In general, a fracturing fluid may break after time, due to extended exposure to reservoir pressure and temperature, however, breakers are used in cross-linked systems to speed up the breaking process, and aid in the flow-back and clean-up process. Breakers tend to be in solid form, either a “raw” powder form, or a slower releasing encapsulated form, which releases the breaker under pressure. A combination of these forms of breaker may be used to achieve the desired fracture fluid breaking time.
Breaker schedules are created by estimating the temperature profile of each stage as pumped during a hydraulic fracturing treatment, that is, time taken for each treatment stage to reach reservoir temperature. Breaker is added to each stage, so that the fluid in each stage will simultaneously break a certain time after the job is complete. This means adding less breaker to the early stages, and more to the later stages. Breakers are typically oxidizing agents, or enzyme based, and breaker testing involves heating samples of each stage (including proppant), and documenting the visual changes in the fluid at certain time intervals, to determine whether a fluid has broken or not, and the time it takes according to the breaker concentration used. It is essential to get the concentration for each stage right, otherwise early fluid break will cause the viscosity to be lost, excess leak-off into the formation to occur, and possible screen-out.