Slickwater fracturing fluids have been successfully applied in hydraulic fracturing of unconventional formations especially shales at shallower depths.When moving on to deeper wells,however,fracturing fluids with higher viscosity and better proppant-carrying properties are needed.Our focus was development of a flowback/produced-water-based fracturing fluid by crosslinking a friction reducer.The advantages of directly crosslinking a friction reducer to form a crosslinked fracturing fluid are several.At first,the logistics and field operation are simpler.No need of another gelling agent considering nowadays most fracturing jobs for unconventional formations are hybrid.Secondly,by using a synthetic polymer instead of a biopolymer such as guar gum,there is much less concern about the premature degradation of the gelling agent in minimally treated flowback/produced water.Thirdly,the carbon-carbon backbones of friction reducer molecules render them better temperature stability.Furthermore,unlike guar-type fluids,when fully broken,there is no residue in the final fluid to cause formation damage.Metal crosslinkers such as zirconium complexs were used to crosslink anionic friction reducers with reactive functional groups.Research on the performance optimization of this type of fracturing fluids in synthetic flowback/produced water,including improved hydration of gelling agent,delayed crosslinking,stabilized viscosity at higher temperatures and complete breaking at the ends of fracturing treatments,was conducted in our laboratory by extensively experimenting with a variety of additives and devising novel performance aids.A suite of tests including hydration tests,high temperature viscosity tests,and static break tests were performed to investigate the aspects of the fluid system,providing a comprehensive evaluation.Anionic friction reducers were successfully crosslinked to form stable gels in synthetic flowback/produced brines.The crosslinking of the fluid system was well controlled and delayed.With a friction reducer being the gelling agent and controlled delay of the crosslinking process,friction pressure of this fluid during pumping is expected to be minimized,and so is mechanical damage to the fluid.Novel breaking aids were devised which completely broke the fluid into a water-thin liquid with no residue.These breaker aids provided slow and/or delayed breaking and are non-toxic and environmentally friendly.
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