Lili Yang

During oil and gas drilling operations, water-based drilling fluids (WBDFs) can infiltrate formations under differential pressure, leading to the hydration and expansion of clay minerals and subsequent wellbore instability. The addition of inhibitors to WBDFs can mitigate clay hydration and expansion, thereby enhancing wellbore stability. Therefore, developing efficient inhibitors is crucial for addressing wellbore instability. In this study, four zwitterionic polymers with excellent solubility─namely P(ATAC-SSS), P(MATAC-SSS), P(ATAC-AMPS), and P(MATAC-AMPS)─were selected as the core research subjects, while P(ATAC-PEA) and P(MATAC-PEMA) served as control polymers. These polymers were synthesized via precise structural design and monomer optimization, and their structure–inhibition relationships were thoroughly investigated. The results indicate that the core polymers, which form homogeneous aqueous solutions, exhibit superior inhibition performance compared to the phase-separated control polymers. Specifically, P(ATAC-AMPS) demonstrated outstanding performance, achieving a rolling recovery rate of 77.85% at 1 wt % and reducing the linear swelling of montmorillonite (MMT) by 73.0% at 4 wt % relative to that in pure water. Mechanistic studies reveal that the absence of a methyl group on the vinyl moiety of P(ATAC-AMPS) promotes chain extension, increases accessible adsorption sites, and enhances interfacial adhesion through synergistic electrostatic and hydrogen-bonding interactions. Atomic force microscopy (AFM) quantified the adhesion forces, which follow the order P(ATAC-AMPS) > P(MATAC-AMPS) > P(MATAC-SSS) > aP(ATAC-SSS), in direct agreement with macroscopic inhibition performance. This work elucidates the critical role of molecular flexibility and functional-group accessibility in designing high-efficiency shale inhibitors, providing a structure-guided strategy for next-generation water-based drilling-fluid additives.

The limitation of conventional shale inhibitors to simultaneously provide effective charge screening and deep intercalation is currently one of the main challenges in the design of high-performance shale inhibitors. In this study, we propose a unified design of amino acid ionic liquids (AAILs) as a suitable solution to this functional deficiency, by combining an anion capable of strongly binding to clay surfaces with a charge-neutralization cation. Experimental investigations were assessed by linear swelling tests, shale recovery tests, immersion tests, viscosity measurements, particle size distribution tests, scanning electron microscopy tests, and X-ray diffraction (XRD) analysis. Our results revealed a correlation between molecular design and performance, where the anion’s size, functional groups, and charge distribution were the key parameters to evaluate the inhibiting performance of AAILs. The superior inhibitor was determined by a small size anion such as glycinate possessing complementary functional groups, allowing for deep intercalation and multipoint hydrogen bonding, acting as a cross-linking agent between the clay layers. The glycine-based AAIL, [Veim][Gly], demonstrated outstanding performance, achieving a shale recovery rate of 88.90% after a remarkable reduction in clay swelling by more than 70%, attributable to the combined synergistic effect. Such an inhibitory approach was difficult to achieve with traditional inhibitors or AAILs with bulky structures or positively charged anions. This study could be used as a reference in designing a fundamental principle for high-performance and environmentally friendly shale inhibitors.

Filtrate reducers critically play a crucial role in determining the filtration and wall-building performance of drilling fluids. However, commercially available filtrate reducers often fall short in resisting high temperatures and simultaneously high-salinity contamination, significantly hindering the safe and efficient drilling and completion of deep and ultra-deep wells. A promising strategy involves developing organic–inorganic hybrid filtrate reducers by the integrating thermally stable inorganic materials with amphoteric polymers resistant to multivalent cations. Lamellar nanomaterials, compared to spherical and fiber nanomaterials, offers superior covering, lapping and filling ability in pores and cracks, enhanced resistance to salinity contamination, greater thermal stability, and promoting the formation of a dense filter cake under high-temperature and high-pressure (HTHP) deep-well conditions. In this study, nano TiO2 plate was selected as the inorganic core and graft copolymerized with several organic monomers to synthesize a novel organic–inorganic hybrid filtrate reducer (TIOF). The filtration performance of TIOF, was systematically evaluated in montmorillonite (MMT) dispersions. The results demonstrated that TIOF exhibits excellent thermal stability up to 240 °C and outstanding salt tolerance, maintaining performance in solutions containing up to 36 wt% NaCl and 15 wt% CaCl2. Compared with other reported filtrate reducers, TIOF exhibits superior thermal stability and exceptional tolerance to high salinity environment. These properties indicate its excellent potential for field applications in ultra-deep well drilling operations.

A malignant leakage presents a significant challenge in drilling engineering, particularly within carbonate formations, where such a leakage is frequently encountered. Currently, there is no effective solution to this problem. In this study, a water-reactive polyurethane sealing agent was developed using multifunctional polypropylene glycol and 1,4-butanediol (BDO) as soft segments, diphenylmethane diisocyanate (MDI) as the hard segment, and a composite catalyst consisting of N, N-dimethyl cyclohexylamine (PC-8) and dibutyltin dilaurate (T-12). The material reacts rapidly with water to form a high-strength gel, with the reaction time being controllable. Through experimental optimization, it was determined that the BDO mass fraction was 1%, and the molar ratio of isocyanate group to hydroxyl group was 1.8. Additionally, the gelation time can be controlled by adjusting the mass fraction of the composite catalyst. Experimental results from sand-bed and fracture-plate tests indicated that the material could withstand pressures exceeding 3 MPa at 93 °C and exhibited resistance to saturated NaCl and CaCl₂ environments. The plugging mechanism was investigated using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) spectroscopy. The results demonstrated that the agent formed a compact, micron-scale porous structure upon reacting with water, exhibiting excellent thermal stability and dual plugging performance through both physical and chemical mechanisms. Due to its water-reactive characteristics, a multi-stage injection process was adopted for field application design. This material shows promising potential for mitigating large-fracture-type malignant leakages in drilling operations.