Inhibiting Shale Hydration Research Articles

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

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.

In situ shale wettability regulation using hydrophobic ionic liquid functionalized nano-silica to enhance wellbore stability in deep well drilling

Shale wellbore instability due to hydration significantly hinders the efficient extraction of clean shale gas resources, making the development of effective shale stabilizers for safe drilling in shale reservoirs an urgent priority. In this study, we proposed an innovative application of hydrophobic ionic liquids functionalized nano-SiO2 (ILs@SiO2) specifically designed to maximize hold wellbore strength and effectively inhibit shale hydration. The chemical composition and microstructure of ILs@SiO2 were characterized, and their effects on wellbore stability were thoroughly investigated along with the underlying mechanisms. The shale stabilizer demonstrated significant clay swelling inhibition (9.5 %), as well as effective hydration and dispersion inhibition of shale cuttings at 150 °C (88.0 %), and a reduced spontaneous imbibition of shale (0.997 g). Particularly, ILs@SiO2 maximized maintained wellbore strength (203.4 MPa) and minimized water invasion (5.5 mL). Mechanism analysis revealed that ILs@SiO2 improved wellbore stability through electrostatic adsorption weakening osmotic hydration, physical plugging establishing a dense preventing water barrier, altering wettability decreasing rocks surface free energy, inhibiting surface hydration, and reversing the direction of capillary forces. This study offers new strategies and insights for constructing methods to plug shale nanopores and inhibit surface and osmotic hydration.

Improving shale hydration inhibition with hydrophobically modified graphene oxide in water-based drilling fluids

Frequent wellbore instability issues caused by shale hydration and dispersion are encountered in water-based drilling fluids. In order to mitigate shale hydration, a hydrophobic graphene oxide (HGO) was prepared as a new shale inhibitor and characterized. The effectiveness of HGO in inhibiting shale hydration was evaluated through hydration expansion, hydration dispersion, and bentonite sheets immersion tests. The expansion height of bentonite in HGO (3.87 mm) was lower than that of commercial shale inhibitors potassium chloride (KCl, 4.64 mm) and polyether amine (PA, 4.33 mm). The shale recovery rate in HGO at 80 °C was 86.25 %, which was superior to KCl (46.60 %) and PA (78.25 %). Furthermore, the morphology of bentonite sheet remained more intact after immersion in HGO. Additionally, the inhibitory mechanism of HGO was studied in-depth, employing zeta potential, particle size, surface tension, wettability, capillary rise height, and scanning electron microscopy (SEM) tests. By virtue of electrostatic attraction, HGO could tightly adsorb to the shale surface, resulting in a hydrophobic blocking membrane, thereby greatly reducing water infiltration. Following interaction with shale at a concentration as low as 0.5 %, the water contact angle exhibited a notable enhancement, rising from 22.49° to 86.69°. And it could also decrease the capillary self-suction capacity of shale, further reducing water adsorption. Consequently, HGO exhibited significant potential for inhibiting hydration in shale drilling.

Achieving the hydrophobic alteration by functionalized nano-silica for improving shale hydration inhibition

Shale hydration is the primary cause of wellbore instability during drilling processes. In this study, two non-fluorinated silane-coupling agents, octyltriethoxysilane (OTES) and (3-Aminopropyl) triethoxysilane (APTES), were grafted onto the nano-silica surface to develop a hydrophobic material (SHM). Various performance characterizations, including infrared spectroscopy, thermogravimetric analysis, surface tension, wetting alteration, capillary self-suction height, bentonite expansion, and shale dispersion, were employed to investigate the shale inhibition properties of SHM comprehensively. Experimental results revealed that SHM could significantly improve shale hydration inhibition. For instance, in a 2 % SHM liquids, the shale hot rolling recovery rate increased from 25.39 % to 83.78 %, and the bentonite expansion height decreased from 7.65 mm to 2.80 mm. The inhibition performance was notably superior to potassium chloride (KCl) and polyether amine (PEA). Inhibition mechanisms analysis unveiled that the outstanding inhibitory effect of SHM was achieved through electrostatic adsorption, wettability alteration, and surface tension reduction. Firstly, SHM contained numerous amine groups that could demonstrate strong adsorption on the clay surface through electrostatic and hydrogen bonding interactions. Secondly, with long hydrophobic alkyl chains, it formed a highly hydrophobic film enveloping the shale surface, effectively preventing water from invading. Thirdly, it reduced liquid surface tension, further minimizing the water infiltration. As a result, the use of SHM significantly enhanced shale hydration inhibition during the shale drilling process.

Environmentally friendly and temperature resistant water-based drilling fluids with highly inhibitory synthetic nanocellulose polymers for deep sea drilling

The ocean is rich in sustainable hydrocarbon. The process of extracting these resources poses challenges such as coexistence of low temperature and high temperature, high pressure of deepwater and unpredictable shale formations. A kind of ionic crosslinking polymer consisting of N, N-dimethylacrylamide (DMA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and Cellulose Nanofibers (CNF) (PADC), was synthesized to address these challenges. Cellulose was first oxidized to nanocellulose (CNF) through 2,2,6,6-tetramethylpiperidinyl-1-oxide (TEMPO) oxidation. Subsequently, the ionic crosslinking polymer, consisting of DMA, AMPS, and CNF, was synthesized using ionic crosslinking polymerization. The surface characteristics and morphology were characterized by transmission electron microscopy (TEM), nanoparticle size analysis, and zeta potential analysis. The structural composition was analyzed by Fourier Transform Infrared Spectroscopy (FT-IR). The shale inhibition mechanism was investigated through contact angle and pressure transmission experiments. The results indicated that the average length of PADC is approximately 1450 nm, with an average diameter of less than 100 nm and contains sulfonic acid groups. The shale contact angle increased from 16.75° to 82°, indicating that PADC increased the hydrophobicity of the shale by 390%. Pressure transfer experiments show that PADC can reduce shale permeability by 37%, which means PADC has good hydration inhibition performance. In addition, a drilling fluid system suitable for deep sea drilling was proposed. The drilling fluid system exhibits good rheological properties at 160 °C and 0 °C. The fluid loss after hot rolling at 160 °C is less than 12 mL. The linear expansion of shale core after 16 h is only 0.7%, and the rolling recovery rate at 160 °C is as high as 99.48%. Luminescent bacteria EC50 is 2.0 × 105 mg/L, which means it is non-toxic and environmentally friendly. And drilling fluid conforms to the power law flow model. Therefore, the drilling fluids proposed in this paper can meet the requirements of deep sea drilling in terms of rheological properties and filtration loss properties at 0–160 °C, and can seal shale pores and inhibit shale hydration through the ionic cross-linking PADC. This research offers insights into the utilization of cellulose in well drilling processes and provides references for designing deep sea drilling fluids.

Acylated Inulin as a Potential Shale Hydration Inhibitor in Water Based Drilling Fluids for Wellbore Stabilization.

Shale hydration dispersion and swelling are primary causes of wellbore instability in oil and gas reservoir exploration. In this study, inulin, a fructo-oligosaccharide extracted from Jerusalem artichoke roots, was modified by acylation with three acyl chlorides, and the products (C10-, C12-, and C14-inulin) were investigated for their use as novel shale hydration inhibitors. The inhibition properties were evaluated through the shale cuttings hot-rolling dispersion test, the sodium-based bentonite hydration test, and capillary suction. The three acylated inulins exhibited superb hydration-inhibiting performance at low concentrations, compared to the commonly used inhibitors of KCl and poly (ester amine). An inhibition mechanism was proposed based on surface tension measurements, contact angle measurements, Fourier-transform infrared analysis, and scanning electron microscopy. The acylated inulin reduced the water surface tension significantly, thus, retarding the invasion of water into the shale formation. Then, the acylated inulin was adsorbed onto the shale surface by hydrogen bonding to form a compact, sealed, hydrophobic membrane. Furthermore, the acylated inulins are non-toxic and biodegradable, which meet the increasingly stringent environmental regulations in this field. This method might provide a new avenue for developing high-performance and ecofriendly shale hydration inhibitors.

Study on the Inhibition Mechanism of Hydration Expansion of Yunnan Gas Shale using Modified Asphalt.

Drilling fluids play an essential role in shale gas development. It is not possible to scale up the use of water-based drilling fluid in shale gas drilling in Yunnan, China, because conventional inhibitors cannot effectively inhibit the hydration of the illite-rich shale formed. In this study, the inhibition performance of modified asphalt was evaluated using the plugging test, expansion test, shale recovery experiment, and rock compressive strength test. The experimental results show that in a 3% modified asphalt solution, the expansion of shale is reduced by 56.3%, the recovery is as high as 97.8%, water absorption is reduced by 24.3%, and the compression resistance is doubled compared with those in water. Moreover, the modified asphalt can effectively reduce the fluid loss of the drilling fluid. Modified asphalt can form a hydrophobic membrane through a large amount of adsorption on the shale surface, consequently inhibiting shale hydration. Simultaneously, modified asphalt can reduce the entrance of water into the shale through blocking pores, micro-cracks, and cracks and further inhibit the hydration expansion of shale. This demonstrates that modified asphalt will be an ideal choice for drilling shale gas formations in Yunnan through water-based drilling fluids.

Synergistic effects of potassium alginate and silicates co-inhibition performance in shale hydration

High performance hydration inhibitors are recognized as an attractive solution to address wellbore instability associated with water-based drilling fluids. Nevertheless, conventional inhibitors still face a dilemma regarding the balance between inhibition performance and compatibility, including rheological and filtration properties. Herein, we proposed an organic–inorganic composite inhibitor that combines polymer adsorption and ion intercalation to provide synergistic inhibition properties. The results demonstrated that the composite inhibitors reduced the clay swelling rate from 50.7 to 22.4 % and increased shale recovery from 71.4 to 90.2 % compared with that in K2SiO3 solution, revealing the synergistic inhibition properties between ion exchange and film coating effect. In addition, the hydrogen bonding interaction between potassium alginate (PA) and clay particles effectively alleviates performance deterioration of base fluids containing K2SiO3, as evidenced by the apparent viscosity increased from 14.0 to 35.5 mPa·s, plastic viscosity increased from 4.0 to 25.0 mPa·s and filtration loss reduced from 35.2 to 20.4 mL after rolling at 120 °C. The intermolecular interaction between clay and PA facilitates the adsorption of polysaccharide chains onto clay surface, which was confirmed by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). Moreover, X-ray diffraction (XRD), zeta potential and particle size distribution verified the suppression of electric double layers caused by K+ ions intercalation. This study validates the feasibility of organic–inorganic hybrid materials as shale hydration inhibitors, utilizing the synergistic effects of polymer adsorption and cation intercalation. Furthermore, the study highlights the great potential of combining PA with silicates to maintain wellbore stability.

Preparation and Application of New Polyhydroxy Ammonium Shale Hydration Inhibitor

Wellbore instability caused by the hydration of shale formations during drilling is a major problem in drilling engineering. In this paper, the shale inhibition performance of polyhydroxy-alkanolamine was evaluated using an anti-swelling test, linear swelling test, wash-durable test and montmorillonite hydration and dispersion experiment. Additionally, the shale inhibition mechanism of polyhydroxy-alkanolamine was studied via Fourier transform infrared spectroscopy (FTIR), particle size, zeta potential, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show that the use of polyhydroxy-alkanolamine (EGP-2) could result in a relatively lower linear swelling rate of montmorillonite, and the linear swelling rate of 0.3% EGP-2 is 26.98%, which is stronger than that of 4% KCl. The anti-swelling rate of 0.3% EGP-2 is 43.54%, and the shrinkage–swelling rate of 0.3% EGP-2 is 34.62%. The study on the inhibition mechanism revealed that EGP-2 can permeate and adsorb on the surface of montmorillonite. The rolling recovery rate of easily hydrated shale was as high as 79.36%, which greatly reduces the dispersion ability of water to easily hydrated shale. The results of this study can be used to maintain the stability of a wellbore, which is conducive to related research.

Application status and prospect of ionic liquids in oilfield chemistry

The ionic liquid, as a new treatment agent, has been increasingly applied in oil fields due to its strong temperature resistance, good solubility and high surface activity. In this paper, we systematically discuss the action mechanism and application effect of ionic liquids in oilfield chemistry. Ionic liquids can inhibit shale hydration expansion and reduce fluid loss through adsorption and intercalation, inhibit the formation of natural gas hydrate through imidazole five-membered ring structure as a space barrier, reduce viscosity of heavy oil by breaking chemical bonds of heavy oil macromolecules and charge transfer, improve oil displacement efficiency by forming ions pairs with carboxyl groups in crude oil, demulsify by forming channels between dispersed water droplets, acidify the formation by reacting with water to produce acid, interacts with organic material through weak hydrogen bonds and extracts it from oilfield wastewater, desulphurize by inserting sulfide molecules into the “stack” structure and form liquid inclusion complex, inhibit corrosion by forming a protective film on the metal surface. Based on the above aspects, the development direction of ionic liquids is proposed. The application of ionic liquids in oilfield chemistry is still in its infancy. It is urgent to fully explore the application performance of ionic liquids in oilfield chemistry, which also provides theoretical and technical supports for efficient reservoir development.

Synthesis of poly(citric acid–aspartic acid) copolymer for efficient inhibition of shale hydration in water-based drilling fluids

Poly (citric acid–aspartic acid) copolymer was synthesized and assessed as a shale hydration inhibitor. The formation of the biomass-based eco-friendly copolymer was verified using Fourier transform infrared spectroscopy, and the structure confirmed by 13C and 1H nuclear magnetic resonance. Thermal degradation of the copolymer was evaluated by thermogravimetric analysis, which suggested that the copolymer has outstanding stability. Characterization using scanning electron microscopy, equipped with an energy-dispersive X-ray spectrometer, was carried out to confirm the shale morphology before and after copolymer treatment. Shale recovery tests, immersion experiments, and anti-swelling measurements were performed to determine inhibitor performance in the drilling process. The copolymer showed the highest shale dispersion recovery compared to a commonly used inhibitor (potassium chloride) and water. The anti-swelling and immersion results indicated that the copolymer was strongly adsorbed over the clay's surface through hydrogen bonding and electrostatic interaction. Consequently, clay hydrophobicity could be increased by producing a hydrophobic film on its surface, which would decrease the number of hydrogen bonds between shale and water, hence reducing the quantity of water invasion.

Investigation of the Mechanism and Effect of Citric Acid-Based Deep Eutectic Solvents Inhibiting Hydration and Expansion of Gas Shale Clay Minerals

This study developed a shale hydration inhibitor using a citric acid-based deep eutectic solvent (Cit-DES) and hexadecylammonium bromide (cetyltrimethylammonium bromide) to aid wellbore instability and collapse caused by drilling of shale gas wells with water-based drilling fluids. Soaking and linear expansion experiments were conducted with Na-bent and Longmaxi formation shale, respectively. The changes in illite interlayer spacing, wettability, and water absorption capacity of shale samples before and after soaking in an inhibitor solution were evaluated, which indicated that the inhibitor reduced shale hydration. The results showed that the inhibitor effectively inhibits the osmotic and surface hydration of the shale. Due to the Cit-DES hydrogen bond, the inhibitor is firmly adsorbed on the shale pore wall and inserted between clay minerals, reducing the shale surface energy, hydrophilicity, and surface potential. The swelling expansion rate of shale inhibitors is only 38.9% compared to a 3% KCl solution. The amount of shale imbibition per unit mass in distilled water is 0.011 g/g. In the inhibitor, the imbibition mass per unit of shale is 0.002 g/g, which is only 23.68% of that in distilled water. The inhibitor is environment-friendly and has a broad application prospect for maintaining shale wellbore stability and preventing wellbore collapse during horizontal shale drilling operations.

Hydrophobic Small-Molecule Polymers as High-Temperature-Resistant Inhibitors in Water-Based Drilling Fluids

Water-based drilling fluids can cause hydration of the wellbore rocks, thereby leading to instability. This study aimed to synthesize a hydrophobic small-molecule polymer (HLMP) as an inhibitor to suppress mud shale hydration. An infrared spectral method and a thermogravimetric technique were used to characterize the chemical composition of the HLMP and evaluate its heat stability. Experiments were conducted to measure the linear swelling, rolling recovery rate, and bentonite inhibition rate and evaluate accordingly the inhibition performance of the HLMP. Moreover, the HLMP was characterized through measurements of the zeta potential, particle size distribution, contact angles, and interlayer space testing. As confirmed by the results, the HLMP could successfully be synthesized with a favorable heat stability. Furthermore, favorable results were found for the inhibitory processes of the HLMP on swelling and dispersed hydration during mud shale hydration. The positively charged HLMP could be electrically neutralized with clay particles, thereby inhibiting diffusion in the double electron clay layers. The hydrophobic group in the HLMP molecular structure resulted in the formation of a hydrophobic membrane on the rock surface, enhancing the hydrophobicity of the rock. In addition, the small molecules of the HLMP could plug the spaces between the layers of bentonite crystals, thereby reducing the entry of water molecules and inhibiting shale hydration.

Synthesis of amyl ester grafted on carbon-nanopolymer composite as an inhibitor for cleaner shale drilling

Wellbore instability in oil and gas industry well drillings is a significant challenge that is linked to shale swelling when shale interacts with free water molecules in the water-based drilling fluid. Strategic design of environmentally benign, biodegradable, and effective shale hydration inhibitors is a prominent objective of contemporary exploration in well-drilling fluids as a replacement for the common KCl which is detrimental to aquatic lives. This work reports the synthesis and potential of novel green acrylic polymer-amyl ester activated carbon (-C) nanocomposite to hinder shale hydration in formations during drilling. Both less hydrophobic acrylic acid-acrylamide-activated carbon-amyl ester (AA-AAm-C-Amyl) and more hydrophobic acrylic acid-acrylamide-octadecene-activated carbon-amyl ester (AA-AAm-OD-C-Amyl) composites were synthesized, characterized, and tested with standard methods as a cleaner fluid additive for shale swelling inhibition, and their results compared with that of KCl. The polymer matrixes displayed remarkable thermal stability. Results also indicate that AA-AAm-C-Amyl and AA-AAm-OD-C-Amyl composites could stabilize wellbore effectively with 95.2% and 93.7% anti-swelling ratio, and shale recovery capacity of 97 and 95.2% respectively. The surface evaluation of the composite fluid-treated bentonite revealed that the mechanism of inhibition could be based on the collaborative action of nanopore plugging of carbon core and strong adsorption of the polymer component of the materials on clay surfaces via encapsulation and hydrogen bonding to form an impressive filter cake which could actively prevent water invasion into formation. Hence, AA-AAm-C-Amyl and AA-AAm-OD-C-Amyl composites could be a sustainable substitute for the conventional KCl as a shale inhibitor for well-drilling.

Effects of a polyamine inhibitor on the microstructure and macromechanical properties of hydrated shale

China is rich in shale gas resources; however, wellbores in shale gas reservoirs are frequently unstable. This has a serious impact on the shale gas drilling cycle. Polyamine, a common additive in water-based shale drilling fluids, can effectively inhibit shale hydration. However, there is a lack of quantitative research on the effect of polyamine inhibitors on the microstructure and macromechanical properties of shale. Therefore, this study investigated those issues via a systematic hydration experiment carried out on shale from the Longmaxi Formation. The results show that microfractures are created and expand during shale hydration, that they also connect to form a complex microfracture network, and that 3% polyamine inhibitors (polyamine solution with volume fraction of 3%) can effectively inhibit their evolution. The ultrasonic velocities and UCS of the Longmaxi shale are significantly anisotropic; the former first increases and then decreases with the laminae angle, reaching its maximum when the laminae angle is 30°. The UCS of the shale is highest and lowest, respectively, when the laminae angles are 0° or 90° and 30°. In general, these UCS appear as a “U" pattern, high on two sides with a dip in the center. Polyamines can effectively inhibit both the expansion of shale and the reduction of P-wave and S-wave velocities, the UCS, and elastic modulus. The UCS of a shale sample was reduced by 28%–40% after immersion for 96 h in water, compared to 2%–20% after immersion in a 3% polyamine inhibitor for the same amount of time. The inhibiting effect of the polyamine was remarkable.

A novel low molecular quaternary polymer as shale hydration inhibitor

Polymer inhibitors for deep shale gas drilling have poor temperature resistance and can influence the rheological attributes of the drilling muds. To overcome this issue, a high temperature resistant and low molecular weight quaternary polymer DVAA was prepared by hydrothermal radical polymerization. The characterizations of the DVAA were evaluated by IR, NMR, TG, and GPC, and the inhibition, rheology, and filtration parameters were examined. The shale inhibition mechanism was evaluated by the SEM, zeta potential, contact angle, and XRD. Initial decomposition temperature of DVAA is 354.83 °C and Mp is 4583. The performance test outcomes suggest that using DVAA could lead to a linear expansion reduction rate of MMT at 73.4%, whereas the rolling recovery rate of cuttings was 86.25%. The API filtration of 4% MMT after hot-rolling is 13.6 ml. The mechanism of DVAA showed that DVAA and MMT form ionic bonds and hydrogen bond through electrostatic attraction and can still maintain a good structure under elevated temperature conditions. DVAA can effectively weaken the surface hydration by entering the crystal layer to replace the inter-layer cations, where it forms a polymer-film on the bentonite surface. In summary, the research and development of the DVAA can provide an effective guarantee for the stability of the wellbore during the development of deep shale gas reservoirs.

In Situ Shale Wettability Regulation Using Sophisticated Nanoemulsion to Maintain Wellbore Stability in Deep Well Drilling.

Wettability alteration of the shale surface is a potential strategy to address wellbore instability issues arising from shale hydration. In this study, we have explored an oil-in-water (o/w) nanoemulsion, in which soluble silicate (lithium silicate and potassium methyl silicate) as the aqueous phase and organosilanes (3-methacryloxypropyltrimethoxysilane (KH570) and n-octyltriethoxysilane (n-OTES)) as the oil phase, as a shale inhibitor via forming a hydrophobic "artificial borehole shield" in situ on shale surfaces to maintain wellbore stability in high-temperature drilling operations. The shale dispersion test showed the highest shale recovery of nanoemulsion was up to 106.4% compared to that of water (20%), and recovered shale cuttings remained at the original integrity after hot rolling at 180 °C, indicating superior inhibition performance and resistance to elevated temperatures. Moreover, recovered shale cuttings manifested water repellency upon reimmersion in water, ascribed to the hydrophobic film, preventing water from permeating into the shale. The results of the contact angle measurement elucidated that the film wettability, from hydrophilic to superhydrophobic (ranging from 9.6-154°), can be achieved by altering the n-OTES-to-KH570 weight ratio from 0.2 to 2.25, and the film with the highest hydrophobicity (154°) and the lowest surface energy (3.17 mJ·m-2) can be obtained at a ratio of 1.3. Scanning electron microscopy images demonstrated that the superhydrophobic film was composed of tightly stacked reticulate nanofilaments with a diameter of 7-17 nm and several micrometers in length and overlapped well-distributed nanospheres with a diameter of 30 nm. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the film was crystalline silica grafted with long-chain alkylsiloxane. It is assumed that the unique micronanostructure combined with the siloxane modification contributed to the hydrophobicity. Consequently, this study provides a potential alternative solution for wellbore stabilization in deep well drilling engineering by employing nanoemulsion as a shale hydration inhibitor via forming a protective film with controllable wettability. Furthermore, it can be conferred a practical application due to easily available, less hazardous, and cost-effective materials.

An amphiphilic polymer as shale inhibitor in water-based drilling fluid

Shale hydration inhibitor in water-based drilling fluids (WBDFs) is the key to solve the problem of shale wellbore instability during drilling. In this study, a new amphoteric polymer was studied as a shale inhibitor. The amphiphilic copolymer ADL was synthesized by using acrylamide (AM), diallyl dimethyl ammonium chloride (DMDAAC) and dodecyl acrylate (LA) as monomers, benzoyl peroxide as initiator and hexadecyl trimethyl ammonium bromide (CTAB) as an emulsifier in aqueous solution. Infrared spectra indicated that the target product was synthesized successfully. TGA showed that the copolymers had good temperature resistance and the decomposition temperature was 240°C. The performance of ADL was evaluated by linear expansion experiment, rolling recovery rate experiment. The inhibition mechanism of the ADL was analyzed by particle size distribution experiment, zeta potential experiment and contact angle experiment. The experimental results show that ADL can adsorb on the surface of shale to change its wettability and increase the repulsive force between shale particles, thus inhibiting the hydration of shale. Because of its excellent shale inhibition performance, ADL has a potential application prospect as a shale inhibitor in WBDF.

Synthesis of a hydrophobic quaternary ammonium salt as a shale inhibitor for water-based drilling fluids and determination of the inhibition mechanism

During the drilling process, when the drill encounters easily hydrated shale formations, the problems generated by the shale hydration are often very serious, and developing a method of effectively inhibiting the shale hydration is a major difficulty. In order to further enhance the ability of small-molecule quaternary ammonium salts to inhibit shale hydration, in this study, a hydrophobic quaternary ammonium salt inhibitor (SJAY) was synthesized via a nucleophilic substitution reaction. The performance of SJAY in inhibiting shale hydration was investigated through mudball immersion, linear swelling, shale recovery, water absorption, and bentonite inhibition experiments. The mechanism by which SJAY inhibits shale hydration was investigated through zeta potential, particle size distribution, contact angle, surface tension, thermogravimetric analysis, and X-ray diffraction analyses. The experimental results revealed that with the addition of 1 wt% SJAY, the shale recovery of easily hydrated shale reached 92.5% (the recovery in deionized water was 11.3%), the 4-h water absorption of modified montmorillonite was only 4.69%, and the water contact angle of the shale slice reached 118.2°. The analysis of the inhibition mechanism revealed that the SJAY was adsorbed onto the clay through electrostatic attraction and hydrogen bonding. First, the SJAY formed a hydrophobic barrier on the surface of the clay, blocking the adsorption of water molecules. Then, the SJAY entered the clay interlayer and expelled the interlayer water molecules. Moreover, the SJAY reduced the capillary force effect by decreasing the surface tension and increasing the contact angle. The results of this study demonstrate that SJAY can be used as an effective inhibitor in water-based drilling fluids.

Study on the Shale Hydration Inhibition Performance of Triethylammonium Acetate

Shale inhibitor is an additive for drilling fluids that can be used to inhibit shale hydration expansion and dispersion, and prevent wellbore collapse. Small molecular quaternary ammonium salt can enter the interlayer of clay crystal, and enables an excellent shale inhibition performance. In this paper, a novel ionic shale inhibitor, triethylammonium acetate (TEYA), was obtained by solvent-free synthesis by using acetic acid and triethylamine as raw materials. The final product was identified as the target product by Fourier transform infrared spectroscopy (FT-IR). The inhibition performance of TEYA was studied by the mud ball immersion test, linear expansion test, rolling recovery test and particle size distribution test. The results demonstrated that the shale inhibitor shows a good shale hydration inhibition performance. The inhibition mechanism was studied by FT-IR and X-ray diffraction (XRD), respectively; the results showed that triethylammonium acetate TEYA could enter the crystal layer of clay and inhibit it through physical adsorption.