H2S-responsive zwitterionic hydrogel as a self–healing agent for plugging microcracks in oil-well cement

During cementing construction, H2S gas leak from micro-cracks of cement ring or cementing interface, seriously damaging wellbore integrity and shortening the life of wells. Therefore, microcrack self-healing cement technology is of great significance for oil wells to maintain the durability of cement rings and adapt to complex underground environments. Herein, acrylamide (AM), acrylonitrile (AN) and N-vinylformamide (NVF) were used as functional monomers, and laponite was added to prepare Laponite-poly(acrylamide-acrylonitrile-n-vinylformamide) nanocomposite hydrogel (L-PMAN) with excellent mechanical strength as micro-crack repair agent for gas-triggered cementing cement sheath. Considering the difference of chemical environment in the process of wellbore cement slurry sealing and subsequent micro-fracture plugging, different structural units were selected to design amphoteric structure. The construction of zwitterionic structure makes it exhibit excellent swelling behavior in salt solution while maintaining 80% of the original mechanical strength. More importantly, after adding L-PMAN powder,cement stone (C1) can achieve good repair of microcracks under the trigger of H2S within 3 days, and the maximum gas breakthrough pressure can reach 2.5 MPa, indicating the great potentials of the L-PMAN for plugging microcracks in cement sheath.