The evaluation of wellbore stability performance of a hydrophobic shale inhibitor using “macroscopic − mesoscopic − microscopic” methods

Shale inhibitors serve as critical components in water-based drilling fluids to ensure wellbore stability. However, current performance evaluation methods for shale inhibitors are often incomplete, which hinders the effective selection of optimal inhibitors for practical drilling engineering applications. This study aims to develop a comprehensive multi-scale evaluation framework (macroscopic, mesoscopic, and microscopic) for shale inhibitors to address the limitations of existing methods. The established method was employed to compare and evaluate the performance of a newly synthesized hydrophobic amine inhibitor, denoted as DAC, against conventional shale inhibitors. The results indicate that DAC exhibits the most superior hydration inhibition performance. Macroscopically, the swelling value of bentonite treated with 1 wt% DAC (2.67 mm) was significantly lower than that of the sample treated with 5 wt% KCl (4.63 mm), and the rolling recovery rate of shale cuttings reached 80.7%. Mesoscopically, the pore volume of shale treated with 1 wt% DAC (0.0088 m 3 /g) did not increase markedly after immersion compared to the dry shale sample (0.0074 m 3 /g), indicating effective pore structure preservation. Microscopically, the nano-scale elastic modulus of the shale after immersion (65.5 GPa) was considerably higher than that of the group treated with 5 wt% KCl (53.5 GPa) The experimental results were comprehensively evaluated from multiple scales to demonstrate the exceptional hydration inhibition performance of DAC. The novel multi-scale evaluation method established in this study provides a significant advancement for fundamental research on shale hydration mechanisms and the practical development of high-performance inhibitors.