Rock self-watering inhibitor, its preparation method and application

Abstract

The application provides a rock self-water-absorption inhibitor and a preparation method and application thereof, and belongs to the technical field of well wall stabilization of drilling fluids. The preparation method of the rock self-water-absorption inhibitor comprises the following steps: (1) dissolving a cationic surfactant and urea in deionized water to obtain an aqueous phase; mixing cyclohexane and a co-surfactant and stirring uniformly to obtain an oil phase; adding the obtained aqueous phase into the oil phase and stirring and emulsifying to obtain an emulsion; (2) under stirring, adding tetraethyl silicate dropwise into the emulsion obtained in step (1); after the dropwise addition is completed, adding a silicone quaternary ammonium salt and a hydroxymethyl diphenyl silane and performing reaction; after the reaction is completed, centrifugation, washing and drying are performed to obtain the rock self-water-absorption inhibitor. The inhibitor can still be stably attached and continuously prevent water-based drilling fluid filtrate from invading in a high-temperature deep formation, and overcomes the problems of insufficient temperature resistance, easy falling off after adsorption and fast attenuation of inhibition effect of the existing rock self-water-absorption inhibitor in deep well wall stabilization.

Description

Technical Field

[0001] This invention relates to a rock self-absorption water inhibitor, its preparation method and application, and more particularly to a rock self-absorption water inhibitor with a dual mechanism of wettability reversal and covalent anchoring adsorption, its preparation method and application, belonging to the field of drilling fluid wellbore stabilization technology. Background Technology

[0002] Deep and ultra-deep oil and gas resources are abundant, and their safe and efficient development is of great significance. However, deep reservoirs are characterized by complex geological conditions, generally exhibiting typical characteristics of "ultra-high temperature, ultra-high pressure, and high ground stress." This extreme mechanical and thermal environment significantly increases the complexity and risk of drilling operations, placing higher demands on the control of wellbore stability.

[0003] Deep reservoirs are characterized by abundant bedding and micro / nanopores within the rock, along with strong hydrophilicity and significant capillary effects. During drilling, driven by both the positive pressure differential in the wellbore and the significant capillary suction of the reservoir rock, drilling fluid readily invades along microfractures and pore throats, triggering hydration and expansion of clay minerals. This leads to strong wedging at the fracture tips, causing bedding plane debonding, fracture propagation, and ultimately, serious engineering accidents such as wellbore spalling and collapse. Traditional methods often employ plugging agents or particulate bridging materials to mechanically seal formation microfractures and prevent drilling fluid loss. However, these plugging measures are often passive and cannot control the hydration initiation mechanism within the rock. As long as the rock retains its hydrophilic and wetting surface properties, the capillary water absorption effect persists, allowing drilling fluid to penetrate the local sealing structure and diffuse deeper, ultimately causing the plugging to fail.

[0004] Some studies have attempted to use surfactants to improve rock wettability and suppress its water absorption tendency. For example, Chinese patent document CN109207131A discloses a polymer gel formed by crosslinking of alkenyl monomers, which can block water in fractures under conventional well depth conditions. However, the mechanical strength of this gel system decreases significantly when the formation temperature exceeds 150°C, making it difficult to maintain long-term stable water control performance. Although the epoxy-based plugging agent disclosed in Chinese patent document CN109423263A has certain interfacial bonding properties, its cured product exhibits significant embrittlement above 200°C, making it highly susceptible to delamination, cracking, or even detachment after wellbore disturbance.

[0005] In addition, the wetting reversal agents currently used for water control generally have the following technical bottlenecks: (1) poor structural stability in high temperature (>200℃) environment, and easy degradation of surface film layer; (2) poor wetting reversal persistence, and the modified hydrophobic surface is prone to failure under high temperature fluid scouring, and hydrophilicity is restored; (3) failed to effectively block the self-absorption process in capillary channels, and there is still a risk of free water migrating to the deep layer.

[0006] Therefore, there is an urgent need to develop a rock self-absorption inhibitor that combines high-temperature stability, surface wettability reversal capability, and capillary permeation inhibition. This inhibitor can work synergistically from two dimensions: constructing a temperature-resistant and durable hydrophobic interface and cutting off the deep migration channels of free water. This will effectively inhibit rock self-absorption under high-temperature conditions and maintain wellbore stability during deep formation drilling. Summary of the Invention

[0007] To address the shortcomings of existing technologies, particularly the deficiencies of current rock self-absorption inhibition technologies such as weak adsorption in high-temperature deep formations, poor durability of wettability control, and insufficient suppression of capillary self-absorption effects, this invention provides a rock self-absorption inhibitor, its preparation method, and its application. The inhibitor of this invention is a rock self-absorption inhibitor chemically grafted with organosilicon quaternary ammonium salt and hydroxymethyldiphenylsilane nano-silica. Through the synergistic effect of the organosilicon quaternary ammonium salt and hydroxymethyldiphenylsilane modified layer on the surface of nano-SiO2 particles and the inorganic SiO2 matrix, on the one hand, it achieves a surface wettability reversal from hydrophilic to hydrophobic on the rock surface and effectively inhibits capillary self-absorption; on the other hand, it utilizes the residual active sites on the particle surface to undergo a condensation reaction with the silanol / aluminol hydroxyl groups on the formation rock surface under high-temperature downhole conditions to form a covalently anchored adsorption layer. This ensures that the inhibitor can maintain long-term stable adhesion in high-temperature deep formations and continuously prevent the intrusion of water-based drilling fluid filtrate, overcoming the problems of insufficient temperature resistance, easy adsorption detachment, and rapid decay of inhibition effect of existing rock self-absorption inhibitors in terms of deep wellbore stability.

[0008] The technical solution of the present invention is as follows:

[0009] A method for preparing a rock self-absorption water inhibitor includes the following steps:

[0010] (1) Dissolve the cationic surfactant and urea in deionized water to obtain an aqueous phase; mix cyclohexane with the co-surfactant and stir until homogeneous to obtain an oil phase; add the obtained aqueous phase to the oil phase and stir to emulsify to obtain an emulsion;

[0011] (2) Under stirring conditions, tetraethyl silicate (TEOS) was added dropwise to the emulsion obtained in step (1); after the addition was complete, organosilicon quaternary ammonium salt and hydroxymethyl diphenylsilane were added to carry out the reaction; after the reaction was completed, the rock self-absorption water inhibitor was obtained by centrifugation, washing and drying.

[0012] According to a preferred embodiment of the present invention, the cationic surfactant in step (1) is hexadecyltrimethylammonium bromide (CTAB) and / or hexadecylpyridine bromide (CPB).

[0013] According to a preferred embodiment of the present invention, the concentration of the cationic surfactant in the aqueous phase in step (1) is 0.02-0.05 g / mL.

[0014] According to a preferred embodiment of the present invention, the co-surfactant in step (1) is n-pentanol and / or n-octanol; the volume ratio of the co-surfactant to cyclohexane is 1:15-25.

[0015] According to a preferred embodiment of the present invention, the volume ratio of deionized water in the aqueous phase to cyclohexane in the oil phase in step (1) is 1:0.8-1.2.

[0016] According to a preferred embodiment of the present invention, the stirring speed in step (1) is 100-200 rpm and the stirring time is 20-40 min.

[0017] According to a preferred embodiment of the present invention, in step (2), the mass ratio of tetraethyl silicate (TEOS) to cationic surfactant is 1.2-1.8:1; the mass ratio of tetraethyl silicate (TEOS) to urea is 2-4:1; and the dropping time of tetraethyl silicate (TEOS) is 5-10 min.

[0018] According to a preferred embodiment of the present invention, the organosilicon quaternary ammonium salt in step (2) is one or both of dimethyloctadecyl(3-trimethoxysilylpropyl)ammonium chloride (CAS No.: 27668-52-6) and dimethyltetradecyl(3-trimethoxysilylpropyl)ammonium chloride (CAS No.: 41591-87-1); the mass ratio of the organosilicon quaternary ammonium salt to tetraethyl silicate (TEOS) is 0.5-0.8:1. The organosilicon quaternary ammonium salt used has a hydrolyzable silane group, wherein the trimethoxysilylpropyl group can condense with the silanol groups on the surface of the nano-silica particles to form Si-O-Si bonds, which are directionally grafted onto the particle surface, while retaining a certain density of uncondensed silane reaction sites on the particle surface.

[0019] According to a preferred embodiment of the present invention, the mass ratio of hydroxymethyl diphenylsilane to tetraethyl silicate (TEOS) in step (2) is 0.05-0.1:1.

[0020] According to a preferred embodiment of the present invention, the reaction temperature in step (2) is 110-130°C, the reaction time is 2-6 hours, and the stirring speed during the reaction process is 300-800 rpm.

[0021] According to a preferred embodiment of the present invention, the centrifugation speed in step (2) is 10000-12000 rpm and the centrifugation time is 5-15 min; the washing is to wash the solid obtained by centrifugation with ethyl acetate, anhydrous ethanol and deionized water in sequence; the drying is to dry at 60-100℃ for 12-30 h.

[0022] The present invention also provides a rock self-water absorption inhibitor, which is prepared by the above preparation method. The rock self-water absorption inhibitor is an organosilicon quaternary ammonium salt and hydroxymethyl diphenylsilane grafted nano silica inhibitor. The inhibitor particles have uniform particle size, regular morphology, and are rich in hydrophobic long carbon chains and diphenyl groups and positive charge centers on the surface, and retain a certain number of uncondensed silane reaction sites.

[0023] According to the present invention, the application of the above-mentioned rock self-absorption inhibitor in water-based drilling fluid is used to suppress the self-absorption effect of shale, dolomite and other hydrophilic rocks in deep and ultra-deep formations, stabilize the wellbore in complex and fractured formations, wherein the deep and ultra-deep formations are ≥8000m deep; and are suitable for wellbore protection in formations with high salinity, high mineralization and complex chemical environments.

[0024] In this invention, room temperature has a commonly known meaning, referring to 25±5℃.

[0025] The technical features and beneficial effects of this invention are as follows:

[0026] 1. This invention uses a cationic surfactant as a cationic template agent and a co-surfactant as an auxiliary agent. Under the action of urea, an oil / water bicontinuous phase microemulsion is constructed in a cyclohexane / water system. Tetraethyl silicate (TEOS) is used as a silicon source to hydrolyze and condense in a confined micro-region to generate nano-SiO2 particles with uniform particle size and rich hydroxyl groups on the surface. The cationic surfactant acts as a cationic template agent in the system to regulate the morphology of the nano-silica particles. Urea acts as a slow-release alkali source, decomposing and releasing ammonia under heating conditions to provide a weakly alkaline environment to promote the hydrolysis and condensation of TEOS. Subsequently, organosilicon quaternary ammonium salt and hydroxymethyl diphenylsilane modifier are added during the generation of nano-silica. The organosilicon quaternary ammonium salt has good thermal stability with Si-O bond as the backbone. The long-chain alkyl group can impart significant hydrophobicity to the particle surface, and the quaternary ammonium cation center can provide a stable positive charge, which is beneficial to the dispersion of particles in the drilling fluid system and the directional adsorption on the negatively charged rock surface. The benzene ring structure in hydroxymethyldiphenylsilane has high rigidity and low rotational freedom, making it less prone to conformational relaxation compared to aliphatic chains, which is beneficial for improving the thermal stability of the inhibitor. This organosilicon quaternary ammonium salt participates in the simultaneous hydrolysis and condensation of tetraethyl silicate and is directionally grafted onto the surface of SiO2 particles. The hydroxyl groups on the surface of hydroxymethyldiphenylsilane undergo a condensation reaction with the hydroxyl groups on the surface of silica, thus preparing a rock self-absorption inhibitor. The particle surface is enriched with hydrophobic long chains, hydrophobic diphenyl groups, and quaternary ammonium cationic groups, while still retaining a certain density of uncondensed silane reaction sites, which can be used for subsequent condensation with hydroxyl groups on the rock surface to achieve covalent anchoring. This invention, through the synergistic effect of emulsion-confined synthesis and surface grafting of organosilicon quaternary ammonium salt and hydroxymethyldiphenylsilane, yields rock self-absorption inhibitor particles with uniform particle size, regular morphology, and controllable surface functional group distribution. These particles can form a continuous hydrophobic layer in crack and microporous systems, providing a stable interfacial basis for rock self-absorption inhibition.

[0027] 2. This invention achieves efficient and sustained suppression of the self-absorption behavior of rocks in high-temperature deep formations through a synergistic mechanism of "surface wettability reversal and covalent anchoring adsorption". On the one hand, the hydrophobic groups and quaternary ammonium cation groups enriched on the particle surface can adsorb onto the rock surface, changing the wettability of the rock surface from hydrophilic to hydrophobic, significantly increasing the water contact angle of the rock surface, and fundamentally weakening the capillary self-absorption driving force. On the other hand, nano-sized SiO2 particles, through particle size matching and space filling, can form physical barriers to the aqueous phase channels in rock microcracks and pores, suppressing the capillary self-absorption effect. At the same time, a certain density of uncondensed silane reaction sites retained on the particle surface can undergo condensation reactions with Si-OH / Al-OH on the rock surface under high-temperature downhole conditions to form Si-O-Si or Si-O-Al covalent bonds, realizing the in-situ chemical anchoring adsorption of the inhibitor at the rock interface, and greatly improving the erosion resistance of the hydrophobic layer. Therefore, the rock self-absorption water inhibitor of the present invention not only maintains excellent water suppression performance under high temperature formation conditions, but also significantly reduces the risk of mechanical strength degradation caused by filtrate intrusion, effectively improving the long-term stability of the wellbore.

[0028] 3. The rock self-absorption water inhibitor of this invention has strong construction adaptability and can be directly mixed with conventional water-based drilling fluid systems without additional cross-linking curing or complex on-site chemical reactions, simplifying the on-site construction process. The organosilicon quaternary ammonium salt grafting significantly improves the chemical bonding and electro-adsorption capacity between nano-SiO2 and the rock interface, giving the inhibitor good shear stability downhole. Simultaneously, the SiO2 framework system exhibits excellent chemical stability and resistance to acid and alkali corrosion, making it suitable for wellbore protection in high-salt, high-mineralization, and complex chemical environments. This rock self-absorption water inhibitor combines high-temperature stability, hydrophobicity, and engineering-friendly characteristics, making it suitable for wellbore stability control in deep and ultra-deep formations with strong hydrophilicity and significant capillary self-absorption effects. Attached Figure Description

[0029] Figure 1 The infrared spectrum of the rock self-absorption water inhibitor prepared in Example 1.

[0030] Figure 2 The image shows a scanning electron microscope (SEM) image of the rock self-absorption water inhibitor prepared in Example 1. Detailed Implementation

[0031] The present invention will be further described below through specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods described in the embodiments are conventional methods; unless otherwise specified, the reagents and raw materials used can be obtained commercially.

[0032] Example 1

[0033] A method for preparing a rock self-absorption water inhibitor includes the following steps:

[0034] (1) Add 1.0 g cetyltrimethylammonium bromide (CTAB) and 0.6 g urea to 30 mL of deionized water and stir until completely dissolved to obtain an aqueous phase; mix 30 mL of cyclohexane with 1.5 mL of n-pentanol and stir magnetically to obtain an oil phase; add the above aqueous phase to the oil phase and stir for 30 min at room temperature and stirring speed of 100 rpm to form an emulsion.

[0035] (2) Under stirring at 500 rpm, 1.4 g of tetraethyl silicate (TEOS) was slowly added dropwise to the emulsion obtained in step (1) for 10 min. After the addition was completed, 0.89 g of dimethyloctadecyl(3-trimethoxysilylpropyl)ammonium chloride and 0.1 g of hydroxymethyldiphenylsilane were added to the system and reacted at 120 °C and stirring at 500 rpm for 4 h. After the reaction was completed, the mixture was naturally cooled to room temperature and centrifuged (11000 rpm, 10 min). The solid obtained by centrifugation was washed once each with ethyl acetate, anhydrous ethanol and deionized water to remove residual surfactants, small molecule salts and unreacted precursors. Then it was dried at 80 °C for 24 h to obtain rock self-water inhibitor A1.

[0036] The infrared spectrum of the rock self-absorption water inhibitor prepared in this embodiment is as follows: Figure 1 As shown, by Figure 1 It can be known that 3433cm -1 The broad peak is attributed to the stretching vibrations of Si-OH and adsorbed water, indicating the presence of silanol groups and residual moisture on the material surface; 2926 cm⁻¹ -1 With 2852cm -1 The asymmetric and symmetric stretching vibrations corresponding to aliphatic CH bonds, respectively, demonstrate that the introduction of long-chain alkyl organic quaternary ammonium salt groups into the material endows the rock self-water-absorbing inhibitor with hydrophobic properties; 3051cm -1 The weak aromatic CH stretching vibration peak at 1431 cm⁻¹, combined with the 1431 cm⁻¹ peak. -1 The characteristic Si-Ph framework vibrational peaks confirmed the successful grafting of hydroxymethyldiphenylsilane onto the surface of nano-silica particles; 1651 cm⁻¹ -1 The weak absorption may originate from the HOH bending vibration of adsorbed water, or it may be related to residual urea hydrolysis products; 1078 cm -1 It is a typical Si-O-Si asymmetric stretching vibration, 804 cm⁻¹ -1 These characteristic peaks are attributed to the symmetrical bending vibration of Si-O-Si. These characteristic peaks together prove that a stable silica network structure has been formed in the material, and dimethyloctadecyl(3-trimethoxysilylpropyl)ammonium chloride and hydroxymethyldiphenylsilane are simultaneously grafted onto the silica surface.

[0037] The scanning electron microscope image of the rock self-absorption water inhibitor prepared in this embodiment is shown below. Figure 2 As shown, by Figure 2 It can be seen that the obtained rock self-absorption water inhibitor is spherical with a rough surface and a particle size between 213-350 nm.

[0038] Example 2

[0039] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that the amount of deionized water added in step (1) is adjusted from 30 mL to 35 mL to obtain rock self-absorption water inhibitor A2.

[0040] Example 3

[0041] A method for preparing a rock self-absorption water inhibitor is described in Example 1, except that the amount of hexadecyltrimethylammonium bromide (CTAB) added in step (1) is adjusted from 1.0g to 0.8g to obtain rock self-absorption water inhibitor A3.

[0042] Example 4

[0043] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that the amount of urea added in step (1) is adjusted from 0.6g to 0.4g to obtain rock self-absorption water inhibitor A4.

[0044] Example 5

[0045] A method for preparing a rock self-absorption water inhibitor is described in Example 1, except that the amount of n-pentanol added in step (1) is adjusted from 1.5 mL to 2.0 mL to obtain rock self-absorption water inhibitor A5.

[0046] Example 6

[0047] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that: in step (2), the amount of dimethyloctadecyl(3-trimethoxysilylpropyl)ammonium chloride added is 0.7g, and rock self-absorption water inhibitor A6 is obtained.

[0048] Example 7

[0049] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that the co-surfactant in step (1) is n-octanol, and a rock self-absorption water inhibitor A7 is obtained.

[0050] Example 8

[0051] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that in step (2), the organosilicon quaternary ammonium salt is replaced by dimethyloctadecyl(3-trimethoxysilylpropyl)ammonium chloride with dimethyltetradecyl(3-trimethoxysilylpropyl)ammonium chloride, and rock self-absorption water inhibitor A8 is obtained.

[0052] Example 9

[0053] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that in step (1), hexadecyltrimethylammonium bromide is replaced with an equal mass of hexadecylpyridine bromide to obtain rock self-absorption water inhibitor A9.

[0054] Example 10

[0055] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that the mass of hydroxymethyldiphenylsilane in step (2) is 0.14 g, and rock self-absorption water inhibitor A10 is obtained.

[0056] Comparative Example 1

[0057] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that: in step (2), the organosilicon quaternary ammonium salt dimethyloctadecyl[3-trimethoxysilylpropyl]ammonium chloride is not added, and rock self-absorption water inhibitor B1 is obtained.

[0058] Comparative Example 2

[0059] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that the reaction temperature in step (2) is room temperature, and rock self-absorption water inhibitor B2 is obtained.

[0060] Comparative Example 3

[0061] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that urea is not added in step (1), and rock self-absorption water inhibitor B3 is obtained.

[0062] Comparative Example 4

[0063] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that cetyltrimethylammonium bromide is not added in step (1), and rock self-absorption water inhibitor B4 is obtained.

[0064] Comparative Example 5

[0065] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that: in step (1), no co-surfactant n-pentanol is added to the oil phase to obtain rock self-absorption water inhibitor B5.

[0066] Comparative Example 6

[0067] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that: in step (2), hydroxymethyldiphenylsilane is not added, and rock self-absorption water inhibitor B6 is obtained.

[0068] Comparative Example 7

[0069] A method for preparing a rock self-absorption water inhibitor is as described in Example 1, except that in step (2), tetraethyl silicate (TEOS) is not added dropwise, but 0.4g of commercially available 300nm silica particles are directly added to the emulsion obtained in step (1) to obtain rock self-absorption water inhibitor D7.

[0070] Experimental Example 1

[0071] The following performance evaluations were performed on the rock self-absorption inhibitors prepared in the examples and comparative examples:

[0072] (1) Evaluation of the compatibility between rock self-absorption water inhibitor and drilling fluid

[0073] Preparation of base slurry: Slowly add 16g of bentonite to 400mL of distilled water while stirring, and then hydrate at room temperature for 24h to prepare bentonite base slurry.

[0074] Sample preparation: Take 400 mL of base slurry and add 8 g of the example and comparative products respectively. Stir at 3000 r / min for 20 min. The percentage of sample mass to base slurry volume is 2%.

[0075] Performance testing: The filtration loss at normal temperature and pressure, the filtration loss at high temperature and high pressure under 220℃ and 3.5MPa, and the rheological parameters (apparent viscosity, plastic viscosity, dynamic shear force) and filtration loss of the base slurry after aging at 220℃ for 16h were tested according to GB / T29170-2012, Petroleum and Gas Industry Drilling Fluid Laboratory Test. The experimental results are shown in Table 1.

[0076] Table 1. Rheological filtration properties of drilling fluid after adding rock self-absorption inhibitor.

[0077]

[0078] As shown in Table 1, the apparent viscosity, plastic viscosity, and dynamic shear force of the drilling fluid system did not change significantly compared to the base slurry after the addition of the rock self-absorption inhibitor, indicating that it had little impact on the rheological properties of the drilling fluid and maintained good fluidity and rock-carrying capacity. The filtration loss in each embodiment was significantly lower than that in the base slurry and the comparative example before and after aging, demonstrating a certain filtration loss reduction effect. This performance improvement is mainly attributed to the positively charged nature of the rock self-absorption inhibitor molecules in water, which allows them to effectively adsorb onto the surface of clay particles and form stable silicon-oxygen covalent bonds with the hydroxyl groups on the wellbore rock surface. This inhibits hydration diffusion on the rock surface, slows filtrate infiltration, and participates in mud cake formation, effectively reducing filtration loss. In conclusion, the rock self-absorption inhibitor can effectively reduce filtration loss without affecting rheological properties, thereby maintaining wellbore stability.

[0079] (2) Evaluation of electrical properties

[0080] The samples from the examples and comparative examples were added to deionized water and ultrasonically dispersed for 15 min to obtain an aqueous dispersion with a concentration of 0.1 wt%. The above dispersions were then injected into the sample cell, which was placed in the instrument. The measurement temperature was set to 25°C, and the measurement was repeated three times to obtain the average zeta potential. The experimental results are shown in Table 2.

[0081] Table 2. Electrostatic properties of rock self-absorption water inhibitors

[0082]

[0083] As shown in Table 2, the inhibitors prepared in the examples all exhibited significant positive charge, ranging from +23.0 mV to +34.0 mV, with Example 1 reaching the highest value of +34.0 mV. This indicates that the introduction of cationic surfactants and organosilicon quaternary ammonium salts formed a dense positively charged layer on the particle surface, resulting in strong electrostatic adsorption between the inhibitor and the rock surface. Comparative Example B6, due to the absence of neutral hydroxymethyldiphenylsilane, reduced competition and shielding for charged sites, resulting in a slightly higher Zeta potential of +35.5 mV. However, Comparative Example B7, using commercially available silica particles, had a significantly reduced number of active sites due to the extensive condensation of surface hydroxyl groups during processing, making it difficult to graft the organosilicon quaternary ammonium salt, thus limiting the grafting rate and causing a substantial decrease in the Zeta potential to +12.5 mV. In summary, Comparative Examples B1-B7 exhibited poor adsorption performance due to their low surface charge density or incomplete functional components.

[0084] (3) Evaluation of the ability of rocks to suppress self-absorption of water

[0085] Aqueous dispersions of rock self-absorption water inhibitors with a mass fraction of 2% were prepared for both the example and comparative examples. Cleaned and dried core sections were immersed in their respective dispersions, ensuring complete submersion. The immersed core sections, along with the dispersions, were then placed in an aging tank and aged at 220°C for 16 hours to simulate the interaction between the inhibitor and the rock surface under high-temperature formation conditions. After aging, the core sections were cooled to room temperature, removed, and rinsed with deionized water to remove any unadsorbed residual inhibitor. They were then dried in an oven at 105°C until constant weight, ensuring no free moisture remained on the surface. The dried core sections were then used for contact angle testing. The treated core sections were placed on the sample platform of a contact angle measuring instrument. A single drop of 5 μL of deionized water was slowly added to the surface of the core section using a microsyringe. The contact angle image formed by the water droplet and the core section surface was recorded using the contact angle measuring instrument, and the angle was automatically calculated. Each core sample was tested three times at different locations, and the average contact angle was taken as the final result to evaluate the hydrophobic properties of the rock surface after treatment with the rock self-absorption inhibitor. The experimental results are shown in Table 3.

[0086] Rock samples were cut into core columns with a diameter of 25 mm and a height of 50 mm. The core columns were dried in an oven at 105 °C until constant weight, and the initial core column mass was recorded. The core columns were suspended and fixed using a thin thread. A beaker containing a 2% (by mass) aqueous dispersion of the self-absorption water inhibitor for the example and comparative examples was placed below the core column. The suspension height of the core column was adjusted so that the surface of the core column was slightly immersed in the aqueous dispersion. After 24 hours, the core column was removed, weighed, and the total mass of the core column was recorded. The difference between the total mass after water absorption and the initial core column mass is the mass of water absorbed by the core column. The experimental results are shown in Table 3.

[0087] Glass capillaries with an inner diameter of 0.3 mm were used. First, the capillaries were washed with deionized water and then dried at 90°C for 24 hours. Subsequently, the dried capillaries were immersed in an aqueous dispersion of the self-absorbing water inhibitor from the examples and comparative examples (2% by mass), and aged at 220°C for 16 hours to allow the inhibitor to be fully adsorbed onto the inner wall of the capillaries. After aging, the capillaries were removed, purged with high-pressure nitrogen to remove any unadsorbed dispersion residue, and dried again. The treated capillaries were then vertically inserted into a container of methylene blue-stained deionized water, allowed to stand for 5 minutes, and the liquid level inside the capillaries was recorded. For ease of comparison, the free liquid level outside the capillaries was defined as 10 mm and defined as the baseline zero liquid level point. A liquid level above this free liquid level was recorded as a positive value, and a liquid level below this free liquid level was recorded as a negative value. The experimental results are shown in Table 3.

[0088] Table 3 Evaluation of Self-Absorption Inhibition Performance

[0089]

[0090] The contact angle test results showed that the core slices treated in the examples all exhibited significant hydrophobicity, with contact angles generally above 114.5°. Example 1 achieved 132.8°, demonstrating the best hydrophobic effect. This indicates that the prepared rock self-water-absorbing inhibitor can effectively adsorb onto the surface of rock or clay particles, significantly improving the hydrophobicity of the rock surface by forming stable silicon-oxygen covalent bonds with surface hydroxyl groups, thereby inhibiting the migration of water molecules into the rock interior. Other examples also improved the contact angle to varying degrees. In contrast, the contact angles of Comparative Examples 1-5 were lower, ranging from 28.1° to 55.2°, indicating significant surface hydrophilicity. Specifically, Comparative Example 1 did not add the hydrophobic modifier organosilicon quaternary ammonium salt, resulting in a contact angle of only 28.1°. Comparative Example 2 did not undergo a high-temperature polycondensation reaction, leading to incomplete hydrolysis of the TEOS organosilicon quaternary ammonium salt and the failure to form a hydrophobic layer. Comparative Example 3 had an incomplete particle structure, preventing stable adsorption. Comparative Examples 4-5 lacked a key surfactant, resulting in unstable emulsion structures and poor hydrophobic effects. Although Comparative Example 6 exhibits a larger contact angle (110.5°) due to the retention of the organosilicon quaternary ammonium salt, its hydrophobic effect is weaker than that of the examples due to the lack of rigid phenyl groups. Comparative Example 7, with a contact angle of 92.5°, shows insufficient hydrophobicity because it uses commercially available silica particles with fewer surface-active hydroxyl groups, hindering the effective grafting of the hydrophobic modifier. In summary, the examples achieve significant hydrophobic modification of the rock surface through structural optimization, effectively suppressing the rock's self-water absorption behavior. In contrast, the comparative examples, lacking key reaction conditions or components, exhibit poor surface hydrophobicity and insufficient self-water absorption suppression.

[0091] After adding the rock self-absorption inhibitor prepared in Examples 1-10, the water absorption mass of the rock core decreased significantly. For example, in Example 1, it was only 0.5142 g, far lower than the 2.1714 g in Comparative Example 1, indicating that the inhibitor can effectively reduce the water absorption capacity of the rock. Rock surfaces are usually negatively charged, while this rock self-absorption inhibitor contains a quaternary ammonium salt structure, which is positively charged and can firmly bind to the rock surface through electrostatic adsorption. Furthermore, the trimethoxysilylpropyl group contained in the inhibitor can undergo a condensation reaction with the hydroxyl groups on the rock surface after high-temperature hydrolysis, forming Si-O-Si covalent bonds. The synergistic effect of electrostatic adsorption and covalent bonds constructs a dense and stable hydrophobic barrier on the rock surface, effectively reducing water penetration.

[0092] Regarding the capillary rise height, the heights in Examples 1-10 were all below the free liquid surface (10 mm), indicating that water could not enter the capillaries treated with the rock self-absorption inhibitor. In contrast, the rise heights in Comparative Examples 1-5 were all positive, such as 52 mm in Comparative Example 1 and 50 mm in Comparative Example 4, indicating that water easily entered the rock interior through capillary action, exhibiting a strong self-absorption phenomenon. Therefore, it is evident that the inhibitor in these examples can significantly reduce the capillary self-absorption effect of rocks.

[0093] In summary, a larger contact angle indicates poorer wettability of water on the rock and stronger hydrophobicity of the rock surface, leading to a decrease in water absorption mass and capillary rise height. Taking Example 1 as an example, its contact angle is 132.8°, exhibiting excellent hydrophobic properties, with a water absorption mass of 0.5142g and a capillary rise height of -9.2mm. The presence of the rock self-absorption inhibitor significantly inhibited water penetration into the rock pores. In contrast, Comparative Example 1 has a contact angle of only 28.1°, strong water wettability on the rock surface, a water absorption mass of 2.2214g, and a capillary rise height of 52mm, exhibiting typical capillary self-absorption behavior. The capillary effect is the core driving mechanism of rock self-absorption. When the liquid has good wettability on the rock surface, capillary force can drive water to continuously penetrate into pores and micro-fractures, leading to clay mineral expansion, structural damage, and a decrease in interparticle bonding, ultimately inducing wellbore instability. The rock self-absorption inhibitor weakens the rock self-absorption caused by capillary force by increasing the surface contact angle. The cationic groups in the rock self-absorption inhibitor can be adsorbed onto the negatively charged rock surface through electrostatic interaction. Some of the unhydrolyzed trimethoxysilylpropyl groups can also condense with the hydroxyl groups on the rock surface to form Si-O-Si covalent bonds, forming a dense and stable hydrophobic layer. This effectively weakens capillary-driven water infiltration, effectively reduces the risk of wellbore instability caused by rock water absorption, and maintains wellbore stability.

Claims

1. A method for preparing a rock self-absorption water inhibitor, characterized in that, The steps include the following: (1) Dissolve the cationic surfactant and urea in deionized water to obtain an aqueous phase; mix cyclohexane and co-surfactant and stir evenly to obtain an oil phase; add the obtained aqueous phase to the oil phase and stir to emulsify to obtain an emulsion; the cationic surfactant is hexadecyltrimethylammonium bromide and / or hexadecylpyridine bromide; the co-surfactant is n-pentanol and / or n-octanol; the volume ratio of the co-surfactant to cyclohexane is 1:15-25; the volume ratio of deionized water in the aqueous phase to cyclohexane in the oil phase is 1:0.8-1.2; the concentration of the cationic surfactant in the aqueous phase is 0.02-0.05 g / mL; (2) Under stirring conditions, tetraethyl silicate is added dropwise to the emulsion obtained in step (1); after the addition is complete, organosilicon quaternary ammonium salt and hydroxymethyl diphenylsilane are added to carry out the reaction; after the reaction is completed, the rock self-water inhibitor is obtained by centrifugation, washing and drying; the mass ratio of tetraethyl silicate to cationic surfactant is 1.2-1.8:1; the mass ratio of tetraethyl silicate to urea is 2-4:1; the organosilicon quaternary ammonium salt is one or two of dimethyloctadecyl(3-trimethoxysilylpropyl)ammonium chloride and dimethyltetradecyl(3-trimethoxysilylpropyl)ammonium chloride; the mass ratio of organosilicon quaternary ammonium salt to tetraethyl silicate is 0.5-0.8:1; the mass ratio of hydroxymethyl diphenylsilane to tetraethyl silicate is 0.05-0.1:1; the reaction temperature is 110-130℃.

2. The method for preparing the rock self-absorption water inhibitor according to claim 1, characterized in that, The stirring speed in step (1) is 100-200 rpm, and the stirring time is 20-40 min.

3. The method for preparing the rock self-absorption water inhibitor according to claim 1, characterized in that, The addition time of tetraethyl silicate in step (2) is 5-10 min.

4. The method for preparing the rock self-absorption water inhibitor according to claim 1, characterized in that, The reaction time in step (2) is 2-6 hours; the stirring speed during the reaction process is 300-800 rpm.

5. The method for preparing the rock self-absorption water inhibitor according to claim 1, characterized in that, In step (2), the centrifugation speed is 10000-12000 rpm and the centrifugation time is 5-15 min; the washing is to wash the solid obtained by centrifugation with ethyl acetate, anhydrous ethanol and deionized water in sequence; the drying is to dry at 60-100℃ for 12-30 h.

6. A rock self-absorption water inhibitor, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. The application of the rock self-absorption water inhibitor according to claim 6 in water-based drilling fluid, characterized in that, Used to suppress the self-absorption effect of shale and dolomite in deep and ultra-deep formations, and to stabilize the wellbore wall of the formation, wherein the deep and ultra-deep formations are at a depth ≥8000m.

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