| dc.description.abstract | Viscoelastic surfactants (VES) have been successfully applied in well stimulation treatments, including acid-diversion and hydraulic fracturing. However, high temperature, interactions of VES with metallic cations, alcohol-based additives, and nano-materials all interfere with the apparent viscosity of the VES-based fluids and reduce the efficiency of these systems and even lead to further damaging the formation. The main purpose of the present thesis is to characterize any possible interaction/reaction of typical VES-based solutions in the oil and gas industry with common acid and fracturing fluids additives and contaminations such as corrosion inhibitors, metal cations, and nano-materials.
Dynamic and static rheological properties of different VES-based acid systems were investigated to study the effects of additives on the viscoelasticity and surface tension of the VES system. Small angle X-ray Scattering was carried out to determine the morphology of the micellar structures in the VES-based systems. Infrared spectroscopy, UV-vis spectroscopy, and single X-ray crystallography were utilized to characterize the molecular interactions/reactions that lead to alteration of the macroscopic behavior of surfactant systems.
Formation of wormlike micelles in a system containing a zwitterionic C22-tailed sulfobetaine surfactant in the presence of Fe3+ in HCl was demonstrated by rheological and SAXS profiles. The transition from viscoelastic behavior to non-Maxwellian elastic gel-like behavior after the addition of Fe3+ is confirmed through dynamic rheological measurements. The addition of different types of corrosion inhibitors to the VES solutions led to changes in the conformation of micellar structures and rheology of the VES-based solutions. The addition of trace amounts of carbon nanotube (CNT), 0.04 to 0.2 wt%, to the VES solutions enhanced the rheological behavior of tested VES systems by approximately 40%. The main interactions/reactions are characterized to be acid-base reactions and hydrogen bonding. The results of this study also show that the amide part of VES is the leading functional group that can react/ interact with corrosion-inhibitor, CNT, and metal cations, screening the repulsion forces between surfactants headgroups and, as a result altering micellar structures.
The results of the present study can be used to design more efficient VES-based acid systems and prevent the occurrence of post-formation damage following the treatment. | en |
