Investigations of rheology and a link to microstructure of oil-based drilling fluids

Towards establishing a first-principles physical link between the field-behavior and microstructure of oil-based drilling fluid (OBDF), we study rheology an OBDF its variation with different contents water, clay viscosifier, or barite weighting agent during steady dynamic rheological phenomena, develop “cryo-preserved” experimental methodology towards in-situ microscopy. Rheological data was collected for shear rate ramps 0.0001 s 1 1000 s−1, under temperatures ranging from 10°C to 60 °C, three water/oil ratios, multiple compositions. Oscillatory constant measurements showed elastic loss modulus co-dominate when stress is below ~1 Pa, but above Pa “apparent yield-stress” reorganizes, elasticity decreases, flow follows viscosity-dominated shear-thinning Herschel–Bulkley behavior. Signs thixotropy are seen in increasing vs. decreasing curves regime, shows time-dependency. Clay particles created more so than other ingredients. Elimination clay, caused approximately equal reduction viscosity. water also led dominating over viscous longer range strain linear-elastic pre-yield state, likely due droplets having shorter length scale which yield-stress broken does water-free mixture. had similar lesser effect on elasticity. Cryological scanning electron microscopy (Cryo-SEM) cryological x-ray spectroscopy (Cryo-EDS) methods show promise future work identify spatial at nanometer micrometer scales state that approximates like state. Chemical identification individual phases within mixture components achieved via quantitative elemental method. Water droplets, base oil, identifiable imaging sheared OBDFs proposed.