g of modified calcium carbonate granules, 0.15g of viscosity stabilizer and drainage aid (ammonium perfluorooctyl sulfonate: potassium chloride = 10:60), and 0.3g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.20g of the modified calcium carbonate granules obtained in Example 1, 0.15g of the modified calcium carbonate granules obtained in Example 3, and 0.05g of the modified calcium carbonate granules obtained in Example 5.

[0082] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0083] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0084] Step 4. Add modified calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0085] The viscosity of the fracturing fluid in this embodiment was measured to be 6 mPa·s, and the pH value was 6.

[0086] Example 9

[0087] Step 1. Accurately weigh 100g of water, 0.6g of acrylamide-acrylic acid copolymer with a number average molecular weight of 15 million, 0.5g of modified calcium carbonate granules, 0.15g of viscosity stabilizer and drainage aid (sodium perfluorononenoxybenzenesulfonate: potassium chloride = 5:50), and 0.4g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.25g of the modified calcium carbonate granules obtained in Example 1, 0.15g of the modified calcium carbonate granules obtained in Example 3, and 0.10g of the modified calcium carbonate granules obtained in Example 5.

[0088] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0089] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0090] Step 4. Add modified calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0091] The viscosity of the fracturing fluid in this embodiment was measured to be 12 mPa·s, and the pH value was 7.

[0092] Example 10

[0093] Step 1. Accurately weigh 100g of water, 0.9g of polyacrylamide with a number average molecular weight of 10 million, 0.6g of modified calcium carbonate granules, 0.2g of viscosity stabilizer and drainage aid (sodium perfluorononenoxybenzenesulfonate: potassium chloride = 10:50), and 0.45g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.30g of the modified calcium carbonate granules obtained in Example 2, 0.18g of the modified calcium carbonate granules obtained in Example 3, and 0.12g of the modified calcium carbonate granules obtained in Example 5.

[0094] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0095] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0096] Step 4. Add modified calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0097] The viscosity of the fracturing fluid in this embodiment was measured to be 18 mPa·s, and the pH value was 7.

[0098] Example 11

[0099] Step 1. Accurately weigh 100g of water, 1.0g of acrylamide-acrylic acid copolymer with a number average molecular weight of 15 million, 0.7g of modified calcium carbonate granules, 0.2g of viscosity stabilizer and drainage aid (sodium perfluorononenoxybenzenesulfonate: ammonium chloride = 5:60), and 0.45g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.35g of the modified calcium carbonate granules obtained in Example 2, 0.21g of the modified calcium carbonate granules obtained in Example 4, and 0.14g of the modified calcium carbonate granules obtained in Example 5.

[0100] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0101] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0102] Step 4. Add modified calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0103] The viscosity of the fracturing fluid in this embodiment was measured to be 27 mPa·s, and the pH value was 7.

[0104] Example 12

[0105] Step 1. Accurately weigh 100g of water, 1.1g of polyacrylamide with a number average molecular weight of 10 million, 0.8g of modified calcium carbonate granules, 0.2g of viscosity stabilizer and drainage aid (sodium perfluorononenoxybenzenesulfonate: ammonium chloride = 1:5), and 0.45g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.40g of the modified calcium carbonate granules were obtained in Example 2, 0.24g in Example 4, and 0.16g in Example 5.

[0106] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0107] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0108] Step 4. Add modified calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0109] The viscosity of the fracturing fluid in this embodiment was measured to be 42 mPa·s, and the pH value was 7.

[0110] Example 13

[0111] Step 1. Accurately weigh 100g of water, 1.2g of polyacrylamide with a number average molecular weight of 10 million, 1.0g of modified calcium carbonate granules, 0.2g of sodium perfluorononenoxybenzenesulfonate (sodium chloride:ammonium chloride = 1:6) as a viscosity stabilizer and drainage aid, and 0.50g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.5g of the modified calcium carbonate granules obtained in Example 2, 0.30g of the modified calcium carbonate granules obtained in Example 4, and 0.20g of the modified calcium carbonate granules obtained in Example 5.

[0112] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0113] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0114] Step 4. Add modified calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0115] The viscosity of the fracturing fluid in this embodiment was measured to be 51 mPa·s, and the pH value was 7.

[0116] Example 14

[0117] The modified calcium carbonate particles used are those of Example 1, with a dosage of 0.3g, and other aspects are the same as in Example 6.

[0118] Example 15

[0119] The modified calcium carbonate particles used are those of Example 3, with an amount of 0.3g, and other aspects are the same as in Example 6.

[0120] Example 16

[0121] The modified calcium carbonate particles used are those of Example 5, with an amount of 0.3g, and other aspects are the same as in Example 6.

[0122] Comparative Example 4

[0123] Step 1. Accurately weigh 100g of clean water, 0.1g of polyacrylamide with a number average molecular weight of 10 million, 0.3g of calcium carbonate granules, 0.1g of viscosity stabilizer and drainage aid (sodium perfluorononenoxybenzenesulfonate: potassium chloride = 5:50), and 0.2g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, 0.1g of calcium carbonate granules have a particle size of 100nm to 200nm, 0.1g of calcium carbonate granules have a particle size of 300nm to 500nm, and 0.1g of calcium carbonate granules have a particle size of 800nm ​​to 1000nm.

[0124] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0125] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0126] Step 4. Add calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0127] The viscosity of the fracturing fluid in this comparative example was measured to be 1.5 mPa·s, and the pH value was 6.

[0128] Comparative Example 5

[0129] Step 1. Accurately weigh 100g of water, 0.1g of polyacrylamide with a number average molecular weight of 10 million, 0.3g of calcium carbonate granules, 0.1g of sodium perfluorononenoxybenzenesulfonate, and 0.2g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, weigh 0.1g of calcium carbonate granules with a particle size of 100nm to 200nm, 0.1g of calcium carbonate granules with a particle size of 300nm to 500nm, and 0.1g of calcium carbonate granules with a particle size of 800nm ​​to 1000nm.

[0130] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0131] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0132] Step 4. Add calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0133] The viscosity of the fracturing fluid in this comparative example was measured to be 1.5 mPa·s, and the pH value was 6.

[0134] Comparative Example 6

[0135] Step 1. Accurately weigh 100g of water, 0.1g of polyacrylamide with a number average molecular weight of 10 million, 0.3g of calcium carbonate granules, 0.1g of potassium chloride, and 0.2g of organozirconium crosslinking agent (Shandong Dongying Shipuri Chemical Co., Ltd.). Specifically, weigh 0.1g of calcium carbonate granules with a particle size of 100nm to 200nm, 0.1g of calcium carbonate granules with a particle size of 300nm to 500nm, and 0.1g of calcium carbonate granules with a particle size of 800nm ​​to 1000nm.

[0136] Step 2. Add polyacrylamide to clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the rotation speed to ensure a vortex state. Continue stirring to fully dissolve and form a uniform solution to obtain the first solution.

[0137] Step 3. While maintaining stirring, add the viscosity stabilizer and drainage aid to the first solution prepared in step 2, and stir slowly until homogeneous to obtain the second solution;

[0138] Step 4. Add calcium carbonate particles and organozirconium crosslinking agent to the second solution prepared in step 3, stir evenly, and obtain fracturing fluid.

[0139] The viscosity of the fracturing fluid in this comparative example was measured to be 1.5 mPa·s, and the pH value was 6.

[0140] Performance Analysis

[0141] The fracturing fluids prepared in the above embodiments and comparative examples were subjected to displacement pressure rise experiments and gas core permeability damage experiments.

[0142] 1. Gas permeability measurement

[0143] 1) Dry the core sample to be tested at 105℃, and determine the basic data of core length, diameter, dry weight, gas porosity and permeability. Select core samples with similar permeability and porosity to carry out the test.

[0144] 2) Vacuum the core and establish the initial water saturation using standard brine (2% KCl + 5.5% NaCl + 0.45% MgCl2 + 0.55% CaCl2 mass ratio) (the concentration of standard brine and the initial water saturation can be determined according to the formation conditions).

[0145] 3) Determination of core permeability before damage: A core with established water saturation is loaded into the core holder and connected to the flow meter. The initial starting pressure for forward gas measurement is P0, increased in increments of 0.1 MPa. After measurement, the pressure is adjusted to 3.5 MPa, and the initial core permeability is measured. Gas permeability formula:

[0146]

[0147] Where: K—permeability of the core, μm 2 ;

[0148] Q0—Volume flow rate of gas at atmospheric pressure, mL / s;

[0149] μ—viscosity of the gas passing through the core, 0.01795 mPa·s;

[0150] L—Core length, cm;

[0151] A—Core cross-sectional area, cm² 2 ;

[0152] p1—Core inlet pressure (displacement pressure + 0.0955), MPa;

[0153] p2—Core outlet pressure, 0.0955 MPa.

[0154] 2. Gas core damage rate

[0155] 1) Core damage: 800 ppm ammonium persulfate was added to the fracturing fluid prepared in each example and comparative example, and the mixture was placed in a constant temperature water bath at 80°C for 60 minutes to obtain a ruptured fluid. The ruptured fluid was added to an intermediate container and pressurized to 3.5 MPa using a pressure source. It was then forced into the core from the other end of the core holder in the reverse direction, with a displacement time of 180 minutes. After completion, the core was removed, and the filter cake on the damaged end face was cleaned as needed.

[0156] 2) Core permeability determination after damage: The damaged and end-faced core is placed in the holder. The forward gas measurement initiation pressure P1 and the core permeability K1 after damage are measured (displacement pressure 3.5 MPa; if the initiation pressure exceeds 3.5 MPa, the gas measurement permeability is measured at the initiation pressure). The increase in displacement pressure is the difference between P1 and P0. The damage rate η is calculated using the following formula:

[0157]

[0158] Where: K0—initial permeability of the core, μm 2 ;

[0159] K1—Core permeability after damage, μm 2 ;

[0160] The fracturing fluid test results are shown in Table 2.

[0161] Table 2

[0162]

[0163] The experimental results in Table 2 clearly show that the fracturing fluids prepared in the above embodiments of the present invention have a significant temporary plugging effect, resulting in a significant increase in pressure after displacement, while maintaining a low core damage rate. Therefore, the fracturing fluid of the present invention is a type of fracturing fluid that can temporarily plug the working fluid outside the matrix core during fracturing operations in tight oil and gas reservoirs, while simultaneously reducing damage. It is widely suitable for fracturing and stimulation of low-porosity, low-permeability oil and gas reservoirs.

Claims

1. A fracturing fluid comprising a thickener, a viscosity stabilizer and flow aid, a crosslinking agent, water, and modified calcium carbonate particles; The modified calcium carbonate particles are oleic acid modified calcium carbonate particles. The modified calcium carbonate particles, with a total mass of 100%, contain 1% to 4% oleic acid and 96% to 99% calcium carbonate. The modified calcium carbonate particles include modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 100 nm to 200 nm, modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 300 nm to 500 nm, and modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 800 nm to 1000 nm. The viscosity stabilizer and drainage aid is a fluorocarbon surfactant and an inorganic salt; The fracturing fluid has a pH value of 6 to 7.

2. The fracturing fluid according to claim 1, characterized in that, The mass ratio of modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 100nm to 200nm, modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 300nm to 500nm, and modified calcium carbonate particles obtained by modifying calcium carbonate particles with a particle size of 800nm ​​to 1000nm is (1-5):(1-3):(1-2).

3. The fracturing fluid according to claim 1, characterized in that, The modified calcium carbonate particles are prepared according to the following steps: 1) Add calcium carbonate particles to ethanol, stir and disperse to obtain calcium carbonate dispersion; 2) Add oleic acid to the calcium carbonate dispersion, stir and disperse to obtain a modified calcium carbonate dispersion; 3) Filter the modified calcium carbonate dispersion and dry the filtered product to obtain the modified calcium carbonate particles.

4. The fracturing fluid according to claim 3, characterized in that, In steps 1) and 2), the dispersion was carried out independently at 40 to 60°C.

5. The fracturing fluid according to claim 3, characterized in that, In steps 1) and 2), the mixture is stirred and dispersed independently for 50 minutes to 2 hours.

6. The fracturing fluid according to claim 1, characterized in that, The thickener is polyacrylamide with a number average molecular weight of 10 million and / or an acrylamide-acrylic acid copolymer with a number average molecular weight of 15 million; and / or The crosslinking agent is an organozirconium crosslinking agent.

7. The fracturing fluid according to claim 1, characterized in that, The fluorocarbon surfactant is ammonium perfluorooctyl sulfonate and / or sodium perfluorononenoxybenzene sulfonate. The inorganic salt is potassium chloride and / or ammonium chloride.

8. The fracturing fluid according to any one of claims 1 to 7, characterized in that, The mass ratio of the fluorocarbon surfactant to the inorganic salt is (5 to 10): (50 to 60).

9. The fracturing fluid according to claim 1, characterized in that, Based on the mass of water (100%), the amount of the thickener is 0.1% to 1.2%, the amount of the viscosity stabilizer and drainage aid is 0.1% to 0.2%, the amount of the crosslinking agent is 0.2% to 0.5%, and the amount of the modified calcium carbonate particles is 0.3% to 1.0%.

10. The application of the fracturing fluid according to any one of claims 1 to 9 in shale gas reservoirs.

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