Effect of Graphene Oxide on the Microstructural Properties and Self-Healing Capacity of Well Cement Slurries Cured for Nine Years

The primary objective of well cementing is to achieve durable zonal isolation, thereby ensuring well integrity and safe long-term operation, which to a large extent depends on the proper design of the cement slurry formulation. In this context, particular importance is placed on the development of cement slurry formulations capable of withstanding harsh downhole conditions and producing set cement with modified microstructural properties and self-healing capacity. Graphene oxide (GO) is one of the potential nanoadditives that may support these mechanisms. Therefore, the aim of this study was to evaluate the long-term effect of GO on the microstructure and autogenous self-healing of microcracks in set well cement intended for wellbore sealing. Cement specimens prepared using CEM I 42.5 R Portland cement, with GO contents of 0.05% and 0.15% by weight of cement (bwoc), were examined after nine years of curing. Scanning electron microscopy (SEM) and micro-X-ray fluorescence (µ-XRF) analyses revealed microstructural features and elemental distribution patterns consistent with GO-induced modifications of the cement matrix. Observations of mineral precipitation within microcracks provided evidence of processes potentially contributing to autogenous crack sealing. Furthermore, porosity measurements demonstrated that the incorporation of GO into cement slurries with a water-to-cement ratio (w/c) of 0.7 reduces the pore volume, including the volume of capillary pores. These findings provide insights into the long-term microstructural behavior of GO-modified set cement and suggest its potential for developing advanced cement slurry formulations intended to enhance the durability of cement sheaths in hydrocarbon production, geothermal, and other demanding wellbore applications.