Plugging performance and mechanism of an oil-absorbing gel for lost circulation control while drilling in fractured formations

Lost circulation of drilling fluid is one of the most common engineering problems in the drilling process of fractured formations. In this study, an oil-absorbing polymer gel synthesized using compound monomers with rigid and flexible chains was applied to control the oil-based drilling fluid loss while drilling. The microstructure, oil-absorbing performance, and plugging performance the gel was investigated. A large number of dense pores on the surface of the gel were observed, which allowed the oil molecules to enter the internal space of the gel. The initial oil absorption capacity of the gel was fast, and it increased with the increase in the temperature and decrease in the particle size, reaching 20.93 g/g at 140 °C. At a high temperature of 140 °C, the bearing pressure capacity of the gel formula containing particles of different particle sizes reached 7.6 MPa for a fracture of a width of 3 mm, showing that the oil-absorbing gel have excellent plugging performance at high temperature. Plugging mechanism of the gel was investigated through visualized fracture plugging experiments. Results show that the dynamic migration, particle-swelling, particle-bridging, particle-aggregation, deformation-filling, and compaction-plugging contribute to the whole lost circulation control process, reflecting that the plugging performance can be effectively enhanced by improving the aggregation and filling degrees of the gel with different particle sizes.