Thermochemical Fluids: A Promising Technology to Enhance Breakers Performance and Ultimate Cleanup of Frac Fluids

Cleanup of fracturing fluids is an imperative key in the success of the whole fracturing operation. Breakers, one of the main fracturing fluids additives, are commonly used to degrade polymers and thus provide better cleanup. Encapsulation of the breakers is a common practice used to avoid premature viscosity reduction of fracturing fluids, allow the placement of elevated breaker concentrations within the proppant pack, and permit a controlled release of the active material after the proppant is placed. Lack of sufficient release of active material from the encapsulated breakers will negatively impact the outcome of the cleanup process and ultimately the outcome of the fracturing treatments in enhancing oil/gas well productivity. Lab tests conducted on guar gum-based fracturing fluids showed that the release of active material from the encapsulated breakers was directly proportional to temperature. Thermochemical fluids (TCFs) of interest in this study were ammonium chloride (NH₄Cl) and sodium nitrite (NaNO₂). The reaction of the TCFs is associated with generation of huge amounts of heat and nitrogen gas. The amounts of heat and nitrogen gas generated from the TCFs were found to be dependent on the TCFs volume and concentration. According to laboratory testing, the heat produced by the TCFs reaction has a tendency to dramatically reduce the viscosity of fracturing fluids from a few hundreds to a few centipoises. Also, the generated nitrogen is expected to reduce the well hydrostatic pressure and ultimately enhance the cleanup process. The TCFs reaction is triggered either by acid or heat. This paper studies in detail the reactivity of TCFs in terms of concentration and volumes using a closed PVT cell and a high temperature high pressure (HTHP) autoclave system. The effect of heat generated by TCFs reaction on the reduction of fracturing fluid's viscosity was investigated using the HTHP filter press.