High temperature resistant polymer gel as lost circulation material for fractured formation during drilling

A cross-linked polymer gel system used for lost-circulation control during drilling with a high-temperature resistance of 160 °C was prepared from a formulation containing 1% of polymer ZB-1/ZB-2 (1:1 ratio), 0.2% of catechol, 0.4% of hexamethylenetetramine, and 0.3% of thiourea. The effects of time, temperature, and salinity on the gelation performance of polymer gel were analyzed. The results indicate that the gelation time of the polymer gel lost-circulation system at high temperature (160 ℃) is 6–20 h, with the maintenance of the storage modulus after gelation at greater than 60 Pa with the loss modulus retained at above 20 Pa. The polymer gel displayed excellent gel strength and viscoelasticity. The salinity has little influence on the viscoelasticity of the gel system, indicating that the gel system has excellent salt-resistance and is suitable for lost circulation control in the drilling process of high-temperature and high-salinity formations. The plugging performance of the polymer gel lost circulation material system on fractures with different widths and roughness was studied. The results show that the bearing resistance capacity of the gel gradually decreases as the fracture width increases, and the lost circulation control performance of the gel is significantly better on rough walls than on smooth walls. In addition, as the fracture width increases, the gel strength contributes to the bearing resistance capacity. This study indicates the excellent lost-circulation-control performance gained using the polymer gel LCM for fractures. To improve lost-circulation-control performance, the gel strength and the cementing force between the gel and the fractured wall must be improved.