Preparation and Performance Evaluation of Small-Molecule Ammonium as a Shale Hydration Inhibitor

Abstract

In this paper, small-molecule quaternary ammonium salts were synthesized by N-alkylation to inhibit hydration swelling and hydration dispersion. The prepared small-molecule quaternary ammonium salt was characterized by Fourier transform infrared (FTIR) spectroscopy, Thermogravimetric analysis (TGA), particle size analysis and Scanning electron microscopy (SEM), and its performance as an inhibitor in clay was evaluated by an anti-swelling test and a linear swelling test. The results show that small-molecule quaternary ammonium salt (TEE-2) synthesized by triethanolamine and epichlorohydrin in ethanol with a molar ratio of 1:1.5 can successfully inhibit the hydration swelling and dispersion of clay. The anti-swelling rate of TEE-2 was 84.94%, the linear swelling rate was 36.42%, and the linear swelling rate of 0.5% TEE-2 was only 29.34%. The hydration swelling of clay in 0.5% TEE-2 solution was significantly inhibited. The hydration inhibition mechanism of the small-molecule quaternary ammonium salt inhibitor 0.5% TEE-2 was analyzed by FTIR, SEM and TGA. It was considered that 0.5% TEE-2 has strong hydration inhibition, which was realized by infiltration and adsorption on the clay surface. Small-molecule quaternary ammonium salts were beneficial for maintaining wellbore stability and reducing the risk of wellbore instability.

1. Introduction

Shale oil has emerged as one of the most outstanding technologies in the world in recent years [1]. In the process of oil field drilling, due to the hydration swelling of water-sensitive shale, drilling instability problems such as drilling scouring, pipe jamming, rock debris disintegration and bit balling often occur during shale formation [2,3]. According to the chemical characteristics of shale and drilling fluid, when water-sensitive shale (with high montmorillonite content) is immersed in water-based drilling fluid, shale may expand and disperse rapidly [4,5]. Therefore, many shale inhibitors have been widely used in water-based drilling fluids. Unfortunately, environmental requirements limit the use of most shale inhibitors [6,7,8].

As is well known, KCl is one of the inorganic salt inhibitors used to inhibit the hydration swelling of clay. K⁺ can enter the clay layer and be adsorbed on the surface, expelling the interlayer water and reducing the interlayer spacing of the clay [9]. However, KCl has limited ability to inhibit clay hydration swelling and has an impact on the environment and rheological properties of drilling fluids. Polymer amine inhibitors have a large number of amine groups that adsorb onto clay surfaces, forming dense films to reduce the hydration of clay. However, the molecular structure of polymer amine inhibitors is too large to effectively embed between clay layers [10].

In recent years, small-molecule amines have attracted extensive attention from researchers because of their good inhibition, lubricity and stable rheology. Therefore, we have proposed the creation of environmentally friendly small-molecule inhibitors with low molecular weight. Small-molecule amine inhibitors can provide multiple adsorption sites on the surface of clay and enhance the adsorption of inhibitors in the clay [11,12]. The binding of clay is mainly realized through hydrogen bonding, anchoring, electrostatic adsorption and hydrophobic action, which effectively inhibits the hydration, swelling and dispersion of clay [13,14]. Small-molecular amines have excellent compatibility with traditional additives and can meet the requirements of environmental protection. They have been applied to many water-based drilling fluids and have very broad application prospects.

In this paper, epichlorohydrin and triethanolamine were used to prepare small-molecule shale inhibitors. The performance was evaluated by experiments such as anti-swelling, linear swelling and drilling fluid performance evaluation. The mechanism of the inhibitor was discussed in detail in terms of its FTIR, SEM, TGA and zeta potential.

2. Experimental Materials and Methods

2.1. Materials and Reagents

Epichlorohydrin was purchased from Chengdu Kelong Chemical Reagent Factory. Triethanolamine and ethanol were purchased from Tianjin Fuyu Fine Chemical Co., Ltd., Tianjin, China. Industrial-grade triethylenetetramine was taken from the site of Changqing Oilfield. Calcium- and sodium-based bentonite were purchased from Xi’an Fengyun Chemical Co., Ltd., China. Sodium carbonate was purchased from Tianjin Shengao Chemical Reagent Co., Ltd., China. Potassium chloride was purchased from Tianjin Zhiyuan chemical reagent factory. Heteropolysaccharide (KD-03), rubber powder (RP), carboxymethyl cellulose (CMC) and modified starch (MS) were purchased from Yangzhou Runda Oilfield Chemical Co., Ltd., Yangzhou, China.

Chemical Composition of Raw Bentonites

Bentonite is an absorbent swelling clay consisting mainly of montmorillonite (a type of smectite), which can be either calcium- or sodium-type. Na–montmorillonite has a significantly greater swelling capacity than Ca–montmorillonite. The common smectite of bentonite is montmorillonite-beidellite The main use of bentonite is in drilling mud and as an absorbent, binder, cleaner, and carrier of fertilizers and others. The oxide composition of calcium and sodium-based bentonite based on XRF is presented in

Table 1. Chemical composition of raw bentonites.

Oxide Composition/Mass%
	SiO2	Al2O3	CaO	Fe2O3	MgO	K2O	Na2O	LOI
Ca-bentonite	65.48	15.85	2.85	2.54	1.85	1.78	1.45	7.35
Na-bentonite	65.20	12.94	3.78	3.45	2.65	0.35	2.58	8.65

.

2.2. Synthesis and Nomenclature of Inhibitors

Triethanolamine and epichlorohydrin were added to the flask in the ratio stated in

Table 2. Nomenclature of inhibitors.

Reagent	Reagent	Solvent	Proportion	Nomenclature
Triethanolamine	Epichlorohydrin	Ethanol	1.0:1.0	TEE-1
			1.0:1.5	TEE-2
			1.0:3.0	TEE-3
		Distilled water	1.0:1.0	TEW-1
			1.0:1.5	TEW-2
			1.0:3.0	TEW-3
		Glycerol	1.0:1.0	TEG-1
			1.0:1.5	TEG-2
			1.0:3.0	TEG-3

. Ethanol was used as the solvent and the reaction was refluxed for 4 h. The mixture was then cooled to room temperature and the ethanol was evaporated to create the final product. The reaction mechanism is shown in Figure 1.

2.3. Optimization of Synthetic Inhibitors

The inhibition performance of synthetic products on clay is affected by the material ratio, concentration and reaction medium of synthetic reaction, and there are many synthetic inhibitors. Therefore, the synthetic products with the best inhibition performance were preliminarily selected through inhibition performance parameters such as the anti-swelling rate and linear swelling rate. Subsequently, we evaluated the inhibition efficiency in water-based drilling fluid and explored its mechanism.

2.4. Anti-Swelling Rate

The industry-standard SY/T 5971-1994 evaluation method of clay stabilizer for drilling fluid was referred to in order to evaluate the influence of the inhibitor on the anti-swelling rate of bentonite. Inhibitor solutions of different concentrations were prepared. First, 0.5 g bentonite was weighed and added to a 10 mL centrifuge tube. A certain amount of inhibitor solution was added to the centrifuge tube and then fully stirred and shaken. After standing for 2 h, it was centrifuged at the speed of 1500 r/min for 15 min, and the volume was recorded (V_a). The inhibitor solution was replaced with water and kerosene, respectively, and the swelling volume of bentonite in water and kerosene was recorded as V_b and V₀, respectively. The calculation formula for the anti-swelling rate of bentonite is shown in Equation (1):

$$\mathrm{B}={\displaystyle \frac{V_b-V_a}{V_b-V_0}}\times 100\%$$

(1)

where B is the anti-swelling rate of bentonite. V_a is the swelling volume of bentonite in inhibitor solution in mL. V_b is the swelling volume of bentonite in water, also in mL. V₀ is the swelling volume of bentonite in kerosene in mL.

2.5. Linear Swelling

The industry-standard SY/T 6335-1997 shale inhibitor evaluation method for drilling fluid was referred to for evaluating the influence of inhibitor on the linear swelling rate of bentonite. The calculation formula of linear swelling rate of bentonite is shown in Equation (2):

$$\mathrm{S}\mathrm{r}={\displaystyle \frac{Ro}{∆L}}\times 100\%$$

(2)

where Sr is linear swelling rate of bentonite. Ro is the swelling of bentonite in mm. ∆L is the core thickness in mm.

2.6. Drilling Fluid Evaluation

The 4% calcium clay-based mud preparation was conducted as follows: Calcium bentonite (14 g) and sodium carbonate (0.7 g) were added to tap water (350 mL), stirred at high speed for 2 h and aged at 298 K for 24 h before use [15]. To prepare the treatment-based mud and treatment agent, they were aged for 6 h, stirred at high speed for 10 min, and their performances were tested [16]. The rheological properties, filtration properties, and lubrication properties of drilling fluid, such as the AV (apparent viscosity), PV (plastic viscosity), YP (yield point), FL (API filtration) and t g (friction coefficient) were evaluated. A viscometer (ZNN-D6S, Hetongda Co. Ltd. Qingdao, China), medium-pressure filtration instrument (GJSS-B12K, Haitongda Co. Ltd. Qingdao, China), and viscosity coefficient instrument (Qingdao Hetongda Co. Ltd. Qingdao) were used according to the formulas described in the Chinese National Standard GB/T 16783.1-2006.

2.7. Inhibition Mechanism Study

2.7.1. FTIR Analysis

The dried inhibitor samples were ground. During the test, the ground samples were mixed with KBr at a ratio of 1:200, put into the tablet press and pressed into transparent pellets, and the soil samples were scanned and analyzed by an infrared spectrometer (Nicolet 6700) [17]. The FTIR spectra were measured using a resolution of 4 cm⁻¹, 64 scans, and a measurement region of 4000–400 cm⁻¹.

2.7.2. Particle Distribution Measurement

The dried inhibitor samples were used to measure the particle size using a laser particle size experiment so as to obtain the median particle size and average particle size of bentonite particles in mud treated with treatment agent. The change in bentonite particle size was analyzed according to these data [18].

2.7.3. Zeta Potential Measurement

The zeta potential of the supernatant of the solution was measured on an omni multiangle particle size and high-sensitivity zeta potential analyzer. The changes in the zeta potential of graphite with different dosages of adsorbent were analyzed [19].

2.7.4. SEM Analysis

The bentonite samples were dispersed in the inhibitor solution and hydrated for 24 h, then the water was separated from the solution and dried at 105 °C for SEM. The surface morphology of the bentonite samples was evaluated by a digital microscope imaging scanning electron microscope (model Vega 3, Tescan, serial no. HI-2102-0003) at a 40.0 kV accelerating voltage on the basis of the reported method [20]. Prior to SEM measurements, the samples were coated with gold.

2.7.5. TGA

The bentonite samples were dispersed in the inhibitor solution and hydrated for 24 h, then the water was separated from it and dried at 105 °C for TGA and SEM. The TGA experiment was conducted on a TGA/DSC thermal analysis instrument (1/1600, METTLER TOLEDO, Inc., Columbus, OH, USA) at a ramp of 20 °C/min from room temperature to 825 °C under nitrogen flow.

2.7.6. XRF Analysis

The calcium and sodium bentonite samples were characterized by X-ray Fluorescence (XRF) and clay samples were obtained through Phillips’ XRF PW2400 model (Bruker, Billerica, Massachusetts, USA), with the scintillation detector having a voltage 40 mV, current of 40 mA and rhodium anode X-ray tube.

3. Results and Discussion

3.1. Optimization Results of Synthetic Inhibitors

The control variable method was adopted, and the optimal solvent, reaction molar ratio and dosage were screened through anti-swelling and linear swelling experiments. The inhibitors with strong inhibitory performance have been identified.

3.1.1. Anti-Swelling Rate

The inhibition performance of the product was preliminarily explored, and the anti-swelling performance of the synthetic product on bentonite was evaluated. The anti-swelling test results are shown in Figure 2. TEE, TEW and TEG have certain anti-swelling effects on bentonite, and their anti-swelling rate is related to the ratio of raw materials, solvent, and inhibitor concentration. It can be seen from Figure 2 that the inhibitory effect of TEE series was significantly better than that of TEW and TEG series. The results show that when the reaction medium of epichlorohydrin and triethanolamine was ethanol, the inhibition performance of the synthetic product was better. It can be seen from Figure 2a that when ethanol was used as the solvent, the inhibitory effect of TEE-2 was better than that of TEE-1 and TEE-3. The results show that when the molar ratio of triethanolamine to epichlorohydrin was 1:1.5, the synthesized product achieved a better inhibition performance. It can be seen from Figure 2a that when ethanol was used as the solvent and the molar ratio was 1:1.5, the anti-swelling rate increased with the increase in inhibitor concentration. When TEE-2 was added in a concentration of 0.5%, the maximum anti-swelling rate was 84.94%.

3.1.2. Linear Swelling

During the drilling process, wellbore collapse and instability have a very bad and irreversible impact on the exploitation of the oilfield [21]. The linear swelling rate measured in laboratory experiments can reflect the degree of wellbore collapse and instability to a certain extent. Therefore, the inhibition performance of synthetic inhibitors on bentonite can be further explored by linear swelling experiments. The experimental results are shown in Figure 3. It can be seen from Figure 3 that at a certain concentration and molar ratio, ethanol as a solvent synthesized inhibitor had a lower swelling rate in bentonite. These concentrations were 40.00%, 36.42% and 41.43%, respectively. It can be seen from Figure 4 that when ethanol was used as solvent and at a certain concentration, the molar ratio of TEE inhibitor was 1:1.5, indicating that it has a better inhibitory effect. The linear swelling rate of 0.1% TEE-2 was 36.42%. Compared with the inhibition of tap water and 4% KCI, the swelling rate decreased by 25.89% and 8.73%. It can be seen from Figure 5 that when ethanol was used as solvent and the molar ratio was 1:1.5, the inhibition effect of 0.5% TEE-2 was the best. The linear swelling rate of 0.5% TEE-2 was only 29.34%. It is obvious that the inhibitory effect of 0.5% TEE-2 was better than that of other concentrations of TEE-2.

3.2. Drilling Fluid Evaluation

A certain amount of TEE-2 was added to the treated mud of low-viscosity CMC, RP, KD-03, and MS. The rheological parameters of several types of water-based drilling fluids were effectively improved, the filtration loss was reduced, and the suspension force of drilling fluid was enhanced. TEE-2 has good compatibility with CMC, RP, MS, and KD-03, and its compatibility with low-viscosity CMC was the best. We added 0.5% TEE-2 to low-viscosity CMC, RP, MS, and KD-03-treated mud at room temperature. The performance parameters of drilling fluid are shown in

Table 3. Effect of 0.5% TEE-2 on compatibility of water-based drilling fluid.

Treatment Agent	AV /(mPa•s)	PV /(mPa•s)	YP /Pa	YP/PV /(m•s)	FL/mL	tg
Base mud	2.0	1.4	0.6	0.43	15.9	0.0437
Base mud + 0.5% TEE-2	3.0	2.0	1.0	0.50	17.0	0.1673
0.5%CMC	10.0	9.0	1.0	0.11	4.8	0.0875
0.5% CMC + 0.5% TEE-2	9.5	7.0	2.5	0.36	4.5	0.1853
1.0% RP	17.5	15.1	2.4	0.16	2.0	0.1495
1.0% RP + 0.5% TEE-2	10.4	8.6	1.8	0.21	2.2	0.1228
0.3%KD-03	2.8	2.0	0.8	0.38	14.0	0.0437
0.3% KD-03 + 0.5% TEE-2	3.0	2.5	0.5	0.20	15.5	0.0963
1.0%MS	6.9	6.0	0.9	0.15	10.8	0.1405
1.0% MS + 0.5% TEE-2	7.5	6.0	1.5	0.25	8.5	0.1673

. It can be seen from Table 3 that the rheological parameters of drilling fluid increase after the addition of treatment agent. After 0.5% TEE-2 was added to CMC-treated mud, the AV decreased by 5.00%, the PV increased by 22.22%, the YP increased by 2.50 times, and the filtration loss and slider resistance coefficient also increased to a certain extent. After 0.5% TEE-2 was added to the RP-treated mud, the AV, PV, and YP of the RP-treated mud increased. With the increase in AV, the suspension capacity was enhanced, and the resistance coefficient of the slider also increased to a certain extent, which had the effect of increasing viscosity. KD-03 has a lubricating effect in water-based drilling fluid and leads to filtration reduction. After 0.5% TEE-2 was added to KD-03-treated mud, AV and PV achieved 1.07 and 1.25 times the rheological parameters of KD-03-treated mud, respectively, and the filtration loss and the resistance coefficient of sliding block were basically unchanged. MS treatment agent can effectively control the filtration of drilling fluid, adjust the rheology of drilling fluid, and have a good anti-sloughing effect. After 0.5% TEE-2 is added to the MS-treated mud, the filtration rate is further effectively controlled, and the filtration rate is reduced from 10.8 mL to 8.5 mL. The AV, PV and YP/PV are 1.09, 1.67 and 1.67 times those of modified starch data, respectively.

3.3. FTIR Analysis

FTIR was used to analyze the functional groups of bentonite and inhibitor molecules, as shown in Figure 6. It can be seen from FTIR spectra (Figure 6) that bentonite treated with water contains the characteristic band near 3620 cm⁻¹ and is assigned to the stretching vibration of structural OH groups. The characteristic band at 3422 cm⁻¹ is related to the stretching vibration of O-H groups of water in montmorillonite and hygroscopic KBr. The characteristic band at 3268 cm⁻¹ observed in the IR spectrum of bentonite treated with TEE-2 is the absorption vibration band of ammonium salt molecules (ᴠNH). This finding confirms the correct preparation of organo-bentonite samples. The strong band at 1630 cm⁻¹ is assigned to the bending vibration of OH groups. The characteristic band near 1034 cm⁻¹ is related to the ᴠSi-O. The absorption band near 469 cm⁻¹ is caused by the coupling vibration of Si-O-Si [22]. The main functional groups of quaternary ammonium salt inhibitors are adsorbed on the surface of bentonite, further restricting the swelling and hydration of shale.

3.4. Particle Distribution Measurement

Inhibitors have a certain microscopic effect on the particle size of bentonite. The changes in particle size of untreated bentonite particles and bentonite particles treated with different solutions were explored by laser particle-size analysis (

Table 4. Average particle size and median particle size of sodium bentonite in 0.5% TEE-2 solution.

Treatment of Bentonite	The Average Particle Size/μm	Median Particle Size/μm
BH	14.270	11.020
AH	7.903	4.660
BH(0.5% TEE-2)	7.544	8.148
AH(0.5% TEE-2)	8.185	6.761

), and the influence of synthetic products on the particle size of bentonite was analyzed [23]. The changes in the particle size of sodium bentonite after 0.5% TEE-2 was added before hydration (BH) and after hydration (AH) were investigated. The results of particle size distribution are shown in Figure 7, and the average particle size and median particle size are shown in Table 3. It can be seen from Table 3 that the average particle size and median particle size of BH were 14.270 μm and 11.020 μm, respectively. The average particle size and median particle size of hydrated bentonite in clean water are 7.903 μm and 4.660 μm, respectively. After the addition of 0.5% TEE-2, the average particle size without hydration was reduced to 47.13% of the original particle size, and the median particle size was reduced to 26.06% of the original median particle size. After hydration, the average particle size and median particle size increased slightly, growing to 1.04 times and 1.45 times those of the original hydration blank group, respectively. In short, the median particle size and average particle size became smaller regardless of hydration status. It can be seen from Figure 7 that the addition of 0.5% TEE-2 to bentonite can significantly inhibit the hydration and dispersion of bentonite.

3.5. Zeta Potential Measurement

The hydration swelling dispersion of bentonite is caused by many factors, which depend not only on the composition and structure of bentonite, but also on the composition of exchangeable cations and the properties of dispersion medium [24]. The zeta potential value of dispersion medium solution is closely related to the dispersion state of bentonite. Therefore, the inhibition performance of 0.5% TEE-2 on the hydration swelling of bentonite was explored by detecting the zeta potential of the adsorbed electric double layer on the surface of bentonite in different concentrations of 0.5% TEE-2 solution. The zeta potential of 0.5% TEE-2 solution is shown in Figure 8. Negative charge was formed by isomorphic substitution of octahedron. The increase in positive charge in the interlayer space breaks the charge balance. The zeta potential of bentonite treated with clean water was −21.41 mv, which has good dispersion in water. With the addition of 0.5% TEE-2, the zeta potential of the solution decreases, the absolute value of zeta potential increases, and the system achieves a stable state again, which effectively inhibits the hydration and dispersion of bentonite.

3.6. SEM Analysis

The micro-morphology of bentonite particles treated and dried with 0.5% TEE-2 and clean water was analyzed by SEM. The effect of 0.5% TEE-2 on the microstructure of bentonite is explored in Figure 9. Figure 9a shows the SEM images of the microstructure of unhydrated bentonite. Figure 9b,c depict the microstructure of bentonite after hydration treatment in clean water and 0.5% TEE-2 solution for 24 h. It can be seen from the microstructure diagram that bentonite was strongly dispersed in clean water. After the addition of 0.5% TEE-2, the fine particles of bentonite decreased significantly. This shows that after the addition of 0.5% TEE-2, the inhibitor enters the bentonite layers and binds the bentonite layers together through electrostatic adsorption and hydrogen bonding. Thus, it can effectively inhibit the hydration swelling and dispersion of bentonite. Macroscopically, the large particles of bentonite increase in number and the particle size decreases, showing a certain inhibition.

3.7. TGA

During the heating process, with the increase in temperature, the adsorbed water, interlayer water and hydroxyl water in bentonite are removed in turn [25]. Therefore, the weight loss rate of bentonite with inhibitors can be determined by TGA. The effect of inhibitors was evaluated based on the hydration swelling and dispersion of bentonite, as shown in Figure 10. It can be seen from Figure 10 that as the temperature gradually increased, the water between the clay layers began to evaporate, and the weight of the clay particles decreased. And the weight loss rate of bentonite processed in TEE-2 was 10%. However, the weight loss rate of untreated bentonite was 13%. This result indicates that TEE-2 can significantly prevent water molecules from penetrating shale and has a certain inhibitory effect on the hydration swelling and dispersion of bentonite.

3.8. Mechanism

The mechanism of inhibiting hydration and swelling of quaternary ammonium salt small-molecule inhibitors in clay was systematically discussed based on N-alkylation and the diffusion double-layer theory. It is generally believed that the core action of inhibitors is to reduce the repulsion between clay crystal layers and prevent contact between water and clay particles [26,27]. It can be seen from Figure 11 that under the action of potential difference and water potential difference, cations will gradually diffuse into the aqueous solution, resulting in the formation of a diffusion electric double layer with uneven cation distribution around the clay. There are exchangeable cations between the crystal layers of clay, which will lead to the swelling of crystal layer spacing after hydration [28]. The main reason is that the repulsion of the clay electric double layer leads to the swelling of the clay lattice. If the amount of lattice swelling is large and the repulsion between clay crystal layers exceeds the attraction between clay crystal layers, the crystal structure will be destroyed. The destruction of crystal structure will reduce the cohesion strength of rock mass and eventually lead to the instability of shaft wall [29]. It can be seen from Figure 12 that surface hydration and osmotic hydration are the scope of the action of clay inhibitors, and their action points are between crystal layers, i.e., small-molecular quaternary ammonium salt inhibitors need to enter into the crystal layers of clay to play a role. Through the adsorption between the primary amine group dissociated by the amine inhibitor and the crystal layer of the active clay, the upper and lower crystal layers of the clay are pulled so as to prevent the crystal layer swelling caused by hydration. Small-molecule quaternary ammonium salt has a polyhydroxy structure, which can provide multiple adsorption sites on the clay’s surface and enhance the adsorption of the inhibitor on the clay. The inhibitor was adsorbed on the clay’s surface to neutralize the negative charge of the clay or attached to the crystal layer of the clay, reducing the charge between the crystal layer and the surface. At the same time, it can bind the clay through electrostatic adsorption, hydrogen bonding, anchoring and hydrophobic action, and effectively inhibit the hydration, swelling and dispersion of the clay. Usually, the clay surface has a negative charge. When lattice substitution occurs, due to the potential difference and following the principle of minimum energy, an equal amount of opposite charge must be adsorbed on the clay surface, compressing the clay and diffusing the electric double layer. It can inhibit the hydration of clay, thus showing a good inhibition performance in clay.

4. Conclusions

In conclusion, a small-molecule quaternary ammonium salt inhibitor was synthesized from triethanolamine and epichlorohydrin. The inhibition performance of 0.5% inhibitor TEE-2 was studied by FTIR spectroscopy and performance evaluation experiments. The results show that 0.5% TEE-2 had an obvious inhibitory effect on hydration. The linear swelling rate of 0.5% TEE-2 was only 29.34%, which was 32.97% and 15.82% lower than that of tap water and 4% KCl, respectively. The performance of inhibitors was also studied by particle size analysis, SEM and TGA. The synthesized inhibitor had the structure of small polyhydroxy molecules, and it can provide multiple adsorption sites on a clay surface and enhance the adsorption of the inhibitor in clay. The inhibitor was adsorbed on the clay’s surface and the clay was negatively charged or attached to the clay crystal layer to reduce the charge between the crystal layer and the surface. At the same time, the binding of clay was realized through electrostatic adsorption, hydrogen bonding, anchoring, and hydrophobic action, which can effectively inhibit the hydration, swelling and dispersion of clay, so as to show a good inhibition performance in clay.