Stability, Rheological Behavior, and pH Responsiveness of CTAB/HCl Acidic Emulsion: Experimental Investigation

Abstract

Cetyltrimethylammonium bromide (CTAB) surfactant was proven to be a reliable emulsifier for creating stable emulsions used for drilling, well stimulation, and EOR. The presence of acids like HCl during such operations may lead to the formation of acidic emulsions. No previous comprehensive investigations have been done to study the performance of CTAB-based acidic emulsions. This paper, therefore, presents experimental investigations of the stability, rheological behavior, and pH responsiveness of a CTAB/HCl-based acidic emulsion. The effects of temperature, pH, and CTAB concentration on the emulsion stability and rheology have been investigated using a bottle test and a TA Instrument DHR1 rheometer. Viscosity and flow sweep were analyzed for the steady state at a shear range of 2.5–250 s–1. For the dynamic tests, the storage modulus (G′) and loss modulus (G″) were observed by applying the oscillation test at the range of shear frequency from 0.1 to 100 rad/s. The results revealed that the emulsion exhibits steady rheological behaviors ranging from Newtonian to shear-dependent (psedosteady), depending on the temperature and CTAB concentration. The tendency of the emulsion to exhibit a solid-like behavior is also dependent on CTAB concentration, temperature, and pH. However, the pH responsiveness of the emulsion is more significantly observed within the acidic range of the pH.

A pH switchable Pickering emulsion stabilised by controlled non-conventional lanthanum sulfide nanoparticles, in situ hydrophobized with a cationic surfactant

“…Mohyaldinn et al previously studied the stability, rheological behaviour, and pH responsiveness of the CTAB/HCl acidic emulsion, and showed that the CTAB-based emulsion destabilised at a higher pH (10), and demulsified within 60 min. 41 Additionally, after the injection of HCl (pH 6.16), the surfactant molecules regain their surface active nature and adsorbed onto the surface of the nanoparticles which made them hydrophobic. This caused the reformation of a stable Pickering emulsion.…”