Investigations of thermochemical fluids as cleanup system for polymer-based fracturing fluids

The cleanup of fracturing fluids, involving polymer degradation and well flowback, is crucial for the success of the fracturing operations and revenue generation. Breakers, such as oxidizers and enzymes, are commonly employed to break down polymers, resulting in lower viscosity, improved flowback, and facilitated well cleanup. However, these conventional breakers, which contribute solely to the cleanup process through polymer degradation, have some drawbacks, such as premature breaking and insufficient release of breakers. In this study, thermochemical fluids (TCFs) are proposed as a cleanup system. This system can improve the cleanup process by lowering viscosity through temperature increase and thermal degradation of polymers, reducing hydrostatic pressure via gas generation, and eliminating phase trapping damage in tight reservoirs through the heat produced. The TCFs investigated in this study were NH₄Cl and NaNO₂ solutions, where a substantial amount of heat was determined from the thermal energy study using an autoclave reactor. In this study, the thermal degradation of guar gum (GG) polymer derivatives, hydroxypropyl guar gum (HPG), and carboxymethyl hydroxypropyl guar gum (CMHPG) were assessed using Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA), viscosity measurements, and coreflood experiments. Both FTIR and TGA analyses of linear gels of GG and its derivatives confirmed alterations in the chemical and thermal properties of these polymers following thermal treatments. The coreflood results showed a regained permeability of 87% for thermally treated HPG borate-crosslinked, 96% for CMHPG dual crosslinked (borate and zirconate), and 90% for slickwater fracturing fluids, respectively. The regained permeability of thermally treated slickwater was even better than that for slickwater with ammonium persulfate breaker.