Environment-friendly high-temperature and high-salt resistant pre-crosslinked particle water shutoff agent, preparation method and application

Abstract

The present application relates to the oil field chemical profile control and water shutoff technical field, and particularly relates to an environment-friendly high-temperature and high-salt pre-crosslinking particle water shutoff agent, a preparation method and application.The raw materials of the pre-crosslinking particle water shutoff agent include polymer monomer materials, an initiator, an organic solvent, a filler and water, and further include methylene bisacrylamide, a silane coupling agent, water glass, an organic metal crosslinking agent and sodium citrate.The water shutoff agent has a high plugging rate and a good plugging effect, is particularly suitable for plugging channels of Darcy levels, and fully meets the requirements of overseas markets in terms of environmental protection and high plugging performance;the water shutoff agent has the characteristics of environmental protection and safety, adjustable particle size, high strength, high temperature resistance, high salt SSS resistance, a simple preparation process, no need for heating, low cost and easy popularization.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical profile control and water shut-off technology, specifically to an environmentally friendly high-temperature and high-salt pre-crosslinked particulate water shut-off agent, its preparation method, and its application. Background Technology

[0002] Water production from oil wells is a common phenomenon encountered in the mid-to-late stages of oilfield development, especially in water-driven oilfields. The heterogeneity of oil reservoirs, as well as inappropriate development plans and extraction measures, can lead to uneven water propagation, causing premature water flooding in individual wells and reservoirs, and a rapid increase in the overall water cut of the oilfield, thereby reducing production and recovery rates. Therefore, during oilfield development, it is crucial to closely monitor water production trends in oil wells, utilize various water-finding methods to identify water-bearing zones, and implement appropriate water-blocking measures. Water blocking, as a primary technical measure for stabilizing oil production and controlling water in oilfields, plays a vital role in oilfield development.

[0003] Currently, the overall water cut of overseas oilfields increases to varying degrees as development progresses, especially in many single wells where the water cut exceeds 80%. For a long-term developed oilfield, due to the heterogeneity of the reservoir in both horizontal and vertical directions, differences in oil and water viscosity, and the imbalance of oil and water well groups, edge water, bottom water, and injected water will inevitably surge towards production wells along the high-permeability zone, causing a series of subsequent problems. Water production in oil wells has a significant impact on economic efficiency, consuming formation energy and reducing the ultimate recovery rate of the oil layer. Some high-yield wells may become industrially worthless. For water-producing wells, if measures are not taken in time, water-trapped dead oil zones may appear in the formation, causing injected water to bypass them, thereby reducing the recovery rate and resulting in significant waste.

[0004] Meanwhile, increased water production inevitably leads to higher dehydration costs at the surface. Therefore, increasing the discharge rate to carry oil away with water is not cost-effective. Water production from oil wells also causes many other problems: reduced pump efficiency; severe corrosion and scaling of pipelines and equipment; damage to non-cemented oil reservoir structures, leading to sand production; increased fluid density and bottomhole pressure, causing flowing wells to stop flowing and requiring mechanical pumping; increased load on dehydration stations; and increased environmental pollution if the extracted water is not reinjected.

[0005] In oilfields, water injection well profile control is often the primary method, with water shut-off in oil wells serving as a supplementary measure. To ensure uniform water injection and reduce water production from oil wells, high-permeability layers can be blocked from the injection well to adjust the water absorption profile of the injected formation—a process known as injection well profile control. Reservoir heterogeneity causes injected water to surge into oil wells along high-permeability channels. To reduce water channeling, these high-permeability layers must be blocked. Blocking high-permeability layers from the oil well reduces the influx of injected water along these layers, thereby reducing water production—this method is called water shut-off. Since water shut-off controls water production from the oil well, the substance injected into the formation to reduce water production is called a water shut-off agent. This agent can block large, high-permeability channels in the formation, allowing oil displacement agents to more effectively displace oil. The advantages of this method are ease of construction, low cost, and rapid results.

[0006] Overseas high-water-cut oilfields are generally high-porosity, high-permeability reservoirs with high formation water salinity. After prolonged periods of high-volume production, the reservoirs transform from an initial single-flow type to a multi-stage flow type. Conventional plugging agents often suffer from problems such as inability to reach deep formations, inability to migrate secondary, and insufficient strength leading to backflow, resulting in poor water shut-off effectiveness and short lifespan. Therefore, it is necessary to develop chemical plugging agents with good injectability and retention properties suitable for the water shut-off needs of overseas oilfields.

[0007] The invention disclosed in application number CN200410096430.4 is a method for synthesizing a bulk-expanding granular profile control agent using oilfield sludge. The synthesized profile control agent is applied to deep profile adjustment in large-pore oil reservoirs. The profile control agent is produced by adding oilfield sludge, an oxidant, and a reducing agent to a ternary copolymer system of acrylic acid, acrylamide, and a crosslinking agent, followed by adiabatic free radical polymerization to generate a gel block. The block is then granulated, dried, and pulverized to the desired particle size. The weight ratio of the reactants is: acrylamide: oilfield sludge: crosslinking agent: acrylic acid solution (10% wt): oxidant: reducing agent = 5.0–12.5: 10.0–27.5: 0.12–0.60: 30–80: 0.1–0.3: 0.1–0.5. The method of preparing a bulk-expanding granular profile control agent using oilfield sludge achieves the harmless and resource-based treatment of oilfield sludge, and simultaneously produces oilfield sludge granules.

[0008] The invention, with application number CN111995995B, discloses an improver for sealing heterogeneous fractures using bulk-swellable particles and its preparation method. The improver comprises, by mass percentage: 79–94.9% coupling agent-modified matrix particles, 5–20% coating resin, and 0.1–1% lubricant. The preparation method is as follows: Step 1: Prepare coupling agent-modified matrix particles; Step 2: Grind the coating resin into powder and preheat it separately with the coupling agent-modified matrix particles obtained in Step 1; Step 3: Mix the lubricant, the coating resin from Step 2, and the coupling agent-modified matrix particles evenly, and heat at 120–180°C; during heating, the mixture is removed every t time interval, stirred evenly, and heating continues for 0.5–1 hour to obtain the desired improver. This invention's improver is convenient to use and has a clever mechanism of action. It does not require any other supporting agents; it only utilizes the high formation temperature and the flushing effect of produced water to improve the sealing effect of heterogeneous fractures using bulk-swellable particles.

[0009] The invention, patent publication number CN1743405, entitled "Hydrophobic Water-Swellable Flooding Agent," can improve water flooding effects. Its characteristic is that the raw material composition by mass ratio is: ① Deionized water 40-70%; ② Acrylamide 20-50%; ③ Calcium-based bentonite 4-15%; ④ Alkyl acrylate 5-10%; ⑤ Sodium persulfate 0.1-0.5%; ⑥ N,N-Methylenebisacrylamide 0.1-0.5%. The preparation method is as follows: ① Raw material mixing: mixing time not less than 30 minutes, mixing temperature below 35℃; ② Polymerization: in a reactor, heating to 70-80℃, vacuuming for 20 minutes, and purging with nitrogen for 1 hour; after polymerization, the material is kept at 70-80℃ for 12-18 hours; ③ Extruding the water-swellable material from the reactor and pulverizing it; ④ Sieving and packaging. Effects: Reduces the hydrophilicity of water-swellable materials; prevents clogging of valves in profile control pumps; reduces the likelihood of water-swellable material settling problems that occurred before 2005.

[0010] There are various water-blocking agents in the existing technology. However, the preparation process of these water-blocking agents requires high heating temperatures (70-80℃, 120-180℃), which makes the preparation difficult and costly. They also require special materials (oilfield sludge), making it difficult to meet the stringent environmental protection requirements overseas. The mixing and cross-linking of organic and inorganic materials, without the addition of coupling agents, easily leads to stratification and separation of organic and inorganic materials during the production process, resulting in unstable performance of the pre-cross-linked particles and easy breakage and pump blockage during the pumping process. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide an environmentally friendly, high-temperature and high-salt resistant pre-crosslinked particulate water-blocking agent, its preparation method and application, so as to solve the problems of poor performance, high cost and difficulty in application to Darcy level channels of the existing water-blocking agents.

[0012] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0013] Based on the above technical solution, the present invention can be further improved as follows.

[0014] This invention provides an environmentally friendly, high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent. The raw materials of the pre-crosslinked granular water-blocking agent include polymer monomer materials, initiators, organic solvents, fillers and water, as well as methylene bisacrylamide, silane coupling agents, water glass, organometallic crosslinking agents and sodium citrate.

[0015] Furthermore, it also includes a reducing agent, which is sodium thiosulfate.

[0016] Furthermore, the organometallic crosslinking agent is zirconium lactate or aluminum citrate.

[0017] Furthermore, the composition and mass percentage of the raw materials are as follows: 17%-21% polymer monomer material, 0.02%-0.1% methylenebisacrylamide, 0.02%-0.1% silane coupling agent, 0.2% initiator, 0.1% sodium thiosulfate, 1%-10% water glass, 1%-5% organic solvent, 0.8%-1% zirconium lactate, 0.1%-0.2% sodium citrate, and the balance being water.

[0018] Furthermore, the polymer monomer material includes acrylic acid and acrylamide, wherein the mass of acrylic acid accounts for 16% of the total mass of the raw materials, and the mass of acrylamide accounts for 1%-5% of the total mass of the raw materials.

[0019] Furthermore, the initiator is ammonium persulfate.

[0020] Furthermore, the organic solvent includes methanol or ethanol, and the filler includes one or more of kaolin, fly ash, and cement.

[0021] This invention also provides a method for preparing the above-mentioned environmentally friendly high-temperature and high-salt pre-crosslinked particulate water-blocking agent, comprising the following steps:

[0022] S1. Mix and stir the water, water glass, the polymer monomer material, methylenebisacrylamide and the initiator;

[0023] S2. Add the filler and stir to obtain the first material;

[0024] S3. The organic solvent and the silane coupling agent are mixed to obtain a second material. The second material and the organometallic crosslinking agent are then added to the first material and stirred to obtain a third material.

[0025] S4. Deoxygenate the third material;

[0026] S5. After standing and completing the polymerization and cross-linking reaction, dry and pulverize to obtain the pre-cross-linked particulate water-blocking agent.

[0027] Furthermore, the temperature range in step S1 is 5℃–35℃.

[0028] Furthermore, in step S4, the deoxygenation method is to introduce nitrogen gas into the third material for a period of 0.5–2 hours.

[0029] This invention also provides the application of the above-mentioned environmentally friendly high-temperature and high-salt pre-crosslinked particulate water shut-off agent in oilfield water shut-off.

[0030] Furthermore, the environmentally friendly high-temperature and high-salt pre-crosslinked particulate water-blocking agent is applied to the water-blocking process of Darcy-level channels.

[0031] This invention also provides a method for plugging water in oil fields, which uses the environmentally friendly, high-temperature resistant, high-salt pre-crosslinked particulate water plugging agent described above for plugging.

[0032] The beneficial effects of this invention are as follows:

[0033] (1) The environmentally friendly high-temperature and high-salt pre-crosslinked particle water plugging agent of the present invention has the effect of modification and crosslinking of methylene bisacrylamide, which is a reinforcing component and can significantly improve the compressive strength of the pre-crosslinked particles, so as to effectively block large channels at Darcy level and above.

[0034] (2) The environmentally friendly high-temperature and high-salt resistant pre-crosslinked particle water plugging agent of the present invention, the water glass, silane coupling agent, sodium citrate and other components can form a composite gel, so that the obtained pre-crosslinked particles are soft, highly elastic, rubber-like irregular particles, and have good high-temperature and high-salt resistance.

[0035] (3) The environmentally friendly high-temperature and high-salt pre-crosslinked granular water plugging agent of the present invention has a plugging rate of over 98.68% and has a good plugging effect;

[0036] (4) The environmentally friendly high-temperature and high-salt pre-crosslinked particulate water plugging agent of the present invention is particularly suitable for sealing Darcy-level channels, fully meeting the requirements of overseas markets for environmental protection and high sealing performance;

[0037] (5) The environmentally friendly high-temperature and high-salt pre-crosslinked granular water-blocking agent of the present invention has the characteristics of being environmentally friendly and safe, having adjustable particle size, high strength, high temperature resistance, and salt resistance SSS, and can pass the EU environmental protection SVHC standard.

[0038] (6) The preparation method of the environmentally friendly high temperature and high salt pre-crosslinked particulate water plugging agent of the present invention is simple, does not require heating, and has the advantages of low cost and easy promotion. Attached Figure Description

[0039] Figure 1 The graph shows the change in particle expansion volume over time in Example 2 of the present invention, which is an environmentally friendly, high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent.

[0040] Figure 2 The aging stability curve of the environmentally friendly, high-temperature and high-salt pre-crosslinked particulate water-blocking agent of the present invention is shown in Example 2.

[0041] Figure 3 In Example 3, the environmentally friendly, high-temperature, high-salt resistant pre-crosslinked granular water-blocking agent of the present invention, at 90°C, has a permeability of 6000 × 10⁻⁶. -3 μm 2 Pressure change curve of pre-crosslinked gel particle system swollen for 48 h in homogeneous rock core;

[0042] Figure 4 The SGS certification report diagram for Example 3 of the present invention is shown. This is the environmentally friendly, high-temperature and high-salt resistant pre-crosslinked particulate water-blocking agent.

[0043] Figure 5 The first page of the performance test report from the China University of Petroleum for Example 3 of the present invention is an environmentally friendly, high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent.

[0044] Figure 6 This is the content page of the performance test report from the China University of Petroleum for Example 3 of the present invention, which describes the environmentally friendly, high-temperature and high-salt resistant pre-crosslinked particulate water-blocking agent. Detailed Implementation

[0045] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0046] The environmentally friendly, high-temperature and high-salt resistant pre-crosslinked particulate water-blocking agent of the present invention comprises polymer monomer materials, initiators, organic solvents, fillers and water, and also includes methylene bisacrylamide, silane coupling agents, water glass, organometallic crosslinking agents and sodium citrate.

[0047] The present invention relates to an environmentally friendly, high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent, which contains methylene bisacrylamide. Methylene bisacrylamide has a modifying and crosslinking effect, and is a reinforcing component that can significantly improve the compressive strength of the pre-crosslinked particles, enabling effective sealing of large pores at the Darcy level and above. Simultaneously, the raw material also contains water glass, silane coupling agent, and sodium citrate. These components can form a composite gel, resulting in pre-crosslinked particles that are soft, highly elastic, and rubber-like irregular particles with excellent high-temperature and high-salt resistance. The high-temperature resistance can reach above 120°C, and the calcium and magnesium ion concentration in high-salt environments can reach 100,000 ppm.

[0048] This invention relates to an environmentally friendly, high-temperature, high-salt pre-crosslinked granular water-blocking agent. The pre-crosslinked granules are a dried solid polymer gel, also known as "dry gel." It is a granular gel produced through a complex chemical reaction involving a crosslinking agent, a proppant, polymer monomers, and an initiator, followed by drying, granulation, and sieving. Due to the presence of water-absorbing groups such as carboxyl and amide groups, it is a high-molecular-weight water-absorbing resin with a pre-crosslinked polymer network structure. This allows it to absorb water and swell. The swollen granules possess certain elasticity, strength, and water retention capabilities. It is easy to apply, causes minimal contamination to non-target formations, and can remain in formation pores for extended periods, achieving the purposes of profile control and water blocking.

[0049] This invention relates to an environmentally friendly, high-temperature, high-salt resistant pre-crosslinked particulate water-blocking agent. The pre-crosslinked particles are ground-based crosslinked prepolymers that exist as dispersed spherical microparticles in water. Belonging to a typical strong gel system, they exhibit a certain degree of volume expansion, with an expansion ratio of 5-10 times. They also possess "amoeba" characteristics, allowing them to penetrate deep into oil reservoirs under certain pressure conditions. Furthermore, they exhibit good stability at high salinity levels and demonstrate superior thermal stability compared to other gels.

[0050] Preferably, the environmentally friendly high-temperature and high-salt pre-crosslinked particulate water-blocking agent of the present invention also includes a reducing agent in its raw materials, namely sodium thiosulfate; the addition of sodium thiosulfate can eliminate the need for heating during the preparation process, thereby optimizing the preparation method.

[0051] Preferably, in the environmentally friendly high-temperature and high-salt pre-crosslinked particulate water-blocking agent of the present invention, the organometallic crosslinking agent is zirconium lactate.

[0052] Preferably, the polymer monomer materials include acrylic acid and acrylamide, wherein the mass of acrylic acid accounts for 16% of the total mass of the raw materials, and the mass of acrylamide accounts for 1%-5% of the total mass of the raw materials.

[0053] Preferably, the initiator is ammonium persulfate.

[0054] Preferably, the organic solvent includes methanol or ethanol, and the filler includes one or more of kaolin, fly ash, and cement.

[0055] A further preferred option is kaolin.

[0056] Preferably, the components of the raw materials and the mass percentage of each component are as follows: 17%-21% polymer monomer material, 0.02%-0.1% methylenebisacrylamide, 0.02%-0.1% silane coupling agent, 0.2% ammonium persulfate initiator, 1%-10% water glass, 1%-5% organic solvent, 0.8%-1% zirconium lactate, 0.1%-0.2% sodium citrate, and the balance being water.

[0057] The preparation method of the environmentally friendly high-temperature and high-salt pre-crosslinked particulate water-blocking agent of the present invention includes the following steps:

[0058] S1. Mix and stir water, water glass, polymer monomer material, methylenebisacrylamide and initiator.

[0059] Preferably, the mixing time in this step should not be less than 10 minutes to ensure uniform mixing. During mixing, the temperature should be below 35°C to prevent sudden polymerization of the components.

[0060] S2. Add filler and stir to obtain the first material; the mixing and stirring time should not be less than 10 minutes to ensure uniform mixing.

[0061] S3. Mix the organic solvent with the silane coupling agent to obtain the second material, then add the second material and the organometallic crosslinking agent together to the first material and stir to obtain the third material.

[0062] S4. Deoxygenate the third material.

[0063] Preferably, nitrogen is introduced to deoxygenate the third material for 0.5–2 hours.

[0064] S5. After standing and completing the polymerization and cross-linking reaction, dry and pulverize to obtain pre-cross-linked particulate water-blocking agent.

[0065] Preferably, the drying temperature is 150℃ and the drying time is 1 hour.

[0066] Preferably, the specific mesh size of the pulverized material is 10-150 mesh.

[0067] The specific chemical reaction mechanism in the preparation method of this invention is as follows:

[0068] (1) Free radical polymerization of polyacrylamide: The polymerization of acrylamide and sodium acrylate follows the general principle of free radical polymerization. The elementary reaction processes are chain initiation, chain propagation, chain termination and chain transfer in sequence. The specific reaction process is as follows:

[0069] Chain initiation: After the initiation reaction, free radicals are formed, including two-step reactions of reaction (1) and reaction (2). In reaction (1), initiator I homolytically cleaves to form a pair of primary free radicals. In reaction (2), the primary free radicals add to the monomer to generate monomer free radicals.

[0070] R·I——>2R· (1)

[0071]

[0072] Chain growth: The monomer free radicals generated by chain initiation continuously combine with monomer molecules to generate chain free radicals. This repeated process is called chain growth reaction, and the reaction process is shown in reaction formula (3).

[0073]

[0074] Chain termination: The reaction in which a chain radical loses its activity and forms a stable polymer molecule is called a chain termination reaction.

[0075] Chain transfer: A growing chain radical takes an atom from another molecule and terminates to become a stable macromolecule.

[0076] (2) Crosslinking reaction mechanism

[0077] Gel formation requires multiple steps, and the gelation process mainly involves two steps:

[0078] (a)Zr 4+ Zr dissociates from the complex. 4+ After further hydrolysis and hydroxy bridging, a zirconium polynuclear hydroxy-bridged complex ion is formed, the molecular structure of which is shown in formula (1):

[0079]

[0080] (b) The polynuclear hydroxy bridged ions of zirconium crosslink with HPAM to form HPAM / organic zirconium gel, the chemical structure of which is shown in formula (2).

[0081]

[0082] (c) The structure of the zirconium lactate crosslinking agent is Zr2(C3H6O3)6. The crosslinking effect is achieved by zirconium ion dimers linked by hydroxyl bridges, with lactic acid molecules acting as ligands to form stable complex structures with zirconium ions. When the carboxyl groups exchange with the lactic acid ligands, each zirconium ion dimer coordinates with two carboxyl groups to form a crosslinked structure. When the crosslinking agent is in excess, some zirconium ion dimers coordinate with only one carboxyl group, forming a structure similar to a capped structure, which cannot form effective crosslinking points, thus reducing the crosslinking point density. When the crosslinking agent is insufficient, the number of effective crosslinking points is controlled by the zirconium ion content, also reducing the effective crosslinking density.

[0083] (3) Enhanced treatment for high permeability, high liquid volume, high temperature, and high mineralization:

[0084] (a) Methylenebisacrylamide, also known as MBA, has high reactivity and crosslinking ability. It is an organic synthetic compound containing two acrylamide groups in its structure, which can undergo a crosslinking reaction with polyacrylamide. The crosslinked polymer has good physical properties and chemical stability, and significantly improves its temperature and salt resistance. The crosslinking reaction process of methylenebisacrylamide and polyacrylamide is shown in reaction formula (4):

[0085] MBA + PAM → PAM-MBA-PAM (4)

[0086] (b) Water glass has good water solubility and does not form a porous structure during the sol-gel process, which can improve the strength of the gel. Water glass is used as a silicon precursor to form a Si-O-Si network structure. At the same time, acrylate is polymerized under the action of crosslinking agent, accelerator and initiator. The final composite gel water-blocking agent has a high advantage in strength and is very suitable for high permeability and high liquid volume environments.

[0087] The environmentally friendly, high-temperature and high-salt resistant pre-crosslinked particulate water plugging agent of the present invention can be applied to water plugging in oil fields.

[0088] Preferably, the specific application method is to use environmentally friendly high-temperature and high-salt pre-crosslinked granular water-blocking agent in the water-blocking process of Darcy-level channels.

[0089] This invention provides a method for plugging water in oil fields, which uses an environmentally friendly, high-temperature resistant, high-salt pre-crosslinked particulate water plugging agent as described above for plugging.

[0090] The present invention will be specifically described below through specific embodiments.

[0091] Example 1: Preparation of Environmentally Friendly High-Temperature and High-Salt Pre-Crosslinked Particulate Water-Ploughing Agent

[0092] The method of the present invention is used to prepare an environmentally friendly high-temperature and high-salt pre-crosslinked particulate water-blocking agent. The specific components and mass percentages of the raw materials in this embodiment are shown in Table 1.

[0093] Table 1

[0094] Element weight% illustrate acrylic acid 16 Polymer Synthesis Monomer Materials Acrylamide 3 Polymer Synthesis Monomer Materials Methylenebisacrylamide 0.08 Crosslinking agent, modifier Silane coupling agent 0.08 Modifier Ammonium persulfate 0.2 Initiator Water glass 5 Composite Gel Synthesis Materials methanol 4 organic solvents Zirconium lactate 0.8 Organometallic crosslinking agents Kaolin 10 filler Sodium citrate 0.2 High mineralization of calcium and magnesium ions water Appropriate amount

[0095] The preparation process in this embodiment is as follows:

[0096] S1. Mix and stir water, water glass, acrylic acid, acrylamide, methylenebisacrylamide and ammonium persulfate for 20 minutes at 30°C.

[0097] S2. Add kaolin and stir to obtain the first material; the mixing and stirring time is 20 minutes.

[0098] S3. Mix methanol with silane coupling agent to obtain the second material, then add the second material and zirconium lactate together to the first material and stir to obtain the third material.

[0099] S4. Nitrogen gas is introduced to deoxygenate the third material for 1 hour.

[0100] S5. After standing and completing the polymerization and cross-linking reaction, dry and pulverize to obtain pre-cross-linked particulate water-blocking agent.

[0101] Example 2: Evaluation of Expansion Performance

[0102] The expansion performance of pre-crosslinked particles under reservoir conditions is a key factor affecting their water-blocking effect. Generally, the initial particle size of the pre-crosslinked particles is required to be smaller than the size of the seepage channels so that the particles can be injected deep into the formation. Secondly, they should have a certain water absorption and expansion capacity to seal the water outlet channels through volume expansion, thus achieving water blocking. Furthermore, they should possess a certain degree of temperature and salt resistance to meet the requirements of reservoir conditions. Therefore, this embodiment evaluates the expansion performance of the pre-crosslinked particle water-blocking agent prepared in Example 1.

[0103] The specific evaluation process in this embodiment is as follows:

[0104] (1) Preparation of simulated water: Prepare high-mineralization simulated water according to the ionic composition in Table 2.

[0105] Table 2

[0106]

[0107] (2) Evaluation method for particle expansion performance:

[0108] Weigh approximately 0.5g of the experimental sample (mass m0) into an ampoule and weigh the total weight of the sample and the ampoule (m1). Then add an appropriate amount of simulated water, seal the ampoule, and place it in an oven for expansion. After swelling for a period of time, filter out the free water using a sieve, and weigh the filtered sample and the total weight of the ampoule to obtain the mass m. n After weighing, add simulated water again and continue soaking. Repeat the previous experimental procedure until the designed experimental duration is reached. The formula for calculating the water absorption and swelling ratio of the sample is shown in formula (1):

[0109]

[0110] In the formula, m n This indicates the total mass of the sample and ampoule after soaking for a certain period of time.

[0111] (3) Effect of temperature on expansion properties: Figure 1The variation of particle expansion volume over time is shown. At 80℃ (simulated low temperature) and 120℃ (simulated high temperature), the trends are the same. Higher temperatures result in increased expansion volume.

[0112] Experimental results show that the prepared particles can expand by more than 5 times at different temperatures. With increasing temperature, the thermal motion of the polymer chain segments intensifies, accelerating water absorption. This results in a faster expansion rate and an increased maximum expansion ratio. At higher temperatures, the cross-linking reaction between the polymer and divalent ions accelerates, increasing the degree of cross-linking between the polymer chain segments of the slow-expanding particles. This leads to partial dehydration, causing a decrease in the expansion ratio. Once the cross-linking reaction reaches a certain level, the degree of cross-linking stabilizes, and therefore the expansion ratio also stabilizes.

[0113] (4) Aging stability: Sample solutions of particles C1 (total mineralization 250,000 ppm, calcium and magnesium ions 50,000 ppm, calcium chloride aqueous type) and C2 (total mineralization 100,000 ppm, calcium and magnesium ions 10,000 ppm, calcium chloride aqueous type) were prepared using simulated water and subjected to an aging test for 150 days at 120℃. The results are as follows: Figure 2 As shown in the figure. Experimental results show that the crosslinking agent can effectively improve the aging stability of the particulate plugging agent, and can maintain an expansion ratio of more than 5 times within 150 days.

[0114] Example 3: Immunization Evaluation

[0115] This embodiment evaluates the sealing performance of the pre-crosslinked particulate water-blocking agent prepared in Example 1. The specific evaluation method is as follows:

[0116] Using the pre-crosslinked particulate water-blocking agent of Example 1, pre-prepared pre-crosslinked gel particle solutions with mass percentages of 1% and 2% were prepared.

[0117] The specific geological conditions tested in this embodiment were a 30cm homogeneous rock core with a permeability of Kw = 6000 × 10⁻⁶. -3 μm 2 During the test, the core was emptied of saturated formation water, specifically simulated water as in Example 2, and the water permeability Kw1 before plugging was recorded.

[0118] Inject 1PV of plugging agent (prepared with simulated water I) sequentially from low to high concentration, and record the injection pressure at each concentration.

[0119] After injection, allow it to solidify at 90℃ for 48 hours; test the permeability Kw2 of the plugged water (simulated water); increase the injection pressure and determine the breakthrough pressure test.

[0120] Experimental Results: The injection capacity and sealing effect of pre-crosslinked gel particle solutions with different mass percentages are shown in Table 3. The relationship curve between injection pressure and PV number is shown in Figure 3. Figure 3 As shown.

[0121] Table 3

[0122]

[0123] Figure 3 At 90℃, with a permeability of 6000×10 -3 μm 2 The pressure change curves of the pre-crosslinked gel particle system swollen for 48 hours in a homogeneous core are shown. When injecting a 1% mass concentration of the pre-crosslinked gel particle system, the pressure change is small, indicating good infusibility at this concentration. When injecting a 2% mass concentration of the pre-crosslinked gel particle system, the pressure increases compared to the 1% concentration, and the pressure change is also larger, indicating that the infusibility at this concentration is worse than that at the 1% concentration. After solidification at 90℃ for 48 hours, water was injected again to test the breakthrough pressure and water permeability. Initially, the pressure rose rapidly, quickly reaching the breakthrough pressure of 1.2 MPa, after which it slowly decreased to 400 kPa and remained at around 380 kPa. Using Darcy's formula, the water permeability after sealing was calculated to be 98.68%, indicating a good sealing effect of the system.

[0124] like Figure 5 and Figure 6 As shown, according to the evaluation by the Institute of Unconventional Oil and Gas Science and Technology of the China University of Petroleum, Kw = 6000 × 10 -3 μm 2 Core samples showed a sealing rate of 99.81%. The product passed stringent EU SVHC (Substances of Very High Concern) testing and obtained SGS certification (e.g., [missing information]). Figure 4 (As shown). This environmentally friendly, high-performance plugging agent provides strong support for the overseas water control and oil stabilization operations of China National Petroleum Corporation Logging Company.

[0125] As can be seen from the above embodiments, the pre-crosslinked particles of the present invention have the characteristics of being environmentally friendly and safe, having adjustable particle size, high strength, and high temperature resistance. This plugging agent can effectively solve the problems of multi-stage large-channel seepage, high porosity, high permeability, high liquid volume, high temperature, and high salinity in overseas oil and gas fields, and achieve the goal of the plugging agent entering, remaining, and blocking effectively. It is a powerful tool for water control and oil stabilization in overseas oil fields.

[0126] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An environmentally friendly, high-temperature resistant, high-salt pre-crosslinked granular water-blocking agent, characterized in that, The raw materials of the pre-crosslinked particulate water-blocking agent include polymer monomer materials, initiators, organic solvents, fillers and water, as well as methylene bisacrylamide, silane coupling agents, water glass, organometallic crosslinking agents and sodium citrate.

2. The environmentally friendly high-temperature and high-salt pre-crosslinked granular water-blocking agent according to claim 1, characterized in that, It also includes a reducing agent, which is sodium thiosulfate.

3. The environmentally friendly high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent according to claim 2, characterized in that, The organometallic crosslinking agent is zirconium lactate or aluminum citrate.

4. The environmentally friendly high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent according to claim 3, characterized in that, The components and mass percentages of the raw materials are as follows: 17%-21% polymer monomer material, 0.02%-0.1% methylenebisacrylamide, 0.02%-0.1% silane coupling agent, 0.2% initiator, 0.1% sodium thiosulfate, 1%-10% water glass, 1%-5% organic solvent, 0.8%-1% zirconium lactate, 0.1%-0.2% sodium citrate, and the balance being water.

5. The environmentally friendly high-temperature and high-salt pre-crosslinked granular water-blocking agent according to claim 4, characterized in that, The polymer monomer material includes acrylic acid and acrylamide, wherein the mass of acrylic acid accounts for 16% of the total mass of the raw materials, and the mass of acrylamide accounts for 1%-5% of the total mass of the raw materials.

6. The environmentally friendly high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent according to claim 4, characterized in that, The initiator is ammonium persulfate.

7. The environmentally friendly high-temperature and high-salt pre-crosslinked granular water-blocking agent according to claim 4, characterized in that, The organic solvent includes methanol or ethanol, and the filler includes one or more of kaolin, fly ash, and cement.

8. A method for preparing an environmentally friendly, high-temperature resistant, high-salt pre-crosslinked granular water-blocking agent as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Mix and stir the water, water glass, the polymer monomer material, methylenebisacrylamide and the initiator; S2. Add the filler and stir to obtain the first material; S3. The organic solvent and the silane coupling agent are mixed to obtain a second material. The second material and the organometallic crosslinking agent are then added to the first material and stirred to obtain a third material. S4. Deoxygenate the third material; S5. After standing and completing the polymerization and cross-linking reaction, dry and pulverize to obtain the pre-cross-linked particulate water-blocking agent.

9. The preparation method of an environmentally friendly high-temperature and high-salt resistant pre-crosslinked granular water-blocking agent according to claim 8, characterized in that, The temperature range in step S1 is 5℃–35℃.

10. The preparation method of an environmentally friendly high-temperature and high-salt pre-crosslinked granular water-blocking agent according to claim 8, characterized in that, In step S4, the deoxygenation method is to introduce nitrogen gas into the third material for 0.5–2 hours.

11. The application of the environmentally friendly high-temperature and high-salt pre-crosslinked particulate water shut-off agent according to any one of claims 1-7 in oilfield water shut-off.

12. The application according to claim 11, characterized in that, The environmentally friendly, high-temperature and high-salt pre-crosslinked particulate water-blocking agent was applied to the water-blocking process of Darcy-level channels.

13. A method for plugging water in an oilfield, characterized in that, The sealing is performed using the environmentally friendly, high-temperature resistant, high-salt pre-crosslinked granular water-blocking agent as described in any one of claims 1-7.

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