A nanometer fracture sealing completion fluid, a preparation method and application thereof

Abstract

The application provides a nanometer fissure sealing completion fluid and a preparation method and application thereof, and the completion fluid raw materials comprise, in parts by weight, 100 parts of clean water, 0.1-0.3 parts of a tackifier, 1-1.5 parts of modified high-temperature-resistant starch, 0.4-0.8 parts of polyanionic cellulose, 0.1-0.3 parts of a bactericide, 1-3 parts of an active nanometer sealing agent, 2-5 parts of a micro sealing agent, 7-10 parts of potassium chloride, 0.4-0.8 parts of NaOH and 0.5-1 parts of a crosslinking agent. The combination of the active nanometer sealing agent and the micro sealing agent in the application significantly improves the sealing performance of the completion fluid, the combination can more effectively seal nanometer fissures and pores, reduce permeability, reduce reservoir pollution caused by liquid phase and solid phase invasion, thereby prolonging the service life of the oil well and improving the oil production efficiency.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well completion technology, specifically to a nano-fracture sealing completion fluid, its preparation method, and its application. Background Technology

[0002] Unconventional oil and gas, especially shale oil and gas, has become an important alternative resource for oil and gas. However, during the completion process of unconventional oil and gas wells, conventional completion fluids are prone to reservoir contamination due to their high solid content. Meanwhile, solid-free brine and salt water completion fluids are prone to leakage into the reservoir, causing damage to oil and gas producing reservoirs, resulting in decreased production and increased costs due to leakage.

[0003] Shale unconventional oil and gas formations exhibit well-developed micropores and microfractures, rich in clay matrix, which readily hydrates and expands. Most of these pores and microfractures are nanoscale, making it easy for completion fluids to infiltrate the formation along these shale pores and microfractures, leading to microfracture propagation. This can easily cause reservoir contamination and significant completion fluid loss during well completion. Existing completion fluid systems lack specific measures for sealing nanoscale microfractures and micropores, or simply add sealing materials that can only seal pores and fractures of micrometers and larger, offering poor sealing effects for nanoscale pores and fractures. This can easily cause reservoir contamination, poor oil and gas testing results, and severe damage to the completion fluid, making it difficult to form a dense and effective sealing layer to prevent drilling and completion fluid infiltration.

[0004] In the traditional well completion fluid preparation process, due to unreasonable formulation or improper preparation process, the key indicators such as viscosity, fluidity and plugging performance of the well completion fluid often fail to meet the actual requirements. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a nano-fracture sealing completion fluid, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides a nano-fracture sealing and completion fluid, which, by weight, comprises the following raw materials: 100 parts water, 0.1-0.3 parts viscosifier, 1-1.5 parts modified high-temperature resistant starch, 0.4-0.8 parts polyanionic cellulose, 0.1-0.3 parts bactericide, 1-3 parts active nano-plugging agent, 2-5 parts micron-plugging agent, 7-10 parts potassium chloride, 0.4-0.8 parts NaOH, and 0.5-1 parts crosslinking agent.

[0007] In the aforementioned nanofracture sealing completion fluid, preferably, the active nano-plugging agent is prepared from the following raw materials in the following molar proportions: 0.5-1.5 parts nano-calcium carbonate, 0.25-0.7 parts silane coupling agent, 1-3 parts acrylamide, 1-2 parts methacrylamide, 0.25-1 part acrylic acid, and 1-3 parts perfluorooctyl methacrylate. The active nano-plugging agent of this invention possesses hydrophobic and oleophobic surface properties.

[0008] In the above-mentioned nanofracture sealing completion fluid, preferably, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane; the median particle size of the nano-calcium carbonate is 30-70 nm, more preferably 50 nm.

[0009] In the above-mentioned nano-fracture sealing completion fluid, preferably, the active nano-plugging agent is prepared by the following method:

[0010] The silane coupling agent was thoroughly mixed with nano-calcium carbonate to perform surface modification, resulting in surface-modified nano-calcium carbonate.

[0011] Acrylamide, methacrylamide, and acrylic acid are dissolved in water to obtain a mixed solution;

[0012] The surface-modified nano-calcium carbonate was dispersed in ethylene glycol, and perfluorooctyl methacrylate and the mixed solution were added, followed by a reflux reaction. The particles in the reaction solution were collected to obtain the active nano-blocking agent.

[0013] In the above-mentioned nano-fracture sealing and completion fluid, preferably, the silane coupling agent and nano-calcium carbonate are mixed and stirred at 50-100°C for 20-50 min, more preferably at 75°C for 30 min.

[0014] In the aforementioned nanofracture sealing completion fluid, preferably, the reflux reaction temperature is 60-90℃ and the time is 3-5h; more preferably, the reflux reaction temperature is 85℃ and the time is 4h.

[0015] In the aforementioned nanofracture sealing completion fluid, preferably, the reflux reaction is carried out under nitrogen protection.

[0016] According to a specific embodiment of the present invention, preferably, the active nano-blocking agent is prepared by the following method:

[0017] Step 1: At room temperature, add 0.5 moles of silane coupling agent and 1 mole of nano-calcium carbonate to a high-speed mixer, stir and heat to 75°C, continue stirring for 30 minutes to perform surface modification, and obtain surface-modified nano-calcium carbonate.

[0018] Step 2: Dissolve 2 moles of acrylamide, 1 mole of methacrylamide, and 0.5 moles of acrylic acid in 250 mL of deionized water at room temperature, and stir at 400 rpm for 40 min.

[0019] Step 3: Add the modified nano-calcium carbonate obtained in Step 1 to 100 mL of ethylene glycol solution, stir at 400 rpm for 10 min, then add the product from Step 2 and 1 mole of perfluoro-n-octyl methacrylate, continue stirring, and heat the reaction mixture to 85 °C in a water bath for reflux reaction for 4 hours. Then filter to obtain the filter residue, wash the filter residue with water, and dry it at 100 °C to obtain the active nano-blocking agent.

[0020] In the above-mentioned nanofracture sealing completion fluid, preferably, the crosslinking agent is prepared from the following raw materials in the following molar proportions: 1-3 parts polyethylene polyamine, 2-4 parts ethanol, 1-2 parts epichlorohydrin, and 0.1-0.3 parts triphenylphosphine.

[0021] In the above-mentioned nanofracture sealing completion fluid, preferably, the crosslinking agent is prepared by the following method: dissolving polyethylene polyamine in ethanol, adding epichlorohydrin and triphenylphosphine, reacting at 40-60℃ for 4-6 hours, more preferably at 50℃ for 5 hours, and removing insoluble matter after cooling to obtain the crosslinking agent.

[0022] According to a specific embodiment of the present invention, preferably, the crosslinking agent is prepared by the following method:

[0023] In a three-necked flask equipped with a stirrer, thermometer, and reflux condenser, 1 molar of polyethylenepolyamine and 3 molar of ethanol were added, heated to 50°C, and stirred until completely dissolved; 1.2 molar of epichlorohydrin and 0.1 molar of triphenylphosphine were slowly added, and the reaction was continued with stirring for 5 hours; the mixture was cooled to room temperature, filtered to remove insoluble matter, and the crosslinking agent was obtained.

[0024] According to a specific embodiment of the present invention, preferably, the above-mentioned nanofracture sealing completion fluid satisfies one or more of the following conditions:

[0025] The modified high-temperature resistant starch is a filtration loss reducer, BIO-LOSE.

[0026] The polyanionic cellulose is a filtration loss reducer, PAC-LV.

[0027] The tackifier is xanthan gum;

[0028] The micron-blocking agent is DRGF-1, a micron-blocking agent produced by China National Petroleum Corporation.

[0029] This invention also provides a method for preparing the above-mentioned nano-fracture sealing completion fluid, which includes the following steps:

[0030] Add potassium chloride and NaOH to water and dissolve them. Then add a thickener and mix well. Next, add modified high-temperature resistant starch and polyanionic cellulose and stir until the solvent is reached to obtain an intermediate solution.

[0031] A bactericide, an active nano-plugging agent, and a micron-plugging agent are added sequentially to the intermediate solution and mixed thoroughly. Finally, a crosslinking agent is added and mixed thoroughly to obtain the nano-fracture sealing and completion fluid.

[0032] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned nanofracture sealing completion fluid specifically includes the following steps:

[0033] (1) Take 100 parts by weight of clean water, and slowly add 7-10 parts by weight of potassium chloride and 0.4-0.8 parts by weight of NaOH to the water while stirring at 600 r / min, until they are completely dissolved;

[0034] (2) Add 0.1-0.3 parts by weight of xanthan gum slowly to the solution obtained in step (1) at a stirring speed of 6000 r / min and stir for 10 min;

[0035] (3) Slowly add 1-1.5 parts by weight of the filtration loss reducer BIO-LOSE and 0.4-0.8 parts by weight of the filtration loss reducer PAC-LV to the solution obtained in step (2), and stir until completely dissolved;

[0036] (4) Then add 0.1-0.3 parts by weight of bactericide, 1-3 parts by weight of active nano-blocking agent, and 2-5 parts by weight of micron-blocking agent to the solution obtained in step (3), and stir at a speed of 3000 r / min for 30 min until the mixture is uniform.

[0037] (5) Add the crosslinking agent to the solution obtained in step (4) at a ratio of 0.5-1.0 parts by weight, and continue stirring until the crosslinking agent is evenly dispersed to obtain the nano-fracture sealing and completion fluid.

[0038] This invention also provides an application of the above-mentioned nanofracture sealing completion fluid in unconventional oil and gas well completion.

[0039] The technical solution provided by this invention has the following beneficial effects:

[0040] (1) The combination of active nano plugging agent and micro plugging agent in this invention significantly improves the plugging performance of the completion fluid. This combination can more effectively plug nano- and micro-fractures and pores, reduce permeability, reduce reservoir pollution caused by liquid and solid phase intrusion, thereby extending the service life of oil wells and improving oil production efficiency.

[0041] (2) The addition of crosslinking agent emulsion in this invention can enhance the structural stability of the completion fluid, which helps to ensure that the completion fluid is not prone to stratification, deterioration or failure during construction, thereby improving its overall performance and reliability.

[0042] (3) By adjusting the amount of clean water added, the present invention can prepare a well completion fluid with moderate viscosity, easy injection and excellent sealing effect. The appropriate amount of clean water added not only ensures the fluidity of the well completion fluid, but also improves its sealing performance, so that the well completion fluid can better adapt to different formation conditions and construction needs in practical applications. Detailed Implementation

[0043] 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.

[0044] In embodiments of the present invention, the modified high-temperature resistant starch is a filtration loss reducer BIO-LOSE; the polyanionic cellulose is a filtration loss reducer PAC-LV; the thickener is xanthan gum; and the micron-blocking agent is DRGF-1 micron-blocking agent produced by China National Petroleum Corporation.

[0045] Example 1

[0046] This embodiment provides a nano-fracture sealing completion fluid, which is made from the following raw materials in parts by weight:

[0047] 100 parts water, 0.3 parts xanthan gum (binder), 1 part modified high-temperature resistant starch, 0.4 parts polyanionic cellulose, 0.1 parts bactericide, 1 part active nano-blocking agent, 2 parts micron-blocking agent, 7 parts potassium chloride, 0.4 parts NaOH, and 0.5 parts crosslinking agent.

[0048] The preparation method of the active nano-blocking agent is as follows:

[0049] Step 1: At room temperature, add 0.5 moles of γ-methacryloxypropyltrimethoxysilane (silane coupling agent) and 1 mole of nano-calcium carbonate (median particle size of 50 nm) to a high-speed mixer, stir and heat to 75°C, continue stirring for 30 min to carry out surface modification, and obtain surface-modified nano-calcium carbonate.

[0050] Step 2: Dissolve 2 moles of acrylamide, 1 mole of methacrylamide, and 0.5 moles of acrylic acid in 250 mL of deionized water at room temperature, and stir at 400 rpm for 40 min to obtain a mixture.

[0051] Step 3: Add the surface-modified nano-calcium carbonate obtained in Step 1 to 100 mL of ethylene glycol solution, stir at 400 rpm for 10 min, then add the mixture from Step 2 and 1 mole of perfluorooctyl methacrylate, continue stirring, and heat the reaction mixture to 85 °C in a water bath. Reflux the reaction under nitrogen protection for 4 hours, then filter to obtain the filter residue. Wash the filter residue with water and dry it at 100 °C to obtain the active nano-blocking agent; this active nano-blocking agent has hydrophobic and oleophobic surface properties.

[0052] The preparation method of the crosslinking agent is as follows:

[0053] In a three-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 1 mole of polyethylenepolyamine and 3 moles of ethanol, heat to 50°C, and stir until completely dissolved; slowly add 1.2 moles of epichlorohydrin; add 0.1 moles of triphenylphosphine, and continue stirring for 5 hours; cool to room temperature, filter to remove insoluble matter, and obtain the crosslinking agent.

[0054] The method for preparing nano-fracture sealing completion fluid in this embodiment includes the following steps:

[0055] Take 100 parts by weight of water and pour it into a beaker. While stirring at 600 r / min, slowly add 7 parts of potassium chloride and 0.4 parts of NaOH to the water until they are completely dissolved.

[0056] Slowly add 0.1 parts of xanthan gum at a stirring speed of 6000 r / min, stir for 10 min, then slowly add 1 part of modified high-temperature resistant starch and 0.4 parts of polyanionic cellulose to the beaker, and stir until completely dissolved.

[0057] Then add 0.1 parts of bactericide, 1 part of active nano-blocking agent, and 2 parts of micron-blocking agent to the beaker in sequence, and stir at a stirring speed of 3000 r / min for 30 min until the mixture is uniform.

[0058] Add 0.5 parts of crosslinking agent to a beaker and continue stirring until the crosslinking agent is evenly dispersed to obtain nanofracture sealing completion fluid.

[0059] Example 2

[0060] This embodiment provides a nano-fracture sealing completion fluid, which is made from the following raw materials in parts by weight:

[0061] 100 parts water, 0.3 parts xanthan gum, 1.5 parts modified high-temperature resistant starch, 0.8 parts polyanionic cellulose, 0.3 parts bactericide, 3 parts active nano-blocking agent, 5 parts micron-blocking agent, 10 parts potassium chloride, 0.8 parts NaOH, and 1 part crosslinking agent.

[0062] The preparation method of the active nano-blocking agent is as follows:

[0063] Step 1: At room temperature, add 0.5 moles of γ-methacryloxypropyltrimethoxysilane (silane coupling agent) and 1 mole of nano-calcium carbonate (median particle size of 50 nm) to a high-speed mixer, stir and heat to 75°C, continue stirring for 30 min to carry out surface modification, and obtain surface-modified nano-calcium carbonate.

[0064] Step 2: Dissolve 2 moles of acrylamide, 1 mole of methacrylamide, and 0.5 moles of acrylic acid in 250 mL of deionized water at room temperature, and stir at 400 rpm for 40 min to obtain a mixture.

[0065] Step 3: Add the surface-modified nano-calcium carbonate obtained in Step 1 to 100 mL of ethylene glycol solution, stir at 400 rpm for 10 min, then add the mixture from Step 2 and 1 mole of perfluorooctyl methacrylate, continue stirring, and heat the reaction mixture to 85 °C in a water bath. Reflux the reaction under nitrogen protection for 4 hours, then filter to obtain the filter residue. Wash the filter residue with water and dry it at 100 °C to obtain the active nano-blocking agent. This active nano-blocking agent has hydrophobic and oleophobic surface properties.

[0066] The preparation method of the crosslinking agent is as follows:

[0067] In a three-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 1 mole of polyethylenepolyamine and 3 moles of ethanol, heat to 50°C, and stir until completely dissolved; slowly add 1.2 moles of epichlorohydrin; add 0.1 moles of triphenylphosphine, and continue stirring for 5 hours; cool to room temperature, filter to remove insoluble matter, and obtain the crosslinking agent.

[0068] The method for preparing nano-fracture sealing completion fluid in this embodiment includes the following steps:

[0069] Take 100 parts by weight of water and pour it into a beaker. While stirring at 600 r / min, slowly add 10 parts of potassium chloride and 0.8 parts of NaOH to the water until they are completely dissolved.

[0070] Slowly add 0.3 parts of xanthan gum at a stirring speed of 6000 r / min and stir for 10 min;

[0071] Slowly add 1.5 parts of modified high-temperature resistant starch and 0.8 parts of polyanionic cellulose to the beaker and stir until completely dissolved;

[0072] Then add 0.3 parts of bactericide, 3 parts of active nano-blocking agent, and 5 parts of micron-blocking agent to the beaker in sequence, and stir at a stirring speed of 3000 r / min for 30 min until the mixture is uniform.

[0073] Add 1 part of the crosslinking agent to a beaker and continue stirring until the crosslinking agent is evenly dispersed to obtain the nano-fracture sealing completion fluid.

[0074] Example 3

[0075] This embodiment provides a nano-fracture sealing completion fluid, which is made from the following raw materials in parts by weight:

[0076] 100 parts water, 0.2 parts xanthan gum, 1.25 parts modified high-temperature resistant starch, 0.6 parts polyanionic cellulose, 0.2 parts bactericide, 2 parts active nano-blocking agent, 3.5 parts micron-blocking agent, 8.5 parts potassium chloride, 0.6 parts NaOH, and 0.75 parts crosslinking agent.

[0077] The preparation method of the active nano-blocking agent is as follows:

[0078] Step 1: At room temperature, add 0.5 moles of γ-methacryloxypropyltrimethoxysilane (silane coupling agent) and 1 mole of nano-calcium carbonate (median particle size of 50 nm) to a high-speed mixer, stir and heat to 75°C, continue stirring for 30 min to carry out surface modification, and obtain surface-modified nano-calcium carbonate.

[0079] Step 2: Dissolve 2 moles of acrylamide, 1 mole of methacrylamide, and 0.5 moles of acrylic acid in 250 mL of deionized water at room temperature, and stir at 400 rpm for 40 min to obtain a mixture.

[0080] Step 3: Add the surface-modified nano-calcium carbonate obtained in Step 1 to 100 mL of ethylene glycol solution, stir at 400 rpm for 10 min, then add the mixture from Step 2 and 1 mole of perfluorooctyl methacrylate, continue stirring, and heat the reaction mixture to 85 °C in a water bath. Reflux the reaction under nitrogen protection for 4 hours, then filter to obtain the filter residue. Wash the filter residue with water and dry it at 100 °C to obtain the active nano-blocking agent. This active nano-blocking agent has hydrophobic and oleophobic surface properties.

[0081] The preparation method of the crosslinking agent is as follows:

[0082] In a three-necked flask equipped with a stirrer, thermometer, and reflux condenser, add 1 mole of polyethylenepolyamine and 3 moles of ethanol, heat to 50°C, and stir until completely dissolved; slowly add 1.2 moles of epichlorohydrin; add 0.1 moles of triphenylphosphine, and continue stirring for 5 hours; cool to room temperature, filter to remove insoluble matter, and obtain an emulsion of crosslinking agent.

[0083] The method for preparing nano-fracture sealing completion fluid in this embodiment includes the following steps:

[0084] Take 100 parts by weight of water and pour it into a beaker. While stirring at 600 r / min, slowly add 8.5 parts of potassium chloride and 0.6 parts of NaOH to the water until they are completely dissolved.

[0085] Slowly add 0.2 parts of xanthan gum at a stirring speed of 6000 r / min and stir for 10 min;

[0086] Slowly add 1.25 parts of modified high-temperature resistant starch and 0.6 parts of polyanionic cellulose to the beaker and stir until completely dissolved;

[0087] Then, add 0.2 parts of bactericide, 2 parts of active nano-blocking agent, and 3.5 parts of micron-blocking agent to the beaker in sequence, and stir at a speed of 3000 r / min for 30 min until the mixture is uniform.

[0088] Add 0.75 parts of crosslinking agent emulsion to a beaker and continue stirring until the crosslinking agent is evenly dispersed to obtain nanofracture sealing completion fluid.

[0089] Comparative Example 1

[0090] This comparative example provides a nano-fracture sealing completion fluid, which is prepared in the same way as in Example 3, except that the weight of the water is 10 parts.

[0091] Comparative Example 2

[0092] This comparative example provides a nano-fracture sealing completion fluid, which is prepared in the same way as in Example 3, except that the weight of water is 30 parts.

[0093] Comparative Example 3

[0094] This comparative example provides a nano-fracture sealing completion fluid, which is prepared in the same way as in Example 3, except that the weight of water is 50 parts.

[0095] Comparative Example 4

[0096] This comparative example provides a nano-fracture sealing completion fluid, which is prepared in the same way as in Example 3, except that no micron-sized plugging agent is added.

[0097] Comparative Example 5

[0098] This comparative example provides a nano-fracture plugging completion fluid, which is prepared in the same way as in Example 3, except that no active nano-plugging agent is added.

[0099] Comparative Example 6

[0100] This comparative example provides a nano-fracture plugging completion fluid, which is prepared in the same way as in Example 3, except that no micron plugging agent or active nano plugging agent is added.

[0101] Comparative Example 7

[0102] This comparative example provides a nano-fracture sealing and completion fluid, which is prepared in the same way as in Example 3, except that no crosslinking agent is added.

[0103] Example 1: Evaluation of Viscosity and Blocking Effect

[0104] I. Methods for evaluating the effectiveness of containment:

[0105] (1) Experimental materials and equipment:

[0106] Completion fluid samples: such as the completion fluids of Examples 1-3 and Comparative Examples 1-3;

[0107] Devices or materials for simulating fractures: such as rock cores or artificial fracture models with specific porosity and permeability;

[0108] High-pressure injection equipment is used to inject completion fluid into simulated fractures.

[0109] Measurement equipment: such as a permeability tester, used to measure the permeability change of simulated fractures before and after well completion fluid injection.

[0110] (2) Experimental steps:

[0111] Prepare the simulated fracture device and ensure it is dry and clean; measure the initial permeability of the simulated fracture; use a high-pressure injection device to inject completion fluid into the simulated fracture until the predetermined injection pressure or injection volume is reached; wait for a period of time to allow the completion fluid to fully act on the simulated fracture; measure the permeability of the simulated fracture again and record the data.

[0112] (3) Evaluation criteria:

[0113] Plugging rate: The plugging rate is calculated by comparing the change in permeability before and after the completion fluid injection. A higher plugging rate indicates a better plugging effect of the completion fluid.

[0114] Permeability change: Directly observe the change in permeability. The greater the decrease in permeability, the stronger the sealing performance of the completion fluid.

[0115] (4) Data Analysis:

[0116] Based on the measured permeability data, the plugging rate and permeability change rate of each completion fluid were calculated. The results were summarized in a table (as shown in Table 1) and compared and analyzed.

[0117] II. Experimental evidence for the effectiveness of unconventional oil and gas well completions

[0118] To demonstrate the effectiveness of the completion fluid of this invention in unconventional oil and gas well completion, the following experiment can be designed:

[0119] (1) Simulate unconventional oil and gas reservoirs: Use rock cores or artificial materials with characteristics such as low permeability and high porosity to simulate unconventional oil and gas reservoirs.

[0120] (2) Injection of completion fluid: The completion fluid of the present invention is injected into the simulated unconventional oil and gas reservoir.

[0121] Measuring reservoir performance changes: Measuring changes in key parameters such as permeability and porosity of the reservoir before and after well completion fluid injection;

[0122] (3) Observe and record the impact of completion fluid on reservoir stability, such as whether it reduces formation hydration expansion and whether it improves the pressure-bearing capacity of the reservoir.

[0123] (4) Data analysis and conclusions: Based on the measured data, the influence of the completion fluid on the performance of unconventional oil and gas reservoirs is analyzed; the conclusions are drawn to illustrate the application effect of the completion fluid of the present invention in unconventional oil and gas well completion.

[0124] The viscosity and plugging effect of the completion fluids in Example 3 and Comparative Examples 1-3 were evaluated, and the results are shown in Table 1.

[0125] Table 1 Evaluation of Viscosity and Blocking Effect

[0126]

[0127] Experimental Analysis:

[0128] Viscosity evaluation:

[0129] Examples 1, 2, and 3: The completion fluid has moderate viscosity, good fluidity, and is easy to inject.

[0130] Comparative Example 1: Insufficient addition of clean water resulted in excessively high viscosity of the completion fluid, poor fluidity, and difficulty in injection.

[0131] Comparative Example 2: The amount of clean water added was moderate to slightly less, and the viscosity of the completion fluid was relatively high, but it still had a certain degree of fluidity and could be injected, but there might be some difficulties.

[0132] Comparative Example 3: The amount of clean water added was moderate to slightly less but more than that of Group B and Group C. The viscosity of the completion fluid was moderate to slightly thick, with good injectability, neither too thin nor too viscous.

[0133] Evaluation of sealing effectiveness:

[0134] Examples 1, 2, and 3: The completion fluid has excellent plugging effect, effectively sealing fractures and reducing permeability.

[0135] Comparative Example 1: Due to its excessively high viscosity, the completion fluid's permeability in the fractures was reduced, resulting in a poor sealing effect.

[0136] Comparative Example 2: The sealing effect was average, possibly because the high viscosity affected its distribution and permeability in the cracks.

[0137] Comparative Example 3: The sealing effect is good. Although the viscosity is slightly higher than that of Group A, it can still effectively seal the cracks. Moreover, due to its good injectability, it may have better adaptability in practical applications.

[0138] Conclusion: By comparing the performance of completion fluids with different amounts of added water, it can be found that the amount of added water has a significant impact on the viscosity and plugging effect of the completion fluid. An appropriate amount of water (e.g., 100 parts) can prepare a completion fluid with moderate viscosity, easy injection, and excellent plugging effect; while too little water leads to excessively high viscosity, poor fluidity, and poor plugging effect; when the amount of water added is moderately low (e.g., 30 or 50 parts), the completion fluid viscosity is relatively high but still injectable, with a moderate to good plugging effect. In practical applications, the appropriate amount of water added should be selected according to specific needs and construction conditions to prepare a completion fluid with excellent performance. Furthermore, considering the balance between injectability and plugging effect, group d (50 parts water) may be a more suitable choice, ensuring both good injectability and a certain degree of plugging effect.

[0139] Evaluation of the sealing effect in Experiment Example 2

[0140] The sealing effect of the completion fluids in the above embodiments and comparative examples was evaluated, and the results are shown in Tables 2 and 3.

[0141] The evaluation method is as follows:

[0142] I. Experimental Materials and Methods

[0143] Experimental materials: completion fluids of Examples 1, 2, and 3; completion fluids of Comparative Examples 1-7 (as control groups); simulated fracture devices or materials; high-pressure injection equipment; permeability tester; viscometer; and other necessary experimental equipment and reagents.

[0144] II. Experimental Methods:

[0145] (1) Viscosity test: Use a viscometer to measure the viscosity of each completion fluid and record the data.

[0146] (2) Sealing effect test: Each completion fluid was injected into the simulated fracture device, and parameters such as sealing onset time, sealing pressure, and permeability after sealing were measured and recorded.

[0147] III. Data Analysis: Based on the test results, calculate the sealing rate, permeability change rate, and other indicators of each completion fluid, and conduct comparative analysis.

[0148] Table 2 Evaluation Results of Blocking Effectiveness

[0149]

[0150] Experimental Analysis:

[0151] Viscosity analysis:

[0152] (1) The completion fluids of Examples 1, 2 and 3 all have moderate or moderately thick viscosity, which makes them easy to inject and less prone to leakage.

[0153] (2) The completion fluid of Comparative Example 1 has too high viscosity, poor fluidity, and is not easy to inject;

[0154] (3) The viscosity of the completion fluid in Comparative Examples 2-7 was in the range of moderate to high, but none of them reached an excessively high level.

[0155] Analysis of the blocking effect:

[0156] Onset time of plugging effect: The completion fluid in Example 3 had the shortest onset time of plugging effect, only 10 minutes, which is much shorter than the traditional completion fluids in Comparative Examples 1-3. This indicates that the completion fluid of the present invention can respond and plug fractures more quickly.

[0157] Sealing pressure: The completion fluids in Examples 2 and 3 exhibited the highest sealing pressure, reaching 20 MPa, significantly higher than the traditional completion fluids in Comparative Examples 1-3. This indicates that the completion fluid of the present invention can maintain a stable sealing effect even under high-pressure environments.

[0158] Post-plugging permeability: The completion fluids of Examples 1, 2, and 3 showed extremely low permeability after plugging, far lower than all completion fluids in Comparative Examples 1-7. This indicates that the completion fluid of the present invention can more effectively reduce permeability and decrease reservoir contamination caused by liquid and solid phase invasion.

[0159] The influence of the type and addition of plugging agent:

[0160] Example 3 (Active Nanoparticle Plugging Agent + Microparticle Plugging Agent): This combination resulted in the shortest onset time, highest plugging pressure, lowest post-plugging permeability, and excellent plugging effect. This demonstrates that the combined use of active nanoparticle plugging agent and microparticle plugging agent can significantly improve the plugging performance of completion fluids.

[0161] Comparative Example 4 (active nano-blocking agent only): The blocking onset time was longer than that of Example 3, the blocking pressure was lower, and the permeability after blocking was higher. This indicates that when only the active nano-blocking agent is used, the blocking performance is somewhat reduced, but a good blocking effect is still maintained.

[0162] Comparative Example 5 (micron-sized plugging agent only): The plugging onset time, plugging pressure, and post-plugging permeability were all between those of Example 3 and Comparative Example 4. This indicates that when only the micron-sized plugging agent is used, the plugging performance is between that of the active nano-plugging agent and the combination of both, and the plugging effect is generally moderate.

[0163] Comparative Example 6 (without plugging agent): It had the longest plugging onset time, the lowest plugging pressure, the highest post-plugging permeability, and the poorest plugging effect. This indicates that completion fluid without plugging agent has almost no plugging performance.

[0164] The effect of crosslinking agents:

[0165] Comparative Example 7 (without crosslinking agent): The plugging onset time, plugging pressure, and post-plugging permeability were all between those of Example 3 and Comparative Example 4 (or Comparative Example 5). This indicates that the absence of crosslinking agent has some impact on the plugging performance of the completion fluid, but not as significant as the impact of the type of plugging agent. The crosslinking agent may mainly play a role in enhancing the structural stability of the completion fluid, while its direct contribution to plugging performance is relatively small.

[0166] Evaluation of sealing effectiveness:

[0167] Example 3, by combining the advantages of active nano-blocking agents and micro-blocking agents, exhibits the best blocking effect.

[0168] Comparative Examples 4 and 5, which used a single sealing agent, showed slightly less effective sealing, but still had some application value.

[0169] Comparative Example 6, without any plugging agent, had the worst plugging effect and is not suitable for well completion operations requiring plugging performance.

[0170] Although Comparative Example 7 did not contain a crosslinking agent, its blocking effect was similar to that of Group C, indicating that the contribution of the crosslinking agent to the blocking performance is relatively limited. However, whether to add it still needs to be considered based on the specific application scenario.

[0171] Comprehensive performance analysis:

[0172] (1) The completion fluids of Examples 1, 2 and 3 all showed excellent performance in terms of viscosity and plugging effect, and were superior to all comparative examples;

[0173] (2) In the comparative examples, Comparative Examples 4-7 had a certain impact on the performance of the completion fluid by changing the type of plugging agent and the addition of crosslinking agent, but none of them reached the level of the examples;

[0174] (3) Comparative Examples 1 and 2 had poor sealing effects due to excessively high or slightly high viscosity.

[0175] in conclusion:

[0176] By comparing the performance of the completion fluids in different embodiments and comparative examples, it can be found that the completion fluids in Examples 1, 2, and 3 all exhibit excellent performance in terms of viscosity and sealing effect. The completion fluids in these embodiments are not only easy to inject, but also able to quickly and effectively seal fractures and reduce permeability. In contrast, the completion fluid in the comparative example has certain performance deficiencies and cannot fully meet actual needs.

[0177] Therefore, it can be concluded that all embodiments of the present invention (including embodiments 1, 2, and 3) achieve good technical effects and are superior to comparative examples in the prior art. In practical applications, the completion fluids of these embodiments will have broad application prospects and market value.

[0178] By comparing the performance of completion fluids with different types of plugging agents and crosslinking agent additions, it can be found that the combined use of active nano-plugging agents and micro-plugging agents can significantly improve the plugging performance of completion fluids. In practical applications, the appropriate type of plugging agent and whether to add a crosslinking agent should be selected according to specific needs and construction conditions to prepare a completion fluid with excellent performance.

[0179] Table 3 Test data on the sealing effect of completion fluid

[0180]

[0181] Data Analysis:

[0182] Viscosity: The completion fluids of Examples 1, 2, and 3 have moderate viscosity, are easy to inject, and are significantly lower than the traditional completion fluid of Comparative Example 1. This indicates that the completion fluid of the present invention can achieve good sealing effect while maintaining good fluidity.

[0183] Onset time of plugging effect: The completion fluid in Example 3 had the shortest onset time of plugging effect, only 10 minutes, which is much shorter than the traditional completion fluids in Comparative Examples 1-3. This indicates that the completion fluid of the present invention can respond and plug fractures more quickly.

[0184] Sealing pressure: The completion fluids in Examples 2 and 3 exhibited the highest sealing pressure, reaching 20 MPa, significantly higher than the traditional completion fluids in Comparative Examples 1-3. This indicates that the completion fluid of the present invention can maintain a stable sealing effect even under high-pressure environments.

[0185] Post-plugging permeability: The completion fluids of Examples 1, 2, and 3 showed extremely low permeability after plugging, far lower than all completion fluids in Comparative Examples 1-7. This indicates that the completion fluid of the present invention can more effectively reduce permeability and decrease reservoir contamination caused by liquid and solid phase invasion.

[0186] Plugging rate: The plugging rates of the completion fluids in Examples 1, 2, and 3 were all above 98.5%, far exceeding those of the completion fluids in Comparative Examples 1-7. This further demonstrates the superiority of the completion fluid of the present invention in terms of plugging effect.

[0187] Permeability change rate: The permeability change rate of the completion fluids in Examples 1, 2, and 3 were all above -99.5%, indicating that they can significantly reduce permeability and are more effective than the completion fluids in Comparative Examples 1-7.

[0188] In summary, the completion fluids of the present invention in Examples 1, 2, and 3 exhibit excellent performance in terms of viscosity, plugging onset time, plugging pressure, post-plugging permeability, plugging rate, and permeability change rate, significantly outperforming traditional and improved completion fluids. This demonstrates the significant advancement of the completion fluid of the present invention in plugging effect and its broad prospects for practical application.

Claims

1. A nanoslit plugging completion fluid, raw materials of which comprise, in parts by weight: 100 parts water, 0.1-0.3 parts thickener, 1-1.5 parts modified high-temperature resistant starch, 0.4-0.8 parts polyanionic cellulose, 0.1-0.3 parts bactericide, 1-3 parts active nano-blocking agent, 2-5 parts micron-blocking agent, 7-10 parts potassium chloride, 0.4-0.8 parts NaOH, and 0.5-1 parts crosslinking agent.

2. The nanofissure-plugging completion fluid of claim 1, wherein, The active nano-blocking agent is prepared from the following raw materials in the following molar proportions: 0.5-1.5 parts of nano-calcium carbonate, 0.25-0.7 parts of silane coupling agent, 1-3 parts of acrylamide, 1-2 parts of methacrylamide, 0.25-1 part of acrylic acid, and 1-3 parts of perfluorooctyl methacrylate.

3. The nanofissure-plugging completion fluid of claim 2, wherein, The silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane; the median particle size of the nano-calcium carbonate is 30-70 nm.

4. The nanofissure-plugging completion fluid of claim 2, wherein, The active nano-blocking agent was prepared by the following method: The silane coupling agent was thoroughly mixed with nano-calcium carbonate to perform surface modification, resulting in surface-modified nano-calcium carbonate. Acrylamide, methacrylamide, and acrylic acid are dissolved in water to obtain a mixed solution; The surface-modified nano-calcium carbonate was dispersed in ethylene glycol, and perfluorooctyl methacrylate and the mixed solution were added, followed by a reflux reaction. The particles in the reaction solution were collected to obtain the active nano-blocking agent.

5. The nanofissure-plugging completion fluid of claim 4, wherein, The silane coupling agent and nano-calcium carbonate were mixed and stirred at 50-100℃ for 20-50 min. And / or, the reflux reaction temperature is 60-90℃, and the time is 3-5h.

6. The nanofissure-plugging completion fluid of claim 1, wherein, The crosslinking agent is prepared from the following raw materials in the following molar proportions: 1-3 parts polyethylene polyamine, 2-4 parts ethanol, 1-2 parts epichlorohydrin, and 0.1-0.3 parts triphenylphosphine.

7. The nanofracture sealing and completion fluid according to claim 6, wherein, The crosslinking agent is prepared by the following method: dissolving polyethylene polyamine in ethanol, adding epichlorohydrin and triphenylphosphine, reacting at 40-60℃ for 4-6 hours, and removing insoluble matter after cooling to obtain the crosslinking agent.

8. The nanofracture sealing and completion fluid according to claim 1, wherein, The nanofracture sealing completion fluid meets one or more of the following conditions: The modified high-temperature resistant starch is a filtration loss reducer, BIO-LOSE. The polyanionic cellulose is a filtration loss reducer, PAC-LV. The tackifier is xanthan gum; The micron-blocking agent is DRGF-1, a micron-blocking agent produced by China National Petroleum Corporation.

9. A method for preparing the nano-fracture sealing completion fluid according to any one of claims 1-8, comprising the following steps: Add potassium chloride and NaOH to water and dissolve them. Then add a thickener and mix well. Next, add modified high-temperature resistant starch and polyanionic cellulose and stir until the solvent is reached to obtain an intermediate solution. A bactericide, an active nano-plugging agent, and a micron-plugging agent are added sequentially to the intermediate solution and mixed thoroughly. Finally, a crosslinking agent is added and mixed thoroughly to obtain the nano-fracture sealing and completion fluid.

10. The application of the nanofracture sealing completion fluid according to any one of claims 1-8 in unconventional oil and gas well completion.

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