Viscoelastic surfactants (VES) are important gelling agents in well stimulation treatments. Proper job design requires that the additives create the desired viscosity for effective proppant or gravel pack sand transport. Post-stimulation production enhancement partially relies on the thoroughness of gelling agent destruction or removal, known as "breaking" the gel. VES gels are non-damaging and do not create a filter cake, and thus are prone to high leak-off. The leak-off fluid potentially has a high zero-shear viscosity and can be challenging to remove from the formation. We propose a breaker system that comprises a monomer and radical initiator that will travel into to the formation with the VES gel. The resulting polymer will disrupt the worm-like micelles of the VES, creating spherical micelles and reducing the viscosity of the fluid. The breaker system presented here is operable at 200 °F. Rheology measurements show that the VES fluid with monomer and initiator has reduced viscosity and becomes less shear-thinning. Optical transmission and backscattering measurements show that the presence of breaker does not greatly accelerate proppant settling. The reduced viscosity would not adversely affect proppant transport. Core flow experiments compared retained permeability of cores treated with VES and VES with reacted monomer and initiator. The core flushed with broken fluid possessed a retained permeability of 79%, while the unmodified VES left only 44% retained permeability.
The use of conventional acid systems in high-temperature, fast-reactive carbonate reservoirs limits the effectiveness of matrix acidizing and acid fracturing. Therefore, during acid stimulation in such conditions, acids with retarded reaction are usually recommended. Industry-employed retarded acid systems have several significant drawbacks—they either dissolve lower rock volume or have higher friction and are more complex to mix than the standard hydrochloric acid system. The introduction of a new single-phase retarded acid enabled minimizing these drawbacks. The sustained increase in productivity index (PI) after the acid fracturing and matrix acidizing treatments under high-pressure/high-temperature conditions was achieved. The treatments were performed on exploration wells drilled in carbonate oil fields of the pre-Caspian and Mangystau oil-bearing provinces of West Kazakhstan.