Experimental Study on Fiber Balls for Bridging in Fractured-Vuggy Reservoir

Summary For conventional particles used for conformance control in fractured-vuggy reservoirs, large-size particles easily plug the wellbore area but have difficulty plugging the zone far from the wellbore, while small-size particles easily move in depth. In this study, fiber balls for bridging in fractured-vuggy reservoirs were developed by wrapping the fiber in the precrosslinked gel. Due to the influence of temperature and salinity in the formation, the gel degraded and the filamentous fibers were released. Then, the released fibers bridged in the fractures while reducing the safety risk of the injection process. As a water plugging agent, the fiber balls can decrease the conductivity in high-permeability fractures and increase the conductivity in low-permeability fractures, thus improving waterflooding efficiency and enhancing oil recovery. The plugging performance of fiber balls was evaluated by coreflooding experiments. The experimental results show that the optimal formulation of fiber balls is 7% acrylamide (AM) + 3% polyamino acid ester + 0.75% potassium persulfate (K2S2O8) + 4% polypropylene fiber + 4% glass fiber + 0.15% polyethylene glycol diacrylate (PDA) + 0.08% N,N-dimethyl acrylamide (MBA) + 0.1% polyacrylamide (PAM). The release time of fibers from the external gel is 42 to 57 hours, meeting the requirements of conformance control. According to the results of the performance evaluation, the larger the fracture width, the worse the bridging effect of fibers. Besides, the rule of “3/2 bridging” fiber was proposed: When the fiber length is 3/2 times the fracture width, the fiber has the strongest bridging and plugging ability. With the increase in fracture width, the fiber concentration needs to be increased to have a good bridging performance. The results of this study can provide a new idea for the technology of conformance control in fractured-vuggy reservoirs.