Development and Characterization of a Thermally Induced Expandable and Acid-Generating Temporary Plugging Agent for Reservoir Formations

For the purpose of efficient temporary plugging and self-removal of the plugging of reservoir formations, the thermally induced expandable and acid-generating temporary plugging agent (TAPA) was prepared with acrylonitrile (AN), methacrylic acid (MAA), <i>N</i>,<i>N</i>-dimethylacrylamide (DMAA), and butyl acrylate (BA) as the shell monomers as well as the carboxylate esters with high boiling points as the core material. The TAPA was structurally characterized, and the properties were studied. The results showed that the TAPA had a good spherical structure with a median particle size (D50) of 16.03 μm. The initial expansion temperature <i>T</i> _start of the TAPA was 134.75 °C, and its maximum expansion temperature <i>T</i> _max was 197.77 °C. The surface was hydrophilic and negatively charged, with excellent shear strength and sealing. The TAPA was suitable for temporary plugging and self-removal of the plugging of the reservoir formation with a temperature of 160 °C. The release of core materials and the effect on self-removal of plugging were not significantly affected with different salinities, weak acid or weak alkali environments, or a small quantity of hydrocarbons. With addition of 1-3 wt % TAPA, the rheological property of water-based drilling fluid changed slightly, but the filtration loss reduced, suggesting a good compatibility of the TAPA with the drilling fluid. Results of plugging and plugging removal experiments in fractured reservoir formations and permeable reservoir formations showed that the TAPA improved the strength of the temporary plugging layer with the elastic deformation due to thermal expansion and realized self-removal of the plugging by corroding the temporary plugging layer with carboxylic acid hydrolyzed from the carboxylic ester released, thereby decreasing the backflow pressure of oil and gas wells in the production stage. The results provided a new method and technological idea for efficient temporary plugging and self-removal of the plugging of reservoir formations.