High-density ultra-micro oil testing completion fluid and preparation method thereof

Abstract

The application provides a high-density ultra-micro oil testing completion fluid and a preparation method thereof, wherein the raw materials include, with the total weight being 1000 parts, calcium silicate powder 200-300 parts, polyacrylamide 50-80 parts, sodium carboxymethyl cellulose 30-50 parts, polyethylene glycol 20-40 parts, sodium dodecyl sulfate 5-10 parts, sodium citrate 10-20 parts, nano zirconium oxide 5-15 parts, modified graphene 10-50 parts, composite stabilizer 15-45 parts, nano silicon dioxide reinforced polymer composite material 30-80 parts, and the rest is water. The application provides a high-density ultra-micro oil testing completion fluid system, and the system can keep a very small specific gravity change under high temperature and high pressure operation, and the density is uniformly distributed, so that the efficiency and success rate of the completion operation are improved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling technology, specifically to a high-density ultra-micro oil testing and completion fluid and its preparation method. Background Technology

[0002] During well completion operations, the completion fluid is required to have good settling stability and rheological properties under high density and high temperature conditions. Generally, deep well testing and completion fluids are directly converted from drilling fluids. High-density drilling and completion fluids are prone to high-temperature failure of treatment agents, aggravated material settling, and poor compatibility during long-term high-temperature downhole testing cycles. This can lead to contamination of oil and gas reservoirs, burial of the testing tubing, obstruction of well completion operations, and even more serious accidents such as stuck pipe, lost circulation, and blowout caused by unstable completion fluids.

[0003] CN103194186A discloses a high-density ultra-micro oil testing working fluid and its preparation method. The oil testing working fluid is composed of a weighting agent, a dispersant, a stabilizer, sodium hydroxide, an anti-agglomeration agent, a flow pattern regulator, and a filtration control agent. This high-density ultra-micro oil testing working fluid has a temperature resistance of no more than 150℃, which can no longer meet the increasingly higher downhole temperatures and increasingly complex drilling and completion conditions in ultra-deep well drilling.

[0004] CN103305195B discloses a method and apparatus for producing a high-density ultra-micro oil testing working fluid. The oil testing working fluid is composed of a composite weighting material, a main dispersant, a secondary dispersant, a main stabilizer, a secondary stabilizer, and a double-layer activator. The patent does not mention the density of the oil testing working fluid or its high-temperature protection, and it is unclear whether it can meet the requirements of current well completion and oil testing operations for ultra-deep wells. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a high-density ultra-micro oil testing and completion fluid and its preparation method.

[0006] To achieve the above objectives, the present invention provides a high-density ultra-micro oil testing and completion fluid, which, based on a total weight of 1000 parts, comprises the following raw materials: 200-300 parts calcium silicate powder, 50-80 parts polyacrylamide, 30-50 parts sodium carboxymethyl cellulose, 20-40 parts polyethylene glycol, 5-10 parts sodium dodecyl sulfate, 10-20 parts sodium citrate, 5-15 parts nano-zirconia, 10-50 parts modified graphene, 15-45 parts composite stabilizer, 30-80 parts nano-silica reinforced polymer composite material, and the balance being water.

[0007] This invention addresses the problems encountered during the completion and testing of high-density drilling and completion fluids in high-temperature deep and ultra-deep wells. These problems include high-temperature failure of treatment agents, increased material settling, and poor compatibility, leading to contamination of oil and gas reservoirs, burial of testing tubing, and obstruction of well completion operations. The invention provides a high-density, ultra-micro drilling and completion fluid system that maintains minimal specific gravity change and uniform density distribution even under high-temperature and high-pressure conditions, thereby improving the efficiency and success rate of well completion operations.

[0008] In the aforementioned high-density ultra-micro oil testing and completion fluid, preferably, the composite stabilizer comprises a combination of 10-30 parts nano-clay and 5-15 parts polyacrylic acid.

[0009] In the above-mentioned high-density ultra-micro oil testing and completion fluid, preferably, the nano-silica reinforced polymer composite material is composed of nano-silica particles and polyacrylamide, wherein the mass fraction of nano-silica particles in the nano-silica reinforced polymer composite material is 5-20 wt%, and the mass fraction of polyacrylamide is 80-95 wt%.

[0010] This invention relates to a high-density, ultra-micro drilling and completion fluid. It utilizes a series of raw materials, including high-purity calcium silicate micropowder, polyacrylamide, and sodium carboxymethyl cellulose, combined with nanoscale materials, composite stabilizers, and nano-silica-reinforced polymer composites. This not only significantly improves the overall stability of the system but also effectively enhances the performance of the completion fluid under extreme conditions such as high temperature and high pressure through the stabilizing effect of the nano-clay and polyacrylic acid composite, and the synergistic effect of the polyimide and nano-silica-reinforced composite. This completion fluid can significantly slow down the settling rate of solid particles, ensuring uniform density distribution and maintaining minimal specific gravity change even under prolonged high-temperature operations. This greatly improves the efficiency and success rate of well completion operations. Furthermore, it exhibits excellent rheological properties and self-cleaning ability, as well as good compatibility with various drilling fluids and treatment fluids.

[0011] In the aforementioned high-density ultra-micro oil testing and completion fluid, preferably, the preparation method of the nano-silica reinforced polymer composite material includes:

[0012] Nano-silica particles and a surface modifier are mixed evenly in water to obtain modified nano-silica particles; the modified nano-silica particles and polyacrylamide are mixed evenly in water to obtain the nano-silica-reinforced polymer composite material.

[0013] According to a specific embodiment of the present invention, preferably, the preparation method of the nano-silica reinforced polymer composite material in the above-mentioned high-density ultra-micro oil testing and completion fluid includes the following steps:

[0014] (1) Surface treatment of nano silica: Disperse nano silica particles in an appropriate amount of solvent (such as ethanol, water, etc.) and perform ultrasonic dispersion to ensure uniform dispersion of particles; add an appropriate amount of surface modifier (such as silane coupling agent) and stir and react for a period of time at a certain temperature to modify the surface of nano silica particles and improve their compatibility with polyacrylamide.

[0015] (2) Preparation of polyacrylamide solution: Dissolve polyacrylamide in an appropriate amount of solvent (such as water) and heat and stir to ensure complete dissolution;

[0016] (3) Preparation of composite material: The modified nano-silica particles are added to the polyacrylamide solution and ultrasonically dispersed or mechanically stirred to ensure that the nano-silica particles are uniformly dispersed in the polyacrylamide solution; the reaction is stirred at a certain temperature for a period of time to allow the nano-silica particles to fully combine with the polyacrylamide to form a nano-silica reinforced polymer composite material.

[0017] (4) Post-treatment: The reacted composite material is centrifuged and washed to remove unreacted surface modifiers and solvents; the composite material is dried to obtain the final nano-silica reinforced polymer composite material.

[0018] In the above-mentioned high-density ultra-micro oil testing completion fluid, preferably, the raw materials of the completion fluid also include 0.3-1 parts of sodium hydroxide as a pH adjuster.

[0019] In the aforementioned high-density ultra-micro oil testing and completion fluid, preferably, the calcium silicate powder is high-purity calcium silicate micro powder with a purity higher than 90% and a particle size of less than 20 micrometers.

[0020] In the above-mentioned high-density ultra-micro oil testing and completion fluid, preferably, the modified graphene is modified graphene GO1212.

[0021] This invention also provides a method for preparing the above-mentioned high-density ultra-micro oil testing and completion fluid, which includes:

[0022] S1: Add the composite stabilizer, polyethylene glycol, and nano-silica reinforced polymer composite material to water, stir evenly, and adjust the pH value with sodium hydroxide to obtain a mixed solution;

[0023] S2: Add calcium silicate powder, polyacrylamide, sodium carboxymethyl cellulose, sodium dodecyl sulfate, sodium citrate, nano-sized zirconium oxide, modified graphene, and the remaining water to the mixed solution, stir and mix evenly to obtain the high-density ultra-micro oil testing and completion fluid.

[0024] In the above-mentioned method for preparing high-density ultra-micro oil testing and completion fluid, preferably, in S1, the pH value of the mixed solution is 7-9.

[0025] In the above-mentioned method for preparing high-density ultra-micro test oil completion fluid, preferably, the stirring speed in S1 and / or S2 is 6000-8000 r / min.

[0026] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned high-density ultra-micro oil testing and completion fluid specifically includes the following steps:

[0027] Add an appropriate amount of deionized water to a clean mixer. While the mixer is set to a stirring speed of 6000 rpm, slowly add the composite stabilizer to the water and continue stirring for 10 minutes to ensure the stabilizer is fully dispersed. Continue stirring at the same speed, then slowly add polyethylene glycol to the beaker and stir until completely dissolved. Next, increase the stirring speed to 8000 rpm, add the nano-silica-reinforced polymer composite material and sodium hydroxide as a pH adjuster, and continue stirring until the mixture is homogeneous. Finally, while maintaining a stirring speed of 8000 rpm, slowly add the remaining high-density ultrafine powder to the beaker, including but not limited to high-purity calcium silicate powder, polyacrylamide, sodium carboxymethyl cellulose, sodium dodecyl sulfate, sodium citrate, nano-zirconia, modified graphene, polyimide, and the remaining deionized water. Continue stirring for 30 minutes to obtain the high-density ultrafine test and completion fluid system.

[0028] The technical solution provided by this invention has the following beneficial effects:

[0029] (1) The present invention uses high-purity calcium silicate micro powder, nano-sized silica-reinforced polymer composite materials and other raw materials, and the density of the completion fluid of the present invention is significantly improved, making it suitable for high-density oil testing operations; the addition of raw materials such as polyacrylamide and sodium carboxymethyl cellulose optimizes the rheological properties of the completion fluid, so that the completion fluid can still maintain good settling stability under high temperature and high pressure conditions.

[0030] (2) The components such as polyacrylamide and sodium carboxymethyl cellulose in the well completion fluid formulation of the present invention act as thickeners and dispersants, which help to improve the density and suspension stability of the well completion fluid and ensure its effective application in ultra-deep wells.

[0031] (3) The composite stabilizer and nano-silica reinforced polymer composite material in the well completion fluid formulation of this invention have excellent high temperature resistance, which can maintain the stability of the well completion fluid in high temperature environment and prevent problems such as high temperature solidification and weighting agent precipitation. Polyethylene glycol and other components, as high temperature resistant dispersants, help to improve the dispersibility and fluidity of the well completion fluid at high temperature and ensure its normal operation in high temperature wells.

[0032] (4) The modified graphene and other components in the well completion fluid formulation of this invention have rheological adjustment properties, which help to further improve the rheological properties and construction performance of the well completion fluid. Detailed Implementation

[0033] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0034] In the embodiments of the present invention, the modified graphene is modified graphene GO1212; the calcium silicate micro powder is high-purity calcium silicate micro powder with a purity of more than 90% and a particle size of less than 20 micrometers.

[0035] Example 1

[0036] This embodiment provides a high-density, ultra-micro oil testing and completion fluid, the preparation method of which is as follows:

[0037] The raw materials of the high-density ultra-micro oil testing and completion fluid, by weight, include: 200 parts of high-purity calcium silicate micro powder, 50 parts of polyacrylamide, 30 parts of sodium carboxymethyl cellulose, 40 parts of polyethylene glycol, 5 parts of sodium dodecyl sulfate, 20 parts of sodium citrate, 5 parts of nano-grade zirconium oxide, 10 parts of modified graphene (G01212), 15 parts of composite stabilizer, 30 parts of nano-silica reinforced polymer composite material, 0.3 parts of sodium hydroxide (as a pH adjuster), and the balance is deionized water, ensuring a total of 1000 parts;

[0038] The composite stabilizer is composed of 10 parts of nano-clay and 5 parts of polyacrylic acid.

[0039] Preparation of the nano-silica reinforced polymer composite material:

[0040] (1) Surface treatment of nano silica: 5g of nano silica particles were dispersed in 100g of water and ultrasonically dispersed to ensure uniform dispersion of particles; 1g of silane coupling agent was added and stirred at 1000r / m for 1h at room temperature to modify the surface of nano silica particles and improve their compatibility with polyacrylamide.

[0041] (2) Preparation of polyacrylamide solution: Dissolve 76g of polyacrylamide in 300ml of water and stir at 1000r / m at room temperature to ensure complete dissolution;

[0042] (3) Preparation of composite material: The modified nano-silica particles are added to the polyacrylamide solution and ultrasonically dispersed or mechanically stirred to ensure that the nano-silica particles are uniformly dispersed in the polyacrylamide solution; the reaction is stirred at a certain temperature for 2 hours to allow the nano-silica particles to fully combine with the polyacrylamide to form a nano-silica reinforced polymer composite material.

[0043] (4) Post-treatment: The reacted composite material is centrifuged and washed to remove unreacted surface modifiers and solvents; the composite material is dried to obtain the final nano-silica reinforced polymer composite material.

[0044] The preparation method of high-density ultra-micro oil testing and completion fluid includes the following steps:

[0045] Add an appropriate amount of deionized water to the mixer. With the stirrer set to 6000 rpm, slowly add the composite stabilizer to the water and stir continuously for 10 minutes to ensure the stabilizer is fully dispersed. Continue stirring at the above speed and slowly add polyethylene glycol to the beaker, stirring until completely dissolved. Next, increase the stirring speed to 8000 rpm and add the nano-silica reinforced polymer composite material in sequence. Adjust the pH value to 7 with sodium hydroxide and continue stirring until the mixture is homogeneous. Finally, while maintaining the stirring speed of 8000 rpm, slowly add the remaining high-density ultrafine powder, including high-purity calcium silicate powder, polyacrylamide, sodium carboxymethyl cellulose, sodium dodecyl sulfate, sodium citrate, nano-zirconia, modified graphene, polyimide, and the remaining deionized water, to the beaker and continue stirring for 30 minutes to obtain the high-density ultrafine test oil completion fluid system.

[0046] Example 2

[0047] This embodiment provides a high-density, ultra-micro oil testing and completion fluid, the preparation method of which is as follows:

[0048] The raw materials of the high-density ultra-micro oil testing and completion fluid, by weight, include: 250 parts of high-purity calcium silicate micro powder, 65 parts of polyacrylamide, 40 parts of sodium carboxymethyl cellulose, 30 parts of polyethylene glycol, 7.5 parts of sodium dodecyl sulfate, 15 parts of sodium citrate, 10 parts of nano-grade zirconium oxide, 30 parts of modified graphene (GO1212), 30 parts of composite stabilizer, 55 parts of nano-silica reinforced polymer composite material, 0.65 parts of sodium hydroxide (as a pH adjuster), and the balance being deionized water, ensuring a total of 1000 parts.

[0049] The composite stabilizer is composed of 20 parts of nano-clay and 10 parts of polyacrylic acid.

[0050] Preparation of the nano-silica reinforced polymer composite material:

[0051] (1) Surface treatment of nano silica: 25g of nano silica particles were dispersed in 200g of water and ultrasonically dispersed to ensure uniform dispersion of particles; 5g of silane coupling agent was added and stirred at 1000r / m for 1h at room temperature to modify the surface of nano silica particles and improve their compatibility with polyacrylamide.

[0052] (2) Preparation of polyacrylamide solution: Dissolve 69.375g of polyacrylamide in 300ml of water and stir at 1000r / m at room temperature to ensure complete dissolution;

[0053] (3) Preparation of composite material: The modified nano-silica particles are added to the polyacrylamide solution and ultrasonically dispersed or mechanically stirred to ensure that the nano-silica particles are uniformly dispersed in the polyacrylamide solution; the reaction is stirred at a certain temperature for 2 hours to allow the nano-silica particles to fully combine with the polyacrylamide to form a nano-silica reinforced polymer composite material.

[0054] (4) Post-treatment: The reacted composite material is centrifuged and washed to remove unreacted surface modifiers and solvents; the composite material is dried to obtain the final nano-silica reinforced polymer composite material.

[0055] The preparation method of high-density ultra-micro oil testing and completion fluid includes the following steps:

[0056] Add an appropriate amount of deionized water to the mixer. With the stirrer set to 6000 rpm, slowly add the composite stabilizer to the water and stir continuously for 10 minutes to ensure the stabilizer is fully dispersed. Continue stirring at the above speed and slowly add polyethylene glycol to the beaker, stirring until completely dissolved. Next, increase the stirring speed to 8000 rpm and add the nano-silica reinforced polymer composite material and sodium hydroxide to adjust the pH to 8, stirring continuously until the mixture is homogeneous. Finally, while maintaining the stirring speed of 8000 rpm, slowly add the remaining high-density ultrafine powder, including high-purity calcium silicate powder, polyacrylamide, sodium carboxymethyl cellulose, sodium dodecyl sulfate, sodium citrate, nano-zirconia, modified graphene, polyimide, and the remaining deionized water, to the beaker, and continue stirring for 30 minutes to obtain the high-density ultrafine test oil completion fluid system.

[0057] Example 3

[0058] This embodiment provides a high-density, ultra-micro oil testing and completion fluid, the preparation method of which is as follows:

[0059] The raw materials of the high-density ultra-micro oil testing and completion fluid, by weight, include: 300 parts of high-purity calcium silicate micro powder, 80 parts of polyacrylamide, 50 parts of sodium carboxymethyl cellulose, 40 parts of polyethylene glycol, 10 parts of sodium dodecyl sulfate, 20 parts of sodium citrate, 15 parts of nano-grade zirconium oxide, 50 parts of modified graphene, 45 parts of composite stabilizer, 80 parts of nano-silica reinforced polymer composite material, 1 part of sodium hydroxide (as a pH adjuster), and the balance being deionized water, ensuring a total of 1000 parts.

[0060] The composite stabilizer consists of 30 parts nano-clay and 15 parts polyacrylic acid.

[0061] Preparation of the nano-silica reinforced polymer composite material:

[0062] (1) Surface treatment of nano silica: 50g of nano silica particles are dispersed in 200g of water and ultrasonically dispersed to ensure uniform dispersion of particles; 10g of silane coupling agent is added and stirred at 1000r / m for 1h at room temperature to modify the surface of nano silica particles and improve their compatibility with polyacrylamide.

[0063] (2) Preparation of polyacrylamide solution: Dissolve 64g of polyacrylamide in 300ml of water and stir at 1000r / m at room temperature to ensure complete dissolution;

[0064] (3) Preparation of composite material: The modified nano-silica particles are added to the polyacrylamide solution and ultrasonically dispersed or mechanically stirred to ensure that the nano-silica particles are uniformly dispersed in the polyacrylamide solution; the reaction is stirred at a certain temperature for 2 hours to allow the nano-silica particles to fully combine with the polyacrylamide to form a nano-silica reinforced polymer composite material.

[0065] (4) Post-treatment: The reacted composite material is centrifuged and washed to remove unreacted surface modifiers and solvents; the composite material is dried to obtain the final nano-silica reinforced polymer composite material.

[0066] The preparation method of high-density ultra-micro oil testing and completion fluid includes the following steps:

[0067] Add an appropriate amount of deionized water to the mixer. With the stirrer set to 6000 rpm, slowly add the composite stabilizer to the water and stir continuously for 10 minutes to ensure the stabilizer is fully dispersed. Continue stirring at the above speed and slowly add polyethylene glycol to the beaker, stirring until completely dissolved. Next, increase the stirring speed to 8000 rpm and add the nano-silica reinforced polymer composite material and sodium hydroxide to adjust the pH to 9, stirring continuously until the mixture is homogeneous. Finally, while maintaining the stirring speed of 8000 rpm, slowly add the remaining high-density ultrafine powder, including high-purity calcium silicate powder, polyacrylamide, sodium carboxymethyl cellulose, sodium dodecyl sulfate, sodium citrate, nano-zirconia, modified graphene, polyimide, and the remaining deionized water, to the beaker, and continue stirring for 30 minutes to obtain the high-density ultrafine test oil completion fluid system.

[0068] Comparative Example 1: Reduce the amount of calcium silicate powder used

[0069] This comparative example provides a well completion fluid, which is prepared in the same way as in Example 2, except that the amount of calcium silicate powder is reduced to 150 parts.

[0070] Comparative Example 2: Polymer composites without nano-silica reinforcement

[0071] This comparative example provides a well completion fluid, which is prepared in the same way as in Example 2, except that no nano-silica reinforced polymer composite material is added.

[0072] Comparative Example 3: No modified graphene used

[0073] This comparative example provides a well completion fluid, which is prepared in the same way as in Example 2, except that no modified graphene is added.

[0074] Application Test Case 1

[0075] The completion fluids of the examples and comparative examples were placed in a high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor was set to simulate a high formation temperature of 180°C and maintained at this temperature for 24 hours. The changes in the appearance, viscosity, density and other performance indicators of the completion fluids were observed and recorded. The parameters are detailed in Table 1 below.

[0076] Table 1. Appearance, viscosity, and density of completion fluid before and after high temperature.

[0077]

[0078]

[0079] In Example 1, the high-density ultrafine oil completion fluid initially exhibited a uniform appearance with no sediment. Even after high-temperature treatment, its appearance remained uniform and sediment-free. The initial viscosity was 50 mPa·s, which decreased slightly to 48 mPa·s after high-temperature treatment; the initial density was 1.8 g / cm³. 3 The density also decreased slightly after high temperature, to 1.79 g / cm³. 3 These data indicate that the completion fluid of Example 1 exhibits good stability under high-temperature conditions;

[0080] In Example 2, the initial appearance of the completion fluid was also uniform and free of sediment, a state maintained even after high-temperature treatment. The initial viscosity was 55 mPa·s, and the viscosity after high-temperature treatment was 53 mPa·s; the initial density was 1.9 g / cm³. 3 The density after high temperature is 1.88 g / cm³. 3 These data also demonstrate that the completion fluid of Example 2 exhibits excellent high-temperature stability;

[0081] In Example 3, the appearance, viscosity, and density of the completion fluid remained relatively stable both initially and after high temperature. The initial viscosity was 60 mPa·s, and the viscosity after high temperature was 58 mPa·s; the initial density was 1.85 g / cm³. 3 The density after high temperature is 1.84 g / cm³. 3 This further verifies the high-temperature stability of the high-density ultra-micro oil testing and completion fluid;

[0082] In contrast, the completion fluids of Comparative Examples 1 and 2 showed obvious stratification and precipitation after high-temperature treatment. The viscosity of Comparative Example 1 decreased from 50 mPa·s to 43 mPa·s, and the density decreased from 1.46 g / cm³. 3 It decreased to 1.41 g / cm³ 3 This indicates that the stability decreased significantly after high temperature; the viscosity of Comparative Example 2 decreased from 40 mPa·s to 20 mPa·s, and the density decreased from 1.50 g / cm³. 3 Decreased to 1.32 g / cm³ 3 This indicates that its high-temperature stability is poor; in Comparative Example 3, there was obvious sediment at the bottom and clear liquid at the top after high temperature, indicating that it could not maintain its stability after high temperature.

[0083] As shown in Table 1 above, through evaluation and testing, the high-density ultra-micro oil completion fluids provided in Examples 1, 2, and 3 can effectively prevent the sedimentation of high-density weighting agents during the completion process, ensuring the performance and effectiveness of the completion fluids.

[0084] Application Test Example 2

[0085] The completion fluids prepared in Examples 1-3 and Comparative Examples 1-3 were placed in a static settling test device. An equal amount of high-density weighting agent was added to the completion fluid to simulate the weighting situation in the actual completion process. The test device was left to stand for 24 hours, and the settling of the weighting agent was observed and recorded. The specific parameters are detailed in Table 2 below.

[0086] Table 2 Density of Completion Fluid After Adding Weighting Agent

[0087]

[0088]

[0089] In Example 1, 50g of barite powder was added as a weighting agent to the high-density ultrafine oil testing completion fluid, and the density before settling was 1.53g / cm³. 3 After 24 hours of settling, the density remained at 1.52 g / cm³. 3 Furthermore, no obvious settlement phenomenon was observed.

[0090] In Example 2, 50g of barite powder was also added, and the density before sedimentation was 1.63g / cm³. 3 After standing for 24 hours, the density after settling was 1.62 g / cm³. 3 No significant subsidence was observed.

[0091] In Example 3, after adding 50g of barite powder, the density before sedimentation was 1.75g / cm³. 3 After standing for 24 hours, the density after settling was 1.73 g / cm³. 3 Similarly, no obvious settlement phenomenon was observed.

[0092] The above results show that the high-density ultra-micro oil testing completion fluids provided in Examples 1, 2, and 3 can effectively prevent the sedimentation of high-density weighting agents during the completion process; in contrast, in Comparative Examples 1-3, after adding 50g of barite powder, obvious sedimentation phenomena were observed.

[0093] As can be seen from the experimental data in the table above, the high-density ultra-micro oil testing completion fluids provided in Examples 1-3 can effectively prevent the sedimentation of high-density weighting agents during the completion process, while the high-density weighting agents in the completion fluids of Comparative Examples 1-3 show obvious sedimentation.

[0094] Application Test Example 3

[0095] The reservoir protection performance of the completion fluid systems provided in Examples 1, 2, 3 and Comparative Example 1 was measured respectively. The specific evaluation method was as follows: Four core samples with similar physical properties were selected, and the original permeability of the core samples was measured using kerosene. The completion fluid systems of Examples 1-4 were used to dynamically contaminate the four core samples in reverse, and the permeability of the contaminated core samples was measured again. The permeability recovery value after dynamic damage to the core samples was calculated. The specific parameters are detailed in Table 3 below.

[0096] Table 3. Dynamic Core Damage Assessment Based on Completion Fluid

[0097]

[0098]

[0099] As shown in the experimental data in the table above, the permeability recovery value of the completion fluid system provided in Example 1 after dynamic damage to the core was 93.42%, indicating that Example 1 has a good reservoir protection effect.

[0100] The completion fluid system provided in Example 2 showed a permeability recovery value of 95.22% after dynamic damage to the core, indicating that Example 2 has a good reservoir protection effect.

[0101] The completion fluid system provided in Example 3 showed a permeability recovery value of 92.21% after dynamic damage to the core, further demonstrating that Example 3 causes extremely low reservoir damage and has a good reservoir protection effect.

[0102] Compared to the 80.14% permeability recovery value of the completion fluid provided in Comparative Example 1 after dynamic damage to the core, the 72.92% permeability recovery value of the completion fluid provided in Comparative Example 2 after dynamic damage to the core, and the 85.42% permeability recovery value of the completion fluid provided in Comparative Example 3 after dynamic damage to the core, these values ​​are significantly lower than the dynamic cuttings permeability recovery value of the completion fluid in the embodiments of the present invention.

[0103] As can be seen from the data in the table above, the permeability recovery values ​​measured by the dynamic core damage experiment of the high-density ultra-micro oil testing completion fluids provided in Examples 1, 2, and 3 are all greater than 90%, indicating that the completion fluids of the present invention cause very little damage to the reservoir during the completion process, and can protect the oil and gas layer to the maximum extent and improve the oil and gas recovery rate.

[0104] Application Test Example 4

[0105] The compatibility of the high-density ultra-micro oil completion fluid system was tested. The rheological properties of the mixed liquid prepared by mixing the present invention Example 2 with soil acid at a ratio of 10:1, the mixed liquid prepared by mixing the present invention Example 2 with diesel at a ratio of 10:1, and the mixed liquid prepared by adding 2% solidified cement to the present invention Example 2 were tested. The specific performance parameters are detailed in Table 4 below.

[0106] Table 4 Compatibility Test of Completion Fluid

[0107]

[0108]

[0109] The mixed liquid prepared by Example 2 and argillaceous acid in a 10:1 ratio showed little change in rheological properties at room temperature compared to that measured in Example 2. After standing at 120°C for 24 hours, the rheological properties also showed little change, with a slight decrease in viscosity. No significant sedimentation was observed, indicating that the high-density ultra-micro oil testing completion fluid of this invention and the argillaceous acid used for acidizing have good compatibility and do not affect the subsequent acidizing effect. The mixed liquid prepared by Example 2 and diesel oil in a 10:1 ratio also showed little change in rheological properties at room temperature. After standing at 120°C for 24 hours, the viscosity decreased slightly, indicating that the high-density ultra-micro oil testing completion fluid of this invention and diesel oil have good compatibility. Adding 2% of solidified cement to the mixture in Example 2 slightly increased the viscosity at room temperature. After standing at 120°C for 24 hours, the rheological properties decreased slightly compared to the room temperature test results, but the change was not significant, indicating that the pulverized cement generated during perforation has little impact on the high-density ultra-micro oil testing completion fluid of this invention.

[0110] As can be seen from the data in the table above, the high-density ultra-micro oil testing and completion fluid provided by the present invention has good compatibility with soil acid, diesel and cement during the completion process.

[0111] The comparative experiments described above demonstrate that the high-density ultra-micro oil testing and completion fluid of this invention exhibits superior performance in terms of calcium silicate powder dosage, nano-silica reinforced polymer composite material, and modified graphene. Therefore, it can be concluded that the high-density ultra-micro oil testing and completion fluid of this invention possesses superior performance and is suitable for high-density, ultra-micro oil testing operations.

Claims

1. A high-density, ultra-micro oil testing and completion fluid, comprising, by weight 1000 parts, the following raw materials: 200-300 parts calcium silicate powder, 50-80 parts polyacrylamide, 30-50 parts sodium carboxymethyl cellulose, 20-40 parts polyethylene glycol, 5-10 parts sodium dodecyl sulfate, 10-20 parts sodium citrate, 5-15 parts nano-zirconia, 10-50 parts modified graphene, 15-45 parts composite stabilizer, 30-80 parts nano-silica reinforced polymer composite material, and the balance being water.

2. The high-density ultra-micro oil testing and completion fluid according to claim 1, wherein, The composite stabilizer comprises a combination of 10-30 parts nano-clay and 5-15 parts polyacrylic acid.

3. The high-density ultra-micro oil testing and completion fluid according to claim 1, wherein, The nano-silica reinforced polymer composite material is composed of nano-silica particles and polyacrylamide, wherein the mass fraction of nano-silica particles in the composite material is 5-20 wt%, and the mass fraction of polyacrylamide is 80-95 wt%.

4. The high-density ultra-micro oil testing and completion fluid according to claim 3, wherein, The preparation method of the nano-silica reinforced polymer composite material includes: Nano-silica particles and a surface modifier are mixed evenly in water to obtain modified nano-silica particles; the modified nano-silica particles and polyacrylamide are mixed evenly in water to obtain the nano-silica-reinforced polymer composite material.

5. The high-density ultra-micro oil testing and completion fluid according to claim 1, wherein, The raw materials for the completion fluid also include 0.3-1 parts of sodium hydroxide as a pH adjuster.

6. The high-density ultra-micro oil testing and completion fluid according to claim 1, wherein, The calcium silicate powder is high-purity calcium silicate micro powder with a purity of over 90% and a particle size of less than 20 micrometers.

7. The high-density ultra-micro oil testing and completion fluid according to claim 1, wherein, The modified graphene is modified graphene GO1212.

8. A method for preparing the high-density ultra-micro oil testing and completion fluid according to any one of claims 1-7, comprising: S1: Add the composite stabilizer, polyethylene glycol, and nano-silica reinforced polymer composite material to water, stir evenly, and adjust the pH value with sodium hydroxide to obtain a mixed solution; S2: Add calcium silicate powder, polyacrylamide, sodium carboxymethyl cellulose, sodium dodecyl sulfate, sodium citrate, nano-sized zirconium oxide, modified graphene, and the remaining water to the mixed solution, stir and mix evenly to obtain the high-density ultra-micro oil testing and completion fluid.

9. The method for preparing high-density ultra-micro oil testing and completion fluid according to claim 8, wherein, In S1, the pH of the mixed solution is 7-9.

10. The method for preparing high-density ultra-micro oil testing and completion fluid according to claim 8, wherein, In S1 and / or S2, the stirring speed is 6000-8000 r / min.

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