Self-degradable gel plugging material for reservoir and preparation method thereof

Abstract

This patent application discloses a self-degradable gel plugging material suitable for reservoirs and its preparation method. The plugging material, by weight, comprises the following raw materials: 180-240 parts water, 70-110 parts monomer, 0.7-1.2 parts crosslinking agent, 0.1-1 part initiator, 0.5-4 parts natural polymer, 0-4 parts acidity neutralizer, and 0-2 parts nano-doped material; the crosslinking agent is polyethylene glycol diacrylate, and the natural polymer is guar gum. The plugging material of this invention not only possesses excellent self-degradable plugging performance but also exhibits good pressure resistance and strength.

Description

Technical Field

[0001] This invention relates to the field of compositions for borehole or well drilling, and more specifically to a self-degrading gel plugging material suitable for reservoirs and its preparation method. Background Technology

[0002] Drilling fluid loss is a critical bottleneck in oil and gas drilling, a major common technical problem that has plagued oil and gas drilling both domestically and internationally. Globally, well leakage occurs in approximately 20-25% of all drilled wells, costing between $2-4 billion annually. It is a major technical challenge hindering economical, safe, and efficient oil and gas drilling. Well leakage occurs when the drilling fluid column pressure exceeds the formation pore pressure difference, causing the drilling fluid to enter the formation and be lost. Based on its causes, it can be divided into human-induced and natural factors. Permeability loss, natural fractures, and cavernous leakage are natural factors; human-induced factors may be due to improper construction or an unsuitable drilling fluid composition. Reservoir rocks are mainly affected by compaction, cementation, and dissolution. The first two decrease permeability, while the third increases it, due to differences in the structure and porosity of different formations.

[0003] Self-degradable polymeric plugging materials are divided into natural and synthetic self-degradable polymeric plugging materials. Natural self-degradable polymeric materials include starch and chitosan, but their pressure resistance and strength properties are insufficient for practical applications. Synthetic self-degradable polymeric materials mainly polymerize monomers into polymers through polymerization or condensation reactions, then introduce low-energy bonds such as ester and amide bonds as connecting "joints" to link different small molecular chains. Under certain conditions, these joints hydrolyze, reverting to smaller molecular chains, leading to a sharp decrease in the overall strength and pressure resistance of the material. This allows for plugging under pressure differential. However, existing synthetic self-degradable polymeric materials have strength defects and are relatively brittle, failing to fully meet practical application requirements. This invention provides a self-degradable gel plugging material for reservoirs and its preparation method, which does not significantly alter the rheological properties or viscosity of drilling fluid, thus meeting the needs of on-site plugging operations. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a self-degradable gel plugging material suitable for reservoirs and its preparation method. The plugging material of this invention not only has good self-degradation and plugging performance, but also has good pressure resistance and strength.

[0005] The technical solution adopted in this invention is as follows:

[0006] A self-degradable gel plugging material suitable for reservoirs, comprising the following raw materials by weight: 180-240 parts water, 70-110 parts monomer, 0.7-1.2 parts crosslinking agent, 0.1-1 parts initiator, 0.5-4 parts natural polymer material, 0-4 parts acidity neutralizer, and 0-2 parts nano-doped material.

[0007] The crosslinking agent is polyethylene glycol diacrylate, and the natural polymer material is guar gum.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0009] The sealing material prepared by the present invention using raw materials within the above-mentioned specific ratio range not only has good self-degradation and unblocking performance, but also has good pressure resistance and strength. This invention introduces polyethylene glycol diacrylate with ester bonds into the self-degradable gel plugging material. Polyethylene glycol diacrylate contains hydrolyzable ester bonds, and its introduction into the polymeric gel plugging material enables it to spontaneously degrade and unblock under high-temperature alkaline formation conditions. Simultaneously, it introduces natural polymeric guar gum and nano-doped materials. In this invention, natural polymeric guar gum participates in the reaction and enters the polymer system, as shown in reaction formulas (1) and (2). In reaction formula (2), GG is the guar gum free radical, a product of reaction formula (1), which effectively enhances the tensile properties and pressure resistance of the gel and extends the degradation time (due to the need for well completion and other operations after plugging, sufficient time is allowed for subsequent operations). The plugging material of this invention can extend the time from the ordinary 68h to 106h, and can continue to extend it under different conditions, reaching a maximum of 162h under simulated formation conditions. Without affecting the degradation performance, it can also effectively enhance the viscosity and strength of the gel material. Furthermore, the inventors discovered in their research that the system does not react without the natural polymeric material guar gum. The plugging material prepared by this invention is pumped to the location of the leakage layer along with the drilling fluid. Under the action of pressure difference, it seals the leakage channel and has the above-mentioned excellent plugging performance. Moreover, it can spontaneously degrade and unblock after a certain period of time, which can effectively reduce drilling fluid loss and facilitate subsequent operations, thus effectively improving drilling efficiency.

[0010] (1)

[0011] (2)

[0012] In a preferred embodiment of the present invention, the composition includes 190-220 parts water, 80-90 parts monomer, 0.8-1.2 parts crosslinking agent, 0.1-0.5 parts initiator, 1-2 parts natural polymer material, 0-2 parts acidity neutralizer, and 0.5-2 parts nano-doped material. The plugging material prepared using this method exhibits better pressure resistance and superior overall performance in terms of spontaneous degradation and unblocking.

[0013] In a preferred embodiment of the present invention, the monomer is one or a combination of two or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid.

[0014] In a preferred embodiment of the present invention, the acidity neutralizing agent is sodium hydroxide.

[0015] In a preferred embodiment of the present invention, the initiator is ammonium persulfate or cerium ammonium nitrate.

[0016] In a preferred embodiment of the present invention, the nano-doped material is one or a mixture of two or more of the following: nano-calcium carbonate, 45-55nm nano-silica, 25-35nm nano-silica, and 10-20nm nano-silica.

[0017] In a preferred embodiment of the present invention, the nano-doped material is 45-55nm nano-silicon dioxide.

[0018] This invention also provides a method for preparing a reservoir self-degradable gel plugging material, comprising the following steps:

[0019] (1) Place the monomer and crosslinking agent in water, stir to form a homogeneous solution, and add an acidity neutralizer to obtain a reaction monomer solution;

[0020] (2) Add natural polymer materials to monomer solution and stir to form a uniform solution. After adding nano-doped materials and stirring thoroughly, perform acoustic dispersion treatment to obtain reaction base liquid.

[0021] (3) After sealing the reaction base liquid, nitrogen gas is introduced, the initiator is added and stirred evenly, and the reaction is carried out for 5-8 hours under ice-water bath conditions to obtain the initial product;

[0022] (4) The initial product is cleaned, dried, crushed and sieved to obtain a self-degradable gel plugging material suitable for reservoirs.

[0023] The self-degradable gel plugging material prepared using this method not only has good self-degradation and plugging performance, but also has excellent pressure resistance and strength.

[0024] In a preferred embodiment of the present invention, in step (1), the pH of the reaction monomer solution is adjusted to 7. Attached Figure Description

[0025] Figure 1 This is a graph showing the degradation rate over time when the sample was placed in a solution simulating formation conditions, as described in Example 1 of this invention.

[0026] Figure 2 This is the dynamic experimental sealing layer used in Example 1 to test the sealing characteristics before degradation.

[0027] Figure 3 This is the dynamic experimental sealing layer used in Example 1 to test the sealing characteristics after degradation. Detailed Implementation

[0028] Typical embodiments embodying the features and advantages of the present invention will be specifically described in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit the present invention.

[0029] In the examples, the monomer is one or a combination of two or more of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and acrylic acid, preferably acrylamide or 2-acrylamide-2-methylpropanesulfonic acid. In the following examples, acrylamide is used as the monomer.

[0030] The nano-doped material is one or a mixture of two or more of the following: nano-calcium carbonate, 45-55nm nano-silica, 25-35nm nano-silica, and 10-20nm nano-silica; preferably, nano-silica with a particle size of 45-55nm.

[0031] Example 1

[0032] This embodiment discloses a reservoir self-degradable gel plugging material, which, by weight, comprises the following raw materials: 210 parts water, 88 parts monomer, 0.9 parts crosslinking agent, 0.3 parts initiator, 1 part natural polymer material, 0.5 parts acidity neutralizer, and 1 part nano-doped material.

[0033] In this embodiment, the monomer is acrylamide; the crosslinking agent is polyethylene glycol diacrylate; the initiator is cerium ammonium nitrate; the natural polymer material is guar gum; the acidity neutralizer is a 15% sodium hydroxide aqueous solution; and the nano-doped material is nano-silica with a particle size of 45-55 nm.

[0034] This embodiment also discloses a method for preparing the above-mentioned reservoir self-degradable gel plugging material, including the following steps:

[0035] (1) Place 92 parts of acrylamide monomer and 0.9 parts of crosslinking agent polyethylene glycol diacrylate in 210 parts of water, stir with a mechanical stirrer to form a uniform solution, and add an acidity neutralizer to obtain the reaction monomer solution;

[0036] (2) Add 1 part of natural polymer material guar gum to the reaction monomer solution, stir for 30 minutes using a mechanical stirrer to form a uniform solution without particle aggregation, then add 1 part of nano-doped material nano silica and stir thoroughly, then place it in an ultrasonic device for dispersion treatment for 30 minutes to obtain the reaction base liquid.

[0037] (3) After sealing the reaction base liquid, nitrogen gas is introduced for 30 minutes. 0.3 parts of cerium ammonium nitrate initiator are added to the reaction base liquid and stirred evenly. The mixture is stirred until a uniform solution is obtained under ice-water bath conditions and then allowed to stand for 6 hours to obtain the initial product.

[0038] (4) The surface of the initial product is cleaned with acetone, dried, crushed and sieved to obtain a self-degradable gel plugging material suitable for reservoirs.

[0039] Example 2

[0040] The difference between this embodiment and Embodiment 1 lies in the amount of raw materials used. By mass, the raw materials include the following: 180 parts water, 70 parts monomer, 0.7 parts crosslinking agent, 0.1 parts initiator, 0.5 parts natural polymer material, 2 parts acidity neutralizer, and 0.5 parts nano-doped material.

[0041] In this embodiment, the monomer is acrylamide; the crosslinking agent is polyethylene glycol diacrylate; the initiator is cerium ammonium nitrate; the natural polymer material is guar gum; the acidity neutralizer is a 15% sodium hydroxide aqueous solution; and the nano-doped material is nano-silica with a particle size of 45-55 nm.

[0042] This embodiment also discloses a method for preparing the above-mentioned reservoir self-degradable gel plugging material, including the following steps:

[0043] (1) Place 70 parts of acrylamide monomer and 0.7 parts of crosslinking agent polyethylene glycol diacrylate in 180 parts of water, stir with a mechanical stirrer to form a uniform solution, and add an acidity neutralizer to obtain the reaction monomer solution;

[0044] (2) Add 0.5 parts of natural polymer material guar gum to the reaction monomer solution and stir for 30 minutes using a mechanical stirrer to form a uniform solution without particle aggregation. Then add 0.5 parts of nano-doped material nano silica and stir thoroughly. Place it in an ultrasonic device for dispersion treatment for 30 minutes to obtain the reaction base liquid.

[0045] (3) After sealing the reaction base liquid, nitrogen gas is introduced for 30 minutes. 0.1 parts of cerium ammonium nitrate initiator are added to the reaction base liquid and stirred evenly. The mixture is stirred until a uniform solution is obtained under ice-water bath conditions and then allowed to stand for 6 hours to obtain the initial product.

[0046] (4) The surface of the initial product is cleaned with acetone, dried, crushed and sieved to obtain a self-degradable gel plugging material suitable for reservoirs.

[0047] Example 3

[0048] This embodiment discloses a reservoir self-degradable gel plugging material, which, by mass, includes the following raw materials: 240 parts water, 110 parts monomer, 1.2 parts crosslinking agent, 1 part initiator, 2 parts natural polymer material, 4 parts acidity neutralizer, and 2 parts nano-doped material.

[0049] In this embodiment, the monomer is acrylamide; the crosslinking agent is polyethylene glycol diacrylate; the initiator is cerium ammonium nitrate; the natural polymer material is guar gum; the acidity neutralizer is a 15% sodium hydroxide aqueous solution; and the nano-doped material is nano-silica with a particle size of 45-55 nm.

[0050] This embodiment also discloses a method for preparing the above-mentioned reservoir self-degradable gel plugging material, including the following steps:

[0051] (1) Place 110 parts of acrylamide monomer and 1.2 parts of crosslinking agent polyethylene glycol diacrylate in 240 parts of water, stir with a mechanical stirrer to form a uniform solution, and add 4 parts of acidity neutralizer to obtain the reaction monomer solution.

[0052] (2) Add 4 parts of natural polymer material guar gum to the reaction monomer solution, stir for 30 minutes using a mechanical stirrer to form a uniform solution without particle aggregation, then add 2 parts of nano-doped material nano silica and stir thoroughly, then place it in an ultrasonic device for dispersion treatment for 30 minutes to obtain the reaction base liquid.

[0053] (3) After sealing the reaction base liquid, nitrogen gas is introduced for 30 minutes. One part of the initiator cerium ammonium nitrate is added to the reaction base liquid and stirred evenly. The mixture is stirred until a uniform solution is obtained under ice-water bath conditions and then allowed to stand for 6 hours to obtain the initial product.

[0054] (4) The surface of the initial product is cleaned with acetone, dried, crushed and sieved to obtain a self-degradable gel plugging material suitable for reservoirs.

[0055] Performance testing experiments:

[0056] The self-degradable gel plugging material of this invention was added to water-based and organic drilling fluids to evaluate its effects on rheology and filtration, and to test its plugging performance.

[0057] Oil-based drilling fluid formulation: 4% bentonite slurry + 0.2% XC + 0.3% CMC + 1% (6~10 mesh) product + 1% (10~20 mesh) calcium carbonate + 4% (20~40 mesh) calcium carbonate + 2% (40~80 mesh) calcium carbonate + 2% ultrafine calcium.

[0058] Prepare 400 mL of drilling fluid. Spread 1% (6-10 mesh) product + 1% (10-20 mesh) calcium carbonate evenly in the fracture and then fill it into the fracture tube. Next, pour the prepared drilling fluid into the drilling fluid storage tank. Place the piston on the drilling fluid storage tank, pressurize it with water, and monitor the pressure and time in real time. After the plugging is completed, remove the fracture and observe the sealing layer. Place the fracture in an 80℃ water bath for 1 hour and then put it back into the plugging instrument, repeating the above process. After the experiment, disassemble the device and clean it. The plugging data are shown in Table 1.

[0059] Table 1. Experimental results of crack sealing before and after degradation.

[0060]

[0061] As shown in Table 1, the flow rate without the self-degradable gel plugging material was 6.23 mL / s, while the flow rate with the self-degradable plugging material was 1.45 mL / s, a reduction of 77%. This demonstrates that the product can effectively seal fractures. After the product was used for fracture sealing and then the degradation experiment was conducted, the flow rate returned to the level of the product with the plugging material, indicating that the product has self-degradation capabilities, significantly reducing drilling fluid loss and meeting the field reservoir plugging requirements.

[0062] The self-degradable gel plugging material of Example 1 of this invention was placed in an alkaline solution at 80°C under simulated formation conditions, and its mass change rate was tested to calculate the degradation rate. The self-degradation performance was as follows: Figure 1 As shown.

[0063] pass Figure 1 It is known that the material achieves a degradation rate of 90% within 72 hours and 99% within 102 hours. It can also unblock under formation pressure differentials, demonstrating excellent self-degradation performance. This effectively reduces subsequent operations, lowers production costs, and meets practical operational needs.

[0064] like Figure 2 The image shows the condition of the sealing layer after the crack was removed following the completion of the leak sealing process in Example 1. Figure 3 This is the cleaning process after the device is disassembled following the completion of the experiment.

[0065] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A self-degrading gel plug material suitable for use in a reservoir, characterized in that, By weight, it includes the following raw materials: 180-240 parts water, 70-110 parts monomer, 0.7-1.2 parts crosslinking agent, 0.1-1 part initiator, 0.5-4 parts natural polymer material, 0-4 parts acidity neutralizer, and 0-2 parts nano-doped material. The crosslinking agent is polyethylene glycol diacrylate, and the natural polymer material is guar gum. The nano-doped material is one or a mixture of two or more of the following: nano-calcium carbonate, 45-55nm nano-silica, 25-35nm nano-silica, and 10-20nm nano-silica. The monomer is one or a combination of two or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid.

2. The self-degrading gel plug material for use in a reservoir according to claim 1, wherein: Water 190-220 parts, monomer 80-90 parts, crosslinking agent 0.8-1.2 parts, initiator 0.1-0.5 parts, natural polymer material 1-2 parts, acidity neutralizer 0-2 parts, nano-doped material 0.5-2 parts.

3. The self-degrading gel plug material for use in a reservoir according to claim 1, wherein: The acidity neutralizer is sodium hydroxide.

4. The self-degrading gel plug material for use in a reservoir according to claim 1, wherein: The initiator is ammonium persulfate or cerium ammonium nitrate.

5. The reservoir self-degradable gel plugging material according to claim 1, characterized in that: The nano-doped material is 45-55nm nano-silicon dioxide.

6. The method for preparing a reservoir self-degradable gel plugging material as described in any one of claims 1-5, characterized in that, The steps include: (1) placing the monomer and crosslinking agent in water, stirring to form a uniform solution, and adding an acidity neutralizer to obtain a reaction monomer solution; (2) Add natural polymer materials to the reaction monomer solution and stir to form a uniform solution. After adding nano-doped materials and stirring thoroughly, perform acoustic dispersion treatment to obtain the reaction base liquid. (3) After sealing the reaction base liquid, nitrogen gas is introduced, the initiator is added and stirred evenly, and the reaction is carried out for 5-8 hours under ice-water bath conditions to obtain the initial product; (4) The initial product is cleaned, dried, crushed and sieved to obtain a self-degradable gel plugging material suitable for reservoirs.

7. The preparation method of the reservoir self-degradable gel plugging material according to claim 6, characterized in that: In step (1), an acid neutralizer with a mass concentration of 15% is used to adjust the pH of the reactant monomer solution to 7.

Images