Polyvinyl Alcohol‐Based Urea Formaldehyde Resin Used as Plugging Agent in Fractured and Caved Reservoirs

ABSTRACT

To address the drawbacks of traditional urea‐formaldehyde (Poly‐UF) plugging agents—high free formaldehyde content, insufficient temperature and salt tolerance, and poor adaptability to fractured‐vuggy reservoirs—this study developed a high‐performance urea‐formaldehyde‐polyvinyl alcohol (UF‐PVA) composite plugging agent via process innovation, structural modification, and multi‐component synergistic optimization. Using a polycondensation process and experimental validation, the optimal preparation parameters of UF‐PVA were determined. Modifying Poly‐UF molecules with PVA reduced the product's free formaldehyde content by 36.59%, increased solid content and viscosity by 1.64% and 39.82% respectively, resolving the dilemma of balancing environmental friendliness and performance in traditional urea‐formaldehyde resins. A synergistic strategy of functional additives was proposed: compounding flow pattern modifiers, curing accelerators, and volume expansion enhancers systematically enhanced the plugging agent's temperature resistance, shear resistance, salt tolerance, and acid‐alkali resistance. The agent has a maximum applicable temperature of 120°C, with minimal impact from shear and salinity; at a dosage of 20 wt%, its core plugging rate reaches 94.64%, demonstrating excellent sealing capability. This study optimizes the performance of traditional urea‐formaldehyde resins, expands the application boundary of UF‐PVA, and provides an environmentally friendly and efficient technical solution for enhanced oil recovery (EOR) in complex and harsh reservoirs.