Research on Temperature‐Responsive Thickening and Expanding Polyurethane Cement Composite Material for Targeted Plugging

ABSTRACT Isocyanate‐based polyurethane is an excellent chemical grouting material with superior injectability, high bonding strength, and foaming expansion properties. However, the application scope is significantly restricted by the high reactivity of isocyanate groups, particularly in long‐duration well construction scenarios. In this study, diethyl malonate, phenol, and n‐butanol were employed as blocking agents to protect the NCO groups. The experiments indicate that the blocking efficiency of the three types of polyurethanes is above 96%, and the deblocking temperatures are 110°C, 140°C, and 180°C, respectively. Focusing on severe fractured lost circulation in the Jurassic Shaximiao Formation, a diethyl malonate‐blocked polyurethane modified cement system was developed. The thickening time of the polyurethane modified cement system could be precisely controlled within 2–5 h by adjusting the retarder content (0.5%–2%). As the content of blocked polyurethane increased (1%–9%), the temperature‐activated slurry consistency increased by 16.20%–61.56% and the expansion ratio improved from 7.14% to 28.57%. Post‐solidification water contact angle was significantly increased from 23.8° to 62.2°. The early‐age compressive strength decreased from 23.5 to 17.4 MPa. A temperature‐responsive polyurethane cement system with tunable thickening and expansion behaviors was developed in this study, which enhanced plugging precision and operational efficiency in oil/gas wells.