Matrix acidizing and acid fracturing treatments have been regularly applied for enhancement of oil and gas production. The success of the acid treatments requires uniform distribution of acid fluids across long treatment intervals or areas especially for vertical, horizontal, extended reach and multilateral wells with open hole completions. The unique properties of viscoelastic surfactant (VES) fluids provide good acid diversion fluids for blocking acid fluid flow into higher permeability sections in order to force the stimulation fluid into the lower permeability sections.
Recent SPE publications have shown that VES fluids used for acid diversion fluids have caused formation damage for matrix acidizing and acid fracturing, requiring a longer flow back periods, particularly for low permeability and depleted gas formations. Internal breaker technologies for VES fluids have been developed for hydraulic fracturing and frac-packing treatments. The internal breakers give a controllable break and go wherever the VES fluid goes, breaking the VES fluid into easily producible fluid.
This paper will introduce a VES organic acid fluid with internal breakers for treating carbonate reservoirs. The VES organic acid system is unique and will not generate noticeable viscosity until the acid starts to spend. The VES within the acid fluid reaches it highest viscosity as the acid completely spends and diverts fresh acid to new locations. After acid treatments, the internal breaker becomes activated to break the VES micelles, and the fluid loses its viscosity and flows back during production, minimizing any potential damage.
The paper will discuss lab results which demonstrate that the VES product generates very high viscosity at low shear rates in the spent acid fluid, and VES fluid will not broken only by contacting hydrocarbons. Further demonstrated is how internal breakers are available that reduce the viscosity of the spent acid diverter fluid over a controllable period of time. Carbonate wormholing core flow tests show non-broken VES fluids in wormholes need much higher pressure drop than than broken VES fluids for mineral oil cleanup.