Design, Preparation and Property Study of Hydrocarbon-Triggered Self-Healing Materials

In the long-time service life of a cement sheath, micro-annuli and microfractures are easy to be generated therein due to the formation stress variations and the complex chemical environment, resulting in sustained casing pressure and loss of interlayer isolation. The use of hydrocarbon-triggered self-healing materials is an effective means of addressing this problem. Under an environment with both cement slurry and methane, a comparison was made of the expansion ratios by hydrocarbon absorption of a self-developed hydrocarbon-triggered self-healing material DBC-CA, namely, borate-crosslinked cyclodextrin-acrylate compounded resin, and a hydrogenated styrene-butadiene block copolymer (SEBS). The expansion mechanisms and thermal stability of these two hydrocarbon-triggered self-healing materials were investigated through 3D computed tomography (CT), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The results of the research show that the expansion performance of DBC-CA in different environments is superior to that of SEBS, and DBC-CA also shows good thermal stability. In a methane environment, the highest expansion rate of DBC-CA is 37%, and DBC-CA is quite responsive to the environment, with its maximum expansion ratio in a cement slurry being less than 8%. A cement slurry containing 10% DBC-CA shows the best performance in minimizing the widths of the microfractures and in eliminating connected seepage channels. Morphological analysis demonstrates that the elastic energy dissipation characteristics of DBC-CA results from a triple protection mechanism involving rigid framework, dynamic bond rearrangement and nanocavities. DBC-CA can slightly reduce the 28-day compressive strength of a set cement. The achievements of this research provide a new idea for the design of downhole self-healing sealing materials for deep gas well application.