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Ensuring wellbore stability is of utmost importance for safety when drilling in deep formations. However, high temperatures severely disrupt the drilling fluid gel system, leading to severe stability issues within ultra-deep formations containing micropores. This study focused on the development of a polymer-based plugging material capable of withstanding high temperatures up to 200 °C. A kind of microsphere, referred to as SST (styrene–sodium styrene sulfonate copolymer), was synthesized with a particle size of 322 nm. Compared to polystyrene, the thermal stability of SST is greatly improved, with a thermal decomposition temperature of 362 °C. Even after subjecting SST to hot rolling at 200 °C for 16 h, the particle size, elemental composition, and zeta potential remained stable within an aqueous dispersion system. The results of core displacement and NMR tests demonstrate that SST considerably reduces the pore diameter with a remarkable plugging efficiency of 78.9%. Additionally, when drilling fluids reach 200 °C, SST still enhances drilling fluid suspension and dispersion, and reduces fluid loss by over 36% by facilitating the dispersion of clay particles, improving the gel structure of the drilling fluid, resisting clay dehydration, and promoting plugging. The development of SST provides valuable insights into the preparation of high-temperature-resistant microspheres and the formulation of effective plugging agents for deep-well drilling fluids. [ABSTRACT FROM AUTHOR]

Lost circulation in fractured formation is the first major technical problem that restricts improvements in the quality and efficiency of oil and gas drilling engineering. Improving the success rate of one-time lost circulation control is an urgent demand to ensure "safe, efficient and economic" drilling in oilfields all over the world. In view of the current situation, where drilling fluid loss occurs and the plugging mechanism of fractured formation is not perfect, this paper systematically summarizes the drilling fluid loss mechanism and model of fractured formation. The mechanism and the main influencing factors to improve the formation's pressure-bearing capacity, based on stress cage theory, fracture closure stress theory, fracture extension stress theory and chemical strengthening wellbore theory, are analyzed in detail. The properties and interaction mechanism of various types of lost circulation materials, such as bridging, high water loss, curable, liquid absorption and expansion and flexible gel, are introduced. The characteristics and distribution of drilling fluid loss in fractured formation are also clarified. Furthermore, it is proposed that lost circulation control technology for fractured formation should focus on the development of big data and intelligence, and adaptive and efficient intelligent lost circulation material should be continuously developed, which lays a theoretical foundation for improving the success rate of lost circulation control in fractured formation. [ABSTRACT FROM AUTHOR]

Based on the existing components of drilling fluids, the construction of a multi-component hydrate inhibitor system is essential for building a high-performance hydrate drilling fluid system and reducing production costs. The constant rate cooling method are performed to investigate the effect of different inhibitor systems on hydrate formation. The results indicate that thermodynamic inhibitors exhibit enhanced effectiveness in inhibiting hydrate formation at higher mass concentrations. In contrast, kinetic inhibitors demonstrate superior performance at lower mass concentrations, and their inhibitory efficacy does not scale up with concentration. Kinetic inhibitors can synergize with other components of the drilling fluid that have thermodynamic inhibitor effects. In particular, the ternary composite system has better synergistic effects compared to the binary composite system. It is of great significance for the construction of efficient hydrate drilling fluid systems in the future. • The inhibition assessed with binary or ternary thermodynamic and kinetic inhibitor. • Thermodynamic inhibitors are only useful at high concentrations. • The mechanism of thermodynamic and kinetic inhibitor combinations was elucidated. • Inhibitors are more effective when compounded than when used individually. [ABSTRACT FROM AUTHOR]

• Laponite could substantially enhance the thermal stability of drilling fluid. • Laponite increased the onset decomposition temperature of AAD terpolymer. • Laponite largely increased the high-temperature viscosity of the solution of AAD. • Strong interactions between laponite and AAD lead to the enhancement. Aiming to overcome the problem of polymer degradation in water based drilling fluids under high temperature, this letter examined the influence of laponite nanoparticles on the thermal stability of drilling fluids. Firstly, a terpolymer (AAD) was synthesized through radical polymerization of acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, and diallyldimethylammonium chloride monomers. The presence of laponite nanoparticles significantly improved the onset decomposition temperature and viscosities of AAD terpolymer at high temperatures, according to thermogravimetric analysis (TGA) and high temperature high pressure (HTHP) rheology results, respectively. Thereafter, water based drilling fluids containing AAD and laponite were formulated and aged under different temperatures. The drilling fluids containing laponite had a substantially higher viscosity than that without laponite ascribing to strong interactions between laponite and functional groups of the ADD terpolymer. This letter provided us a novel strategy to develop high temperature resistant drilling fluids for deep reservoir excavation. [ABSTRACT FROM AUTHOR]

Integrating the advantages of inorganic and polymeric nanoscale plugging agents, this paper introduced the synthesis of a nanoscale acrylic resin/nano-SiO 2 composite (AR/SiO 2 ) with a core-shell structure for water based drilling fluid (WBM), which can enhance the plugging efficiency of shale pores, reduce fluid invasion and improve wellbore stability in shale gas drilling process. The core-shell structure of AR/SiO 2 was characterized by transmission electron microscope (TEM). Thermal Gravity Analysis (TGA) indicated the thermal resistance of AR/SiO 2 up to 250 °C. Theoretical analysis implied that improved plugging property of AR/SiO 2 might be due to good adhesion of deformable shell parts with shale matrix and the supporting provided by rigid core parts. The plugging ability was evaluated by pressure transmission tests and N 2 adsorption tests. The results demonstrated that WBM containing AR/SiO 2 can substantially enhance plugging efficiency and reduce fluid invasion. Characterization of filter cakes revealed that AR/SiO 2 improved the quality of filter cakes, which resulted in a considerable improvement in filtration properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hydrophobic quaternary ammonium salt SJAY was synthesized as shale inhibitor. • SJAY with hydrophobic groups made shale slice surface wetting reversal. • SJAY showed surfactant properties to reduce surface tension. • SJAY could effectively inhibit the hydration of shale and increase clay stability. 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. [ABSTRACT FROM AUTHOR]

Research progress of self-healing hydrogels based on both reversible covalent and reversible non-covalent bonds are systematically reviewed. The preparation methods, mechanical properties, healing mechanisms, and effects of self-healing hydrogels with different healing methods are compared and analyzed. Based on the unique characteristics of different types of self-healing hydrogels and current problems of conventional polymer gels used in the fields of drilling fluids and enhanced oil & gas recovery, the self-healing hydrogel-based materials used as blocking agent, lost circulation control agent, and wellbore strengthening agent that can significantly improve the performance of drilling fluids, as well as profile control agent, water shutoff agent, and profile control-displacement agent that can significantly enhance oil & gas recovery are proposed. This article will provide theoretical and technical references for the future application of self-healing hydrogels in the field of oil–gas drilling and development engineering. • Self-healing hydrogels based on covalent and non-covalent bonds are reviewed. • Hydrogels with different healing mechanisms show different performances. • Action mechanisms of self-healing gels used in drilling fluid are described. • Action mechanisms of self-healing gels used in enhanced oil recovery are shown. [ABSTRACT FROM AUTHOR]

Nano-plugging agents (NPAs) are very important to stabilize the wellbore by reducing pressure transmission and drilling fluid invasion during drilling engineering. A functionalized polystyrene latex (FPL) was synthesized by micellar polymerization as a NPA for drilling fluids. The particle size and thermal stability of FPL were characterized by particle size analysis and thermogravimetric analysis (TGA). The experimental results showed that the initial thermal decomposition temperature of FPL was 310.6 ℃. The medium value of particle size distribution (D50) of FPL decreased from to 371–235 nm after aging at 220 ℃, indicating that FPL had good temperature resistance property. The plugging method and plugging performance of FPL for four filter media with pore sizes from 0.01 µm to 10 µm were introduced. FPL itself was difficult to plug the filter papers and ceramic filter disks, but FPL could reduce fluid loss of bentonite suspensions. SEM observation indicates that FPL could improve the quality of mud cakes and plug the small pores of ceramic filter disks. For microporous membranes and artificial mud cakes with low permeability, FPL aqueous suspensions had a good plugging performance. The plugging experimental results conformed well to the 2/3 bridging rule. This paper provides a good reference for the development of high temperature NPAs and the establishment of evaluation methods of NPAs. [Display omitted] [ABSTRACT FROM AUTHOR]

With the acceleration of deep oil and gas development, the problem of high temperature and high salinity in the formation is prominent, which seriously affects the rheology and filtration performance of water-based drilling fluid and causes drilling accidents such as formation collapse and wellbore instability. Therefore, in this work, a novel thickening and fluid loss control additive (i.e., ASML) with significant hydrophobic association characteristics as well as outstanding temperature- and salt-resistance was synthesized using acrylamide, sodium p-styrenesulfonate, maleic anhydride and lauryl methacrylate as monomers. The experiments of fluorescence spectroscopy, SEM, Zeta potential, rheology and filtration show that ASML makes the drilling fluid have more networked structure under the conditions of high temperature and high salt through hydrophobic association. At the same time, it also brings more negative charge to the bentonite by adsorbing ASML on the surface of bentonite, which effectively maintains its uniform colloidal dispersion, leading to higher viscosity, denser mud cake, and lower fluid loss under high temperature and high salinity conditions. Under the condition of 200 °C and 30 wt% NaCl, the fluid loss of ASML-based drilling fluid is only 5 ml, which is 94.3% lower than that of carboxymethyl cellulose-based drilling fluid. This study provides a new strategy for the development of temperature- and salt-resistant drilling fluid treatment agent, which is important for accelerating the efficient development of deep oil and gas. • One kind of filtration reducer (i.e., ASML) with hydrophobic association properties was developed. • The hydrophobic association structure of ASML and its promotion by NaCl were observed by TEM. • The performance of the filtration reducer for water-based drilling fluids has been improved to 200 °C and 30 wt% NaCl. • The mechanism of ASML in drilling fluids was revealed. [ABSTRACT FROM AUTHOR]

• The shale inhibition ability was enhanced after introducing hydrophobic group. • HCPA had a better performance than commonly used shale inhibitors. • HCPA could greatly increase the water contact angle of the rock and the mud cake. • The ability of clay to adsorb water was reduced after treatment of HCPA. • HCPA could reduce the water imbibition capacity of rocks. Wellbore instability in complex shale formations is a major technical problem that threatens drilling safety and efficiency. In this paper, a hydrophobic cationic polyamine shale inhibitor (HCPA) was prepared by introducing a hydrophobic group in the molecular structure of an amine-based shale inhibitor having a branched structure. The shale inhibition performance of HCPA and the amine-based shale inhibitor without the hydrophobic group (CPA) was investigated. The hydration inhibition mechanism of HCPA was studied by experiments of zeta potential, particle size, contact angle, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), etc. The evaluation results show that HCPA had a better performance than CPA in terms of inhibition of hydration swelling, hydration dispersion and mud making, which indicates that the hydrophobic group is beneficial to improve the inhibition ability of the amine-based shale inhibitor. The mechanism study shows that there is no hydrogen bond between HCPA and clay. The adsorption on the clay surface is mainly driven by electrostatic interaction, which reduces the repulsion of the electric double layer and thus inhibits the osmotic swelling of clay. HCPA could increase the water contact angle of the rock from 36.6° to 133° at a concentration 0.5%, beneficial to reduce surface free energy. The bentonite modified by HCPA had a lower weight loss of at 200 °C than bentonite modified by CPA according to TGA test, and the interlayer spacing of HCPA-modified bentonite was reduced compared with that of the unmodified bentonite, indicating that the ability of bentonite to adsorb water molecules is reduced after the introduction of hydrophobic groups, beneficial to inhibit the crystalline swelling of clays. In addition, HCPA can reduce the imbibition capacity of rocks by reducing the surface tension of water. Therefore, the concept of introducing hydrophobic groups in the molecular structure proposed herein could provide an avenue to develop high-performance shale inhibitors. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Nano-lignosulfonate (Nano-LS) was formed gradually from the inside to outside through the layer by layer self-assembly method under the interaction of π-π bond and synergistic effect of ultrasound. Then acrylamide (AM) and 2-Acrylamido-2-methylpropanesulfonic acid (AMPS) were grafted onto Nano-LS in aqueous solution, potassium persulfate used as initiator. The structure of resulting the graft copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR) methods. Thermogravimetric analysis (TGA) revealed the thermal stability of the graft copolymer and the results showed that the thermal decomposition of the graft copolymer was after 295.16 ℃. The graft copolymers with different additions were prepared in water-based drilling fluids (WBDFs) and the action mechanism of graft copolymer in water-based drilling fluid was revealed by scanning electron microscopy (SEM). The rheological and filtration properties of drilling fluids were evaluated before and after hot rolling (BHR and AHR) at 200.0 ℃ for 16.0 h. The results revealed that the fluid exhibit shear thinning behavior under static conditions as a gelatinous structure. When the amount of graft copolymer is 3.0 wt%, the result showed that the fluid loss (FL API) can be significantly reduced to 7.5 mL after hot rolling at 200.0 ℃ for 16.0 h. Moreover, the results showed that the thermal stability, salt resistance and calcium resistance of the graft copolymers are high enough to be used as effective additives in high temperature, high salinity and high calcium water-based drilling fluids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Silicone quaternary ammonium salt was used as shale inhibitor in drilling fluid. • SQAS can chemically react with the shale and form a seamless hydrophobic film. • SQAS can significantly increase the contact angle of water on the shale surface. • SQAS can effectively inhibit the hydration of shale and stabilize wellbore. Wellbore instability caused by the hydration of shale formations during the drilling process is the main technical problem in drilling engineering. The existing shale inhibitors mainly inhibit shale hydration through charge neutralization, intercalation, activity reduction, and/or plugging. Few shale inhibitors focus on reverse the wettability of shale surface. In the paper, the shale inhibition performance of silicone quaternary ammonium salt (SQAS), a material that can reverse the wettability of shale surface, was evaluated and the shale inhibition mechanism of SQAS was studied via particle size, zeta potential, contact angle, scanning electron microscopy (SEM), and shale water absorption analyses. The experimental results show that the use of SQAS could result in a relatively lower linear swelling rate of clay, and its rolling recovery rate of easily hydrated shale was as high as 64.25%, which is better than those of polyamine inhibitors. The study on the inhibition mechanism revealed that SQAS can chemically react with the shale surfaces to form a seamless hydrophobic film. The water contact angle on the shale surface was increased from 28.7° to 110.7°, which greatly reduces water penetration into shale and the water absorption capacity of clay minerals. The results of this study provide new technical ideas for the development of high-performance shale inhibitors. [ABSTRACT FROM AUTHOR]