Self-filling and plugging performance of a thixotropic polymer gel for lost circulation control in fractured formation

Abstract

Drilling fluid loss in fractured formations hinders the progress of oil and gas exploration and its development worldwide. Improving the success rate of lost circulation control in fractured formations of oilfields worldwide is crucial for safe, efficient, and economical drilling. The thixotropy of gel solution is an important factor affecting the fracture space filling and plugging performance of thixotropic polymer gel. In this work, a thixotropic polymer gel with shear thinning and static thickening is used as a plugging agent for fractured formations. The self-filling behaviour and plugging performance of the gel in fractures were studied by visual physical simulation. The results showed that the thixotropic polymer gel was less affected by the fracture width when filling in the fracture, which could realize the uniform filling of the 12 mm wide fracture space. In addition, the thixotropic polymer gellant could be pumped in at high shear rates and retained in the loss space at low shear rates. Meanwhile, the plugging performance of the thixotropic gel on different scales of fractures was studied. Thixotropic polymer gel system could reside in different fracture types (uniform fracture, wedge-shaped fracture) and different fracture sizes. The breakthrough pressure of the thixotropic polymer gel in the wedge-shaped fracture was higher than that in the uniform fracture for identical outlet sizes. The thixotropic polymer gel had a pressure bearing capacity of 6.6 MPa in a wedge-shaped fracture with 5 mm width. The pressure bearing capacity of the gel to the wedge-shaped fracture with a width of 3 mm at the outlet reached 7.3 MPa, showed excellent pressure bearing capacity. The study on the self-filling behaviour and plugging performance of thixotropic polymer gel could provide theoretical and technical reference for efficient plugging in the drilling process of fractured formations.