Nanomaterial compositions are useful for applications in drilling and completion fluids as enhancers of electrical and thermal conductivity, emulsion stabilizers, wellbore strength improvers, drag reduction agents, wettability changers, corrosion coating compositions and the like. These nanomaterials may be dispersed in the liquid phase in low volumetric fraction, particularly as compared to corresponding agents of larger size. Nanofluids (fluids containing nano-sized particles) may be used to drill at least part of the wellbore. Nanofluids for drilling and completion applications may be designed including nanoparticles such as carbon nanotubes. These fluids containing nanomaterials, such as carbon nanotubes, meet the required rheological and filtration properties for application in challenging HPHT drilling and completions operations.