Self-Repair of Cement Paste with Gas-Sensitive Graft Polymer

Summary To solve the problem of annular gas channeling in natural gas well cementing, isoprene rubber was used as graft matrix material, natural gas absorbing methyl methacrylate and octadecyl acrylate were used as functional monomers, a gas-inspired expansion graft polymer was prepared by graft copolymerization, and a natural gas-triggered self-repair cementing slurry was developed. The structure of gas-sensitive grafted polymer was characterized by Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR), and the effects of monomer concentration and copolymer feed ratio on equilibrium swelling degree were investigated. For the cement stone (ring) samples with microcracks and microgaps, the gas-triggered repair performance of the system was evaluated by using a self-designed testing instrument. The results show that the gas-sensitive material can increase the gas channeling resistance of fractured cement paste by one to two orders of magnitude. The material system has been applied to 20 deep gas wells in Daqing Field, and the test results show that the system can guarantee the effective sealing of the cement sheath.