摘要
Lost circulation in fractured formations is a worldwide problem experienced in drilling engineering characterized by low plugging efficiency and poor plugging effect. Adhesive materials are introduced to solve the problems of poor self-adaptation of the conventional composite bridging plugging systems in fractured formations and repeated lost circulation caused by pressure fluctuations. As a thermoplastic resin with low price and good chemical stability, aging resistance and adhesive properties, ethylene vinyl acetate (EVA) can be filling and adhesion in the form of particles in fracture channels. Therefore, this study evaluated the viscoelasticity, high-temperature stability and glass transition characteristics of EVA particles as well as quantitatively analyzed the degree of melting of EVA based on visualization, thermogravimetric, dynamic thermodynamic and particle size analysis experiments. The optimal formulation of the bridging system with adhesive material was optimized through fracture pressure-bearing plugging experiments and the mechanism of action of the system was revealed. The experimental results reveal that the adhesive EVA particles have good thermal stability (thermally decomposes after 374 °C) and viscoelasticity. A simulation experiment involving plugging a 2-mm fracture using the bridging system with adhesive material reveals that the pressure-bearing capacity is 12 MPa, the cumulative filtration loss is only 50 mL, and the plugging performance is excellent. We inferred that the surface of the adhesive material softened at a specific temperature and possessed strong viscoelasticity, which strengthened the bridging, filling, and twisting of the conventional composite bridging plugging system and increased coherence with the fracture channel surface and increased its stationary capacity. The plugging is synergistic, the plugging zone is strengthened, and the success rate of primary plugging is improved.
危险品化学品经营许可证（带存储）