It can be difficult to effect a timely fracturing fluid break, after a hydraulic fracturing treatment, in reservoirs above 190 F. Fracturing fluid systems often are quite stable at temperatures up to 300 F. At elevated temperatures the treatment designer is faced with the selection of a fracturing fluid breaker from three main categories: oxidizers, acids and enzymes.
Typical oxidizing breakers systems, used at temperatures up to 250 F, are persulfates often encapsulated by a thin film of polymer. Encapsulated persulfates often "leak" allowing some of the encapsulated breaker to be rapidly released into the fracturing fluid. Early release of oxidizing breaker degrades the fracturing fluid during the fracturing treatment—before the desired time.
Acids can be used as breakers but are usually limited to lower temperatures. In addition, the buffering capacity of the formation and the fracturing fluid can significantly impact the performance of acids and finally, acids are usually less cost effective than other breakers.
Polymer specific enzymes, while an effective breaker at elevated temperatures, do not provide a rapid break in fluids with a high pH.
The industry has developed an appreciation of minimizing gel loadings in fracturing fluids because of perceived high insitu polymer concentrations brought about during fracture closure. For this reason, it is desirable to use breaker systems that do not prematurely attack fluid viscosity, allowing use of the minimum gel loading that adequately transports proppant
A high temperature, fracturing fluid breaker system that circumvents many of the problems discussed has been developed. The breaker system, instead of relying on a micro-thin coating on a very reactive substrate, provides a different approach to the problem. The alternative breaker system discussed here utilizes a non-encapsulated, oxidizing breaker that effects a delayed break by slowly releasing free radicals in water based fracturing fluids, thus degrading fracturing fluids in a controlled manner.