Big data nanoindentation characterization of cross-scale mechanical properties of oilwell cement-elastomer composites

Intensive big data nanoindentation (BDNi) characterization was performed to reveal the cross-scale mechanical properties of, and hence distinguish the different phases in, inorganic–organic hybrid oilwell cement-elastomer composites, hydrothermally cured at 160 °C and 20 MPa for 28 days. Totally-three emulsified and particulate elastomers, including styrene-butadiene latex (SBL) emulsion (6, 12, and 14 wt.%), polypropylene (PP) powder (12 wt.%), and nitrile rubber (NR) powder (6 wt.%), and a weighting agent, hematite (50 wt.%), were used as additives to finely adjust the mechanical properties and microstructure of the hybrid composites, which were respectively examined by the BDNi and mercury intrusion porosimetry and scanning electron microscopy. BDNi data were statistically deconvoluted by the Gaussian mixture modeling (GMM) to discern mechanically distinct phases and their Young’s moduli and hardness at the micro/nano scale and the bulk composites’ properties at the macro scale. Results show that the SBL emulsion can be more homogeneously dispersed into the cement matrix, due to its emulsified soft consistency and hydrophilicity, resulting in the formation of soft coatings on, and softer infills intermixed with, the cement hydration products (CHPs). In contrast, the two hydrophobic, inert, particulate elastomers, PP and NR powders, only act as isolated soft inclusions embedded in the hydrated cement matrix. The NR melts at high temperatures and permeates into the pores of the cement matrix, leading to the formation of complex intervened micromorphology and hence functions better than the PP. All elastomers can effectively reduce the composites’ Young’s moduli: with increasing the elastomer contents, while the modulus of a BDNi-identified major CHP phase decreases from 20.9 to 11.3 GPa, the bulk composites’ counterpart from 17.3 to 10.7 GPa. The BDNi enables the identification of multiple mechanically distinct phases in the hybrid composites and quantification of the property changes of these phases.