Manipulation of Pickering emulsion rheology using hydrophilically modified silica nanoparticles in brine.

HYPOTHESIS

Previous work on Pickering emulsions has shown that bromohexadecane-in-water emulsions (50% oil) stabilized with fumed and spherical particles modified with hexadecyl groups develop a noticeable zero shear elastic storage modulus (G') of 200Pa and 9Pa, respectively, while in just 50mM NaCl. This high G' can be problematic for subsurface applications where brine salinities are higher and on the order of 600mM NaCl. High reservoir salinity coupled with low formation pressure drops could prevent an emulsion with a high G' from propagating deep into formation. It is hypothesized that G' of an emulsion can be minimized by using sterically stabilized silica nanoparticles modified with the hydrophilic silane (3-glycidyloxypropyl)trimethoxysilane (glymo).

EXPERIMENTS

Bromohexadecane-in-water emulsions were stabilized with low and high coverage glymo nanoparticles. Oscillatory rheology was used to monitor G' asa function of nanoparticle concentration, oil volume fraction, salinity, and pH. Cryogenic scanning electron microscopy was used to make observations on the emulsion microstructure.

FINDINGS

G' of bromohexadecane-in-water emulsions were minimized by using particles with a high coverage of glymo on the particle surface, which reduced the Ca/silanol site interactions. Emulsions that were stabilized with low surface coverage particles had noticeably higher G', however, their G' could be reduced by a factor of 3.3 by simply lowering the solution pH to 3. Cryo-SEM images showed that nanoparticle bridging was more pronounced with nanoparticles that had low glymo coverage as opposed to high coverage.