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Summary Boron-based crosslinkers are used commonly to increase viscosity and to improve fluid-loss control and proppant transportability of guar and its derivative fluids. Boron crosslinkers are usually preferred because of their ability to reheal after shearing and their favorable environmental properties. More-efficient crosslinkers capable of crosslinking fluids with reduced polymer loading have always been of great interest, to reduce both the formation and the proppant-pack damage from polymer residues and to reduce overall fluid cost, especially with the reduced availability and higher cost of guar. Recently, we reported in paper SPE 140817 (Sun and Qu 2011( the synthesis of polyaminoboronates, bulky compounds containing multiple boron sites and capable of interacting with multiple polysaccharide strands to form more complex crosslinking networks at lower polymer loadings than conventional guar fluids. However, to improve the marketability and acceptance of the product, a lower-cost combination of raw materials is sought. In addition, a delaying mechanism to improve the control of the fluid-viscosity buildup can make the product fit into broader applications. A readily available polyamine was used as the base scaffold, and boron was incorporated by means of intermediate borate formed in the condensation reaction between boric acid and ethylene glycol to replace volatile and highly flammable trimethylborate. New chemistry was developed to produce more-controlled crosslinking. The resulting compound exhibited desired adjustable delay characteristics. This paper shows the effect of a series of new crosslinkers in terms of delay properties. The testing results of fluids with a 20%-lower polymer loading, crosslinked with the new crosslinker, are reported and compared with those of conventional fluids. Analysis and discussion of the chemistry, crosslinker performance, and economics are presented.

Most conventional fracturing fluid systems are based on guar and guar derivatives. Therefore, fracturing costs are strongly influenced by guar price. In addition, when pumped in unconventional formations, these fluid systems can cause significant formation damage due to insoluble protein components in guar. While Polyacrylamide (PAM) based copolymers are often used in unconventional formation stimulation, they are often considered to be hard to break. A possible solution that can mitigate the problems associated with the conventional fracturing fluid systems is a new fluid system based on a carefully designed synthetic polymer. The synthetic nature of the polymer translates into a stable operating cost without being impacted by market fluctuations like in the case of guar. This new synthetic polymer system is crosslinked and applied similarly to polysaccharide-based fluids. To alleviate concerns that synthetic polymer is hard to break, this polymer incorporates special linkages, periodically distributed along its backbone, to make it easily broken into small fragments with conventional oxidative breakers under downhole conditions to leave minimal formation or fracture damage. The polymer also incorporates functional groups that resist damage from water hardness. In addition, the polymer hydrates almost instantaneously and allows rapid viscosity generation and adjustment without a hydration unit, which greatly reduces footprint of hydraulic fracturing treatments. While this new polymer system can be used in slickwater hydraulic fracturing and linear gel applications, laboratory testing also showed that it can be effectively crosslinked with conventional metal crosslinkers. This paper investigates the possibility of using this new polymer as a total package to be applied throughout hybrid fracturing operations for tight formations besides using it as fracturing fluids for conventional formations. Laboratory work also investigated other applications of the new polymer such as acid gelling, acid fracturing, and diversion, to name a few. This paper presents the laboratory performance and the underlying mechanisms of the novel polymer fluid system.