A Temperature-Responsive Expandable Gel Lost Circulation Material for Oil Drilling toward Deep Strata

Lost circulation is a significant and complex issue in drilling operations, often prolonging the drilling cycle, increasing costs, and potentially leading to borehole abandonment. In this paper, we developed a temperature-responsive expandable gel polymer, PDNN, to prevent lost circulation in deep formations at temperatures exceeding 150 °C. This was achieved using cationic and anionic monomers, a temperature-controlled hydrolysis monomer, and a cross-linking monomer. This material exhibits exceptional temperature-controlled water absorption and expansion capabilities. When immersed in water at temperatures of 120 °C or below for 24 h, the dried gel particles swell by less than 2.50 times, but at temperatures above 150 °C, they expand more than 19.53 times. This material only expands significantly upon reaching deep formation, overcoming the issue confronted by conventional swelling gel particles that swell before entering the loss channels. The particle size of the PDNN gel can be adjusted to effectively block consolidated sand discs (150 μm), unconsolidated sand beds (20–40, 40–60, and 60–80 mesh), and fracture plates (2, 3, and 4 mm). The generated gel layer can withstand pressure exceeding 6 MPa. The amide groups in the heptacyclic rings of the side chains of PDNN undergo hydrolysis and ring-opening at high temperatures, generating –COOH and –OH. This enhances hydrophily, allowing the gel to absorb large amounts of water and expand to fill in lost circulation channels, resulting in a tight sealing layer that effectively reduces drilling fluid loss and ensures safe, efficient, and smart drilling.