A polymer gel isolation system with a cross-linked network structure and its application

Abstract

The present invention provides a polymer gel isolation system with a cross-linked network structure and its application, which belongs to the field of drilling fluid isolation technology. The polymer gel isolation system includes a catalytic solution and a gelling solution, wherein the volume ratio of the catalytic solution to the gelling solution is 0.1-3:10; the catalytic solution includes the following raw materials in parts by mass: 1-5 parts of modified cellulose solution, 0.1-3 parts of inorganic compound, and 0.01-10 parts of initiator; the gelling solution includes the following raw materials in parts by mass: 10-30 parts of unsaturated fatty acid, 1-15 parts of amide monomer, 1-3 parts of sulfonic acid monomer, 0.01-0.03 parts of cross-linking agent, and the rest is water, and the total amount of each component in the gelling solution is 100 parts. The polymer gel isolation system of the present invention has the advantages of controllable gelling time and high strength, and can effectively isolate formation fractures.

Description

Technical Field

[0001] The invention relates to a polymer gel isolation system with a cross-linked network structure and application thereof, belonging to the technical field of drilling fluid isolation. Background Art

[0002] With the continued growth of energy demand, unconventional oil and gas formations have gradually become the primary targets for exploration and development. However, during unconventional oil and gas exploration and development, drilling encounters are complex and variable, drilling accidents are frequent, and drilling fluid loss is a particularly prominent problem. Lost circulation refers to the abnormal loss of drilling fluid into formation pores, fractures, or cave systems under the influence of positive pressure differentials during the drilling process. Lost circulation not only leads to significant loss of drilling fluid, but also destabilizes the wellbore and can even induce complex downhole conditions such as well collapse and well kicks, severely hindering the efficient development of unconventional oil and gas resources.

[0003] From the perspective of the causes of fluid loss, drilling fluid loss pathways can be divided into two categories: first, artificial loss pathways, which occur during the drilling process due to improper operation, poor drilling fluid performance, and other factors, resulting in bottomhole pressure exceeding the formation fracture pressure, thus creating fractures and triggering drilling fluid loss; second, naturally developed loss pathways in the formation, such as cracks and holes. In such formations, even extremely low bottomhole pressure differentials can induce fluid loss, resulting in fracture-induced fluid loss. Notably, fracture-induced fluid loss accounts for over 80% of total fluid loss and can further trigger downhole complications such as well collapse and well kicks, resulting in significant non-drilling time and financial losses.

[0004] In response to the problem of leakage due to fractures, the main treatment methods currently used include bridge plugging materials and downhole cross-linked plugging materials. Bridge plug plugging materials fill the fractures by bridging to form a dense sealing layer, thereby preventing further leakage of drilling fluid and improving the pressure bearing capacity of the formation. However, the successful application of this method is highly dependent on the accurate understanding of the crack conditions of the leaking layer, especially the judgment of the crack width. In actual application, since it mainly relies on the experience observation of engineers or the leakage conditions of the same block, there is a large deviation between the actual crack width of the leaking layer and the estimated value, which in turn affects the success rate of plugging. Downhole cross-linked materials are cross-linked underground by physical or chemical means to effectively seal the fractures in the formation. Chinese patent document CN118165712A discloses a three-dimensional network gel plugging agent synthesized from acrylamide monomers and sulfonic acid monomers, which is used in combination with conventional plugging materials to seal the fractures. Chinese patent document CN114854380A synthesizes a composite gel plugging agent using modified plant gum, propylene-based polymer, limestone powder, and plant fibers. This plugging agent effectively increases flow resistance in leakage channels, effectively preventing drilling fluid loss. However, this gel plugging material is difficult to precisely control its downhole crosslinking time, resulting in significant loss of the polymer gel solution, insufficient gel strength, and weak isolation capabilities.

[0005] Therefore, there is an urgent need to develop a downhole cross-linked plugging material with controllable gelation time and strong sealing ability. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, especially the problems of uncontrollable gelation time and weak sealing ability of downhole cross-linked plugging materials, the present invention provides a polymer gel sealing system with a cross-linked network structure and its application. The present invention improves the structural strength of the polymer gel by constructing non-covalent bond interactions such as multiple hydrogen bonds and coordination bonds, and adopts a segmented injection method to add a catalytic solution to accurately control the gelation time, thereby developing a gel sealing system with a multi-mechanism synergistic cross-linked network. The polymer gel sealing system of the present invention has the advantages of controllable gelation time and high strength, and can effectively seal formation fractures.

[0007] The technical solutions of the present invention are as follows:

[0008] A polymer gel sealing system with a cross-linked network structure, comprising a catalytic solution and a gelling solution, wherein the volume ratio of the catalytic solution to the gelling solution is 0.1-3:10;

[0009] The catalytic solution is prepared by comprising the following raw materials in parts by weight: 1-5 parts of modified cellulose solution, 0.1-3 parts of inorganic compound, and 0.01-10 parts of initiator;

[0010] The gelling solution is prepared by including the following raw materials in parts by mass: 10-30 parts of unsaturated fatty acid, 1-15 parts of amide monomer, 1-3 parts of sulfonic acid monomer, 0.01-0.03 parts of crosslinking agent, and the rest is water, and the total amount of each component in the gelling solution is 100 parts.

[0011] According to the preferred embodiment of the present invention, the modified cellulose solution is prepared according to the following method:

[0012] Cellulose is added into water and stirred evenly, the pH of the system is adjusted to 8-10, and polyphenol compounds are added to react to obtain a modified cellulose solution.

[0013] According to the preferred embodiment of the present invention, in the preparation of the modified cellulose solution, the cellulose is nanocellulose fibrils or nanocellulose crystals, a common commercially available product, or prepared according to an existing preparation method; the mass ratio of the cellulose to water is 1:15-75, more preferably 1:25.

[0014] Preferably, according to the present invention, in the preparation of the modified cellulose solution, a NaOH aqueous solution with a concentration of 0.01 mol / L is used to adjust the pH of the system to 8-10.

[0015] According to a preferred embodiment of the present invention, in the preparation of the modified cellulose solution, the polyphenol compound is one or a combination of two or more of resveratrol, tannic acid, and quercetin; the mass ratio of the polyphenol compound to cellulose is 5-8:1-3, more preferably 7:3.

[0016] Preferably according to the present invention, in the preparation of the modified cellulose solution, the reaction time is 30-40 hours and the reaction temperature is room temperature.

[0017] According to the present invention, preferably, the inorganic compound is ferric chloride hexahydrate.

[0018] According to the present invention, the initiator is preferably one or a combination of two or more of potassium persulfate, sodium persulfate, benzoyl peroxide, tert-butyl peroxyvalerate or ammonium persulfate.

[0019] According to the preferred embodiment of the present invention, the catalytic solution is prepared according to the following method:

[0020] An inorganic compound is added to the modified cellulose solution, stirred for 1-3 hours, and then an initiator is added and stirred for 0.5-1.5 hours to obtain a catalytic solution.

[0021] According to the present invention, preferably, the unsaturated fatty acid is one or a combination of two or more of 2,4-hexadienoic acid, acrylic acid, methacrylic acid and oleic acid.

[0022] According to the present invention, preferably, the amide monomer is acrylamide and / or methacrylamide.

[0023] According to the present invention, the sulfonic acid monomer is preferably one or a combination of two or more of aminosulfonic acid, perfluoro(2-ethoxyethane)sulfonic acid, and 2-acrylamide-2-methylpropanesulfonic acid.

[0024] According to the present invention, the crosslinking agent is preferably one or a combination of N,N-methylenebisacrylamide, diethylenetriamine, and polyethylene glycol diacrylate; the average molecular weight of the polyethylene glycol diacrylate is 400-600, and its structural formula is shown in Formula I below:

[0025]

[0026] I.

[0027] According to the preferred embodiment of the present invention, the gelling solution is prepared according to the following method:

[0028] Unsaturated fatty acid is added into water and stirred evenly, then amide monomer, sulfonic acid monomer and cross-linking agent are added and stirred evenly to obtain a gelling solution.

[0029] According to the preferred embodiment of the present invention, in the preparation of the gelling solution, the stirring time after adding the unsaturated fatty acid is 1-4 hours, more preferably 2-3 hours.

[0030] According to the present invention, the above-mentioned polymer gel sealing system with a cross-linked network structure is used in the crude oil extraction and drilling process; preferably, the specific application method is as follows: using a staged injection method, first injecting a gelling solution into the formation, and then injecting a catalytic solution, and forming a gel at the formation temperature to seal the formation cracks; the formation temperature is 40-100°C.

[0031] According to the present invention, during drilling, the amount of the polymer gel isolation system having a cross-linked network structure and the injection method can be the same as those in the prior art.

[0032] The room temperature in the present invention has a well-known meaning in the art, which refers to 25±5°C.

[0033] The technical features and beneficial effects of the present invention are as follows:

[0034] 1. The present invention provides a new polymer gel isolation system based on multi-mechanism synergistic cross-linking. Its molecular structure design and mechanism of action break through the limitations of the traditional single cross-linking mode and exhibit excellent isolation performance and process controllability under complex geological conditions.

[0035] 2. The present invention adopts a multi-element cross-linking mechanism to enhance the performance of the gel. In the present invention, firstly, based on amide monomers, sulfonic acid monomers and unsaturated fatty acids, a stable covalent cross-linking network is formed through free radical polymerization, which provides a solid network structure for the gel. Secondly, metal ions are introduced into the system, which react with the carboxyl groups in the unsaturated fatty acids. At the same time, the hydroxyl groups in the cellulose solution are interconnected with other molecular chains through hydrogen bonds, further enhancing the complexity and stability of the gel network. This multi-mechanism cross-linking mode breaks through the limitations of the traditional single cross-linking system and significantly improves the gel's anti-deformation ability and blocking effect. In addition, the introduction of sulfonic acid monomers improves the salt resistance of the system, ensuring that the gel can still maintain good physical properties and blocking effects under complex salinity conditions, thereby broadening the application range of the gel.

[0036] 3. The present invention accurately controls gelation and optimizes the plugging process. The present invention constructs a catalytic control system, which produces efficient catalysts by introducing polyphenol compounds, cellulose and inorganic compounds to accelerate the cross-linking reaction of the polymer. At the same time, by adjusting the ratio of inorganic compounds and initiators in the catalytic solution, the generation rate of free radicals can be flexibly adjusted, thereby achieving accurate control of the gelation time. When the free radical generation rate is high, the gelation time of the gel is significantly shortened, and it can be quickly solidified to effectively seal the cracks; when the free radical generation rate is low, the viscosity of the system increases, which slows down the loss rate of the gelation solution in the cracks and ensures the effective retention of the gel in a complex crack environment. In addition, a staged injection process is adopted, in which the gelation solution is first injected into the formation cracks, and then the solution containing the catalyst is injected. This method avoids premature cross-linking of the gelation solution during transportation, ensures that the cross-linking reaction occurs accurately at the target location, and provides a new technical idea for controlling the gelation time of polymer gel materials.

[0037] 4. The polymer gel isolation system of the present invention is simple to prepare and facilitates large-scale production. The cross-linked network polymer gel isolation system proposed in the present invention has a simple preparation process, low equipment and process requirements, and does not require complex synthesis steps or special reaction conditions. This facilitates large-scale industrial production and lays a solid foundation for its widespread application in oil and gas fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 1 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0039] Figure 2 This is the infrared spectrum of the polymer gel obtained in Example 1.

[0040] Figure 3Graph showing the variation of the elastic modulus and loss modulus of the polymer gel obtained in Example 4 with angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0041] Figure 4 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 5 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0042] Figure 5 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 6 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0043] Figure 6 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 7 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0044] Figure 7 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 8 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0045] Figure 8 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 9 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0046] Figure 9 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 10 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0047] Figure 10 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 11 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0048] Figure 11 Graph showing the variation of the elastic modulus and loss modulus of the polymer gel obtained in Example 12 with angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0049] Figure 12 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 13 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0050] Figure 13 Graph showing the elastic modulus and loss modulus of the polymer gel obtained in Example 14 as a function of angular frequency, wherein G' is the elastic modulus and G" is the loss modulus.

[0051] Figure 14 This is the displacement curve of the polymer gel isolation system of Example 1 in Experimental Example 1.

[0052] Figure 15 Graph showing the elastic modulus and loss modulus of the polymer gel (with NaCl added) obtained in Experimental Example 2 as a function of angular frequency, where G' is the elastic modulus and G" is the loss modulus. DETAILED DESCRIPTION

[0053] The present invention will be further described below with reference to specific examples, but is not limited thereto.

[0054] The raw materials used in the examples are conventional materials and are commercially available. The methods described are all based on existing technologies unless otherwise specified.

[0055] The nanocellulose fibrils used in the examples, i.e., cellulose nanofibers, are commercially available from Nanjing Tianlu Nanotechnology Co., Ltd., model TEMPO oxidized nanocellulose TL-010-5, with a diameter of 10-20 nm, a length of 500-1000 nm, a colorless gel, and a solid content of 5 wt %; the nanocellulose crystals used are commercially available from Nanjing Tianlu Nanotechnology Co., Ltd., model cellulose nanocrystals TL-003, with a diameter of 10-50 nm, a length of 200-500 nm, a white gel, and a solid content of 8 wt %.

[0056] The "parts" described in the examples are all parts by mass.

[0057] Example 1

[0058] A polymer gel sealing system with a cross-linked network structure, comprising a catalytic solution and a gelling solution; the volume ratio of the catalytic solution to the gelling solution is 1:10;

[0059] The catalytic solution is prepared by including the following raw materials in parts by weight: 3 parts of modified cellulose solution, 1 part of inorganic compound, and 1 part of initiator; the inorganic compound is ferric chloride hexahydrate, and the initiator is ammonium persulfate;

[0060] The modified cellulose solution is prepared according to the following method:

[0061] 3 parts of cellulose were added to 75 parts of water, and the mixture was stirred at room temperature and a stirring speed of 1000 r / min. After the mixture was uniformly stirred, the pH of the system was adjusted to 8 using a 0.01 mol / L NaOH aqueous solution. 7 parts of tannic acid were added, and the mixture was stirred at room temperature and a stirring speed of 1000 r / min for 36 hours to obtain a modified cellulose solution.

[0062] The catalytic solution was prepared according to the following method:

[0063] An inorganic compound was added to the modified cellulose solution, and the mixture was stirred at a speed of 1000 r / min at room temperature for 2 hours. Then, an initiator was added, and the mixture was stirred at a speed of 1500 r / min at room temperature for 30 minutes to obtain a catalytic solution.

[0064] The gelling solution is prepared by including the following raw materials in parts by weight: 20 parts of unsaturated fatty acid, 10 parts of amide monomer, 2 parts of sulfonic acid monomer, 0.02 parts of cross-linking agent, and the remainder of water, with the total amount of each component in the gelling solution being 100 parts; the unsaturated fatty acid is acrylic acid, the amide monomer is acrylamide, the sulfonic acid monomer is 2-acrylamido-2-methylpropanesulfonic acid, and the cross-linking agent is N,N-methylenebisacrylamide;

[0065] The gelling solution is prepared according to the following method:

[0066] Unsaturated fatty acids were added to water and stirred at room temperature at a rotation speed of 1200 r / min for 2 hours. Then, amide monomers, sulfonic acid monomers and cross-linking agents were added and stirred evenly at room temperature at a rotation speed of 1500 r / min to obtain a gelling solution.

[0067] The gelation time of the polymer gel isolation system obtained in this example was tested by adding a catalytic solution to the gelation solution, allowing the mixture to stand at 60°C and starting a timer. The elastic modulus of the system was measured using a Haake rheometer. When the mixed solution began to gel, the elastic modulus increased and remained essentially constant after reaching a certain maximum value. The time when the elastic modulus reached the highest point was considered the gel formation time. The timer was stopped to obtain the gelation time. The gelation time of the polymer gel isolation system obtained in this example was 30 minutes.

[0068] The elastic modulus and loss modulus of the polymer gel obtained in this example vary with angular frequency as shown in the figure below: Figure 1 As shown by Figure 1 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 14005 Pa. The larger the elastic modulus, the higher the strength of the gel. It can be seen from the above that the gel of the plugging system in this embodiment has a higher strength after gelation.

[0069] The polymer gel was dried at 50°C and ground before testing its infrared spectrum. Figure 2 As shown, at 620cm -1 The characteristic absorption peak observed at 1714 cm-1 can be attributed to the stretching vibration of the sulfonic acid group. -1 The strong absorption band at 2924 cm corresponds to the C=O stretching vibration in unsaturated fatty acids and tannic acid molecules. -1 The 3133 cm-1 The characteristic peak at 3560 cm corresponds to the contraction vibration of the amide group. -1 The broad peak appearing nearby can be attributed to the stretching vibration of hydroxyl groups (-OH) in the polysaccharide, which indicates that there are intermolecular hydrogen bonding interactions of cellulose substances in the gel system, and the characteristic functional groups of the synthesized monomers are all reflected in the infrared spectrum.

[0070] Example 2

[0071] The gelation time of the polymer gel isolation system of the present invention is controllable. The speed of the gelation time mainly depends on the content of inorganic compounds, tannic acid and initiator in the system. 3+ Persulfate can be activated to produce free radicals through single electron transfer, and catechol in tannic acid can be oxidized into semiquinone, thereby activating persulfate, which is equivalent to activating the initiator to produce monomer cross-linking. The speed of polymerization mainly depends on the number of free radicals. The more free radicals are initiated, the shorter the cross-linking time, and the fewer free radicals are initiated, the longer the cross-linking time.

[0072] This example studies the effect of inorganic compound content on gelation time.

[0073] The content of the inorganic compound in the catalytic solution of Example 1 was adjusted. The added amounts of the inorganic compound were 0.1 parts, 0.5 parts, 1 parts, 1.5 parts, 2 parts, 2.5 parts, and 3 parts, respectively. The other conditions were as described in Example 1. The gelation time was tested according to the method of Example 1, as shown in Table 1. It can be seen from Table 1 that with the increase of the content of the inorganic compound, the gelation time gradually shortens. The gelation time of the sealing system can be adjusted by adjusting the content of the inorganic compound according to the specific actual situation.

[0074] Table 1 Gelation time at different concentrations of inorganic compounds

[0075]

[0076] Example 3

[0077] This example studies the effect of the ratio of the gelling solution to the catalytic solution on the gelling time. The volume ratios of the catalytic solution to the gelling solution in Example 1 were adjusted to 0.1:10, 0.5:10, 1:10, 1.5:10, 2:10, 2.5:10, and 3:10, respectively. Other conditions were the same as those described in Example 1. The gelling time was tested according to the method of Example 1, as shown in Table 2.

[0078] Table 2 Gelation time at different ratios of catalytic solution to gelling solution

[0079]

[0080] When the proportion of the catalytic solution increases, the concentration of the initiator and the catalyst increases relatively, which can generate free radicals faster, promote the polymerization reaction, and thus shorten the gelation time; on the contrary, when the proportion of the catalytic solution decreases, the concentration of the reactants in the reaction system increases relatively, the rate of the polymerization reaction slows down, and the gelation time is prolonged. According to the experimental results, the present invention can accurately control the gelation time within a wider range by adjusting the proportion to meet the needs of different application scenarios. This has important guiding significance for adjusting the gelation time according to specific needs in practical applications. In addition, since the present invention adopts a staged injection method, the catalytic solution is only pumped in after the gelation solution enters the formation, so it will not solidify prematurely, resulting in complex situations such as blocking the wellbore.

[0081] The data in Tables 1 and 2 show that, considering the speed of leakage in formation fractures, we can control the gelation time by adjusting the concentrations of initiator, modified cellulose and inorganic compounds in the isolation system according to the actual situation.

[0082] Example 4

[0083] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that in the preparation of modified cellulose in the catalytic solution, the amount of cellulose added is 1 g. Other preparation steps and conditions are the same as in Example 1.

[0084] The catalytic solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 60 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 3 As shown by Figure 3 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 11682 Pa. It can be seen that the gel of the plugging system in this embodiment has a higher strength after gelation. However, due to the decrease in cellulose content in the system, the hydrogen bonding effect in the system is weakened, and the gel strength is slightly lower than that in Example 1.

[0085] Example 5

[0086] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that the unsaturated fatty acid in the gelling solution is 15 parts.

[0087] The catalytic solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 35 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 4 As shown by Figure 4It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 10276 Pa. It can be seen that the gel of the plugging system of this embodiment has a higher strength after gelation, but it is slightly lower than that of Example 1. This is because the unsaturated fatty acid serves as a comonomer and provides a part of the basic skeleton for the gel. The reduction of its concentration means that the number of polymer chains available for cross-linking by the cross-linking agent is reduced, and the number of cross-linking points decreases, resulting in a decrease in the structural strength of the gel.

[0088] Example 6

[0089] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that the amount of amide monomer in the gelling solution is 8 parts.

[0090] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 33 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 5 As shown by Figure 5 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 12367 Pa. It can be seen that the gel of the plugging system in this embodiment has a higher strength after gelation, but it is slightly lower than that in Example 1. This is because amide monomers are network nodes of polymer cross-linking. A decrease in concentration means a decrease in the number of polymerization reaction monomers, resulting in a decrease in structural strength.

[0091] Example 7

[0092] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that the amount of sulfonic acid monomer in the gelling solution is 3 parts.

[0093] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 29 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 6 As shown by Figure 6 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 13112 Pa. It can be seen that the gel of the plugging system of this embodiment has a higher strength after gelation, but it is slightly lower than that of Example 1. This is mainly because when the concentration of sulfonic acid monomers increases, the negative charge density on the gel molecular chain increases, and the electrostatic repulsion between the molecular chains is enhanced. This repulsion will cause the molecular chains to stretch, destroying the originally relatively tight gel network structure, and affecting the integrity and strength of the gel.

[0094] Example 8

[0095] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that the ratio of the catalytic solution to the gelling solution is 0.1:10.

[0096] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 50 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 7 As shown by Figure 7 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 13401 Pa. It can be seen that the gel of the plugging system in this embodiment has a higher strength, but it is slightly lower than that of Example 1. This is mainly because although the hydrogen bonds between cellulose and the molecular chain in the catalytic solution and Fe 3+ The coordination effect with acrylic acid, as well as the interaction between tannic acid and the molecular chain and cellulose, caused the structural strength to decrease due to the reduction of catalyst solution.

[0097] Example 9

[0098] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that the ratio of the catalytic solution to the gelling solution is 3:10.

[0099] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 20 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 8 As shown by Figure 8 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 15349 Pa. It can be seen that the gel of the plugging system in this embodiment has a higher strength after gelation. The reason for the increase in gel strength is that the amount of catalytic solution added is increased, and the cellulose and Fe 3+ As the concentration of increases, the strength of the system increases due to hydrogen bonding and metal coordination.

[0100] Example 10

[0101] A polymer gel isolation system having a cross-linked network structure is as described in Example 1, except that:

[0102] The catalytic solution is prepared by including the following raw materials in parts by weight: 5 parts of modified cellulose solution, 3 parts of inorganic compound, and 10 parts of initiator;

[0103] The gelling solution is prepared by including the following raw materials in parts by mass: 30 parts of unsaturated fatty acid, 15 parts of amide monomer, 3 parts of sulfonic acid monomer, 0.03 parts of crosslinking agent, and the rest is water, and the total amount of each component in the gelling solution is 100 parts.

[0104] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 5 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 9 As shown by Figure 9 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 13772 Pa. It can be seen that the gel of the plugging system of this embodiment has a higher strength after gelation.

[0105] Example 11

[0106] A polymer gel isolation system having a cross-linked network structure is as described in Example 1, except that:

[0107] The catalytic solution is prepared by including the following raw materials in parts by weight: 1 part of modified cellulose solution, 0.1 part of inorganic compound, and 0.01 part of initiator;

[0108] The gelling solution is prepared by including the following raw materials in parts by mass: 10 parts of unsaturated fatty acid, 1 part of amide monomer, 1 part of sulfonic acid monomer, 0.01 part of crosslinking agent, and the rest is water, and the total amount of each component in the gelling solution is 100 parts.

[0109] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 150 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 10 As shown by Figure 10 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 8821 Pa. It can be seen that the gel of the plugging system of this embodiment has a higher strength after gelation, but it is lower than that of the embodiment. This is because the concentration of each monomer is reduced, resulting in larger pores or uneven pore distribution inside the gel, which reduces the overall strength of the gel.

[0110] Example 12

[0111] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that during the preparation of the modified cellulose, the polyphenol compound is resveratrol.

[0112] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 90 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 11 As shown by Figure 11 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 10558 Pa. It can be seen that the gel of the plugging system of this embodiment has a high strength after gelation. However, since the content of catechol in resveratrol is far less than that of tannic acid, the hydrogen bonding effect is reduced at the same concentration, resulting in a decrease in gel strength.

[0113] Example 13

[0114] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that the unsaturated fatty acid in the gelling solution is 2,4-hexadienoic acid.

[0115] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 32 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 12 As shown by Figure 12 It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 9247 Pa. It can be seen that the gel of the plugging system of this embodiment has a higher strength after gelation, which is lower than that of Example 1. This may be because the cross-linking effect of 2,4-hexadienoic acid with other monomers and cross-linking agents may not be as good as acrylic acid due to the differences in its molecular structure and reactivity. The number and quality of cross-linking points may be affected, resulting in an imperfect cross-linking network of the gel and a decrease in strength.

[0116] Example 14

[0117] A polymer gel isolation system with a cross-linked network structure is as described in Example 1, except that nanocellulose crystals are used instead of nanocellulose fibrils.

[0118] The catalyst solution was added to the gelling solution of this embodiment, and the gelling was carried out at 60°C for 45 minutes to obtain a polymer gel. The elastic modulus and loss modulus of the obtained polymer gel varied with the angular frequency as shown in FIG. Figure 13 As shown by Figure 13It can be seen that the elastic modulus and loss modulus of the gel increase with the increase of angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 10966 Pa. The long fiber structure of nanocellulose fibers can form a physical cross-linked network in the gel, while the short rod-like structure of nanocellulose crystals provides rigidity enhancement, but lacks a long-range network, resulting in lower strength than the gel reinforced with nanocellulose fibers.

[0119] Comparative Example 1

[0120] A polymer gel sealing system is as described in Example 1, except that: a catalytic solution is prepared according to the following method: 7 parts of tannic acid are added to 75 parts of water and stirred uniformly to obtain a modified solution; 1 part of ferric chloride hexahydrate and 1 part of ammonium persulfate are added to 3 parts of the modified solution and stirred uniformly to obtain a catalytic solution. The other preparation steps and conditions are the same as in Example 1.

[0121] The catalytic solution was added to the gelling solution of this comparative example, and gelling was carried out at 60° C. The gelling time was 27 min. Due to the lack of the cellulose reinforcing material, the gelling strength decreased to 7589 Pa compared with Example 1.

[0122] Comparative Example 2

[0123] A polymer gel isolation system is as described in Example 1, except that no unsaturated fatty acid is added to the gelling solution, a component is omitted and replaced with the same amount of water, and the other preparation steps and conditions are the same as in Example 1.

[0124] The catalytic solution was added to the gelling solution of this comparative example, and gelling was carried out at 60° C. for 45 minutes to obtain a polymer gel. The elastic modulus of the obtained gel was tested, and the maximum value was 6175 Pa.

[0125] Comparative Example 3

[0126] A polymer gel isolation system is as described in Example 1, except that no amide monomer is added to the gelling solution, a component is omitted and replaced with the same amount of water, and the other preparation steps and conditions are the same as in Example 1.

[0127] The catalytic solution was added to the gelling solution of this comparative example, and gelling was carried out at 60° C. for 42 minutes to obtain a polymer gel. The elastic modulus of the obtained gel was tested, and the maximum value was 7124 Pa.

[0128] Comparative Example 4

[0129] A polymer gel isolation system is as described in Example 1, except that no sulfonic acid monomer is added to the gelling solution, a component is omitted and replaced with the same amount of water, and the other preparation steps and conditions are the same as in Example 1.

[0130] The catalytic solution was added to the gelling solution of this comparative example, and gelling was carried out at 60° C. for 35 min to obtain a polymer gel. The elastic modulus of the obtained gel was tested, and the maximum value was 8147 Pa.

[0131] Comparative Example 5

[0132] A polymer gel isolation system is as described in Example 1, except that: a catalytic solution is prepared according to the following method: 3 parts of cellulose are added to 75 parts of water and stirred uniformly to obtain a cellulose solution; 1 part of ferric chloride hexahydrate and 1 part of ammonium persulfate are added to the 3 parts of cellulose solution and stirred uniformly to obtain a catalytic solution. The other preparation steps and conditions are the same as those in Example 1.

[0133] The catalytic solution was added to the gelling solution of this comparative example, and gelling was carried out at 60°C for 150 minutes. Tannic acid, which would have accelerated the gelling time, was not added, so an effective cross-linking structure could not be formed within 30 minutes, resulting in a decrease in strength. Due to the lack of tannic acid catalysis, the gelling time was extended to 150 minutes, and the gel strength decreased slightly, reaching 8014 Pa.

[0134] Comparative Example 6

[0135] A polymer gel isolation system is as described in Example 1, except that no inorganic compound is added to the catalytic solution. Other preparation steps and conditions are the same as in Example 1.

[0136] A catalytic solution was added to the gelling solution of this comparative example, and gelation was carried out at 60°C for 240 minutes to obtain a polymer gel. No inorganic compound was added, which affected the gelling time. Since the effect of the inorganic compound on the gelling strength is greater than that of tannic acid, the strength of the gel is lower than that of comparative example 5, and the gelling strength is 6432 Pa.

[0137] Comparative Example 7

[0138] A polymer gel sealing system is as described in Example 1, except that: no modified cellulose solution is added to the catalytic solution, 1 part ferric chloride hexahydrate and 1 part ammonium persulfate are added to 75 parts water, and stirred uniformly to obtain a catalytic solution. The other preparation steps and conditions are the same as in Example 1.

[0139] Catalytic solution was added to the gelling solution of this comparative example, and gelling was carried out at 60°C for 150 min. Without adding modified cellulose solution, the catalytic time was also affected to a certain extent, the strength was reduced, and the maximum gelling strength was 6121 Pa.

[0140] Comparative Example 8

[0141] A polymer gel sealing system is as described in Example 1, except that: no modified cellulose solution and inorganic compound are added to the catalytic solution, 1 part of ammonium persulfate is added to 75 parts of water, and stirred uniformly to obtain a catalytic solution. The other preparation steps and conditions are the same as in Example 1.

[0142] A catalytic solution was added to the gelling solution of this comparative example, and gelling was carried out at 60°C without adding modified cellulose solution and inorganic compound. This indicates that it is difficult for the solution to form an effective cross-linked structure at this temperature, resulting in low strength. Since no catalytic solution was added and only 1 part of ammonium persulfate was introduced, the complete gelling time was 360 min and the gelling strength was 5681 Pa.

[0143] Test Example 1

[0144] In order to evaluate the plugging performance of the polymer gel isolation system, the compressive strength of the polymer gel prepared in Example 1 was simulated using a high-temperature and high-pressure displacement device. The specific operating steps are as follows:

[0145] The gelling solution in Example 1 was injected into the sand-filled tube at a rate of 3.99 mL / min. The sand-filled tube was filled with quartz sand of 160-180 mesh. After the gelling solution was filled, the catalytic solution was injected into the addition tube at a rate of 3.99 mL / min. The injection amount was one-tenth of the volume of the gelling solution. Because some free radicals gradually induce monomer cross-linking with the increase of time, the gelling strength will show an increasing trend. Therefore, in order to increase the strength, we gelled at 60°C for 30 minutes and tested its breakthrough pressure. The results are as follows: Figure 14 As shown by Figure 14 It can be seen that the maximum pressure bearing capacity of the polymer gel isolation system of the embodiment for the sand-filled pipe is 6.0 MPa.

[0146] Test Example 2

[0147] Salt resistance

[0148] In downhole operations such as oil drilling, the formation environment is complex and changeable, and high salinity is also a common problem. The actual formations on site are often rich in various salt substances, such as sodium chloride, calcium chloride, etc. If the gel is cross-linked in a high-salt environment, it will cause unstable performance, and its sealing effect will be greatly reduced, seriously affecting the smooth progress of drilling operations and the efficiency of oil and gas resource extraction. Therefore, in order to ensure that the gel can play a role in actual applications, it is crucial to systematically test the salt resistance. We added 7 parts of NaCl to the gelling solution to test the gelling strength of the gel after adding salt ions. The results are as follows Figure 15The elastic modulus and loss modulus of the gel increase with increasing angular frequency. When the angular frequency is 84 rad / s, the elastic modulus reaches a maximum value of 7578 Pa. Due to the presence of salt-tolerant groups such as sulfonate groups and the interaction of multiple hydrogen bonds and metal coordination bonds, the gel prepared by the present invention has a certain salt resistance potential in its formulation design.

Claims

1. A polymer gel isolation system with a cross-linked network structure, characterized in that: The method comprises a catalytic solution and a gelling solution, wherein the volume ratio of the catalytic solution to the gelling solution is 0.1-3:10; The catalytic solution is prepared by comprising the following raw materials in parts by weight: 1-5 parts of modified cellulose solution, 0.1-3 parts of an inorganic compound, and 0.01-10 parts of an initiator; the inorganic compound is ferric chloride hexahydrate; the initiator is one or a combination of two or more of potassium persulfate, sodium persulfate, benzoyl peroxide, tert-butyl peroxyvalerate, or ammonium persulfate; The modified cellulose solution is prepared by the following method: adding cellulose to water, stirring evenly, adjusting the pH of the system to 8-10, adding a polyphenol compound, and reacting to obtain a modified cellulose solution; The cellulose is nanocellulose fibrils or nanocellulose crystals, the mass ratio of the cellulose to water is 1:15-75, the polyphenol compound is one or a combination of two or more of resveratrol, tannic acid, and quercetin; the mass ratio of the polyphenol compound to the cellulose is 5-8:1-3; The gelling solution is prepared by including the following raw materials in parts by mass: 10-30 parts of unsaturated fatty acid, 1-15 parts of amide monomer, 1-3 parts of sulfonic acid monomer, 0.01-0.03 parts of crosslinking agent, and the remainder being water, with the total amount of each component in the gelling solution being 100 parts. The unsaturated fatty acid is one or a combination of two or more of 2,4-hexadienoic acid, acrylic acid, methacrylic acid, and oleic acid; the amide monomer is acrylamide and / or methacrylamide; the sulfonic acid monomer is one or a combination of two or more of aminosulfonic acid, perfluoro(2-ethoxyethane)sulfonic acid, and 2-acrylamide-2-methylpropanesulfonic acid; and the crosslinking agent is one or a combination of two of N,N-methylenebisacrylamide, diethylenetriamine, and polyethylene glycol diacrylate.

2. The polymer gel isolation system having a cross-linked network structure according to claim 1, characterized in that: In the preparation of the modified cellulose solution, the mass ratio of the cellulose to water is 1:

25.

3. The polymer gel isolation system having a cross-linked network structure according to claim 1, characterized in that: In the preparation of the modified cellulose solution, a 0.01 mol / L NaOH aqueous solution was used to adjust the pH of the system to 8-10.

4. The polymer gel isolation system having a cross-linked network structure according to claim 1, characterized in that: In the preparation of the modified cellulose solution, the mass ratio of the polyphenol compound to the cellulose is 7:

3.

5. The polymer gel isolation system having a cross-linked network structure according to claim 1, characterized in that: In the preparation of the modified cellulose solution, the reaction time is 30-40 hours and the reaction temperature is room temperature.

6. The polymer gel isolation system having a cross-linked network structure according to claim 1, characterized in that: The catalytic solution is prepared according to the following method: adding an inorganic compound to a modified cellulose solution, stirring for 1-3 hours, then adding an initiator, stirring for 0.5-1.5 hours, to obtain a catalytic solution.

7. The polymer gel isolation system having a cross-linked network structure according to claim 1, characterized in that: The average molecular weight of the polyethylene glycol diacrylate is 400-600.

8. The polymer gel isolation system having a cross-linked network structure according to claim 1, characterized in that: The gelling solution is prepared according to the following method: unsaturated fatty acid is added into water, stirred evenly, and then amide monomer, sulfonic acid monomer and cross-linking agent are added and stirred evenly to obtain the gelling solution.

9. The polymer gel isolation system having a cross-linked network structure according to claim 8, characterized in that: In the preparation of the gelling solution, the stirring time after adding the unsaturated fatty acid is 1-4 hours.

10. Use of the polymer gel isolation system having a cross-linked network structure according to any one of claims 1 to 9 in a crude oil production and drilling process, characterized in that: The specific application method is as follows: using a staged injection method, first injecting the gelling solution into the formation, and then injecting the catalytic solution, the gelling is used to seal the formation cracks at the formation temperature; the formation temperature is 40-100℃.

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