Effects of Stimulation additives on the rheology of VES-based acids

Utilizing an efficient diverter ensures uniform distribution of injected fluids across entire treated interval in a matrix stimulation operation. Viscoelastic surfactants are one of the most effective chemical diverters. VES fluids demonstrate both viscous and elastic properties to divert flow to untreated sections. However, addition of acidizing additives to VES solution can greatly affect the rheology of spent VES specially at high temperatures. In this study, the effect of several available commercial additives including corrosion inhibitor, non-emulsifier, iron chelating agents, methanol, mutual solvent, and iron reducing is investigated on the rheology of a new medium temperature VES over temperature range of 80 to 220 ˚F.Results of our study indicate that corrosion inhibitor reduces the spent VES viscosity at high temperatures. Increasing corrosion inhibitor concentration shifts the viscosity graph to lower temperatures. Non-emulsifiers also shift the viscosity graph to lower temperatures and higher viscosities. Contrary to previous studies, no drastic reduction in viscosity is observed by addition of 0.2 vol% compatible non-emulsifier. In addition, 1 vol% of iron chelating agents slightly reduces the viscosity of spent VES. However, iron reducing agent exhibits no significant change in viscosity graph of spent VES. As per rheology measurements, an overflush containing mutual solvent can easily break the rod-like micelles and convert the gelled fluid to a water-like solution to facilitate faster post acid clean-ups.

Keywords:

Viscoelastic surfactant , well stimulation , chemical diversion , acidizing additives