Bentonite-based metal catalyst for reducing viscosity of thickened oil while drilling as well as preparation method and application of bentonite-based metal catalyst

Abstract

The invention provides a bentonite-based metal catalyst for reducing viscosity of thickened oil while drilling as well as a preparation method and application of the bentonite-based metal catalyst, and belongs to the field of oilfield chemistry in the petroleum industry. The preparation method of the catalyst comprises the following steps: hydrating bentonite, dropwise adding a hydrophilic monomer aqueous solution, sequentially adding a reducing agent aqueous solution and an initiator aqueous solution, and reacting to obtain a polymer modified bentonite aqueous phase; dropwise adding a first transition metal ligand solution for reaction; and then adding a second transition metal ligand solution to react. The catalyst disclosed by the invention can be used for efficiently catalyzing and cracking the thickened oil while drilling, so that the efficient viscosity reduction of the thickened oil is realized, and meanwhile, the lasting efficient viscosity reduction effect of the thickened oil can be kept. Moreover, the catalyst and the drilling fluid have good compatibility, negative effects on wall fixing and chip carrying capacity of the drilling fluid are avoided, the catalyst can be blended into the water-based drilling fluid, and chip carrying efficiency, rheological stability and high-temperature adaptability are maintained or enhanced.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemistry in the petroleum industry, specifically relating to a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling, its preparation method, and its application. Background Technology

[0002] Carbonate reservoirs are important oil and gas producing formations; however, they are often severely fractured and vulnerable, allowing heavy oil to easily flow into the wellbore during drilling. Because heavy oil is less dense than drilling fluid, it gradually rises to the surface after entering the wellbore. As the temperature decreases from bottom to top within the wellbore, the rising heavy oil solidifies in the upper part of the wellbore, leading to wellbore blockage, pipe jamming, and other problems, severely hindering the safe and efficient development of heavy oil.

[0003] To address the problem of stuck pipe in heavy oil wells, existing technologies typically introduce metal ions or metal-based catalysts as viscosity reducers. However, these metal-catalyzed viscosity reducers generally suffer from insufficient stability in practical applications. Active metals are prone to sedimentation, aggregation, or deactivation in the aqueous phase, making it difficult to maintain catalytic efficiency over the long term. Simultaneously, high-valence metal ions, during contact with bentonite, easily penetrate the bentonite interlayer structure and replace existing hydrated cations, thereby weakening the interlayer hydration capacity, significantly reducing the swelling and mud-forming properties of bentonite, and even causing instability in the drilling fluid system. Therefore, a catalyst is invented that uses bentonite, the main component of drilling fluid, as a carrier to adsorb metal complexes. Using this catalyst, in addition to catalytic viscosity reduction, the catalyst exhibits better compatibility with the drilling fluid itself, with less disturbance to the baseline rheology and filtration control of the system. Furthermore, existing metal viscosity reducers mostly employ single-metal systems, resulting in relatively simple catalytic pathways. In complex downhole environments, they are easily affected by temperature, salinity, and shear conditions, leading to limited duration of viscosity reduction and difficulty in achieving stable and sustained viscosity reduction effects.

[0004] For example, patent document CN 110743552 A discloses a clay-supported zero-valent metal hydrothermal pyrolysis catalyst for heavy oil and its preparation method. The process involves dissolving a transition metal salt in water; adding a polyamine compound and stirring until homogeneous; adding bentonite to the transition metal complex and stirring; adding borohydride to the mixture; filtering; washing with deionized water until no transition metal ions are detected; drying; cooling; and mixing with a co-catalyst urea until homogeneous. This catalyst can reduce the pour point of heavy oil by more than 6°C and reduce viscosity by more than 50% during hydrothermal pyrolysis. The residual catalyst metal content in the crude oil after the reaction is less than 1 μg / kg, and the catalyst reuse efficiency is higher than 90%. Although this invention uses bentonite, a major component of drilling fluid, as a carrier, the viscosity-reducing effect on heavy oil needs further improvement. Furthermore, it employs a single metal system, resulting in a relatively simple catalytic pathway, making it susceptible to the effects of temperature, salinity, and shear conditions in complex downhole environments. The viscosity-reducing effect has a limited duration, making it difficult to achieve a stable and sustained viscosity-reducing effect.

[0005] Therefore, there is an urgent need to develop a catalyst material that has good compatibility with drilling fluids, multiple catalytic pathways, and can achieve excellent, stable, and long-lasting catalytic viscosity reduction to meet the needs of high-performance drilling fluids. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a bentonite-based metal catalyst for viscosity reduction of heavy oil during drilling, its preparation method, and its application. The catalyst of this invention addresses both the requirements of the drilling fluid system and the viscosity reduction needs of heavy oil, possessing a "multi-purpose" attribute. This catalyst can efficiently catalyze the cracking of heavy oil during drilling, achieving efficient viscosity reduction. It can adapt to wellbore temperatures below 150°C and also effectively reduce the viscosity of heavy oil at high temperatures, while maintaining a sustained high-efficiency viscosity reduction effect. Furthermore, the catalyst of this invention has good compatibility with drilling fluids, avoiding negative impacts on the drilling fluid's wall-solidifying and cuttings-carrying capabilities. It can be integrated into water-based drilling fluids, maintaining or enhancing cuttings-carrying efficiency, rheological stability, and high-temperature adaptability.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling, comprising the following steps:

[0009] (1) Add the aqueous solution of the first transition metal salt to the aqueous solution of the first water-soluble ligand, and after the reaction, adjust the pH to obtain the solution of the first transition metal ligand; add the aqueous solution of the second transition metal salt to the aqueous solution of the second water-soluble ligand, and after the reaction, adjust the pH to obtain the solution of the second transition metal ligand;

[0010] (2) After hydrating the bentonite, add the hydrophilic monomer aqueous solution dropwise, mix thoroughly and evenly, then add the reducing agent aqueous solution and the initiator aqueous solution in sequence, and obtain the polymer-modified bentonite aqueous phase through reaction;

[0011] (3) The first transition metal ligand solution was added dropwise to the polymer-modified bentonite aqueous phase for reaction; then the second transition metal ligand solution was added, and after reaction, centrifugation, washing and drying were performed to obtain the bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling.

[0012] According to a preferred embodiment of the present invention, in step (1), the first transition metal salt and the second transition metal salt are each independently selected from one of manganese chloride, nickel chloride, copper chloride, ferric chloride or cobalt chloride; preferably, the first transition metal salt is ferric chloride, nickel chloride or copper chloride, and the second transition metal salt is manganese chloride or cobalt chloride.

[0013] According to a preferred embodiment of the present invention, in step (1), the first water-soluble ligand and the second water-soluble ligand are each independently selected from one of disodium ethylenediaminetetraacetate, citric acid, ethylenediamine di-o-phenylacetic acid, 8-hydroxyquinoline, ethylenediamine, N,N'-ethylbis(2-[2-hydroxyphenyl]glycine) or 2,2'-bipyridine; preferably, the first water-soluble ligand is disodium ethylenediaminetetraacetate, 2,2'-bipyridine or ethylenediamine, and the second water-soluble ligand is citric acid or N,N'-ethylbis(2-[2-hydroxyphenyl]glycine).

[0014] According to a preferred embodiment of the present invention, in step (1), the molar ratio of the first transition metal salt to the first water-soluble ligand is 0.45-0.9:1, preferably 0.9:1; and the molar ratio of the second transition metal salt to the second water-soluble ligand is 0.43-0.85:1, preferably 0.85:1.

[0015] According to a preferred embodiment of the present invention, in step (1), the concentration of the first transition metal salt aqueous solution is 0.045-0.09 mol / L; the concentration of the first water-soluble ligand aqueous solution is 0.1-0.5 mol / L; the molar concentration of the second transition metal salt aqueous solution is 0.032-0.064 mol / L; and the molar concentration of the second water-soluble ligand aqueous solution is 0.05-0.1 mol / L.

[0016] According to a preferred embodiment of the present invention, in step (1), the reaction temperature is room temperature and the reaction time is 40-60 min during the preparation of the first transition metal ligand solution and the second transition metal ligand solution, and the reaction is carried out under stirring conditions.

[0017] According to a preferred embodiment of the present invention, in step (1), after the first transition metal salt aqueous solution and the first water-soluble ligand aqueous solution react, the pH is adjusted to 5.5-6.5 to obtain the first transition metal ligand solution; after the second transition metal salt aqueous solution and the second water-soluble ligand aqueous solution react, the pH is adjusted to 6.0-6.8 to obtain the second transition metal ligand solution.

[0018] According to a preferred embodiment of the present invention, in step (2), the bentonite is sodium-based bentonite or calcium-based bentonite.

[0019] According to a preferred embodiment of the present invention, in step (2), the bentonite hydration method is as follows: add bentonite to water and stir at room temperature for 0.5-2 hours to hydrate; wherein the mass ratio of bentonite to water is 1:5-50.

[0020] According to a preferred embodiment of the present invention, in step (2), the hydrophilic monomer is one or a combination of two of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) or acrylamide. The mass concentration of the aqueous solution of the hydrophilic monomer is 0.067-0.17 g / mL.

[0021] According to a preferred embodiment of the present invention, in step (2), the mass ratio of bentonite to hydrophilic monomer is 1:0.05-1.25, preferably 1:0.125.

[0022] According to a preferred embodiment of the present invention, in step (2), the initiator is K2S2O8 or (NH4)2S2O8; the mass of the initiator is 8-75 wt% of the mass of the hydrophilic monomer, preferably 30 wt%; the reducing agent is NaHSO3 or Na2S2O5; the mass of the reducing agent is 8-75 wt% of the mass of the hydrophilic monomer, preferably 30 wt%; and the mass concentration of the initiator aqueous solution and the reducing agent aqueous solution is 10-50 g / L.

[0023] According to a preferred embodiment of the present invention, in step (2), the reaction temperature is 40-50°C, the reaction time is 2-4 hours, and the reaction is carried out under stirring conditions.

[0024] According to a preferred embodiment of the present invention, in step (3), the mass ratio of the transition metal salt in the first transition metal ligand solution to the bentonite in the polymer-modified bentonite aqueous phase is 1:4.13-82.6, preferably 1:41.3; the mass ratio of the transition metal salt in the second transition metal ligand solution to the bentonite in the polymer-modified bentonite aqueous phase is 1:15.87-317.5, preferably 1:158.7.

[0025] According to a preferred embodiment of the present invention, in step (3), the reaction temperature after adding the first transition metal ligand solution is room temperature, the reaction time is 40-60 min, the reaction is carried out under stirring conditions, and the pH is adjusted to 5-6 after the reaction; the reaction temperature after adding the second transition metal ligand solution is room temperature, the reaction time is 1-3 h, and the reaction is carried out under stirring conditions.

[0026] A bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is prepared by the above method.

[0027] The aforementioned application of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is used as a viscosity reducer in drilling fluid to achieve viscosity reduction in heavy oil.

[0028] According to a preferred embodiment of the present invention, the mass of the bentonite-based metal catalyst used for viscosity reduction of heavy oil during drilling is 0.1-1% of the mass of the drilling fluid, preferably 0.6%.

[0029] According to a preferred embodiment of the present invention, the applicable temperature range for the bentonite-based metal catalyst used for viscosity reduction of heavy oil during drilling is 130℃-300℃.

[0030] The technical features and beneficial effects of this invention are as follows:

[0031] 1. This invention uses bentonite, hydrophilic monomers, water-soluble ligands, and transition metal salts as the main raw materials. The raw materials are inexpensive and readily available, the preparation method is simple, and it is easy to carry out industrial production.

[0032] This invention involves fully hydrating and dispersing bentonite before introducing hydrophilic monomers. Controlled polymerization of these monomers is promoted by adding initiators and reducing agents, resulting in low-polymerization-degree hydrophilic polymers within the bentonite interlayers. This expands the interlayer distance of the bentonite while reducing the risk of migration and spillage of hydrophilic components during use. The ligands in this invention coordinate with transition metal ions through their hydroxyl, carboxyl, or amino groups. These ligands assist metal ions in forming complex precursors, maximizing the fixation of metal ions while enhancing their dispersion and stability, laying the foundation for the subsequent construction of catalytic active sites. First and second transition metal ligands are added to the interlayer-modified bentonite, and reactions are carried out to obtain bentonite-based metal catalysts for reducing viscosity in heavy oil during drilling. Bentonite, as a layered silicate mineral, possesses high specific surface area, excellent suspension stability, and high-temperature resistance, making it suitable as a catalyst carrier to improve the heat resistance and dispersibility of the system.

[0033] 2. This invention enhances the dispersion ability of the catalyst in the aqueous phase of drilling fluid by introducing hydrophilic monomers to hydrophilically functionalize the surface of the carrier. The metal catalytic center can be closer to the macromolecular structure of the oil phase (such as asphaltene and resin), which is conducive to the coordination or electron transfer of heteroatoms (such as S, N, O), thereby promoting the breaking of CC, CO, CS, CN bonds, generating smaller molecules and reducing the viscosity of heavy oil.

[0034] 3. This invention first constructs a stable first transition metal chelate layer on the surface of bentonite, creating a metal-enriched organic coordination environment on the particle surface. Then, a second transition metal chelate is introduced. Utilizing the difference in affinity between different coordination environments, the second transition metal chelate is preferentially distributed on the outer side of the first transition metal chelate layer, thereby achieving spatial hierarchical loading of the bimetallic compound. This allows the inner metal component (such as Fe) to... 3+ Chelates are stably anchored to the carrier surface in a strong coordination manner, serving as a metal reserve layer; the outer metal component (such as Mn) 2+ Chelates exist in a relatively weak coordination mode and preferentially participate in the reaction during use, thereby avoiding the instantaneous concentrated release of metal active sites and improving the system's sustained action capability.

[0035] 4. The catalyst of this invention also has the function of improving the performance of drilling fluid system. By introducing hydrophilic monomers into the bentonite interlayer and achieving controlled in-situ polymerization under the action of initiator, the hydrophilic components are stably fixed in the bentonite interlayer structure. This not only effectively expands the interlayer spacing and enhances hydration and dispersion capabilities, but also avoids the problems of easy migration and loss of monomers during use. Thus, while maintaining the structural stability of bentonite, it significantly improves its mud-making performance and resistance to environmental interference in drilling fluid system.

[0036] 5. The catalyst of this invention addresses both the requirements of drilling fluid systems and the viscosity reduction needs of heavy oil, possessing a "multi-purpose" attribute. In the wellbore, it can achieve in-situ viscosity reduction and improve fluidity, adapting to wellbore temperatures below 150°C while effectively reducing the viscosity of heavy oil at high temperatures, and maintaining a sustained and efficient viscosity reduction effect. The catalyst of this invention exhibits good compatibility with drilling fluids, avoiding negative impacts on the drilling fluid's wall-solidifying and cuttings-carrying capabilities. It can be integrated into water-based drilling fluids, maintaining or enhancing cuttings-carrying efficiency, rheological stability, and high-temperature adaptability. Compared to conventional viscosity reducers, the catalyst of this invention is more suitable for practical applications in offshore or complex wellbore environments. Attached Figure Description

[0037] Figure 1 These are the infrared spectra of the bentonite-based metal catalyst and sodium-based bentonite prepared in Example 1;

[0038] Figure 2 These are SEM images and mapping images of sodium bentonite;

[0039] Figure 3 These are SEM images and mapping diagrams of the bentonite-based metal catalyst prepared in Example 1. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other examples that are improved or modified by those skilled in the art are within the scope of protection of the present invention.

[0041] All raw materials used in the embodiments are conventional and commercially available; unless otherwise specified, the methods described are existing technologies.

[0042] Example 1

[0043] A method for preparing a bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling, comprising the following steps:

[0044] (1) The specific preparation method of the Mn(II)-CA and Fe(III)-EDTA complex is as follows:

[0045] Dissolve 0.664 g (2 mmol) of EDTA-2Na (disodium ethylenediaminetetraacetate) in 20 mL of deionized water. Stir at room temperature until completely dissolved. Dissolve 0.484 g (1.8 mmol) of FeCl3·6H2O in 20 mL of deionized water and stir until completely dissolved. Slowly add the FeCl3 solution dropwise to the EDTA solution and stir at room temperature for 50 min. Adjust the pH of the system to 5.5–6.5 with 0.1 M NaOH aqueous solution. The first transition metal ligand solution is obtained.

[0046] 0.144 g (0.75 mmol) of citric acid and 0.126 g (0.64 mmol) of MnCl₂·4H₂O were dissolved separately in 10 mL of deionized water and stirred at room temperature until dissolved to obtain citric acid solution and MnCl₂ solution. The MnCl₂ solution was slowly added dropwise to the citric acid solution and stirred at room temperature for 50 min. The pH was adjusted to 6.0–6.8 using 0.1 mol / L NaOH aqueous solution to stabilize the complex. A solution of the second transition metal ligand was obtained.

[0047] (2) The specific preparation method of AMPS modified sodium bentonite is as follows:

[0048] Add 20 g of dry sodium-based bentonite to 100 mL of deionized water; gently stir with a magnetic stirrer at room temperature for one hour to fully disperse and hydrate the bentonite; dissolve 2.5 g of AMPS in 15 mL of deionized water, and slowly add the monomer aqueous solution to the hydrated bentonite system under stirring, stirring for 30 min to allow the monomer to fully penetrate the interlayer. Dissolve 0.75 g of initiator K2S2O8 and 0.75 g of reducing agent NaHSO3 in 15 mL of deionized water respectively. First, slowly add the reducing agent aqueous solution to the bentonite-monomer mixture, stirring for 5 min, then add the initiator aqueous solution, and stir in a water bath at 45℃ for 3 h. After polymerization, allow the system to cool naturally to room temperature to obtain the polymer-modified bentonite aqueous phase.

[0049] (3) The specific preparation method of Mn(II)-CA-Fe(III)-EDTA@AMPS modified sodium-based bentonite is as follows:

[0050] The first transition metal ligand solution was slowly added dropwise to the polymer-modified bentonite aqueous phase, and stirred at room temperature for 50 min to allow Fe to precipitate. 3+ It is mainly fixed on the surface of bentonite or near the surface between layers. The pH is adjusted to 5-6 using a 0.1 M NaOH aqueous solution to prevent Fe... 3+ Hydrolysis precipitation; Fe has been fixed in the inner layer 3+A bentonite suspension was slowly added dropwise with a second transition metal ligand solution, and the mixture was gently stirred at room temperature for 2 h to allow Mn-CA to form a gradient release shell on the outer layer. The mixture was then centrifuged, washed with deionized water, and dried to obtain a bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling.

[0051] The infrared spectrum of the bentonite-based metal catalyst prepared in this embodiment is as follows: Figure 1 As shown, compared with unmodified bentonite, the modified samples showed differences at 1446, 1627, and 3427 cm⁻¹. -1 A distinct absorption peak appears at 1446 cm⁻¹. -1 The absorption peaks near the corresponding carboxyl groups indicate that the carboxyl groups in the citric acid and EDTA-modified components have been successfully introduced into the bentonite system, where the carboxyl groups may participate in metal coordination in a deprotonated form; 1627 cm⁻¹ -1 The absorption peak originates from the amide C=O in AMPS, indicating successful AMPS integration; 3427 cm⁻¹ -1 The enhancement of the broad peak indicates an increase in hydroxyl, amino, or hydrogen bonding association in the sample. These results demonstrate that the surface chemical environment of the modified bentonite has undergone significant changes, proving that components such as AMPS, citric acid, and EDTA have been successfully assembled onto the bentonite support.

[0052] Scanning electron microscope (SEM) images and mapping images of sodium-based bentonite and the bentonite-based metal catalyst prepared in this example are shown below. Figure 2 and 3 As shown in the image, scanning electron microscopy reveals that the surface of the unmodified bentonite matrix exhibits a lamellar structure, achieving thixotropic and rheological behavior through hydration. In a static state, the dispersed lamellar layers easily recombine to form a spatial network, giving the slurry a certain gel strength. The modified bentonite, however, has a thinner and more uniform lamellar structure, thus achieving better rheological properties. Mapping tests show that the unmodified bentonite contains no Mn or N elements and contains a very small amount of Fe; while the modified bentonite exhibits a significant increase in the content of Mn, N, and Fe elements, indicating the successful incorporation of Mn, Fe, and AMPS.

[0053] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is as follows:

[0054] 0.6g of bentonite-based metal catalyst for viscosity reduction of heavy oil during drilling was mixed with 100g of drilling fluid (composed of 3.25g bentonite, 0.25g caustic soda, 0.15g soda ash, 0.35g polymer filtration reducer, 0.4g polyanionic cellulose, 2.5g sulfonated phenolic resin, 2.5g asphalt anti-collapse agent, 1.5g calcium carbonate, and 89.1g water) and then placed in an aging tank. 30g of heavy oil (1932g / mol) was added, and the aging tank was placed in a roller heating furnace and rolled at 130℃ or 250℃ for 10 hours to obtain heat-treated drilling fluid. The viscosity reduction rate of the heavy oil in the fluid was then tested.

[0055] Example 2

[0056] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is as described in Example 1, except that: in step (2), the amount of bentonite used is 2g; other steps and conditions are the same as in Example 1.

[0057] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0058] Example 3

[0059] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is as described in Example 1, except that: in step (2), the amount of AMPS used is 1g; other steps and conditions are the same as in Example 1.

[0060] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0061] Example 4

[0062] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is as described in Example 1, except that: the amount of ferric chloride hexahydrate used in step (1) is 0.242 g (0.9 mmol); other steps and conditions are the same as in Example 1.

[0063] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0064] Example 5

[0065] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is as described in Example 1, except that in step (2), the amount of initiator K2S2O8 is changed to 0.2 g and the amount of reducing agent NaHSO3 is changed to 0.2 g; other steps and conditions are the same as in Example 1.

[0066] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0067] Example 6

[0068] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is as described in Example 1, except that: in step (1), the amount of manganese chloride tetrahydrate is 0.063 g (0.32 mmol); other steps and conditions are the same as in Example 1.

[0069] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0070] Example 7

[0071] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is described in Example 1, except that in step (2), sodium-based bentonite is replaced with the same mass of calcium-based bentonite; other steps and conditions are the same as in Example 1.

[0072] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0073] Example 8

[0074] A method for preparing a bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling is described in Example 1, except that in step (1), EDTA-2Na is replaced with the same molar amount of ethylenediamine during the preparation of the first transition metal ligand solution. Other steps and conditions are the same as in Example 1.

[0075] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0076] Example 9

[0077] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is described in Example 1, except that: in step (1), citric acid is replaced with the same molar amount of N,N'-ethylbis(2-[2-hydroxyphenyl]glycine during the preparation of the second transition metal ligand solution; other steps and conditions are the same as in Example 1.

[0078] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0079] Example 10

[0080] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is described in Example 1, except that in step (1), FeCl3·6H2O is replaced with the same molar amount of nickel chloride; other steps and conditions are the same as in Example 1.

[0081] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0082] Example 11

[0083] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is described in Example 1, except that in step (1), FeCl3·6H2O is replaced with the same molar amount of copper chloride; other steps and conditions are the same as in Example 1.

[0084] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0085] Example 12

[0086] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is described in Example 1, except that in step (1), MnCl2·4H2O is replaced with the same molar amount of cobalt chloride; other steps and conditions are the same as in Example 1.

[0087] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0088] Example 13

[0089] A method for preparing a bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling is described in Example 1, except that in step (1), EDTA-2Na is replaced with the same molar amount of 2,2'-bipyridine. Other steps and conditions are the same as in Example 1.

[0090] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0091] Example 14

[0092] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is as described in Example 1, except that in step (2), AMPS is replaced with the same mass of acrylamide; other steps and conditions are the same as in Example 1.

[0093] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0094] Comparative Example 1

[0095] A method for preparing a catalyst, comprising the steps of:

[0096] Step (1) is the same as step (1) in Example 1;

[0097] Step (2): Add 20 g of dry sodium-based bentonite to 100 mL of deionized water; use a magnetic stirrer to gently stir and hydrate at room temperature for one hour to fully disperse and hydrate the bentonite to obtain the bentonite aqueous phase.

[0098] Step (3): Slowly add the first transition metal ligand solution dropwise into the bentonite aqueous phase, stir at room temperature for 50 min, so that Fe3+ It is mainly fixed on the surface of bentonite or near the surface between layers. The pH is adjusted to 5-6 using a 0.1 M NaOH aqueous solution to prevent Fe... 3+ Hydrolysis precipitation; Fe has been fixed in the inner layer 3+ A bentonite suspension was slowly added dropwise with a second transition metal ligand solution, and the mixture was gently stirred at room temperature for 2 h to allow Mn-CA to form a gradient release shell on the outer layer. The mixture was then centrifuged, washed with deionized water, and dried to obtain the catalyst.

[0099] The catalyst application process is the same as in Example 1.

[0100] Comparative Example 2

[0101] A method for preparing a catalyst, as described in Example 1, except that: the preparation of the second transition metal ligand solution in step (1) is omitted; the second transition metal ligand solution is not added in step (3); the specific steps are as follows:

[0102] Step (1): The preparation method of the first transition metal ligand solution is the same as in Example 1;

[0103] Step (2) is the same as step (2) in Example 1;

[0104] Step (3): Slowly add the first transition metal ligand solution dropwise into the polymer-modified bentonite aqueous phase, and stir at room temperature for 50 min to allow Fe to precipitate. 3+ The catalyst is mainly fixed on the surface of bentonite or near the surface of the interlayer. The pH is adjusted to 5–6 using a 0.1 M NaOH aqueous solution, then centrifuged, washed with deionized water, and dried to obtain the catalyst.

[0105] The catalyst application process is the same as in Example 1.

[0106] Comparative Example 3

[0107] A method for preparing a catalyst, as described in Example 1, except that: the preparation of the first transition metal ligand solution in step (1) is omitted; the first transition metal ligand solution is not added in step (3); the specific steps are as follows:

[0108] Step (1): The preparation method of the second transition metal ligand solution is the same as in Example 1;

[0109] Step (2) is the same as step (2) in Example 1;

[0110] Step (3): Slowly add the second transition metal ligand solution to the bentonite suspension, gently stir at room temperature for 2 hours, then centrifuge, wash with deionized water, and dry to obtain the catalyst.

[0111] The catalyst application process is the same as in Example 1.

[0112] Comparative Example 4

[0113] A method for preparing a catalyst, as described in Example 1, except that in step (2), bentonite is replaced with kaolin of the same mass; other steps and conditions are the same as in Example 1.

[0114] The catalyst application process is the same as in Example 1.

[0115] Comparative Example 5

[0116] A method for preparing a bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling is as described in Example 1, except that in step (2), the step of hydrating 4.00 g of sodium bentonite for one hour in advance is removed, and 4.00 g of sodium bentonite is directly mixed with the hydrophilic monomer of AMPS; other steps and conditions are the same as in Example 1.

[0117] The application process of bentonite-based metal catalysts for viscosity reduction in heavy oil during drilling is the same as in Example 1.

[0118] Test case

[0119] The catalysts prepared in the examples and comparative examples were evaluated for performance as follows.

[0120] 1. Evaluation of viscosity-reducing properties of heavy oil

[0121] Evaluation of the viscosity-reducing performance of heavy oil is the most intuitive and effective method for testing catalyst performance. To intuitively evaluate the effect of the catalyst on the viscosity of heavy oil, the drilling fluids in the examples and comparative examples were placed at 50°C for 24 hours after heat treatment. The heavy oil and water were then separated by centrifugation. The viscosity of the remaining heavy oil was tested using a Hacker rheometer at room temperature to obtain the change in viscosity reduction rate and compare the viscosity-reducing effects.

[0122] Table 1. Viscosity reduction rate of each group of heavy oils after catalytic reaction at 130℃

[0123]

[0124] Table 2. Viscosity reduction rate of each group of heavy oils after catalytic reaction at 250℃

[0125]

[0126] Example 1, reacting at 130°C, achieved a viscosity reduction rate of 82.3%, demonstrating good performance. In comparison, Example 1, reacting at 250°C, achieved an even higher viscosity reduction rate of 99.3%. The comparison between Examples 1 at 130°C and 250°C illustrates that this invention can be used at both low and high temperatures, exhibiting good thermal stability, and its high-temperature performance is comparable to other high-temperature catalytic viscosity reducers on the market.

[0127] 2. Evaluation of heavy oil molecular weight

[0128] Evaluation of heavy oil molecular weight is the simplest and most direct method for testing the catalytic cracking effect of a catalyst. To visually evaluate the effect of the catalyst on the viscosity of heavy oil, the drilling fluids heat-treated at 130°C in the examples and comparative examples were placed at 50°C for 24 hours. After centrifugation, the heavy oil and water were separated. The weight-average molecular weight of the remaining heavy oil was measured using gel permeation chromatography to obtain the change in molecular weight before and after the reaction, and the catalytic cracking effect was compared.

[0129] Table 3. Molecular weight of each group of heavy oils after being placed at 50℃ for 24 hours.

[0130]

[0131] 3. Performance evaluation of the four components of heavy oil

[0132] Evaluation of the four components of heavy oil is a commonly used method to examine the internal changes of heavy oil after catalytic cracking. To visually evaluate the effect of the catalyst on the viscosity of heavy oil, the drilling fluids heat-treated at 130°C in the examples and comparative examples were placed at 50°C for 24 hours, and then heavy oil and water were separated by centrifugation. The content of the four components in the separated heavy oil was tested.

[0133] Table 4. Four components of each group of heavy oils after being placed at 50℃ for 24 hours.

[0134]

[0135] Comparing Examples 1 and 2, it was found that the viscosity reduction rate was lower. This is because bentonite has limited adsorption sites, and the reduced amount of bentonite resulted in insufficient catalyst loading, insufficient active sites, and poor catalytic effect, ultimately leading to a less significant viscosity reduction effect than in Example 1. The reduced amount of bentonite may have resulted in poor catalyst dispersibility and ineffective reaction, ultimately preventing a significant reduction in viscosity. This is also reflected in the comparison of molecular weight and four components in Examples 1 and 2.

[0136] Example 3 involved reducing the amount of AMPS. The reduction in AMPS led to a decrease in the number of hydroxyl groups in the catalyst, ultimately resulting in a decrease in hydration capacity. The modified catalyst also exhibited poor dispersibility, reducing its probability of contact with heavy oil.

[0137] Example 4: Reducing the amount of iron ions resulted in a decrease in the loading and active site density of Fe-EDTA. The reduced iron ions decreased the catalyst's catalytic efficiency, reduced its reaction efficiency with heavy oil, and affected its viscosity-reducing effect.

[0138] AMPS polymerization typically improves the apparent viscosity and low-shear proppant carrying capacity of drilling fluids. In Example 5, reducing the amount of initiator used in the polymerization reaction prevented AMPS from forming a sufficiently strong network structure, thus weakening its contact ability with heavy oil.

[0139] In Example 6, the reduced amount of manganese ions resulted in a decrease in the loading and active site density of Mn-CA. The lower manganese ion content led to a decrease in the catalyst's catalytic efficiency, reducing its reaction efficiency with heavy oil and affecting the viscosity-reducing effect.

[0140] In Example 7, calcium bentonite was used instead of sodium bentonite. Calcium bentonite generally has poorer swelling properties than sodium bentonite, which means that its surface area and adsorption capacity are lower, resulting in insufficient loading and uneven modification, which affects the catalytic effect on heavy oil.

[0141] In Example 8, after replacing EDTA with ethylenediamine in the complex between the metal and bentonite, the coordination environment of the metal ions in the material will change from strong polydentate chelation to weaker bidentate coordination. This usually weakens the metal fixation ability and the stability of the composite structure, reduces the carboxylate bridging effect, and causes the functional groups on the material surface to change from carboxyl group-dominated to amino group-dominated, thereby affecting the catalytic effect.

[0142] In Examples 10-12, the metal catalyst was changed from iron ions to other metal ions. Iron ions exhibit different activities in the catalytic reaction compared to copper, nickel, and cobalt ions. Iron generally shows better activity in catalytic viscosity reduction reactions, especially when complexed with organic molecules (such as EDTA). The other three metal ions have relatively weaker catalytic abilities, which may result in a less significant viscosity reduction effect compared to iron ions.

[0143] In Example 14, after replacing AMPS with acrylamide, the material can still form an organic modified layer on the surface or between layers of bentonite through polymerization reaction, and improve the viscosity and hydration stability of the system to a certain extent. However, due to the disappearance of sulfonic acid groups, the strong hydrophilicity and ionic hydration ability of the material usually decrease significantly, resulting in a weaker catalytic effect in complex drilling fluid environments than the AMPS modified system.

[0144] In Comparative Examples 2 and 3, the second transition metal ligand Mn-CA and the first transition metal ligand Fe-EDTA were not added, resulting in a single metal catalyst that could not form a heterojunction. Therefore, the electron transfer ability was weakened and the catalytic ability decreased.

[0145] In Comparative Example 4, the kaolin is a 1:1 type layered aluminosilicate mineral, with its layers tightly bound together by hydrogen bonds, lacking expandability and ion exchange capacity. Therefore, during the modification process, functional monomers and metal complex components have difficulty entering the interlayer structure, resulting in poor viscosity reduction performance.

[0146] In Comparative Example 5, failure to pre-hydrate for 1 hour resulted in insufficient dispersion of bentonite in the solution, affecting the loading of AMPS and metal complexes and weakening the catalytic effect.

[0147] 4. Evaluation in drilling fluid systems

[0148] The performance of water-based drilling fluids was determined according to the latest national standard GB / T 16783.1-2014, "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids". The prepared water-based drilling fluid was then aged at 200℃ for 16 hours, and its performance was again determined according to the aforementioned standard. The results are shown in Table 5.

[0149] The drilling fluid comprises the following components: 4000 mL of fresh water; 120 g of modified bentonite and sodium-based bentonite prepared in the examples or comparative examples (the mass ratio of modified bentonite to sodium-based bentonite is 1:1); 6 g of caustic soda; 12 g of soda ash; 9 g of polyanionic cellulose; 120 g of lignite resin; and barite weighted to a density of 2.0 g / cm³. 3 Meanwhile, the modified bentonite was replaced with an equal amount of sodium-based bentonite as a control group.

[0150] Table 5 Drilling fluid properties before aging

[0151]

[0152] Table 6. Drilling fluid properties after aging at 200℃

[0153]

[0154] A higher dynamic cutting force indicates a higher cuttings carrying efficiency. As shown in Tables 5 and 6, after 16 hours of aging at 200℃, the drilling fluid performance of this invention showed little overall change, indicating good high-temperature adaptability.

[0155] Comparative Example 1, due to the lack of hydrophilic monomer modification in the bentonite interlayer, did not show a significant improvement in dynamic shear force and filtration performance compared to drilling fluid without catalyst. Comparative Example 4, due to the absence of hydrophilic groups in the interlayer structure of the kaolinite carrier, had very poor hydration ability and could not exist uniformly and stably in water, leading to severe precipitation; therefore, its dynamic shear force and filtration performance parameters were extremely poor.

[0156] In Example 3, the reduction of AMPS led to a decrease in the number of hydroxyl groups in the catalyst, resulting in a decline in hydration capacity, rheological properties, and sand-carrying capacity. In Example 5, the reduction in the amount of initiator used in the polymerization reaction prevented AMPS from forming a network structure of sufficient strength, leading to a decrease in dynamic shear force.

[0157] 5. Durable performance test

[0158] 0.6g of the catalyst prepared in the examples or comparative examples was mixed with 100g of drilling fluid (composed of 3.25g bentonite, 0.25g caustic soda, 0.15g soda ash, 0.35g polymer filtration loss reducer, 0.4g polyanionic cellulose, 2.5g sulfonated phenolic resin, 2.5g asphalt anti-collapse agent, 1.5g calcium carbonate, and 89.1g water) and placed in an aging tank. 30g of heavy oil (1932g / mol) was added, and the aging tank was placed in a roller heating furnace and rolled at 130°C for 2 hours, 5 hours, 10 hours, and 20 hours respectively to obtain the heat-treated drilling fluid. Then, the viscosity reduction rate of the heavy oil in the fluid was tested.

[0159] Table 7 Durability Test Data

[0160]

[0161] The catalyst of this invention exhibits good durability, with Example 1 being the best. Examples 4 and 6 show limited viscosity reduction and extension effects due to reduced metal addition; this is because the bilayer metal complex prolongs the metal release time, providing a buffer against catalyst failure. Comparative Examples 2 and 3 suffer from decreased catalyst durability due to the loss of the second and first transition metal layers, respectively.

[0162] 6. Pulping performance test

[0163] Measure 50 mL of deionized water into a graduated cylinder, slowly add 2 g of the catalyst prepared in the examples and comparative examples, let stand at room temperature for 24 h, and read the volume corresponding to the height of the gel column formed after bentonite hydration in the graduated cylinder.

[0164] Table 8. Pulping Performance Test

[0165]

[0166] A higher expansion volume indicates stronger mud-forming performance in the drilling fluid system. Table 8 shows that the catalyst of this invention has significant hydration and expansion capabilities, significantly improving its mud-forming performance in the drilling fluid system. In Example 14, because acrylamide was used in the bentonite interlayer, the number of hydrophilic groups in the interlayer was less than that of AMPS, resulting in limited expansion volume. In Comparative Example 1, no hydrophilic monomers were added to the interlayer, resulting in virtually no increase in its water absorption and expansion volume. In Comparative Example 4, kaolinite was used as the support. Kaolinite, also a clay mineral, contains almost no hydrophilic functional groups such as hydroxyl groups that can participate in hydration in its interlayer. Its hydroxyl groups are mainly located on the inner surface of the crystal layers and are firmly bonded by hydrogen bonds; therefore, the interlayer does not possess significant hydration and expansion capabilities.

Claims

1. A method for preparing a bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling, characterized in that, Including the following steps: (1) Add the aqueous solution of the first transition metal salt to the aqueous solution of the first water-soluble ligand, and after the reaction, adjust the pH to obtain the solution of the first transition metal ligand; add the aqueous solution of the second transition metal salt to the aqueous solution of the second water-soluble ligand, and after the reaction, adjust the pH to obtain the solution of the second transition metal ligand; (2) After hydrating the bentonite, add the hydrophilic monomer aqueous solution dropwise, mix thoroughly and evenly, then add the reducing agent aqueous solution and the initiator aqueous solution in sequence, and obtain the polymer-modified bentonite aqueous phase through reaction; (3) The first transition metal ligand solution was added dropwise to the polymer-modified bentonite aqueous phase for reaction; then the second transition metal ligand solution was added, and after reaction, centrifugation, washing and drying were performed to obtain the bentonite-based metal catalyst for reducing viscosity of heavy oil during drilling.

2. The preparation method of the bentonite-based metal catalyst for viscosity reduction of heavy oil during drilling according to claim 1, characterized in that, Step (1) includes one or more of the following conditions: i. The first transition metal salt and the second transition metal salt are each independently selected from one of manganese chloride, nickel chloride, copper chloride, ferric chloride or cobalt chloride; ii. The first water-soluble ligand and the second water-soluble ligand are each independently selected from one of the following: disodium ethylenediaminetetraacetate, citric acid, ethylenediamine di-o-phenylacetic acid, 8-hydroxyquinoline, ethylenediamine, N,N'-ethylbis(2-[2-hydroxyphenyl]glycine or 2,2'-bipyridine; iii. The molar ratio of the first transition metal salt to the first water-soluble ligand is 0.45-0.9:1; the molar ratio of the second transition metal salt to the second water-soluble ligand is 0.43-0.85:1; iv. The concentration of the aqueous solution of the first transition metal salt is 0.045-0.09 mol / L; the concentration of the aqueous solution of the first water-soluble ligand is 0.1-0.5 mol / L; the molar concentration of the aqueous solution of the second transition metal salt is 0.032-0.064 mol / L; and the molar concentration of the aqueous solution of the second water-soluble ligand is 0.05-0.1 mol / L.

3. The preparation method of the bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling according to claim 2, characterized in that, Step (1) includes one or more of the following conditions: i. The first transition metal salt is ferric chloride, nickel chloride or copper chloride, and the second transition metal salt is manganese chloride or cobalt chloride; ii. The first water-soluble ligand is disodium ethylenediaminetetraacetate, 2,2'-bipyridine, or ethylenediamine, and the second water-soluble ligand is citric acid or N,N'-ethylbis(2-[2-hydroxyphenyl]glycine).

4. The preparation method of the bentonite-based metal catalyst for viscosity reduction of heavy oil during drilling according to claim 1, characterized in that, Step (1) includes one or more of the following conditions: i. In the preparation of the first transition metal ligand solution and the second transition metal ligand solution, the reaction temperature was room temperature, the reaction time was 40-60 min, and the reaction was carried out under stirring conditions. ii. After reacting the aqueous solution of the first transition metal salt and the aqueous solution of the first water-soluble ligand, the pH is adjusted to 5.5-6.5 to obtain the solution of the first transition metal ligand; After reacting the aqueous solution of the second transition metal salt and the aqueous solution of the second water-soluble ligand, the pH is adjusted to 6.0-6.8 to obtain the solution of the second transition metal ligand.

5. The preparation method of the bentonite-based metal catalyst for viscosity reduction of heavy oil during drilling according to claim 1, characterized in that, Step (2) includes one or more of the following conditions: i. The bentonite is sodium-based bentonite or calcium-based bentonite; ii. The hydration method of bentonite is as follows: Add bentonite to water and hydrate by stirring at room temperature for 0.5-2 hours; wherein, the mass ratio of bentonite to water is 1:5-50. iii. The hydrophilic monomer is one or a combination of two of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) or acrylamide; the mass concentration of the aqueous solution of the hydrophilic monomer is 0.067-0.17 g / mL; iv. The mass ratio of bentonite to hydrophilic monomer is 1:0.05-1.

25.

6. The method for preparing the bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling according to claim 1, characterized in that, Step (2) includes one or more of the following conditions: i. The initiator is K2S2O8 or (NH4)2S2O8; the mass of the initiator is 8-75 wt% of the mass of the hydrophilic monomer; the reducing agent is NaHSO3 or Na2S2O5; the mass of the reducing agent is 8-75 wt% of the mass of the hydrophilic monomer; the mass concentration of the initiator aqueous solution and the reducing agent aqueous solution is 10-50 g / L; ii. The reaction temperature is 40-50℃, the reaction time is 2-4h, and the reaction is carried out under stirring conditions.

7. The preparation method of the bentonite-based metal catalyst for viscosity reduction of heavy oil during drilling according to claim 1, characterized in that, Step (3) includes one or more of the following conditions: i. The mass ratio of the transition metal salt in the first transition metal ligand solution to the bentonite in the polymer-modified bentonite aqueous phase is 1:4.13-82.6; the mass ratio of the transition metal salt in the second transition metal ligand solution to the bentonite in the polymer-modified bentonite aqueous phase is 1:15.87-317.

5. ii. The reaction temperature after adding the first transition metal ligand solution was room temperature, the reaction time was 40-60 min, the reaction was carried out under stirring, and the pH was adjusted to 5-6 after the reaction; the reaction temperature after adding the second transition metal ligand solution was room temperature, the reaction time was 1-3 h, and the reaction was carried out under stirring.

8. A bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling, prepared by the method described in any one of claims 1-7.

9. The application of the bentonite-based metal catalyst for viscosity reduction in heavy oil during drilling as described in claim 8, characterized in that, It is used as a viscosity reducer in drilling fluids to reduce the viscosity of heavy oil.

10. The application according to claim 9, characterized in that, Includes one or more of the following conditions: i. The mass of the bentonite-based metal catalyst used for viscosity reduction in heavy oil during drilling is 0.1-1% of the drilling fluid mass; ii. The applicable temperature range for bentonite-based metal catalysts used for viscosity reduction in heavy oil during drilling is 130℃-300℃.

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