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Drilling fluid loss is a major problem with serious economic and environmental consequences. The use of traditional lost circulation materials (LCMs) to seal wide fractures increases the risk of bit nozzle plugging. In this work, smart LCMs based on shape memory polyurethane (SMPU) are proposed for the first time. SMPU can be programmed to recover at temperatures suited to a given well. As such, SMPU smoothly passes through the bit nozzles, while effectively seal wide fractures once activated. The SMPU is prepared by two step pre-polymerization and characterized by Fourier transform infrared spectra, X-ray diffraction, and differential scanning calorimeter. The SMPU is programmed by changing and fixing the original shape to a temporary shape through a thermo-mechanical process. The shape memory behavior of SMPU is analyzed by tensile apparatus. Compatibility of SMPU with WBMs is determined from mud rheology and filtration tests. Fracture sealing efficiency and shape recovery of SMPU are evaluated by a modified particle permeability apparatus fitted with a model fracture. The results confirm high sealing and shape recovery attributes of SMPU. The plug formed at 114 kg m -3 SMPU and 80 °C experiences a sealing pressure of 100 bar with 71.5 cm 3 cumulative fluid loss.

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This study aims at evaluating the performance of thiamine as a new eco-friendly shale inhibitor in water-based drilling fluids (WBDFs). The evaluation experiments include sedimentation, bentonite inhibition, filtration, zeta potential, thermal gravimetric analysis, scanning electron microscopy, X-ray diffraction, shale cuttings recovery, linear swelling and Fourier transform infrared spectroscopy (FTIR). The performance of thiamine was compared to potassium chloride. In contrast to deionized water, the aqueous solution of thiamine exhibited greater power to inhibit montmorillonite (Mt) dispersion, much more Mt loading capacity (280 g/L) and fluid loss, lower Mt mass loss, larger aggregated Mt particles, lower interlayer space of the Mt particles, less shale cuttings disintegration and lower linear swelling. Adsorption of thiamine on Mt led to a significant shift in the value of zeta potential (from −17.1 to +8.54 mV). Thiamine demonstrated superior inhibitive performance than potassium chloride. FTIR analysis confirmed that thiamine is adsorbed on Mt particles. The compatibility test revealed the compatibility of thiamine with conventional WBDF additives. It was concluded that the main probable inhibition mechanisms of thiamine are the cation exchange and Mt surface coating. In view of its prominent inhibition capacity and great environmental acceptability, thiamine is a promising inhibitor for drilling in water-sensitive formations.

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