Abstract

Viscoelastic surfactants (VES) are viable alternative to polymer-based stimulation fluids due to potential risks of formation damage associated with polymer-based acid diverters. Internal breakers clean up VES-stimulated wells by reducing viscosity of the gel with much ease compared to polymer-stimulated wells. The objective of this work was to compare the effects of different breakers on a long-tail amphoteric VES solution for well stimulation. Solutions of a VES system (3.96 wt %) with erucamidopropyl hydroxypropyl sulfobetaine as the main surfactant reagent were prepared with varying concentrations of breakers and a fixed concentration of CaCl2 (6.2 wt %). The breakers used were Uthmaniya crude oil, n-decane and extra virgin olive oil. The concentration range of the breakers was 0.1-3 wt %. Rheology was used to determine the effect of these breakers. The samples were equilibrated for a week at 30°C and 60°C before testing at these temperatures. The VES solution showed three regimes of viscosity changes at both temperatures after the addition of n-decane within the tested breaker concentrations. The regime changes were in the following order: (i) the high viscosity regime (ii) the transition regime (iii) the low viscosity regime. Crude oil and olive oil induced only the high viscosity regime at 30°C, and the high viscosity and transition regimes at 60°C within the tested breaker concentration range. There was no low viscosity regime at both test temperatures after the addition of crude oil and olive oil within the tested breaker concentration range. Thus, n-decane was the most efficient breaker than crude oil and olive oil at both test temperatures. The work enhances the fundamental understanding of breaking mechanism at different temperature and for different types of oils. Low molecular weight oils such as n-decane are efficient breakers compared to high molecular weight oils. High molecular weight oils such as olive oil and crude oil are more efficient at high temperatures.

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