Selective temporary plugging agent as well as preparation process and application thereof

Abstract

The invention belongs to the field of workover treatment in the petroleum industry and discloses a selective temporary plugging agent as well as a preparation process and application thereof. A polyvinylidene fluoride-co-hexafluoropropylene copolymer and nano silicon dioxide form an enhanced gel system, meanwhile, a certain amount of polyethylene glycol diglycidyl ether is added to form a composite temporary plugging system, and the temporary plugging system has excellent temperature stability and chemical stability, can keep performance under the high-temperature condition, meanwhile, can achieve controllable degradation, and can be applied to the field of temporary plugging. And moreover, degradation products do not cause pump blocking accidents, and meanwhile, the oil well plugging agent has the advantages of high temperature resistance, chemical corrosion resistance, harmlessness to a reservoir stratum and excellent performance.

Description

Technical Field

[0001] This invention pertains to the field of well workover operations in the petroleum industry, and relates to a selective temporary plugging agent, its preparation process, and its application. Background Technology

[0002] During SAGD and steam-driven well workover operations, the complex block connectivity and severe gas channeling interference due to the steam flushing effect result in incomplete wellbore pressure release. This increases the preparation time by more than 5 days compared to conventional wells, severely impacting workover efficiency and production rate. SAGD and steam-driven blocks are located in the late stages of development with high recovery rates and formation pressure coefficients less than 0.5. Workover operations suffer from low formation pressure coefficients and severe well-killing fluid loss. Currently available clean water, hot wastewater, and brine have a specific gravity greater than 1, resulting in large wellbore pressure differentials that prevent the establishment of pressure balance.

[0003] Currently, there are two main types of temporary plugging agents used in well workover operations. One type is the polyacrylamide gel system type, which has strong plugging performance and good filtration reduction effect, and is widely used in oilfield well workover operations. The other type is the oil-soluble temporary plugging agent, which can be dissolved by oil and automatically released from the blockage at reservoir temperature after plugging, and is a pollution-free temporary plugging agent.

[0004] In the specific implementation process, the inventors found that the existing technology has at least the following problems: Polyacrylamide gel-type temporary plugging agents are not easy to degrade or break down. In light oil well operations, they are very likely to damage the formation, causing a decrease in permeability, resulting in a decrease in production, or even blocking the well. In addition, polyacrylamide gel shear fragments are very likely to stick to the pump, affecting the normal production of the oil well. Oil-soluble temporary plugging agents are expensive. If the dosage is large, it will easily solidify the well. If the dosage is small, it will not play a temporary plugging role. The field implementation is difficult and it is limited to use in reservoirs with small formation deficits and low permeability. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a selective temporary plugging agent, its preparation process, and its application. The agent forms a reinforced gel system by combining polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) copolymer with nano-silica, and simultaneously adds a certain amount of polyethylene glycol diglycidyl ether to form a composite temporary plugging system. This system exhibits excellent temperature and chemical stability, maintaining its performance under high-temperature conditions while achieving controllable degradation. It does not permanently block the oil well, and the degradation products do not cause pump jamming accidents. Furthermore, it possesses advantages such as high-temperature resistance, chemical corrosion resistance, and harmlessness to the reservoir, demonstrating excellent performance.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] A selective temporary plugging agent, the raw materials of which include polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) copolymer, nano-silica, polyethylene glycol diglycidyl ether, cetyltrimethylammonium chloride, sodium citrate, calcium peroxide, and water.

[0008] The PVDF-HFP copolymer is selected from products with a molecular weight between 200,000 and 400,000.

[0009] The polyethylene glycol diglycidyl ether is selected from products with a molecular weight between 500 and 1000.

[0010] Furthermore, the aforementioned selective temporary plugging agent is formulated with the following raw materials in the following weight percentages: 0.3-0.5% PVDF-HFP copolymer, 0.1-0.3% nano silica, 4-8% polyethylene glycol diglycidyl ether, 0.2-0.4% hexadecyltrimethylammonium chloride, 0.05-0.1% sodium citrate, 0.01-0.03% calcium peroxide, and the balance being water.

[0011] In selective temporary plugging agents, PVDF-HFP copolymers and nano-silica form a reinforced gel system. The plugging efficiency of the gel system of the selective temporary plugging agent is not less than 98%.

[0012] The preparation process of the above-mentioned selective temporary plugging agent includes the preparation of the base liquid and the on-site addition of compounding.

[0013] The prepared base liquid is a composite base liquid system prepared by mixing PVDF-HFP copolymer, polyethylene glycol diglycidyl ether, hexadecyltrimethylammonium chloride, sodium citrate, calcium peroxide, and water in a certain proportion. The on-site addition of the compound is implemented by adding nano-silica to the composite base liquid system obtained from the prepared base liquid during on-site implementation to obtain a selective temporary plugging agent.

[0014] Application of the selective temporary plugging agent prepared by the above process in high temperature and high pressure oil wells.

[0015] In practical applications, the selective temporary plugging agent is pumped into the required well bottom to carry out the work.

[0016] The selective temporary plugging agent prepared by the above process is used in high-temperature and high-pressure oil well workover operations.

[0017] The advantages of this invention compared to the prior art are:

[0018] This invention provides a selective temporary plugging agent, its preparation process, and its application. A reinforced gel system is formed by combining a PVDF-HFP copolymer with nano-silica, while a certain amount of polyethylene glycol diglycidyl ether is added to form a composite temporary plugging system. This gel system exhibits excellent temperature and chemical stability, maintaining its performance in high-temperature environments below 200°C and resisting extreme chemical environments such as strong acids and alkalis. The addition of calcium peroxide allows for controlled degradation of the temporary plugging system, preventing permanent well blockage and avoiding pump sticking accidents caused by degradation products. Furthermore, this temporary plugging system possesses advantages such as high-temperature resistance, chemical corrosion resistance, reservoir non-toxicity, excellent performance, and moderate cost, making it particularly suitable for well workover operations in high-temperature, high-pressure reservoirs. Detailed Implementation

[0019] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0020] The selective temporary plugging agent formulation provided by this invention comprises the following raw materials in the following weight percentages: 0.3-0.5% polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) copolymer, 0.1-0.3% nano-silica, 4-8% polyethylene glycol diglycidyl ether, 0.2-0.4% hexadecyltrimethylammonium chloride, 0.05-0.1% sodium citrate, 0.01-0.03% calcium peroxide, and 90.57-95.34% water.

[0021] The selective plugging agent provided by this invention is a selective plugging agent used in high-temperature and high-pressure oil wells. The main components function as follows:

[0022] A PVDF-HFP copolymer is used in this invention to form a reinforced gel system with nano-silica. The PVDF-HFP copolymer is chosen because of its excellent high-temperature resistance and chemical stability. Compared to traditional water-soluble polymers, the PVDF-HFP copolymer maintains stable performance in high-temperature environments below 200℃ and is resistant to extreme chemical environments such as strong acids and alkalis. The reinforced gel system formed by the PVDF-HFP copolymer and nano-silica exhibits very high mechanical strength and elasticity. The gelation time can be controlled by adjusting the concentration of nano-silica, generally ranging from 15 to 45 minutes, which well meets the requirements of on-site construction. This gel system achieves optimal performance at 150℃, with a plugging rate of not less than 98%, effectively sealing reservoir porosity and microfractures in the near-wellbore zone.

[0023] In this embodiment, polyethylene glycol diglycidyl ether (PEGDGE) acts as a crosslinking agent and toughening agent. PEGDGE can undergo a crosslinking reaction with the PVDF-HFP copolymer at high temperatures, further enhancing the gel network structure. Simultaneously, PEGDGE exhibits good thermal and chemical stability, maintaining its performance at high temperatures. The addition of PEGDGE improves the toughness and elasticity of the selective plugging agent, enhancing its compressive strength and erosion resistance. At reservoir temperatures, PEGDGE slowly hydrolyzes, forming new channels, which is beneficial for subsequent unblocking.

[0024] The cetyltrimethylammonium chloride added to the selective temporary plugging agent acts as a surfactant and stabilizer. It can reduce the interfacial tension between the PVDF-HFP copolymer and water, promoting the dispersion of the copolymer in water. Simultaneously, it can adsorb onto the surface of nano-silica, preventing nanoparticle aggregation and improving the stability of the system. This long-chain quaternary ammonium salt maintains good performance at high temperatures, contributing to the stability of the selective temporary plugging agent in high-temperature environments.

[0025] Sodium citrate acts as a pH buffer and chelating agent in this formulation. It can regulate and stabilize the pH of the system, optimizing the gel formation process. Simultaneously, sodium citrate can form chelates with polyvalent metal ions in the reservoir, preventing these ions from interfering with gel formation and performance. Furthermore, sodium citrate also possesses certain antioxidant properties, which helps improve the thermal stability of the selective temporary plugging agent.

[0026] Calcium peroxide is a key component in this formulation, used to achieve controlled degradation of the selective plugging agent. Under high-temperature conditions, calcium peroxide slowly decomposes to produce oxygen and calcium hydroxide. The generation of oxygen helps disrupt the gel network structure, while calcium hydroxide neutralizes formation acidity, providing a protective effect. By adjusting the amount of calcium peroxide, the degradation time of the selective plugging agent can be controlled, typically within 12-72 hours. This controlled degradation mechanism ensures that the selective plugging agent does not permanently clog the oil reservoir, and that the degradation products do not cause secondary pollution or pump jamming.

[0027] The selective temporary plugging agent provided in this invention is applied to high-temperature and high-pressure oil wells. In field application, 0.3-0.5 wt% of the PVDF-HFP copolymer is first dissolved in a small amount of N,N-dimethylformamide (DMF). Then, 4-8 wt% of polyethylene glycol diglycidyl ether, 0.2-0.4 wt% of hexadecyltrimethylammonium chloride, 0.05-0.1 wt% of sodium citrate, 0.01-0.03 wt% of calcium peroxide, and most of the water are added and stirred until homogeneous to form a base fluid. During field implementation, 0.1-0.3 wt% of pre-dispersed nano-silica aqueous solution is added to the base fluid, and after thorough mixing, it can be pumped into the bottom of the well to be operated on, followed by relevant operations.

[0028] The selective temporary plugging agent provided by this invention forms a reinforced gel system by combining PVDF-HFP copolymer with nano-silica, and simultaneously adds polyethylene glycol diglycidyl ether to form a composite cross-linked network. This temporary plugging system exhibits excellent high-temperature resistance and chemical stability, maintaining good performance in high-temperature environments below 200°C. The addition of calcium peroxide enables controlled degradation of the selective temporary plugging agent, preventing permanent blockage. This temporary plugging system possesses advantages such as high strength, high elasticity, high-temperature resistance, chemical corrosion resistance, and harmlessness to the reservoir, making it particularly suitable for various operations in high-temperature, high-pressure oil reservoirs.

[0029] To obtain optimal performance, the PVDF-HFP copolymer used in this embodiment is selected from products with a molecular weight between 200,000 and 400,000; the polyethylene glycol diglycidyl ether is selected from products with a molecular weight between 500 and 1,000; the nano silica particles have a particle size of 10-50 nm; and the hexadecyltrimethylammonium chloride, sodium citrate, and calcium peroxide are all analytical grade reagents with a purity of not less than 98%.

[0030] Example 1

[0031] A selective temporary plugging agent, the raw materials of which include polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) copolymer, nano-silica, polyethylene glycol diglycidyl ether, hexadecyltrimethylammonium chloride, sodium citrate, calcium peroxide, and water.

[0032] The PVDF-HFP copolymer used is a product with a molecular weight of 300,000, manufactured by Arkema.

[0033] The polyethylene glycol diglycidyl ether used is a product with a molecular weight of 800, manufactured by Sigma-Aldrich.

[0034] Furthermore, the aforementioned selective temporary plugging agent is formulated with the following raw materials in the following weight percentages: 0.4% PVDF-HFP copolymer, 0.2% nano silica, 6% polyethylene glycol diglycidyl ether, 0.3% hexadecyltrimethylammonium chloride, 0.08% sodium citrate, 0.02% calcium peroxide, and the balance being water.

[0035] In selective temporary plugging agents, PVDF-HFP copolymers and nano-silica form a reinforced gel system. The plugging efficiency of the gel system of the selective temporary plugging agent is not less than 98%.

[0036] The specific preparation steps are as follows:

[0037] Dissolve 0.4 g of PVDF-HFP copolymer in 10 mL of N,N-dimethylformamide (DMF) and stir at 60 °C for 2 hours until completely dissolved.

[0038] In another beaker, dissolve 6g polyethylene glycol diglycidyl ether, 0.3g hexadecyltrimethylammonium chloride, 0.08g sodium citrate and 0.02g calcium peroxide in 80mL of deionized water and stir until well mixed.

[0039] Slowly pour the PVDF-HFP solution from step 1 into the aqueous solution from step 2, and stir vigorously for 30 minutes at room temperature.

[0040] The DMF solvent was removed by vacuum distillation at 50°C using a rotary evaporator to obtain a clear base liquid.

[0041] When using, add 0.2g of pre-dispersed nano-silica aqueous solution (particle size 20nm, concentration 10wt%) to the base solution, and ultrasonically disperse for 10 minutes to obtain the final selective temporary plugging agent.

[0042] Performance test results: gel time: 25 minutes (70℃); gel strength: 1200 Pa (80℃, 24 hours); temperature resistance: stable at 180℃ for 72 hours; salt resistance: stable in 20 wt% NaCl solution; blocking rate: 98.5% (API RP 63 standard test); gel breaking time: 36 hours (150℃).

[0043] Example 2

[0044] A selective temporary plugging agent, the raw materials of which include polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) copolymer, nano-silica, polyethylene glycol diglycidyl ether, hexadecyltrimethylammonium chloride, sodium citrate, calcium peroxide, and water.

[0045] The PVDF-HFP copolymer used is a product with a molecular weight of 350,000, manufactured by Solvay.

[0046] The polyethylene glycol diglycidyl ether used is a product with a molecular weight of 600, manufactured by DOW Corporation.

[0047] Furthermore, the aforementioned selective temporary plugging agent is formulated with the following raw materials in the following weight percentages: 0.5% PVDF-HFP copolymer, 0.3% nano silica, 8% polyethylene glycol diglycidyl ether, 0.4% hexadecyltrimethylammonium chloride, 0.1% sodium citrate, 0.03% calcium peroxide, and the balance being water.

[0048] In selective temporary plugging agents, PVDF-HFP copolymers and nano-silica form a reinforced gel system. The plugging efficiency of the gel system of the selective temporary plugging agent is not less than 99%.

[0049] The specific preparation steps are as follows:

[0050] Dissolve 0.5 g of PVDF-HFP copolymer in 12 mL of N,N-dimethylformamide (DMF) and stir at 65 °C for 2.5 hours until completely dissolved.

[0051] In another beaker, dissolve 8g of polyethylene glycol diglycidyl ether, 0.4g of cetyltrimethylammonium chloride, 0.1g of sodium citrate and 0.03g of calcium peroxide in 75mL of deionized water and stir until well mixed.

[0052] Slowly pour the PVDF-HFP solution from step 1 into the aqueous solution from step 2, and stir vigorously for 45 minutes at room temperature.

[0053] The DMF solvent was removed by vacuum distillation at 55°C using a rotary evaporator to obtain a clear base liquid.

[0054] When using, add 0.3g of pre-dispersed nano-silica aqueous solution (particle size 15nm, concentration 15wt%) to the base solution, and ultrasonically disperse for 15 minutes to obtain the final selective temporary plugging agent.

[0055] Performance test results:

[0056] Gel time: 20 minutes (75℃);

[0057] Gel strength: 1500 Pa (85℃, 24 hours);

[0058] Temperature resistance: Stable at 200℃ for 96 hours;

[0059] Salt tolerance: Stable in 25 wt% NaCl solution;

[0060] Blocking rate: 99.2% (API RP 63 standard test);

[0061] Break-through time: 48 hours (180℃).

[0062] Application Example 1

[0063] A selective temporary plugging agent comprises 0.2 tons of PVDF-HFP copolymer, 0.1 tons of nano-silica, 3 tons of polyethylene glycol diglycidyl ether, 0.15 tons of hexadecyltrimethylammonium chloride, 0.04 tons of sodium citrate, 0.01 tons of calcium peroxide, and 46.5 tons of water.

[0064] Well X1 in a certain oilfield is located in an ultra-deep, high-temperature reservoir, with a depth of 6,500 meters and a bottom layer temperature reaching 185℃. This well has five oil-producing layers with permeability ranging from 500 to 2000 × 10⁻³ μm. 2In the past, acidizing operations suffered from severe acid leakage due to high temperature and pressure, resulting in poor effectiveness. On March 15, 2023, the aforementioned selective plugging agent was used for temporary plugging. First, 40 ml of the selective plugging agent was injected. 3 Then use 10m 3 Water was used for displacement. After temporary plugging, the bottomhole pressure rose to 15 MPa, followed by acidizing operations. During acidizing, the acid flowback rate reached 85%, significantly higher than the previous level of 50%. After acidizing, the selective plugging agent degraded spontaneously within 48 hours. The well's production capacity increased from 50 tons / day before acidizing to 150 tons / day, an increase of 200%. No pump sticking or other equipment failures occurred throughout the entire process, greatly improving acidizing efficiency and safety.

[0065] Application Example 2

[0066] A selective temporary plugging agent comprises 0.25 tons of PVDF-HFP copolymer, 0.15 tons of nano-silica, 4 tons of polyethylene glycol diglycidyl ether, 0.2 tons of hexadecyltrimethylammonium chloride, 0.05 tons of sodium citrate, 0.015 tons of calcium peroxide, and 45.335 tons of water.

[0067] Well Y2 in a certain offshore oil field is a horizontal well with a horizontal section length of 2000 meters, located in a complex fault zone. During a major workover operation on January 10, 2024, the well encountered a serious leakage problem, despite an initial investment of 200m³. 3 All workover fluid was lost. To resolve this issue, the aforementioned selective temporary plugging agent was used. 60m of the selective temporary plugging agent was injected. 3 Then use 20m 3 Water was used for temporary plugging. After the plugging, the wellbore pressure stabilized at 8 MPa, meeting the requirements for subsequent operations. The overhaul was then successfully completed, with well workover fluid loss not exceeding 5 m³ throughout the entire process. The selective plugging agent degraded spontaneously after 72 hours, without affecting subsequent production. The well's production capacity increased from 200 tons / day to 350 tons / day after the overhaul, an increase of 75%. Compared to traditional plugging agents, this invention's selective plugging agent shortened the operation time by approximately 40%, saving significant offshore operation costs.

[0068] Application Example 3

[0069] A selective temporary plugging agent comprises 0.3 tons of PVDF-HFP copolymer, 0.2 tons of nano-silica, 5 tons of polyethylene glycol diglycidyl ether, 0.25 tons of hexadecyltrimethylammonium chloride, 0.06 tons of sodium citrate, 0.02 tons of calcium peroxide, and 44.17 tons of water.

[0070] On May 20, 2024, a multi-stage fracturing operation was conducted on Well Z3 in a shale oilfield. The well has a vertical depth of 3500 meters and a horizontal section length of 1500 meters, with a total of 8 fracturing stages designed. Severe channeling occurred during the first two stages, resulting in fracturing fluid utilization of less than 60%. To improve the fracturing effect of subsequent stages, the aforementioned selective temporary plugging agent was used before the third stage. 50m... 3 A selective temporary plugging agent was injected into the target section, and fracturing was performed after a 2-hour settling period. Results showed that the selective temporary plugging agent effectively sealed natural fractures and microfractures, increasing fracturing fluid utilization to 85%. The subsequent six fracturing stages were successfully completed, with an average fracturing fluid utilization rate remaining above 80%. The selective temporary plugging agent began to degrade spontaneously 24 hours after fracturing, and the wellbore was clear after 48 hours. This well ultimately achieved a daily oil production of 60 tons, 40% higher than adjacent wells. Furthermore, due to the improved fracturing efficiency, the overall fracturing fluid consumption was reduced by 20%, lowering environmental impact and treatment costs. The selective temporary plugging agent provided in this invention is a temporary plugging agent with strong sealing performance, easy degradation, immediate gel breaking, no damage or pollution to the reservoir, and a certain degree of oil solubility.

[0071] These three application cases fully demonstrate the superior performance of the selective temporary plugging agent in various complex environments, including high-temperature deep wells, offshore horizontal wells, and shale reservoirs. The new formulation not only overcomes the limitations of traditional temporary plugging agents under extreme conditions but also significantly improves operational efficiency and well productivity while reducing environmental impact and operating costs. These application cases prove the wide applicability and significant value of the selective temporary plugging agent of this invention in modern oilfield development.

[0072] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A selective bridging agent, characterized in that, The raw materials include polyvinylidene fluoride-co-hexafluoropropylene copolymer, nano-silica, polyethylene glycol diglycidyl ether, cetyltrimethylammonium chloride, sodium citrate, calcium peroxide, and water. The raw materials are proportioned by weight percentage as follows: polyvinylidene fluoride-co-hexafluoropropylene copolymer 0.3-0.5%, nano-silica 0.1-0.3%, polyethylene glycol diglycidyl ether 4-8%, cetyltrimethylammonium chloride 0.2-0.4%, sodium citrate 0.05-0.1%, calcium peroxide 0.01-0.03%, and the balance is water.

2. The selective bridging agent of claim 1 wherein, In the selective temporary plugging agent, the polyvinylidene fluoride-co-hexafluoropropylene copolymer and the nano-silica form a reinforced gel system.

3. The selective bridging agent of claim 1 wherein, The plugging rate of the gel system of the selective temporary plugging agent is not less than 98%.

4. A selective bridging agent as claimed in any one of claims 1 to 3, characterised in that, The nano-silica has a particle size of 10-50 nm.

5. The process for preparing a selective bridging agent according to any one of claims 1 to 3, characterized in that, The preparation process includes configuring a base fluid and adding a complex on site.

6. The process for preparing a selective bridge plug according to claim 5, wherein the step of mixing the water-soluble polymer and the water-soluble salt is performed at a temperature of 20 to 100°C. The polyvinylidene fluoride-co-hexafluoropropylene copolymer, polyethylene glycol diglycidyl ether, cetyltrimethylammonium chloride, sodium citrate, calcium peroxide, and water are mixed in proportion to configure a composite base fluid system.

7. The preparation process of the selective temporary plugging agent as described in claim 5, characterized in that, On-site complex implementation is to add nano-silica to the composite base fluid system obtained by configuring the base fluid to obtain the selective temporary plugging agent.

8. The use of the selective temporary plugging agent prepared by the preparation process of any one of claims 6-7 in high-temperature and high-pressure oil wells.

9. Use according to claim 8, wherein the compound is ###0002### The selective temporary plugging agent is pumped into the required bottom hole and implemented.

10. The use according to claim 8, wherein the compound is ###00002### 8 The use of the selective temporary plugging agent in high-temperature and high-pressure oil well workover operations.